CT and MRI Features of ACC

Anatomic Imaging

CT and MRI features of adrenocortical carcinoma (ACC) are the structural imaging findings used to detect, characterize, stage, and monitor this rare primary adrenal cortical malignancy within Anatomic Imaging. In contemporary adrenal mass evaluation, contrast-enhanced CT is the standard first-line anatomic study, while MRI serves mainly as a complementary modality when CT is indeterminate, iodinated contrast is undesirable, or venous and soft-tissue relationships require further definition.¹²³

On cross-sectional imaging, ACC most often appears as a unilateral adrenal mass that is large, lipid-poor, and heterogeneous because of necrosis, hemorrhage, cystic change, and irregular enhancement.⁴⁵⁶⁷ Suspicion increases further when imaging shows local invasion, nodal or distant metastatic disease, or tumor extension into the adrenal vein, renal vein, or inferior vena cava.⁸⁹³ These findings primarily support risk stratification and staging rather than definitive histologic diagnosis.

A central limitation is that CT and MRI cannot reliably distinguish ACC from all benign or noncortical adrenal masses. Important overlap exists with lipid-poor or degenerative adenoma, pheochromocytoma, oncocytic adrenal neoplasms, metastases, vascular tumors, hemorrhagic lesions, and cystic adrenal masses.¹⁰¹¹¹²¹³ The reverse problem also occurs: some ACCs are small, relatively smooth, or may show washout or chemical-shift behavior that resembles adenoma.¹⁴¹⁵¹⁶ As a result, imaging contributes most reliably to identifying lesions that are clearly benign, clearly aggressive, or indeterminate but concerning enough to require endocrine and surgical assessment.

The evidence base is limited by the rarity of ACC. Most available data come from retrospective referral-center series, surgical cohorts, reviews, and case reports, which tend to overrepresent larger and more advanced tumors and may not generalize to incidentalomas or early-stage disease.¹⁷¹⁸¹⁹ Accordingly, the most consistent conclusions concern broad malignant morphology and anatomic extent, whereas precise imaging thresholds for separating ACC from adenoma remain probabilistic.

Diagnostic context

CT and MRI are used in ACC for two related tasks: determining whether an adrenal mass is suspicious for malignancy and defining disease extent once ACC is suspected. CT remains the backbone of this assessment because it is rapid, widely available, and able to evaluate the adrenal lesion together with the retroperitoneum, liver, and lungs in a single staging examination.²⁰²¹³ MRI is generally reserved for problem-solving, especially when the organ of origin is uncertain or when vascular extension and adjacent soft tissues need clearer multiplanar assessment.⁹²²²³

Within adrenal incidentaloma workflows, features that increase concern for ACC include increasing size, elevated unenhanced attenuation, internal heterogeneity, irregular margins, interval growth, and evidence of invasion or metastasis.²⁴²⁵²⁶²⁷ What is reliable here is the ability of CT and MRI to identify masses that are very unlikely to be benign. What is less reliable is confident preoperative tumor typing based on morphology alone, so imaging findings usually need to be integrated with hormonal testing and clinical context.²⁸¹⁸¹⁹

This diagnostic framework helps explain why the same imaging studies are used both for initial suspicion and for operative staging.

Major imaging phenotypes

Typical primary tumor appearance

Across reviews and confirmed series, ACC usually presents as a solitary adrenal mass with heterogeneous architecture caused by necrosis, hemorrhage, or cystic degeneration.²⁹³⁰³¹ Most tumors are larger than 4 cm at diagnosis, and many exceed 6 cm, although smaller ACCs are increasingly recognized and may resemble other lipid-poor adrenal lesions.³²³³¹⁵³⁴

On unenhanced CT, ACC generally has attenuation above the range typical of lipid-rich adenoma, and contrast-enhanced CT often shows irregular or heterogeneous enhancement with central nonviable low-attenuation areas.³⁵³⁶³⁷³⁸ MRI commonly demonstrates heterogeneous T1 and T2 signal intensity, including hemorrhagic T1-hyperintense regions and relatively high T2 signal in viable tumor.³⁹⁴⁰²³ Calcification is a recurrent but nonspecific finding.⁴⁴¹⁴²

These features are reasonably consistent as a malignant pattern, especially when several are present together. However, individual signs such as necrosis, hemorrhage, or calcification have limited standalone specificity, so practical interpretation depends on the overall combination of size, density, heterogeneity, and invasive behavior rather than any single imaging feature.⁴³⁴⁴⁴⁵

Invasion, thrombus, and metastatic pattern

Once an adrenal lesion appears suspicious, imaging emphasis shifts from lesion characterization to extent of disease. CT and MRI may show direct invasion of liver, kidney, diaphragm, or retroperitoneal tissues, as well as nodal disease and distant metastases, particularly in the liver and lungs.⁴⁹⁴⁶³ Venous extension into the adrenal vein, renal vein, inferior vena cava, and occasionally the right atrium is a recognized ACC pattern with major implications for resectability and operative planning.⁴⁷⁴⁸⁸

MRI may be particularly helpful for defining the cranial extent of tumor thrombus, although CT remains central for routine staging and is often sufficient for management decisions.⁴⁹⁵⁴⁶ In this setting, anatomic extent is more reliably assessed than histologic subtype, and identification of invasion or thrombus often has greater immediate clinical relevance than additional characterization maneuvers.

This focus on extent also clarifies the main differential problem: many lesions can mimic ACC morphology, but fewer reproduce the full pattern of aggressive local and vascular spread.

Differentiation from adenoma and other mimics

The principal limitation of CT and MRI in ACC is overlap with other adrenal and upper retroperitoneal masses. Large adrenal adenomas, particularly lipid-poor or degenerative adenomas, may show heterogeneity, hemorrhage, cystic change, calcification, and irregular enhancement that closely simulate ACC.¹⁰⁵⁰⁵¹ Other important mimics include pheochromocytoma, malignant oncocytic adrenal neoplasms, hemangioma, organized hemorrhagic or cystic lesions, metastasis, and large renal or hepatic masses with obscured organ of origin.¹¹⁵²⁵³⁵⁴

The reverse pitfall is also clinically important: some ACCs appear less aggressive than expected. Reported tumors under 4 cm, lesions with adenoma-range washout, and rare lesions with small microscopic or macroscopic fat components show that simplified rules based only on size, washout, or lipid content may miss malignancy.¹⁴¹⁵⁵⁵⁵⁶ Interval growth, persistently high unenhanced attenuation, irregular morphology, or subtle invasion may therefore outweigh otherwise reassuring washout or chemical-shift findings.⁵⁷⁵⁸⁵⁹

What is most reliable in this differential setting is that a homogeneous lesion with very low unenhanced attenuation is unlikely to be ACC. What is not reliable is assuming that a single benign-appearing parameter excludes carcinoma, particularly in lipid-poor, enlarging, or heterogeneous lesions.⁴³³⁸⁶⁰

Evidence on specific imaging parameters

Among routine CT variables, unenhanced attenuation and tumor size are the most reproducible markers associated with ACC risk.⁶¹⁴³²⁶ Homogeneous lesions with very low attenuation are rarely ACC, whereas lipid-poor masses above standard benign thresholds warrant closer evaluation in the appropriate clinical setting.³⁶⁶²³⁸ These measures are relatively objective and reproducible, but they are insufficient in isolation, especially for atypical or small lesions.⁶³²⁷

Washout CT and chemical-shift MRI remain useful for confirming many adenomas, but their reliability decreases when ACC is part of the differential diagnosis. ACC often shows poor delayed washout and absent opposed-phase signal loss, yet overlap is well documented, including carcinomas that meet adenoma washout thresholds or show some signal drop from intracellular lipid.⁶⁴⁶⁵¹⁴²³¹⁶ The practical implication is that attenuation, morphology, growth, and signs of invasion usually outweigh isolated washout or chemical-shift results when the dataset is discordant.⁵⁶⁶⁶⁶⁰

More recent work has explored structured imaging scores, multiparametric MRI, and radiomics to improve discrimination between localized ACC and common mimics such as lipid-poor adenoma or pheochromocytoma.⁶⁷⁶⁸⁶⁹⁷⁰⁷¹ These approaches suggest that combined-feature analysis may outperform single-parameter interpretation, but current evidence is predominantly retrospective and requires broader external validation before routine use.

Role in management and research

In clinical management, CT and MRI are most valuable for referral decisions, surgical planning, baseline staging, and surveillance rather than for replacing pathology. Imaging may demonstrate unresectable metastatic disease, define the need for en bloc resection, and identify caval or atrial thrombus that changes operative strategy.⁴⁹⁷²³ Compared with biopsy-driven pathways, anatomic imaging usually comes first, and suspected resectable ACC is often managed without biopsy because tissue sampling may add limited value and may introduce procedural risk.⁷²

For research, the literature supports relatively strong conclusions about malignant phenotype and staging utility but weaker conclusions about exact diagnostic cutoffs across heterogeneous populations. Clinically, CT and MRI are best understood as high-value tools for suspicion assessment and anatomic definition, while definitive diagnosis generally still depends on integrated endocrine, surgical, and histopathologic evaluation.¹⁸³¹⁹

Included Articles

PMID 1731841: In a 15-patient series, CT showed ACC extent well but often could not determine adrenal origin in the largest tumors, which were commonly ill-defined and inhomogeneous, sometimes with calcifications. Smaller tumors up to 10 cm were more often correctly identified as adrenal in origin.⁷³

PMID 2191266: In pediatric ACC, ultrasonography, CT, and MRI can identify large heterogeneous suprarenal masses and detect inferior vena cava tumor thrombus with right atrial extension. MRI and ultrasound helped define cavoatrial involvement preoperatively, whereas CT findings of heterogeneity, necrosis, and calcification were nonspecific for malignancy.⁷⁴

PMID 2279500: In ACTH-independent Cushing’s syndrome, non-visualization on radiocholesterol scintigraphy does not necessarily indicate adrenocortical carcinoma because a benign black adenoma composed of lipid-poor compact cells may also fail to image. The report also notes that black adenomas can show higher CT density than typical adrenal adenomas.⁷⁵

PMID 2705336: In this small CT series of pathologically confirmed adrenal tumors, homogeneous slightly negative attenuation on noncontrast CT was seen in some lipid-rich adrenocortical adenomas, especially primary aldosteronism and a nonfunctioning adenoma, but not in the single ACC case, which showed higher attenuation.⁷⁶

PMID 1289268: A case report highlights the diagnostic challenge of distinguishing a large hypovascular upper-pole renal mass from an adrenal tumor when CT, ultrasound, MRI, and angiography are inconclusive. Preserved symmetric visualization of both adrenal glands on I-131 cholesterol adrenocortical scintigraphy suggested a nonadrenal origin, later confirmed as renal cell carcinoma.⁷⁷

PMID 3454029: A pediatric ACC case describes CT and sonographic features of a large, well-defined suprarenal mass displacing but not invading adjacent kidney, with heterogeneous internal architecture, prominent peripheral vessels, and striking central low attenuation consistent with necrosis. The report notes that a large adrenal mass with central necrosis is a typical imaging appearance of ACC.⁷⁸

PMID 3492881: In a 38-patient CT series of primary adrenocortical carcinoma, common findings included central necrosis, irregular peripheral enhancement, calcification, and occasional thin enhancing capsulelike rims, with CT also demonstrating metastatic spread and venous extension. The report additionally notes that some ACCs 6 cm or smaller can appear smooth, homogeneous, and functioning on CT.²⁹

PMID 3554925: In a sonographic series of 26 pathologically proven ACCs, small tumors were often homogeneous, whereas larger lesions were usually well-defined but heterogeneous with necrosis, hemorrhage, and occasional calcification. The study also notes that ultrasound patterns were not specific enough to reliably distinguish adenoma from carcinoma.⁷⁹

PMID 3669172: In a single ACC case with inferior vena cava tumor thrombus, preoperative MRI identified caval involvement but underestimated intermittent right atrial extension. The report suggests MRI can help define thrombus extent noninvasively, while additional venography or cardiac assessment may be needed when atrial involvement is suspected.⁸⁰

PMID 7137460: In a 1970s surgical adrenal series that included 35 adrenocortical carcinomas, preoperative localization improved from about 50 percent to nearly 100 percent over the decade, largely after the introduction of computed tomography. CT showed the highest overall diagnostic accuracy, approaching 90 percent, and increasingly replaced other localization studies for adrenal mass lesions.²⁰

PMID 7766978: This small MR series found ACC commonly appears as a large solitary adrenal mass with internal hemorrhage, central necrosis, and peripheral enhancing nodules. MRI also helped depict extrarenal adrenal origin, liver metastases, and inferior vena cava invasion, while heterogeneous signal loss on out-of-phase imaging did not exclude malignancy.³⁹

PMID 8197653: In two ACC cases with vena caval tumor thrombus, preoperative MRI provided more precise delineation of thrombus extent than CT or venacavography and matched operative findings. Multiplanar MRI helped define infrahepatic versus more cephalad extension, informing surgical planning and the anticipated need for cardiothoracic bypass.⁴⁹

PMID 8819372: This review describes imaging features of adrenocortical carcinoma as typically a large, well-defined but heterogeneous adrenal mass, often with central necrosis, peripheral heterogeneous contrast enhancement, and calcification in about 30% of cases. It also emphasizes assessing liver, lung, nodal metastases and possible inferior vena cava invasion when resection is considered.⁴

PMID 8819376: A case report shows that chemical shift MRI can identify a lipid-rich adrenal adenoma by signal loss on opposed-phase imaging, but a small non–signal-dropping focus within the mass corresponded to metastatic adenocarcinoma. The report emphasizes that incomplete signal loss within an adrenal lesion should prompt concern for a nonadenomatous component rather than exclusive benign characterization.⁸¹

PMID 9015085: This case report highlights that a low-grade adrenocortical carcinoma may lack signal loss on opposed-phase MRI despite resembling an atypical adenoma histologically, and that recurrent invasive tumor can later show high T2 signal with only small lipid foci. The report underscores limitations of chemical-shift MRI for confidently distinguishing benign adenoma from ACC.⁸²

PMID 9725326: This case-based review emphasizes imaging features of adrenocortical carcinoma, including very large heterogeneous adrenal masses with central necrosis, hemorrhage, calcifications, irregular contrast enhancement, and displacement of adjacent organs. It also highlights sonographic, CT, and MR assessment of venous extension into the adrenal vein, inferior vena cava, and possible intracardiac spread for surgical planning.⁴⁷

PMID 9821195: This review notes that adrenocortical carcinoma can contain intracellular lipid detectable on opposed-phase gradient-echo MRI as signal loss relative to in-phase imaging. It also emphasizes that matched acquisition parameters are needed because T2* effects can confound interpretation.⁸³

PMID 10096147: In ACTH-independent Cushing’s syndrome from an adrenal mass, CT or MRI can identify unilateral adrenal neoplasms, with tumor size being the most important preoperative clue favoring carcinoma over adenoma. Carcinomas are typically larger than 6 cm, heterogeneous, necrotic, and sometimes calcified, while MRI T2 hyperintensity may support malignancy but overlaps with adenoma.³²

PMID 10207419: Large degenerated adrenal adenomas can mimic adrenocortical carcinoma on CT and MR imaging, showing marked heterogeneity, cystic change, calcification, hemorrhagic degeneration, and irregular enhancement. Imaging alone did not reliably distinguish these adenomas from ACC, although metastatic disease or venous tumor thrombus was seen only in some carcinomas.¹⁰

PMID 10598161: This review outlines CT and MRI features relevant to distinguishing adrenal adenomas from nonadenomas, including ACC. For ACC, it highlights typically large heterogeneous masses with frequent necrosis or calcification, limitations of morphology alone in smaller tumors, and the added value of delayed contrast CT washout and MRI for assessing local invasion.⁸⁴

PMID 10663510: In pediatric ACC, CT and MRI commonly show a large well-defined suprarenal mass with calcifications, a thin capsule, and central necrosis or hemorrhage; ultrasound can better assess inferior vena cava wall involvement. Chest CT and bone scintigraphy were recommended to evaluate metastatic spread, particularly to lungs and liver.⁸⁵

PMID 11809539: This review outlines CT as the preferred first-line modality for adrenal mass evaluation, with MRI as a complementary tool. It notes that while some large adrenocortical carcinomas may have distinctive imaging appearances, smaller ACC can overlap with adenomas and metastases, and MRI helps assess extension into adjacent structures.¹

PMID 11809540: In a histologically correlated series of adrenal masses, MRI showed high overall accuracy for distinguishing benign from malignant lesions. The excerpt describes MRI features supporting ACC, including heterogeneous T1 and T2 appearance, peripheral nodular enhancement with central hypoperfusion, absent chemical-shift signal loss, and local invasion such as adjacent organ or inferior vena cava involvement.⁴⁰

PMID 12701316: This case report describes a large nonfunctioning ACC incidentally detected by ultrasonography and further characterized on CT as a 16 cm heterogeneous right adrenal mass with moderate enhancement, small calcifications, necrotic hypodense areas, and displacement of the right kidney. The authors present ultrasound as an initial test and CT as the reference examination for adrenal mass evaluation.⁸⁶

PMID 12721644: This review outlines CT and MRI approaches for characterizing adrenal tumors relevant to ACC differential diagnosis. Unenhanced CT attenuation, delayed contrast washout, and MRI chemical-shift plus T1/T2 signal analysis are emphasized, with CT as the main broadly available test and MRI as a problem-solving tool in indeterminate cases.²¹

PMID 12777180: This case report describes right-sided adrenocortical carcinoma extending through the inferior vena cava into the right atrium, with transthoracic echocardiography detecting intracardiac involvement and informing combined abdominal-cardiac operative planning. The authors also note complementary roles for CT, venography, and MRI in defining tumor extent.⁴⁸

PMID 15008991: This review emphasizes that adrenal mass size is the strongest imaging indicator of malignancy in ACC, with tumors often exceeding 6 cm at diagnosis. It describes typical CT and MRI features including heterogeneous appearance, irregular margins, necrosis or calcification, slow contrast washout, and MRI superiority for detecting inferior vena cava invasion.⁵

PMID 15448327: This case report describes retroperitoneal hemorrhage arising from ACC and suggests 3D sonography can better delineate continuity between intratumoral and extratumoral hemorrhage than CT in selected cases. It also highlights heterogeneous tumor appearance, necrosis, enlarged paracaval nodes, and vessel mapping consistent with adrenal tumor origin.⁸⁷

PMID 15671003: In delayed contrast-enhanced CT, adrenocortical carcinomas showed higher noncontrast attenuation, large tumor size, and substantially less 10-minute contrast washout than adrenal adenomas, with washout behavior similar to pheochromocytomas and adrenal metastases. Absolute and relative washout thresholds helped distinguish adenomas from these nonadenomas.³⁵

PMID 15688105: This case report highlights that ACC can rarely contain a small focus of pure mature fat on MRI, which can mimic myelolipoma. In fat-containing adrenal masses, accompanying malignant features such as large size, necrosis, and peripheral heterogeneous enhancement should weigh against assuming a benign diagnosis.⁸⁸

PMID 16201176: In a series of aldosterone-producing adrenal cortical tumors that included one ACC, CT had higher localization performance than ultrasonography and retroperitoneal pneumography. The excerpt also notes imaging clues that may suggest aldosterone-producing ACC rather than adenoma, including tumor size greater than 4 cm, heterogeneous density, hemorrhage, necrosis, calcification, local mass effect, nodal enlargement, and liver or kidney metastases.⁸⁹

PMID 16357562: This review summarizes imaging clues for suspected adrenocortical carcinoma, emphasizing CT as first-line and MRI as complementary. ACCs are typically larger, irregular, necrotic or cystic lesions on CT, while delayed contrast washout may help separate adenomas from malignant tumors; FDG-PET is described as a promising emerging adjunct.¹⁷

PMID 16794135: This retrospective CT study of seven pathologically proven ACCs found relative contrast retention on delayed contrast-enhanced imaging, with all tumors showing relative percentage washout below 40%. The tumors were also large, heterogeneous, non-fat-containing lesions with necrosis, supporting delayed washout analysis as an adjunct to distinguish ACC from adrenal adenoma.⁶⁴

PMID 17656234: This case-based review highlights that giant nonfunctioning ACC can be misidentified on MRI as renal cell carcinoma when the tumor compresses or obscures the kidney. It suggests maintaining suspicion for adrenal origin in very large upper abdominal masses and using preoperative imaging to assess local invasion and kidney involvement.⁹⁰

PMID 18226485: In incidentally detected adrenal masses assessed on routine abdominal CT, non-contrast attenuation was more accurate than lesion size or contrast enhancement for distinguishing adenomas from non-adenomas. ACC cases in this series were very large lesions with higher attenuation and central necrotic hypodense areas on CT.⁶¹

PMID 18425368: In a 12-patient ACC series, contrast-enhanced liver ultrasound detected hepatic metastases more often than multislice CT, including small hypervascular lesions missed even on retrospective CT review. The authors suggest it as a supplemental staging tool, especially when CT shows no liver metastases.⁹¹

PMID 18566172: This MRI technical study included one ACC among adrenal nonadenomas and found that at 3.0 T, adrenal tumor characterization with in-phase and opposed-phase imaging depends on echo-time pairing. Signal intensity index was most reliable when opposed-phase echo was acquired before in-phase echo, whereas the reverse order could misclassify nonadenomas as adenomas.⁹²

PMID 19218775: A case of adrenal endothelial cyst associated with adrenocortical adenoma showed a large enlarging heterogeneous adrenal mass with calcification, thick wall, fluid content, and minimal fat, creating a preoperative radiologic appearance that closely simulated adrenocortical carcinoma. The report emphasizes that heavily organized thick-walled adrenal cysts may be nearly impossible to distinguish from ACC on CT and MRI alone.⁹³

PMID 19755599: This review describes CT features that help distinguish adrenocortical carcinoma from other adrenal masses: ACC is usually a large, heterogeneous lesion, often with necrosis, occasional calcifications, local mass effect, and sometimes venous invasion or tumor thrombus. Relative percentage washout is typically below 40%, but size and heterogeneity are emphasized as more reliable clues than washout values alone.⁶⁵

PMID 20489083: This review summarizes imaging features that help distinguish malignant adrenal lesions, including suspected adrenocortical carcinoma, from benign adenomas. ACC should be considered for adrenal masses larger than 4 cm without another known malignancy, especially when lesions are heterogeneous, enlarging, necrotic, or calcified and remain indeterminate after CT densitometry or washout assessment.²⁴

PMID 21051577: This article outlines imaging clues that help distinguish ACC from benign adrenal adenomas, emphasizing CT as the preferred first-line study. Suspicious features include size, high unenhanced attenuation, heterogeneity, irregular borders, calcifications, local invasion, lymphadenopathy, and low contrast washout, with MRI reserved for assessing local or vena cava invasion.⁹⁴

PMID 21067996: This case report highlights that macroscopic fat within an adrenal mass, although classically linked to myelolipoma, does not exclude adrenocortical carcinoma. In a large heterogeneous adrenal lesion, features such as marked size, necrosis, and heterogeneous predominantly peripheral enhancement should keep ACC in the imaging differential despite small foci of fat.⁹⁵

PMID 21167383: This review outlines imaging features that help distinguish ACC from other adrenal incidentalomas, emphasizing that ACC usually presents as a large heterogeneous adrenal mass with necrosis, hemorrhage, calcifications, low T1 and high T2 signal, and irregular peripheral contrast enhancement on CT or MRI.³⁰

PMID 21606258: This review summarizes CT and MRI features that raise suspicion for adrenocortical carcinoma, including size greater than 4 cm, heterogeneous enhancement, central necrosis or hemorrhage, calcification, local invasion, venous extension, and slow contrast washout. It also notes MRI advantages for defining inferior vena cava involvement and overall local and distant extent.⁸

PMID 21783181: This retrospective CT series of histopathologically proven ACCs found that tumors were usually larger than 6 cm, heterogeneously enhancing, often had a thin enhancing rim and central stellate low attenuation, and could extend into the IVC. Most lesions also showed washout behavior typical of non-adenomas rather than adenomas.⁴¹

PMID 21813169: This case report highlights that a 5-6 cm adrenocortical carcinoma can show CT washout characteristics typically interpreted as a benign lipid-poor adenoma, despite heterogeneous imaging and lack of MRI signal drop-out. It underscores a limitation of adrenal washout studies when tumor size is concerning.¹⁴

PMID 21868539: This review summarizes CT and MRI features that help distinguish cortisol-secreting adrenal adenomas from adrenocortical carcinoma in Cushing syndrome. Suspicious carcinoma findings include size greater than 4 cm, irregular or unclear margins, heterogeneous appearance, attenuation above 10 HU, low contrast washout, invasiveness, and lack of signal drop on opposed-phase MRI.⁹⁶

PMID 21997291: This review emphasizes CT as the primary imaging modality for suspected ACC, with MRI as a complementary option when CT is contraindicated or inconclusive. ACC typically appears as a large heterogeneous adrenal mass with necrosis or hemorrhage, irregular margins, calcifications, local invasion, venous tumor thrombus, and common metastatic spread to liver, lungs, and lymph nodes.⁹

PMID 22070943: This commentary summarizes CT features of adrenocortical carcinoma as typically large lesions, usually over 6 cm, with heterogeneous attenuation and enhancement, central low attenuation, and frequent punctate calcification; occasional intrinsic macroscopic fat may also occur. It also emphasizes that contrast washout overlaps with other non-adenomatous adrenal lesions and can even fall in the adenoma range, so CT washout alone is not definitive.⁹⁷

PMID 22462796: This review notes that ACC is usually large at diagnosis, with most tumors exceeding 6 cm, and emphasizes that malignancy risk rises with lesion size. It describes ACC as typically inhomogeneous on imaging with ill-defined margins and heterogeneous enhancement, contrasting with adenoma washout behavior.³³

PMID 22486993: This review summarizes multimodality imaging features used to distinguish benign from malignant adrenal neoplasms, including CT attenuation, chemical-shift MRI, adrenal CT washout, and FDG-PET. It provides practical imaging thresholds and emphasizes CT as a first-line characterization tool for adrenal lesions.⁹⁸

PMID 23169720: This review emphasizes the imaging spectrum of ACC, noting that tumors are often large and heterogeneous with necrosis, hemorrhage, or calcification, but can also present as incidental lesions smaller than 5 cm. It outlines CT as the key modality for adrenal mass characterization, using unenhanced attenuation and delayed contrast washout to help distinguish benign adenomas from malignant lesions.⁹⁹

PMID 23210583: This pictorial review notes that ACC can rarely present as bilateral adrenal masses, occurring in about 10% of cases. Reported imaging features include large size at presentation, frequent heterogeneity with central necrosis, calcification in some cases, heterogeneous or peripheral rim enhancement, and slow contrast washout.¹⁰⁰

PMID 23562276: In a surgical series of adrenal incidentalomas, hormonal hyperfunction was not associated with higher malignancy risk, whereas imaging features such as adjacent-structure invasion, lymphadenopathy, metastasis, irregular margins, heterogeneity, and tumor size over 6 cm were the strongest predictors of malignancy. A 6 cm cutoff showed better specificity than 4 cm.²⁵

PMID 23673867: This case report highlights early CT features that may suggest ACC despite small size, including high unenhanced attenuation above 30 HU, focal calcification, irregular shape, and ill-defined borders. It also notes that short-term stability and washout values overlapping adenoma thresholds do not exclude early ACC.¹⁰¹

PMID 24271078: This CT comparison study found that malignant oncocytic adrenal neoplasms can closely mimic ACC, with overlapping large size, heterogeneity, necrosis, low contrast washout, and occasional nodal enlargement. Venous invasion appeared only in ACC in this cohort, while benign oncocytomas were smaller, more homogeneous, and showed high washout.¹¹

PMID 24345440: This case-based review highlights CT and MRI features that can raise suspicion for ACC, including a unilateral irregular heterogeneous adrenal mass with calcifications, necrosis or hemorrhagic change, and possible venous or adjacent organ involvement. It also notes that larger tumors are usually evaluated with contrast to assess adrenal vein, inferior vena cava, or local extension.¹⁰²

PMID 24434021: This review describes how CT and MRI can identify heterogeneous adrenal collision tumors that may include an adrenocortical carcinoma component, emphasizing differences in attenuation, lipid content, washout, signal drop on chemical shift imaging, and interval growth that help separate benign adenomatous elements from malignant foci.¹⁰³

PMID 24605256: This review summarizes CT and MRI features used to characterize adrenal masses and distinguish benign lesions from malignant lesions including adrenocortical carcinoma. It emphasizes CT as the primary modality, MRI as complementary, and notes limitations when lipid-poor adenomas overlap with carcinoma and other nonadenomatous masses.²⁸

PMID 24647823: In patients with hyperattenuating adrenal masses, 15-minute delayed contrast-enhanced CT showed higher accuracy than chemical shift MRI for lesion characterization, with relative percentage washout performing best. Larger lesion size and higher unenhanced CT attenuation were associated with greater odds of a non-adenoma diagnosis.¹⁰⁴

PMID 25060750: In a retrospective surgical series comparing large adrenal adenomas with adrenocortical carcinomas, dedicated adrenal CT performance depended strongly on region-of-interest placement for attenuation and washout measurements. A large ROI preserved 100% sensitivity for carcinoma, whereas a high ROI misclassified half of carcinomas as adenoma; lesion size overlapped substantially, and calcification was more frequent in carcinoma.¹⁰⁵

PMID 25246052: This review outlines CT and MRI as the main modalities for adrenal mass characterization, emphasizing unenhanced CT attenuation of 10 HU or less for lipid-rich adenoma, delayed contrast washout thresholds for lipid-poor adenoma, and MRI chemical-shift signal loss as key benign imaging features. PET is described as mainly useful in oncology patients rather than routine evaluation of incidental adrenal masses.¹⁰⁶

PMID 25419344: This study reports that large adrenal cortical adenomas greater than 5 cm can closely mimic adrenocortical carcinoma on CT, often appearing as bulky, heterogeneous, variably circumscribed masses with patchy low-attenuation foci, calcification, and heterogeneous enhancement. CT findings favoring carcinoma in this series were recurrence, distant metastasis, and venous tumor thrombus.⁵⁰

PMID 25593820: This review summarizes CT and MRI features that help distinguish adrenocortical carcinoma from benign adrenal adenoma, emphasizing large size, heterogeneity, necrosis or hemorrhage, calcifications, low contrast washout, local organ or vena cava invasion, and common metastatic sites. It also notes that pediatric ACC may be smaller and mimic adenoma.¹⁰⁷

PMID 25599706: In a retrospective comparative analysis of unenhanced CT, adrenocortical carcinomas showed substantially higher attenuation than benign adrenal tumors, with 21 HU providing the best overall accuracy but missing two ACC cases. A threshold around 13 HU maximized sensitivity, supporting cautious interpretation of intermediate values alongside tumor size, heterogeneity, and margin features.³⁶

PMID 25794486: In pediatric adrenocortical neoplasms, carcinomas were larger and more often heterogeneous on post-contrast CT or MRI than adenomas, with frequent overlap and occasional calcification limiting definitive imaging discrimination. Metastatic disease and inferior vena cava invasion were observed in a subset of carcinomas at diagnosis.¹⁰⁸

PMID 26038204: This review outlines imaging features that help distinguish ACC from benign adrenal incidentalomas, emphasizing that noncontrast CT attenuation is more informative than size alone. ACC is described as typically showing higher attenuation, and malignancy assessment should integrate heterogeneity, necrosis, calcification, irregular borders, local invasion, and washout behavior in lipid-poor lesions.⁶²

PMID 26045561: In ACTH-independent Cushing’s syndrome, adrenal CT is the preferred preoperative imaging test to localize and subtype adrenal cortical lesions. The review summarizes ACC imaging clues as a usually solitary mass larger than 4 cm with irregular margins, heterogeneous content, necrosis, hemorrhage, calcification, attenuation above 10 HU, and contrast washout below 60%.¹⁰⁹

PMID 26121453: In a tertiary-center incidentaloma cohort, ACC was rare but presented as markedly larger lesions than nonfunctioning adenomas, with mean size about 9 cm and occasional hormone excess. The local adrenal mass workflow used unenhanced CT attenuation of 10 HU or less and 15-minute absolute washout of 60% or greater to support benign adenoma classification.¹¹⁰

PMID 26206754: In a retrospective ACC series with prior imaging, many preexisting adrenal masses were initially small yet radiologically suspicious, often showing heterogeneity and lipid-poor attenuation with median precontrast density of 36 HU. The study suggests that relying on size alone, especially lesions under 4 cm, can delay ACC recognition despite concerning CT features.¹⁵

PMID 26321451: This review outlines imaging features that raise suspicion for adrenocortical carcinoma among adrenal masses, including size greater than 4 cm, heterogeneity, irregular margins, necrosis, growth, and possible vascular invasion on contrast-enhanced MRI. It also notes that suspected ACC should not be biopsied because of tumor spillage risk.⁷²

PMID 26694019: In a retrospective cohort of patients without known cancer, small incidental adrenal nodules 4 cm or smaller were not associated with subsequent adrenocortical carcinoma over prolonged clinical follow-up. The study suggests routine serial imaging may be unnecessary for these lesions, even when unenhanced CT attenuation exceeds 10 HU or MRI lacks signal drop on out-of-phase imaging.¹¹¹

PMID 27330637: This case report emphasizes CT and MRI findings that support suspicion for ACC in a hormonally active adrenal mass, including large size, heterogeneity, ill-defined margins, possible retroperitoneal fat invasion, and low relative contrast washout inconsistent with adenoma. The article also summarizes imaging features used for pretreatment staging and surgical planning.¹¹²

PMID 27567750: This case report describes use of CT-based 3D reconstruction and dynamic video to define a large right adrenal mass and its relationships to nearby organs and vessels before surgery. The authors suggest this imaging approach may improve preoperative anatomic assessment for large ACC undergoing retroperitoneal laparoscopic resection.¹¹³

PMID 28110892: This case highlights CT with intravenous contrast as the preferred initial imaging test for suspected ACC, emphasizing features that favored malignancy: a large unilateral irregular adrenal mass with heterogeneous enhancement, calcifications, high unenhanced attenuation, delayed washout, and partial compression of the inferior vena cava.¹¹⁴

PMID 28126216: This review outlines adrenal imaging features relevant to distinguishing benign adenomas from malignant adrenal lesions, including ACC. CT is presented as the main characterization tool, with MRI as a complement for heterogeneous masses or when iodinated contrast is contraindicated; ACC is illustrated as a large heterogeneous adrenal mass with necrosis.¹¹⁵

PMID 28183214: In a young woman with cortisol- and androgen-secreting ACC, a new thymic mass appeared eight months after adrenalectomy and later regressed, supporting rebound thymic hyperplasia after normalization of hypercortisolism. The report highlights CT pattern clues that may help distinguish benign rebound hyperplasia from thymic neoplasia and avoid unnecessary thoracic surgery.¹¹⁶

PMID 28222025: This review summarizes imaging evaluation of adrenal incidentalomas relevant to ACC suspicion, emphasizing CT as the primary modality. It highlights lesion size, attenuation, washout behavior, interval growth, and the limits of imaging specificity in distinguishing benign adenoma from malignant adrenal tumors.¹⁸

PMID 29332161: In surgically treated adrenal cortical tumors, ACC was much larger than adenoma on CT, while cortisol-secreting adenomas frequently had unenhanced attenuation above 10 HU. Relative washout analysis often still classified these cortisol-secreting adenomas as benign, highlighting a limitation of the standard 10 HU threshold.¹¹⁷

PMID 29671009: In pathologically confirmed adrenal tumors larger than 4 cm, CT features associated with benign adenoma rather than ACC included precontrast attenuation below 10 HU, visible macroscopic fat, and round shape. Precontrast attenuation showed high interobserver agreement, whereas necrosis, heterogeneity, and overall radiologic impression were less reproducible.⁴³

PMID 29749133: In a prospective CT-based multicenter cohort of 1005 Korean adrenal incidentalomas, improved computed tomography detected smaller lesions and suggested that a lower tumor size cutoff may be appropriate for identifying adrenocortical carcinoma in this population. The study also notes that suspected malignant masses were selected for surgery based on CT features such as large size, heterogeneity, or irregular shape.¹¹⁸

PMID 29984033: This case report highlights that adrenal hemangioma can closely mimic adrenocortical carcinoma on CT, including large size, heterogeneous appearance, calcifications, irregular enhancement, and delayed washout. It underscores that indeterminate adrenal masses larger than 4 cm with suspicious imaging often proceed to adrenalectomy because preoperative distinction may be unreliable.¹²

PMID 30031460: This review outlines cross-sectional imaging features used to characterize adrenal masses when ACC is in the differential, emphasizing CT as the primary modality and MRI as a complementary tool for heterogeneous lesions or contrast contraindications. It also notes that ACC can appear as a large heterogeneous adrenal mass with necrosis on PET/CT, while imaging must distinguish it from adenoma and metastasis.²²

PMID 30102237: A large right-sided ACC can mimic hepatocellular carcinoma on CT when abutting the liver, including arterial enhancement and venous washout with secondary cholestatic laboratory abnormalities. Recognition of a small fat plane separating the mass from the liver or kidney can suggest retroperitoneal origin and redirect diagnosis toward adrenal malignancy.⁵²

PMID 30225430: In a retrospective cohort of large adrenal tumors measuring at least 4 cm, ACCs were notably larger than other groups and malignant lesions were more often nonincidental and had higher unenhanced CT attenuation. Unenhanced attenuation above 10 HU was highly sensitive but poorly specific for malignancy, underscoring the need to interpret size and density within clinical context.⁶³

PMID 30980285: In this contemporary single-center ACC series, 79% of adult tumors were diagnosed incidentally, and all assessed lesions showed nonenhanced CT attenuation above 20 HU despite widely variable size, including tumors as small as 2-2.5 cm. The report emphasizes that small size alone does not exclude ACC and that lipid-poor CT appearance should prompt malignant differential diagnosis.³⁴

PMID 31169702: This case report describes intrahepatic adrenocortical adenoma arising from adrenohepatic fusion as a rare imaging mimic of hepatocellular carcinoma or hepatic metastasis. A key diagnostic clue on CT or MRI is continuity between a subcapsular right hepatic lesion and the right adrenal gland, which may prompt biopsy and prevent unnecessary surgery.¹¹⁹

PMID 31252396: In a retrospective multiphase contrast-enhanced CT study of malignant adrenal masses, early arterial wash-in features distinguished pheochromocytoma from ACC, lymphoma, and adrenal metastases, whereas ACC, lymphoma, and metastases had overlapping enhancement and washout patterns. ACCs were significantly larger than pheochromocytomas and metastases.¹²⁰

PMID 31559189: This review describes MRI features of adrenocortical carcinoma as a typically large adrenal cortical mass with heterogeneous signal, necrosis or cystic degeneration, possible T1 hyperintense hemorrhagic areas, and frequent venous invasion involving the inferior vena cava. It also notes that some ACCs can show out-of-phase signal loss, potentially mimicking benign lesions on chemical shift imaging.²³

PMID 31571425: This case report describes a rare adrenal collision tumor containing ACC and myelolipoma, in which CT showed a large adrenal mass with both macroscopic fat and a distinct peripherally heterogeneously enhancing soft-tissue component with calcifications. The report highlights that apparent myelolipoma should not exclude ACC when enhancement characteristics suggest a malignant cortical component.¹²¹

PMID 31672302: This review summarizes imaging features that help distinguish malignant adrenocortical tumors from benign lesions, emphasizing CT as the general first-line modality. ACC is associated with larger size, irregular or invasive appearance, necrosis, heterogeneous enhancement, lipid-poor high attenuation, delayed contrast washout, and lack of signal loss on chemical-shift MRI.¹²²

PMID 31691613: A systematic review found only seven reported ACC cases with macroscopic fat on CT or MRI, typically as large symptomatic tumors over 6 cm with a very small fat component, often less than 5%. The review suggests macroscopic fat does not fully exclude ACC in large symptomatic adrenal masses, although evidence quality is limited by uncertain pathologic confirmation.⁵⁵

PMID 31842905: In adrenal lesions 5 cm or larger, adrenocortical carcinoma was associated on CT with larger size, infiltrative appearance, ill-defined margins, and heterogeneous texture, while benign adenomas more often showed pre-contrast attenuation below 10 HU. The study emphasizes that CT can suggest malignancy but cannot fully determine tumor nature.¹²³

PMID 31894378: This review summarizes imaging findings that raise suspicion for ACC on adrenal evaluation, emphasizing CT and MRI for initial characterization and FDG-PET for staging or recurrence. Reported CT clues include large size, marked heterogeneity, necrosis, calcification, irregular margins, local or vascular invasion, and low contrast washout compared with adenoma.¹²⁴

PMID 32322909: This review summarizes characteristic imaging features of adrenocortical carcinoma across pediatric and adult patients, emphasizing typically large adrenal masses with irregular margins, heterogeneous enhancement, central hemorrhage or necrosis, calcifications, possible fat, and venous extension into the renal vein or inferior vena cava. It notes that tumor size greater than 4 cm and heterogeneous enhancement are the most predictive imaging factors of malignancy in an adrenal mass.⁶

PMID 33209542: This case report highlights MRI and CT features that can help distinguish adrenal abscess or infected pseudocyst from necrotic adrenocortical carcinoma in a large cystic adrenal-region mass. The excerpt contrasts ACC-associated findings such as irregular wall morphology, heterogeneity, necrosis, calcifications, delayed washout, and high unenhanced CT attenuation with smoother benign-appearing cystic lesions.¹²⁵

PMID 33226356: This case report highlights that adrenal hemangioma can mimic adrenocortical carcinoma on CT and MRI, with nonspecific heterogeneous enhancement, possible calcification, and uncertain organ of origin. It emphasizes MRI as the most informative modality for defining lesion structure and relationships, while noting that definitive diagnosis often still requires histopathology.⁵³

PMID 33658437: This case report describes a benign cortisol-producing adrenocortical adenoma with organized and recanalized venous thrombus that appeared radiologically suspicious for malignancy. Large size, heterogeneous or peripheral enhancement, and hemorrhagic-appearing internal components on CT and MRI can mimic ACC or even angiosarcoma.¹²⁶

PMID 33677483: This pilot study suggests that CT radiomics and texture analysis may help distinguish localized, nonfunctioning adrenocortical carcinoma from adenoma or benign incidentaloma when conventional attenuation and washout criteria are indeterminate. Multiple first- and second-order features across unenhanced and contrast-enhanced phases showed high diagnostic performance, though two calcified carcinomas behaved as outliers.⁶⁷

PMID 33807178: In right-sided ACC, preoperative CT focal tumor bulge into hepatic parenchyma and MRI contour disruption are highly reproducible imaging signs strongly associated with direct liver involvement. MRI did not outperform CT for this assessment, supporting CT-based surgical planning for possible en bloc liver resection.⁴⁶

PMID 33829304: In adrenal nodule characterization, dual-layer dual-energy CT virtual unenhanced images overestimated lesion attenuation compared with true unenhanced CT, making the standard 10 HU cutoff unreliable for identifying lipid-rich adenomas. A higher virtual unenhanced threshold of 22 HU improved sensitivity but reduced specificity and requires further validation.¹²⁷

PMID 33889224: This case report emphasizes that non-functioning ACC may present with nonspecific symptoms and a large adrenal mass on CT showing heterogeneity, density above 10 HU, hypervascular heterogeneous enhancement, necrosis or hemorrhagic features, and local mass effect. The article summarizes CT and MRI features that help distinguish malignant adrenal lesions from adenoma.¹²⁸

PMID 34011673: This case report highlights a CT contrast-enhancement clue in adrenal masses: ganglioneuroma may show progressive delayed wash-in with higher attenuation at 15 minutes than at 1 minute, unlike ACC, which is described as peaking in the early venous phase with delayed wash-out.¹²⁹

PMID 34297499: This review summarizes adrenal imaging for differentiating benign from malignant adrenal masses, including ACC. It emphasizes contrast-enhanced CT as the principal first-line modality, MRI as sensitive but limited for malignancy specificity, and PET/CT as an adjunct for detecting malignant lesions, metastases, and postoperative recurrence.²

PMID 34503194: This review emphasizes CT as the first-line modality for suspected ACC, highlighting tumor size and unenhanced attenuation as key malignancy indicators, with 4 cm and 20 HU proposed as useful thresholds. It also summarizes the supportive but more limited roles of contrast washout, MRI, and FDG-PET/CT in indeterminate adrenal masses.²⁶

PMID 34792039: In pediatric adrenocortical carcinoma, imaging typically shows a large heterogeneous suprarenal mass with solid and cystic components, necrosis, calcifications, heterogeneous enhancement, local invasion, venous tumor thrombus, and distant metastases. MRI diffusion features and out-of-phase signal loss do not reliably distinguish benign from malignant pediatric adrenocortical tumors.¹³⁰

PMID 34804773: A retrospective two-center study evaluated endoscopic ultrasound features of adrenocortical carcinoma and found ACC lesions were larger than pheochromocytomas, commonly round, nodular, heterogeneous, and often contained hypo-/anechoic areas, with less hyperperfusion than pheochromocytoma. However, EUS morphology alone did not reliably distinguish ACC from other malignant or benign adrenal tumors.¹³¹

PMID 34950566: This case report describes a large nonfunctional adrenal cortical adenoma that showed imaging features classically concerning for ACC, including large size, heterogeneous contrast enhancement, T2 hyperintensity, and intense FDG uptake. It highlights that imaging alone may not reliably distinguish ACC from benign adrenal cortical masses.⁵¹

PMID 34987692: This case report highlights that an ectopic adrenocortical adenoma in the renal hilum can mimic renal cell carcinoma on CT and MRI, showing low attenuation, early enhancement with delayed washout, and signal drop on out-of-phase imaging. For a lipid-containing mass adjacent to the kidney, ectopic adrenocortical tumor should be considered in the imaging differential.¹³²

PMID 35037990: In heterogeneous adrenal masses, CT and MRI evidence of microscopic or macroscopic fat was highly specific for adenoma rather than non-adenoma, including ACC. A multivariable imaging model using fat, lesion diameter under 5.5 cm, calcifications, and hemorrhage achieved high discriminative performance.¹³³

PMID 35508935: This case report describes a nonfunctioning adrenal incidentaloma with an initially small, lipid-poor appearance on CT at 1.8 cm and 40 Hounsfield units that enlarged progressively over six years to 8.0 × 4.3 cm before resection confirmed ACC. It underscores interval growth on serial CT as an imaging clue to malignancy even when hormonal studies remain negative.⁵⁷

PMID 35536326: In indeterminate adrenal masses, adrenal washout CT showed limited specificity for adenoma, and the introduction notes that a substantial minority of adrenocortical carcinomas can display washout values in the adenoma range. The study’s single ACC case was heterogeneous on unenhanced CT and demonstrated non-adenoma washout.¹³⁴

PMID 35748977: In a single-center adrenalectomy cohort, all ACCs were larger than 50 mm, had unenhanced CT attenuation above 40 HU, and showed low lipid content; 57% also had necrosis or calcifications. Tumor size alone had good discrimination for ACC, but lesions with HU below 40 had no observed ACC regardless of size.³⁷

PMID 35934796: This case report describes ACC arising from a small adrenal incidentaloma that remained radiographically stable for 5 years before rapid enlargement. It highlights that initial unenhanced CT attenuation above 10 HU, later heterogeneity, irregular shape, and growth can signal malignancy even when the lesion is initially small.⁵⁸

PMID 36104962: This retrospective CT study of 67 patients with adrenocortical carcinoma found that ACC most often showed heterogeneous structure, tumor size 3-9 cm, native density above 30 HU, absolute contrast washout below 60%, and relative washout below 40%, while no single CT feature was pathognomonic. The article supports standardized contrast-enhanced CT as the main preoperative imaging method for suspected adrenal malignancy.³¹

PMID 36244817: This retrospective single-center study developed a 9-variable cross-sectional imaging score to distinguish localized adrenocortical carcinoma from lipid-poor cortical adenoma in adrenal masses with attenuation greater than 10 HU. Discriminating features included size, attenuation, rim enhancement patterns, heterogeneity, calcification, necrosis, fat infiltration, and lymph node prominence, with very high negative predictive performance for excluding ACC.⁶⁸

PMID 37347698: This article emphasizes imaging pitfalls in adrenal mass evaluation relevant to ACC, noting that ACC can mimic adenoma by meeting conventional washout CT thresholds and may rarely contain small foci of macroscopic fat. It highlights the need to integrate lesion size, heterogeneity, growth, enhancement, and clinical context rather than relying on washout criteria alone.⁵⁶

PMID 37369921: A retrospective single-center study found that a CT-based 3D DenseNet model distinguished stage 1-2 adrenocortical carcinoma from large lipid-poor adrenal adenoma with high cross-validated sensitivity and accuracy on single time-point contrast-enhanced CT. The study highlights this as a potential imaging aid for indeterminate adrenal masses but notes the need for external multicenter validation before clinical adoption.⁶⁹

PMID 37908270: This case report highlights that macroscopic fat on adrenal CT, although strongly suggestive of myelolipoma, does not exclude adrenocortical carcinoma. In reported ACC cases, fat was typically a very small component of the lesion, so suspicious clinical or radiologic features such as hormone excess, metastases, or rapid growth should outweigh reassurance from isolated fat findings.¹³⁵

PMID 38411694: In surgically proven lipid-poor adrenal masses, modified adrenal CT criteria improved identification of non-adenomas, including adrenocortical carcinoma, compared with conventional washout criteria. Features incorporated beyond washout included high unenhanced or contrast-phase attenuation and intralesional cystic degeneration, reducing false-negative classification of non-adenomas.⁶⁶

PMID 38458314: This case report describes CT features of ACC as a large heterogeneous adrenal mass with necrosis, coarse calcification, irregular hypervascular enhancement, collateral vessels, compressive local effects, and paraaortic nodes, with triphasic CT showing hypervascular liver metastases that enhance arterially and wash out on delayed images.¹³⁶

PMID 38575426: This retrospective two-center study evaluated a multiparametric MRI algorithm using apparent diffusion coefficient and chemical shift signal intensity index to distinguish adrenocortical carcinoma from lipid-poor adrenal adenoma. In validation, the algorithm alone had 75% accuracy and 76% specificity, while adding a 4 cm size cutoff increased sensitivity to 96%.⁷⁰

PMID 38660483: This case-based review highlights CT features used to assess malignant potential in adrenal cortical tumors, emphasizing tumor size, noncontrast attenuation, and contrast washout. It notes that attenuation above 20 HU raises concern for malignancy while benign lipid-poor adenomas may overlap, making washout characteristics and, when needed, postoperative pathology important for distinction from ACC.¹³⁷

PMID 38706490: This case report highlights that adrenal haemangioma can mimic ACC on CT because of large size, heterogeneity, calcifications, necrosis or haemorrhagic change, while MRI may show peripheral nodular enhancement with progressive fill-in and PET may show low-grade peripheral uptake. It underscores persistent diagnostic uncertainty when imaging findings are discordant.¹³

PMID 39051607: In a retrospective surgical series of primary adrenal masses, contrast-enhanced CT with adrenal protocol showed 75% sensitivity and 95.6% specificity for malignancy compared with histopathology. Malignant radiologic features were associated with larger tumors, particularly masses over 6 cm, and low washout values below standard APW and RPW thresholds.¹³⁸

PMID 39384399: This review summarizes imaging clues that help distinguish adrenocortical carcinoma from benign adrenal adenoma, including typical large size, heterogeneous density from necrosis or hemorrhage, heterogeneous T2 signal, irregular contour, loss of intervening fat planes, venous tumor thrombus, and poor contrast washout without signal drop on opposed-phase MRI.¹³⁹

PMID 39417086: This veterinary case emphasizes imaging features of ACC evaluation, with ultrasound showing adrenal enlargement, heterogeneity, mineralization, and progressive growth, while CT defined irregular contours, heterogeneous enhancement, and close relationship to the vena cava for surgical planning. The report also describes elastography as an adjunct for assessing tissue stiffness and possible malignancy.¹⁴⁰

PMID 39503236: In adults with small atypical adrenal masses measuring 10 to 39 mm and greater than 10 HU, ACC accounted for 11.2% of lesions and showed much faster growth than adenomas. Absolute contrast washout above 60% occurred in most evaluated ACC cases, indicating washout is unreliable for excluding malignancy in this setting.¹⁶

PMID 39606180: In unilateral lipid-poor adrenal masses, ACC in this prospective cohort was usually large and showed poor washout, but post-contrast attenuation overlapped with adenoma and metastatic or infiltrative lesions. The study also notes that a rare nonsecretory ACC can show good washout, limiting washout alone as a discriminator.¹⁴¹

PMID 39851941: In a retrospective cohort of adrenocortical tumors at least 40 mm, possible necrosis on preoperative CT or MRI was strongly associated with ACC, with 81% sensitivity and 75% specificity, while histologic necrosis was even more accurate. The study supports necrosis as a useful noninvasive imaging clue that should be interpreted alongside tumor size and endocrine evaluation.⁴⁵

PMID 39914911: This update reviews multimodal imaging for suspected ACC, emphasizing contrast-enhanced CT as the standard first-line modality for diagnosis, staging, and preoperative assessment, with MRI as a complementary problem-solving tool. It summarizes malignant imaging clues including large size, heterogeneous enhancement, necrosis or hemorrhage, calcifications, irregular margins, local invasion, venous involvement, interval growth, and metastatic spread.³

PMID 40075696: This review summarizes radiologic evaluation of adrenal incidentalomas with emphasis on CT as first-line imaging and MRI or FDG-PET for indeterminate lesions. It highlights malignancy-suspicious features such as lesion size of at least 4 cm, heterogeneity, higher unenhanced attenuation, necrosis, and washout behavior relevant when ACC is in the differential.¹⁴²

PMID 40250886: This review outlines imaging evaluation of adrenal masses relevant to suspected ACC, emphasizing noncontrast CT as the first-line test and highlighting size, attenuation, heterogeneity, necrosis, irregular borders, and local invasion as key features associated with malignancy. It also notes limitations of washout CT and MRI, and the role of FDG PET mainly for staging suspected ACC.¹⁹

PMID 40273001: This case report highlights that CT washout criteria can misclassify adrenocortical carcinoma as a benign adenoma when pre-contrast attenuation is high. In indeterminate adrenal lesions, especially in younger patients or those with values above 10-20 HU, high washout should be interpreted cautiously and may warrant additional or follow-up imaging.⁵⁹

PMID 40750857: A multicenter retrospective study developed an interpretable contrast-enhanced CT radiomics model to distinguish large adrenal ACC from pheochromocytoma, achieving high external-test accuracy and outperforming radiologists. The model retained useful performance in hormonally atypical or biochemically negative cases where conventional CT interpretation is challenging.⁷¹

PMID 41217476: This review summarizes CT features that help distinguish ACC from other large adrenal masses, noting that ACC usually appears as a large heterogeneous, inhomogeneous lesion with necrosis or hemorrhage, attenuation rarely below 20 HU, limited washout, possible calcifications, local invasion, IVC tumor thrombus, and metastases.⁷

PMID 41322946: A large nonfunctional adrenal cavernous hemangioma can mimic presumed ACC on CT and MRI, with heterogeneous hypervascular appearance, peripheral enhancement, central hypoattenuation or infarction, hemorrhagic components, and mass effect despite no metastatic disease or vascular invasion. The report highlights a benign imaging mimic within the differential diagnosis of large adrenal masses.⁵⁴

PMID 41625906: In a unilateral adrenal incidentaloma cohort, ACC cases were larger than lipid-poor adenomas and had mean non-contrast CT attenuation of 29.7 HU. Central necrosis, adjacent fat changes, local invasion, and vascular invasion clustered in ACC, while one ACC measured under 4 cm, underscoring that size alone is insufficient.²⁷

PMID 41649000: In a surgically confirmed adrenal mass cohort, all adrenocortical carcinomas were measured at 10 HU or higher on non-contrast CT, supporting the practical use of low attenuation to exclude ACC. The study also found excellent interobserver reliability for attenuation measurements performed by non-radiologist surgeons using a simple ROI method.³⁸

PMID 41652884: This review summarizes imaging features of adrenocortical carcinoma in endocrine hypertension workup: ACC is usually a large, unilateral, heterogeneous adrenal mass with necrosis, hemorrhage, and sometimes calcification, with non-necrotic areas typically measuring over 10 HU on unenhanced CT and frequent local invasion or metastases.¹⁴³

PMID 41788772: In large adrenal tumors at least 4 cm, unenhanced CT attenuation remained highly sensitive for malignancy, with no malignancies identified among homogeneous lesions under 10 HU, while MRI chemical shift imaging could be misleading and FDG PET/CT showed high sensitivity. The cohort also illustrates that some ACCs may initially appear relatively indeterminate on washout and chemical shift imaging.⁶⁰

PMID 2351599: A veterinary comparative study found CT localized all hyperfunctioning adrenocortical tumors and occasionally suggested caval invasion, but CT features usually did not reliably distinguish adenoma from carcinoma and were limited for predicting resectability. Although indirect to human ACC, it supports the historical framing of CT as strong for localization and anatomic assessment but not pathognomonic characterization.¹⁴⁴

PMID 3410782: A veterinary radiography series of functioning adrenocortical tumors found that adrenal calcification occurred in both adenomas and carcinomas and that noncalcified enlargement was harder to detect, reinforcing the nonspecific nature of calcification. The study is indirect to human ACC and predates modern cross-sectional imaging, but it aligns with the note’s caution about overinterpreting isolated structural findings.⁴²

PMID 39160654: A 2024 ex vivo canine MRI-histology pilot study including three adrenocortical carcinomas found high specificity but low overall sensitivity for adrenal lesions, with negative MRI not excluding histologic abnormality. This indirect evidence supports the note’s emphasis on the limits of MRI as a sole discriminator or exclusion test in ACC evaluation.¹⁴⁵

PMID 34183180: A 2022 Surgery article examined whether CT-identified necrosis can distinguish malignant from benign adrenocortical tumors and supports a cautious interpretation: necrosis may be associated with malignancy but is not reliable as a standalone parameter. This refines the note’s discussion of heterogeneity by emphasizing the limited independent specificity of one component feature.⁴⁴

PMID 9106974: A 1997 veterinary case report described canine ACC on ultrasound as a large hypoechoic adrenal mass with internal calcification, vessel displacement, contralateral gland atrophy, and hepatic metastases. Although indirect to human CT/MRI practice, it reinforces that calcification and local vascular distortion are not specific for malignancy and that metastatic findings may be more diagnostically helpful.¹⁴⁶

Quartz 4

Explorer

ct_and_mri_features_of_acc

CT and MRI Features of ACC

Diagnostic context

Major imaging phenotypes

Typical primary tumor appearance

Invasion, thrombus, and metastatic pattern

Differentiation from adenoma and other mimics

Evidence on specific imaging parameters

Role in management and research

Included Articles

References

Graph View

Table of Contents

Quartz 4

Explorer

ct_and_mri_features_of_acc

CT and MRI Features of ACC

Diagnostic context

Major imaging phenotypes

Typical primary tumor appearance

Invasion, thrombus, and metastatic pattern

Differentiation from adenoma and other mimics

Evidence on specific imaging parameters

Role in management and research

Included Articles

References

Footnotes

Graph View

Table of Contents