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Adrenal Mass Imaging with Multidetector CT: Pathologic Conditions, Pearls, and Pitfalls1
CME FEATURE
See the questionnaire on pp 1537-1544.
LEARNING OBJECTIVES FOR TEST 3
After reading this article and taking the test, the reader will be able to:
List the typical CT findings of various benign and malignant adrenal neoplasms.
Describe pitfalls in CT image inter- pretation specific to adrenal pathologic conditions.
Discuss the util- ity of multiplanar CT display with 2D multiplanar reforma- tion and 3D render- ing in characterizing adrenal lesions.
TEACHING POINTS
See last page
Pamela T. Johnson, MD · Karen M. Horton, MD . Elliot K. Fishman, MD
The adrenal gland is involved by a range of neoplasms, including pri- mary and metastatic malignant tumors; however, the most common tumor detected is the incidental benign adenoma. Although computed tomographic (CT) findings will not always yield a definitive diagnosis, attention to these findings provides a road map to guide image inter- pretation. Adenomas typically demonstrate rapid washout, which is defined as an absolute percentage washout (APW) of more than 60% and a relative percentage washout (RPW) of more than 40% on de- layed images. Adrenocortical carcinoma typically has an RPW of less than 40%; however, large size and heterogeneity are more reliable in- dicators of the diagnosis than are washout values. Washout characteris- tics of pheochromocytoma are variable; in conjunction with high levels of dynamic enhancement, pheochromocytomas may mimic adenoma (ie, APW > 60%, RPW > 40%). Myelolipomas appear as well-defined masses with variable quantities of fat and soft tissue. After contrast material administration, metastases usually demonstrate slower washout on delayed images (APW < 60%, RPW < 40%) than do ad- enomas, although hypervascular metastases may enhance similarly to pheochromocytoma. Finally, a number of nonadrenal pathologic con- ditions have been reported to mimic adrenal masses at CT.
CRSNA, 2009 · radiographics. rsna.org
Abbreviations: APW = absolute percentage washout, IVC = inferior vena cava, RPW = relative percentage washout
RadioGraphics 2009; 29:1333-1351 . Published online 10.1148/rg.295095027 . Content Codes: CT GU|01
1From the Russell H. Morgan Department of Radiology and Radiologic Science, Johns Hopkins School of Medicine, 601 N Caroline St, Room 3140D, Baltimore, MD 21287. Recipient of an Excellence in Design award for an education exhibit at the 2008 RSNA Annual Meeting. Received February 10, 2009; revision requested March 13; final revision received April 28; accepted April 29. E.K.F. receives research support from Siemens and General Electric, is on the advisory boards of Siemens and General Electric, and is cofounder of HipGraphics; all other authors have no financial relationships to disclose. Address correspondence to P.T.J. (e-mail: pjohnso5@jhmi.edu).
See also the article by Johnson et al (pp 1319-1331) in this issue.
Teaching Point
Introduction
The adrenal glands (Fig 1) are routinely visual- ized on every computed tomographic (CT) scan of the abdomen and on most CT scans of the chest. Although the adrenal gland is involved by a range of diseases, including primary and metastatic malignant tumors, the most common lesion detected is the incidental benign adrenal adenoma. In fact, the majority of lesions de- tected at CT are benign, be they myelolipomas, cysts, or the sequelae of prior trauma.
In this article, we present a comprehensive look at the “signatures” of the various adrenal masses, with the goal of setting a clear strategy for manag- ing these lesions with CT. The cases demonstrated herein display the typical CT findings of a range of both benign and malignant neoplastic adrenal lesions, as well as the utility of a multiplanar CT display incorporating two-dimensional multiplanar reformation and three-dimensional rendering to characterize adrenal lesions.
Adrenal Neoplasms
Adenoma
The prevalence of adrenal adenoma is age related. Kloos et al (1) reported the frequency of unsus- pected adenoma according to age, citing 0.14% for patients aged 20-29 years and 7% in those older than 70 years. The majority of lesions are not functioning. Although CT does not allow differen- tiation of functioning from nonfunctioning masses, the presence of contralateral adrenal atrophy sug- gests that a lesion may be functioning, because pituitary adrenocorticotropic hormone secretion is suppressed by elevated cortisol levels (2).
Adenomas are typically well-defined (Fig 2) and often homogeneous in attenuation (87% homogeneous on precontrast images, 58% homo- geneous on postcontrast images) (3,4). Although size is not a definitive indicator of benignity, several investigations that measured diameter reported average diameters of 2-2.5 cm, with the largest lesions measuring around 3 cm. Other studies have included larger adenomas (diameters approximately 4-6 cm) (5-10).
The precontrast attenuation varies accord- ing to the presence or absence of lipid, with mean attenuation in the range of -2 to 16 HU (3,8,10-14) in lipid-rich adenomas and higher
attenuation (20-25 HU) seen in the setting of lipid-poor adenomas (15-17). Lipid-poor adenomas (Figs 3, 4) represent 10%-40% of adenomas (15,16). Tables 1-3 present the CT
| Study* | No. of Adenomas | No. of Nonadenomas | Mean Precontrast Attenuation (HU) | |
|---|---|---|---|---|
| Adenomas | Nonadenomas | |||
| Caoili et al 2000 (15) | 56 LRAs; 18 LPAs | 40+ | LRAs =- 5.7; LPAs = 26 | 29 |
| Caoili et al 2002 (16) | 105 LRAs; 22 LPAs | 391 | LRAs =- 2; LPAs = 25.9 | 29.5 |
| Jhaveri et al 2007 (17) | 24 LPAs | ... | 23 (12-47)* | ... |
| Ho et al 2008 (18) | 65 LRAs; 31 LPAs | 36 metastases | LRAs = 1.8; LPAs = 20.2 | 35.6 |
Note .- LPA = lipid-poor adenoma, LRA = lipid-rich adenoma.
*Numbers in parentheses are references.
tBenign lesions are grouped with adenomas.
Numbers in parentheses are the range.
| Table 2 Delayed Postcontrast CT Findings of Lipid-poor Adenomas | ||||
|---|---|---|---|---|
| Study* | No. of Adenomas | No. of Nonadenomas | Mean Delayed Attenuation (HU)t | |
| Adenomas | Nonadenomas | |||
| Caoili et al 2000 (15) | 56 LRAs; 18 LPAs | 40± | LRAs = 12; LPAs = 41 | 54 |
| Caoili et al 2002 (16) | 22 LPAs | 39 | LPAs = 40.6 | 53.3 |
Note .- LPA = lipid-poor adenoma, LRA = lipid-rich adenoma.
*Numbers in parentheses are references.
+Timing of delayed images = 15 minutes.
Benign lesions are grouped with adenomas.
| Study* | No. of Adenomas | No. of Non- adenomas | Mean Percentage Washoutt | Washout Threshold (%) | Sensitivity for LPAs (%) | Specificity for LPAs (%) | |
|---|---|---|---|---|---|---|---|
| Adenomas | Non- adenomas | ||||||
| Caoili et al | 18 LPAs | 40± | APW = 75 | APW = 19 | APW = 60 | 89 | 95 |
| 2000 (15) | RPW = 47 | RPW = 11 | RPW = 40 | 83 | 93 | ||
| Caoili et al | 22 LPAs | 39¢ | APW = 70.7 | APW = 22.5 | APW = 60 | 86 | 92 |
| 2002 (16) | RPW = 46.8 | RPW = 12.9 | RPW = 40 | 82 | 92 | ||
| Park et al | 37 LPAs | 6¢ | ... | ... | APW = 60 | 100 | 83 |
| 2007 (19) | RPW = 40 | 97 | 100 | ||||
Note .- LPA = lipid-poor adenoma.
*Numbers in parentheses are references.
+Timing of delayed images = 15 minutes.
Benign lesions are grouped with adenomas.
24HU pre-contrast
50HU post-contrast
24HU delayed
Teaching Point
characteristics of lipid-poor adenomas reported in published studies (15-19). As shown by Caoili et al (15,16) in 2000 and 2002, regardless of lipid content (Fig 4), adenomas typically demonstrate rapid washout, which is defined as an APW of more than 60% and an RPW of more than 40% on delayed images.
Rarely, an adenoma can hemorrhage, usu- ally in a patient receiving anticoagulant therapy. The presence of hemorrhage results in regions of higher attenuation and heterogeneity. At CT, het- erogeneity and regions of increased attenuation have been shown to correlate with hemorrhage at pathologic analysis (Fig 5) (20). Before liquefac- tion, the precontrast attenuation will be higher than 10 HU.
Adrenocortical Carcinoma
Adrenocortical carcinoma (Fig 6) has a bimodal peak (1st and 4th decades); however, this tumor is often identified earlier in children because it tends to be hormonally active (21,22). A review of 15 published series revealed that on average, 55% (range, 26%-94%) were functional, mani- festing as Cushing syndrome, feminization, viril- ization, or mixed Cushing syndrome-virilization. Hypertension is common in all syndrome types (21). Alternatively, patients may have pain, a palpable mass, or gastrointestinal complaints
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due to the mass (21). With respect to size and ap- pearance, adrenocortical carcinoma is typically a large mass (Figs 7, 8), with the majority measur- ing more than 6 cm in a case compilation from a literature review (23) and diameters of 4-25 cm (mean, 9.8 cm) in the review article by Ng and Libertino (22). In 38 lesions evaluated with CT, diameters were 3-25 cm and the rate of hor- monal activity was inversely related to size (24).
Fishman et al (24) reported CT findings in 38 patients and noted that larger masses compressed the kidney posteriorly and the pancreas and stomach anteriorly. Tumors were inhomogeneous at nonenhanced CT, particularly masses larger than 6 cm, owing to the presence of necrosis. Af- ter contrast material infusion, adrenocortical car- cinoma enhances heterogeneously, often periph- erally, with a thin rim of enhancing capsule seen in some cases. Studies of lesion washout have reported that adrenocortical carcinoma typically has an RPW of less than 40%, with specific mea- sures reported in Table 4 (14,25). However, the large size and heterogeneity are more reliable in- dicators of the diagnosis than are washout values, which vary depending on which part of the mass is sampled. In 19%-33% of cases, calcifications have been identified, more commonly microcalci- fications. In the series of Fishman et al (24), the liver was the most common metastatic location at CT (identified in some patients at presentation),
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| Study* | No. of Tumors | Size (cm) | Attenuation (HU) by Phase | Percentage Washout on Delayed Images | |
|---|---|---|---|---|---|
| Precontrast | Portal Venous | ||||
| Szolar et al 2005 (14) | 7 | 4.5-16 | 23-52 | 51-108 | APW = 34 ± 9 at 10 min RPW = 13 ± 12 at 10 min |
| Slattery et al 2006 (25) | 11 | 5-14 | 32-45 | 64-95 | RPW = 14-32 at 7-17 min |
| *Numbers in parentheses are references. | |||||
particularly with left-sided masses. Other sites included the lung and lymph nodes, along with direct extension and tumor thrombus.
Invasion of the IVC (Fig 8) is a well-known complication of adrenocortical carcinoma. Patients with IVC involvement may present with hormonal syndromes, constitutional symptoms, abdominal pain, lower extremity edema, or pulmonary embo- lism (26). In one series of 15 adrenocortical carci-
nomas that invaded the IVC, 12 were on the right side. Also presented in that article was a summary of the literature, which revealed that the highest level of venous extension in 51% of patients was the suprahepatic IVC among those for whom this information was provided (26).
When masses arising in the region of the adre- nal become large, it can be difficult to determine their origin. Furthermore, lesions other than adre- nocortical carcinoma can invade the IVC (Fig 9). Cuevas et al (27) reviewed 21 cases and found
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that, in addition to primary leiomyosarcoma of the IVC (Fig 10), IVC involvement occurred with re- nal cell carcinoma, leiomyosarcoma of the adrenal, hepatocellular carcinoma (Fig 9), and a retroperi- toneal metastasis. Some benign tumors can invade the IVC, such as uterine leiomyoma; in addition, reports indicate that pheochromocytoma rarely invades the IVC (28).
Pheochromocytoma
Pheochromocytoma (Fig 11) is present in 0.1%-0.2% of adults with hypertension (29). Among patients with pheochromocytomas identi- fied incidentally, 53% have hypertension (30). Mittendorf et al (29) described the most frequent symptom as “new onset, refractory, paroxysmal or recently exacerbated” hypertension. Patients may also present with palpitations, headache, dia- phoresis, and flushing; however, 10% of patients are asymptomatic (29,31,32).
These tumors are associated with a number of syndromes (in 10% of patients), including multiple endocrine neoplasia type 2, von Hippel-
Lindau syndrome, neurofibromatosis, tuberous sclerosis, and Sturge-Weber syndrome (29). Ap- proximately 10%-15% of pheochromocytomas are malignant (29,31). The diagnosis is made clinically
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| Study* | No. of Lesions | Size (cm) | Attenuation (HU) by Phase | Percentage Washout on Delayed Images | |
|---|---|---|---|---|---|
| Precontrast | Portal Venous | ||||
| Blake et al | 8 | 1-6.7 | 9-42 | 74-90 | APW = 36-69 at 10 min |
| 2003 (32)+ | RPW = 16-83 at 10 min | ||||
| Szolar et al 2005 (14) | 17 | 4.7-10.8 | 28-60 | 72-131 | APW = 22 ± 12 at 10 min RPW = 14 ± 7 at 10 min |
| Motta-Ramirez et al 2005 (30) | 33 | 2.6-11.2 | 17-59 | 94.7 and 104.3+ | ... |
| Park et al 2006 (13) | 31 | ... | 37 ± 9 | ... | APW = 54 ± 21 at 15 min |
*Numbers in parentheses are references.
tSeries of low-attenuation pheochromocytomas.
Mean of 94.7 HU for incidental lesions and 104.3 HU for symptomatic lesions.
by using a 24-hour urine assessment for vanillyl- mandelic acid, catecholamines, and metanephrines (29). Alternatively, plasma-free metanephrine level can be measured. This level has been shown to have high sensitivity (29); however, specificities of 84%-89% prompted Young (33) to recommend measuring this level only in the setting of high clinical suspicion for pheochromocytoma.
The comparative study of Szolar et al (14) showed that pheochromocytomas were signifi-
cantly larger than adenomas but not larger than metastases. Blake et al (32) noted that nonsecre- tory lesions were larger than functional masses. Table 5 reports the sizes and CT findings from four studies (13,14,30,32). At CT, the attenu- ation of pheochromocytomas can be homoge- neous (particularly if small) (Fig 12) or het- erogeneous (ie, larger lesions with hemorrhage
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and necrosis) (Fig 13). Pheochromocytomas may have abundant intracellular fat or regions of cystic degeneration (Fig 14), resulting in re- duced precontrast attenuation (31). Calcification was present in 29% of suspected versus 0% of incidental pheochromocytomas in the study of Motta-Ramirez et al (30), which stratified cases by clinical presentation.
Pheochromocytoma is classically characterized as brightly enhancing but has a range of CT ap- pearances. Washout characteristics are variable, and in conjunction with high levels of dynamic enhancement, pheochromocytomas may mimic adenoma (ie, APW > 60%, RPW > 40%) (Fig 15) (32,34). This was the pattern for 16% of pheo- chromocytomas in one series (13). Park et al (13) in 2006 showed that pheochromoctyomas had significantly greater 15-minute washout than me-
Teaching Point
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tastases (mean washout value, 54% vs 11%). A subset of lesions (3%-19%) are of fluid attenu- ation (35). These appear as cystic masses with thick enhancing walls (Fig 14). Andreoni et al (35) reported that cystic lesions were less likely to be symptomatic owing to a lower prevalence of biochemical markers. In 2007, Park et al (36) demonstrated that some lesions with myxoid degeneration show enhancement on delayed images in regions that have low attenuation on venous phase images.
Myelolipoma
Myelolipoma is a relatively uncommon benign tumor composed of hematopoietic tissue and ma- ture adipose that is usually identified incidentally (37). These tumors can arise in the adrenal gland or, much less frequently, from an extraadrenal location. If there are symptoms, they are generally due to mass effect, tumor necrosis, or hemor- rhage, as myelolipomas are nonfunctioning tu- mors (37). However, clinical symptoms may occur when the tumors arise in conjunction with other adrenal masses or syndromes (37). In a study of 21 masses by Han et al (38), 60% occurred in women, and the mean patient age was 63 years. Several authors have reported right-sided predom- inance of unilateral masses (68%-78%) (38,39). Lesion size was 2-17 cm in the series of Han et al (38), and follow-up of 13 tumors revealed that two decreased in size and six enlarged.
CT shows a well-defined mass with variable quantities of fat and soft tissue (Figs 16-18). Kenney et al (39) reported a series of cases from the Armed Forces Institute of Pathology. Their study analyzed different subtypes by using pre- defined criteria and found that isolated adrenal myelolipoma is most commonly composed of 50%-90% fat with an average size of 10 cm; calcification occurred in 24% of lesions, and the majority (75%) had a pseudocapsule.
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Myelolipomas that existed in conjunction with other pathologic conditions were significantly dif- ferent from isolated myelolipomas, being smaller (mean, 7 cm) with less fat (most frequently <10%), a higher prevalence of calcification (52%), and lower frequency of a pseudocapsule (33%) (39). When myelolipomas hemorrhage, patients may present with pain, nausea, vomiting, or hypoten- sion. In the series of Kenney et al (39), such myelo- lipomas had a mean size of 14 cm and fat content similar to that of uncomplicated masses (usually 50%-90%); calcification occurred in 10%, and all hemorrhagic myelolipomas had a pseudocapsule.
A number of different adrenal tumors have been reported to demonstrate focal macro- scopic fat in case reports. These include adrenal adenoma, pheochromocytoma, adrenocortical carcinoma, and even a metastatic adenocarci- noma (40-44). In addition, collision tumors, formed by coexisting lesions of different patho- logic origins, manifest with atypical imaging appearances. For example, myelolipomatous le- sions are nonfunctional; however, an adenoma- myelolipoma collision tumor may manifest with hormonal syndrome owing to the functional adenoma component (Fig 19) (45). Another scenario for creation of a collision tumor would be metastasis to a preexisting adenoma.
Teaching Point
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Lymphoma
Lymphoma can involve the adrenal gland secon- darily or arise as a primary adrenal tumor (uncom- mon) (Fig 20); the latter lesion is frequently bi- lateral. Paling and Williamson (46) reviewed 173 cases of non-Hodgkin lymphoma and found that
4% had secondary adrenal involvement; 43% of these cases were bilateral. According to Scully et al (47), 25% of patients with non-Hodgkin lym- phoma have adrenal involvement at autopsy.
Paling and Williamson (46) reported the CT find- ings of non-Hodgkin lymphoma involving the ad- renal, which include a discrete mass of variable at- tenuation or an infiltrative, ill-defined appearance.
Metastases
In a review of 30 years experience at one institu- tion, adrenal metastases (Fig 21) were found at autopsy in 3% of patients (48). Lam and Lo (48) also reported that metastases were bilateral in 49% of cases (Fig 22); unilateral involvement was more common on the left side (ratio of 1.5:1) (Fig 23). Common primary tumors in patients less than 40 years of age included lymphoma-leu- kemia, lung cancer, and stomach cancer. Patients with lymphoma or with breast, colorectal, stom- ach, or prostate cancer may develop adrenal in- volvement more than 5 years after occurrence of their primary tumor. In the study of Lam and Lo (48), 90% of adrenal metastases were carcinomas (lung, gastric, esophageal, hepatic-biliary, pancre- atic, colon, renal, breast). Of these lesions, 56% were adenocarcinomas and 15% were squamous
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cell carcinomas; the remainder included he- matopoietic tumors, sarcomas, and melanomas.
Several CT studies have reported mean pre- contrast and postcontrast attenuations, as well as washout values (Table 6) (14,49,50). Hy- pervascular metastases (Fig 24) may enhance similarly to pheochromocytomas (Fig 25) (51), in particular metastases from renal cell
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| Study* | No. of Lesions | Attenuation (HU) by Phaset | Percentage Washout on Delayed Imagest | ||
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| Precontrast | Venous | Delayed | |||
| Boland et al 1997 (49) | 23 | 27.5 (14-38) | 61 (25-99) at 40 or 70 sec | 46 (25-67) at 12-18 min | ... |
| Blake et al 2006 (50) | 14 | 14-47 | 47-95 at 75 sec | 40-70 at 10 min | APW = 30.8 (0-73) RPW = 15.3 (0-37.3) |
| Szolar et al | 21 | 34 (17-55) | 81 (49-110) at 60 | 66 (50-84) at 10 | APW =31 ± 16 |
| 2005 (14) | sec | min | RPW = 19 ± 11 | ||
*Numbers in parentheses are references.
tNumbers in parentheses are ranges.
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carcinoma. After contrast material administra- tion, metastases usually demonstrate slower washout at delayed imaging (APW < 60%, RPW < 40%) than do adenomas (14,49,50).
It is important to recognize the variable appear- ance of the normal adrenal, particularly when im- aging cancer patients. Benitah et al (52) evaluated 197 patients with lung cancer and no focal adrenal mass. They reported that the normal adrenals were smoothly enlarged at CT (both limbs > 6 mm) in 11%-18% of patients and nodular in 18%-23%. The left adrenal was more commonly nodular, a finding that was also associated with older age. However, there was no association between base- line morphology and the risk of developing adrenal metastases at follow-up in cancer patients.
Teaching Point
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Pseudolesions
As demonstrated by Gokan et al (53), a number of nonadrenal pathologic conditions have been reported to mimic the appearance of an adrenal mass at CT. A gastric diverticulum (54) or gas- tric fundus, splenules, varices (55) (Fig 26), an
exophytic hepatic mass, a dilated colon, splenic lobulation, and an upper pole renal cyst are among the causes of this pitfall. In addition, an aneurysm of the splenic artery (Fig 27) or renal artery can be misinterpreted as an adrenal mass on nonenhanced images, but it will be properly diagnosed after intravenous administration of contrast material; in these cases, diagnosis may be aided by multiplanar display, which clearly demonstrates the relationship of the aneurysm to the artery from which it arises (56).
Conclusions
In this review, we have provided a comprehen- sive look at the signatures of the various adrenal masses. Although CT characteristics (eg, lesion size, washout values, the presence of calcification, fat, or hemorrhage, unilateral vs bilateral distribu- tion) will not always allow one to arrive at a de- finitive diagnosis, attention to these findings pro- vides a road map to guide image interpretation.
Acknowledgment: The anatomic drawings were cre- ated by Frank M. Corl, MS, the Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins School of Medicine, Baltimore, Md.
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Adrenal Mass Imaging with Multidetector CT: Pathologic Conditions, Pearls, and Pitfalls
Pamela T. Johnson, MD, et al
RadioGraphics 2009; 29:1333-1351 . Published online 10.1148/rg.295095027 . Content Codes: CT GU 01
Page 1334
The majority of lesions are not functioning. Although CT does not allow differentiation of functioning from nonfunctioning masses, the presence of contralateral adrenal atrophy suggests that a lesion may be functioning, because pituitary adrenocorticotropic hormone secretion is suppressed by elevated cortisol levels (2).
Page 1336
As shown by Caoili et al (15,16) in 2000 and 2002, regardless of lipid content (Fig 4), adenomas typically demonstrate rapid washout, which is defined as an APW of more than 60% and an RPW of more than 40% on delayed images.
Page 1342
Pheochromocytoma is classically characterized as brightly enhancing but has a range of CT appearances. Washout characteristics are variable, and in conjunction with high levels of dynamic enhancement, pheochromocytomas may mimic adenoma (ie, APW > 60%, RPW > 40%) (Fig 15) (32,34).
Page 1344
In addition, collision tumors, formed by coexisting lesions of different pathologic origins, manifest with atypical imaging appearances. For example, myelolipomatous lesions are nonfunctional; however, an adenoma-myelolipoma collision tumor may manifest with hormonal syndrome owing to the functional adenoma component (Fig 19) (45). Another scenario for creation of a collision tumor would be metastasis to a preexisting adenoma.
Page 1348
It is important to recognize the variable appearance of the normal adrenal, particularly when imaging cancer patients. Benitah et al (52) evaluated 197 patients with lung cancer and no focal adrenal mass. They reported that the normal adrenals were smoothly enlarged at CT (both limbs > 6 mm) in 11%- 18% of patients and nodular in 18%-23%. The left adrenal was more commonly nodular, a finding that was also associated with older age. However, there was no association between baseline morphology and the risk of developing adrenal metastases at follow-up in cancer patients.