Assessment of survey radiography and comparison with x-ray computed tomography for detection of hyperfunctioning adrenocortical tumors in dogs
George Voorhout, DVM, PhD; Ruurd Stolp, DVM, PhD; Ad Rijnberk, DVM, PhD; Paul F.G.M. van Waes, MD, PhD.
Summary: Results of abdominal survey radiography and x-ray computed tomography (CT) were compared in 13 dogs with hyperadrenocorticism histologically attributed to adrenocortical tumors. X-ray computed tomography enabled accurate localization of the tumor in all 13 dogs. Apart from 2 poorly demarcated irregular-shaped and mineralized carcinomas, there were no differences between adenoma (n=3) and car- cinoma (n=10) on CT images. In 1 dog, invasion of the caudal vena cava by the tumor was suggested on CT images and was confirmed during surgery. Suspi- cion of adhesions between tumors of the right adrenal gland and the caudal vena cava on the basis of CT im- ages was confirmed during surgery in only 2 of 6 dogs.
Survey radiography allowed accurate localization of the tumor in 7 dogs (4 on the right side and 3 on the left). In 6 of these dogs, the tumor was visible as a well-demarcated soft tissue mass and, in the other dog, as a poorly demarcated mineralized mass. The smallest tumor visualized on survey radiographs had a diameter of 20 mm on CT images. Six tumors with diameter ≤ 20 mm were not visualized on survey ra- diographs. In 1 of these dogs, a mineralized nodule was found in the left adrenal region, without evidence of a mass.
In a considerable number of cases, survey radiog- raphy can provide presurgical localization of adreno- cortical tumors in dogs with hyperadrenocorticism; CT is redundant in these instances. In the absence of pos- itive radiographic findings, CT is valuable for local- ization of adrenocortical tumors.
C linical findings in and diagnosis and surgical management of dogs with hyperadrenocorti- cism caused by adrenocortical tumor have been well documented.1-10 The preoperative localiza- tion of adrenocortical tumors has been accom-
From the Department of Radiology (Voorhout) and the Small Animal Clinic (Stolp, Rijnberk), Faculty of Veterinary Medicine, and the Department of Radiology, Faculty of Medi- cine (van Waes), State University of Utrecht Yalelaan 10, 3584 CM Utrecht, The Netherlands.
The authors thank Anneke Hamersma for technical assis- tance, Dr. Bart E. Sjollema for performing surgery, and Dr. Ted S.G.A.M. van den Ingh for performing histologic examinations.
plished successfully by use of scintigraphy,11 ultrasonography,12,13 and x-ray computed tomog- raphy (CT).14-16 Successful visualization of adreno- cortical tumors by use of survey radiography has been reported in dogs with large or mineralized tumors.3,4,9,17 Also, in a recent study18 in which survey radiography was assessed systematically for detection of adrenocortical tumors in dogs, tumors were only identified when they were mineralized.
We compared results of survey radiography with those of CT for localization and characteriza- tion of adrenocortical tumors in 13 dogs with hy- peradrenocorticism. X-ray computed tomography data for 5 of these dogs have been reported elsewhere. 16
Materials and methods
Diagnosis of hyperadrenocorticism-Hyper- adrenocorticism was diagnosed in 13 dogs. In 8 dogs, the diagnosis was made on the basis of results of the low-dose dexamethasone suppression test, that is plasma cortisol concentration > 1.4 µg/dl at 8 hours after IV administration of 0.01 mg of dex- amethasone/kg of body weight.2 An adrenocortical tumor was suspected on the basis of results of the high-dose dexamethasone suppression test, that is suppression of plasma cortisol concentration by less than 50% at 3 hours after IV administration of 0.1 mg of dexamethasone/kg.1,2
In 5 other dogs, the diagnosis of hyperadreno- corticism was based on urinary corticoid-to-creat- inine ratios exceeding 10 × 10-6.19,20 When the urinary corticoid-to-creatinine ratio decreased by less than 50% after 3 orally administered doses of dexamethasone (0.1 mg/kg) at 8-hour intervals, dogs were categorized as being dexamethasone resistant.21
Diagnosis of adrenocortical tumor was con- firmed by histopathologic findings after surgery or necropsy.
X-ray computed tomography-Food was with- held from all dogs for 24 hours prior to CT. After preanesthetic medication with methadone, dro- peridol, and atropine sulfate, anesthesia was in- duced by Iv administration of thiopental and
maintained by use of halothane, nitrous oxide, and oxygen. Scans were made, using a third-generation CT scanner,ª with the dog positioned in left lateral recumbency, and using 4.8 seconds scanning time, with 120 kV, 180 mA, and 9-mm-thick sections at 5-mm intervals. On a lateral scoutview, the left re- nal hilus was identified, and scans were made from that plane to a plane cranial to the right kidney. Regions of interest were rescanned after bolus ad- ministration of 1 to 2 ml of contrast mediumb/kg via a cephalic vein.
Radiography-Survey radiography of the ab- domen was performed in 8 unsedated dogs after food was withheld for 24 hours and in 5 unsedat- ed, unfasted dogs. Lateral and ventrodorsal radio- graphs were obtained with the dog positioned in left lateral and dorsal recumbency, respectively, and using a 3-phase 12-pulse generator capable of 150 kV and 1,250 mA, a built-in 7:1 ratio grid with 24 lines/cm mounted in a Bucky device, and reg- ular x-ray filmd in combination with par-speed in- tensifying screens.e
Exposures were made at 60 to 75 kV, depend- ing on the size of the dog, with automatic mAs pro- gramming via an ionization chamber at a focus-film distance of 110 cm. All films were developed, us- ing a daylight processing system.f
Comparison of radiography and CT-Survey ra- diographs and CT images were interpreted by one of the authors (GV). For each dog, survey radio- graphs were obtained and interpreted prior to CT. Survey radiographs and CT images were examined for the presence of a soft tissue mass medial, dor- somedial, or craniomedial to the kidneys. Local- ization, delineation, and shape of the masses were recorded, together with a description of minerali- zation, when present. On CT images, the largest di- ameter of the masses in cross section was measured on the display monitor by use of a lightpen and CT computer software.
Results
X-ray computed tomography enabled identifi- cation of adrenocortical tumor in all 13 dogs (Ta- ble 1): on the left side in dogs 2, 3, and 10-13, and on the right side in dogs 1 and 4-9. In these dogs, the tumor was located at the origin of the cranial mesenteric artery. Left adrenal gland tu- mors were located between the aorta, the caudal vena cava, the left kidney, and the dorsal extrem- ity of the spleen. In one dog, the tumor was in
aPhilips Tomoscan 310, Philips NV, Eindhoven, The Neth- erlands.
bIsopaque 440, Nyegaard and Co, Oslo, Norway.
“Maximus M 150, Philips NV, Eindhoven, The Netherlands.
dCronex 4 DDS, Du Pont de Nemours GmbH, Frankfurt, Federal Republic of Germany.
eCronex Par Speed Screens, Du Pont de Nemours GmbH, Frankfurt, Federal Republic of Germany.
fCronex T6 Daylight Film Processor, Du Pont Co, Wilming- ton, Del.
| Tumor diameter dog No. | Side involved | Radiographic findings | CT findings |
|---|---|---|---|
| < 20 mm | |||
| 6 | R | Neg | Pos |
| 12 | L | Neg | Pos |
| 13 | L | Neg | Pos |
| 20 mm | |||
| 1 | R | Neg | Pos |
| 2 | L | Pos | Pos |
| 4 | R | Neg | Pos |
| 10 | L | Neg | Pos |
| > 20 mm | |||
| 3 | L | Pos | Pos |
| 5 | R | Pos | Pos |
| 7 | R | Pos | Pos |
| 8 | R | Pos | Pos |
| 9 | R | Pos | Pos |
| 11 | L | Pos | Pos |
Neg = tumor not seen by use of indicated technique; Pos = tumor seen by use of indicated technique.
contact with all these surrounding structures, In a second dog, the tumor was in contact with the caudal vena cava and the left kidney and, in a third dog, with the aorta and the spleen. In 3 dogs, there was no contact between the tumor and surround- ing structures. Right adrenal gland tumors were in contact with the right diaphragmatic crus, the cau- dal vena cava, and except for one small tumor, with the right kidney. Three large tumors were also in contact with the liver.
Three adenomas (dogs 1-3) and 7 carcinomas (dogs 5, 6, 8-11, and 13) were homogeneous, well demarcated and round (Fig 1). In 2 of these carci- nomas, some mineralization was detected. One carcinoma (dog 4) was homogenous, well demar- cated, and oval. The remaining 2 carcinomas (dogs 7 and 12) were nonhomogeneous, poorly demar-
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cated, irregularly shaped, and mineralized (Fig 2).
Cross-sectional diameter ranged from 20 to 28 mm (mean, 22.7 mm) for adenomas and from 16 to 59 mm (mean, 31.2 mm) for carcinomas. Visual comparison of pre- and postcontrast CT images re- vealed contrast enhancement of the tumor in all dogs, with homogeneous appearance of 5 carcino- mas; cloudy appearance of 3 adenomas and 3 car- cinomas; and irregular pattern of contrast en- hancement in 2 carcinomas. Postcontrast CT images revealed compression of the caudal vena cava in
the 7 dogs with right adrenal gland tumor. The in- terface between the tumor and the caudal vena cava was not clear in these dogs. Invasion of the caudal vena cava was only apparent in 1 dog.
Survey radiography indicated adrenocortical tumor in 7 dogs (Table 1)-on the left side in dogs 2, 3, and 11 and on the right side in dogs 5, 7, 8 and 9. Tumors were visible on ventrodorsal radio- graphs in all 7 dogs and on lateral radiographs in 5. Two adenomas (dogs 2 and 3) and 4 carcinomas (dogs 5, 8, 9, and 11) were well demarcated, round, and not mineralized (Fig 3). The carcinoma in 1 dog was poorly demarcated and mineralized (Fig 4). In these 7 dogs, tumors were medial, cranio- medial, or dorsomedial to and in contact with the cranial pole of the ipsilateral kidney. In dogs 8 and 9, a large right adrenal gland tumor had displaced the right kidney. In dog 12 with carcinoma, a small mineralized nodule was found medial to the cranial pole of the left kidney, but a soft tissue mass could not be detected. In the remaining 5 dogs (1 adenoma, 4 carcinomas) evidence of an adrenal mass or mineralization in the adrenal regions was not found on survey radiographs.
The smallest tumor visualized on survey ra- diographs had a diameter of 20 mm on CT images. Six larger tumors were all visualized on survey ra- diographs. Six tumors with diameter ≤ 20 mm were not visible on survey radiographs.
Surgery via the paracostal approach was not complicated by adhesions or invasion of the tumor in 5 dogs with left adrenal gland tumor (dogs 2, 3, 10, 11, and 13) and in 4 dogs with right adrenal gland tumor (dogs 1, 4, 8, and 9). In dog 6, a right adrenal gland tumor was adhered to the caudal vena cava, but was removed. The remaining 3 dogs (dogs 5, 7, and 12) were euthanatized during sur- gery, because the tumor could not be removed.
Discussion
X-ray computed tomography was accurate in localizing adrenocortical tumors, which was con- sistent with earlier findings in dogs14-16 and find- ings in people.22-25 In people, attempts have been made to differentiate between malignant and be- nign adrenal masses on the basis of the CT appear- ance. Poor demarcation, irregular texture with mineralization, irregular contrast enhancement, and large size (9 cm or more), have been indicated as signs of malignancy.24,26,27 However, adreno- cortical carcinoma may also be observed as a well- demarcated, homogeneous mass ≤ 6 cm in diameter,28 and differentiation between adreno- cortical adenoma and carcinoma is usually impossible.23,28,29 In the dogs of this study, the combination of poor demarcation, irregular shape, nonhomogeneous texture with mineralization, and irregular contrast enhancement, as found in dogs 7 and 12, together with invasion of the caudal vena cava in dog 7, indicated malignancy. It was not possible to differentiate between the other 8 carci- nomas and the 3 adenomas on the basis of demar- cation, shape, mineralization, contrast enhance- ment, or size. Mineralization was found in 2 of the
8 carcinomas and in none of the adenomas. How- ever, mineralization has also been reported for adrenocortical adenomas in people30 and dogs.15,18 Although the mean diameter of the car- cinomas was larger than that of the adenomas, the range of diameters of the adenomas was completely within the range of diameters of the carcinomas.
In most instances, CT did not provide reliable information about resectability of the tumor. Sug- gested adhesions between right adrenal gland tumors and the caudal vena cava were confirmed at surgery in only 2 of 6 dogs, which was in agree- ment with findings of others. 15
Visualization of soft tissue masses on survey radiographs of the abdomen is influenced by the amount of intra-abdominal fat, patient prepara- tion, size of the mass, and the thickness of the body part being radiographed.31 Intra-abdominal fat was abundant in our dogs with hyperadrenocorticism and facilitated the visualization of the adrenal masses, as it does in human patients with hyper- adrenocorticism.32 Patient preparation for survey radiography of the abdomen aims at an empty gas- trointestinal tract and an empty urinary bladder, but this may present a problem in dogs with hyperadrenocorticism, who frequently have poly- dipsia, polyuria, and polyphagia. Instructing the owners to withhold food for 24 hours did not re- sult in a completely empty gastrointestinal tract in most of the dogs of this study. Especially on ven- trodorsal radiographic views, a distended stomach, as well as small intestine and colon, may obscure adrenal masses. Nevertheless, tumors with diame- ter ≥ 20 mm on CT images were recognized on survey radiographs in 7 dogs.
In people, 40 to 53% of adrenal gland tumors, the smallest with diameter of 2 cm, were reported to be identified by use of conventional excretory urography.33 The smallest tumor detected on sur- vey radiographs had a diameter of 20 mm on CT images and was found in a Dachshund weighing 9 kg. Three other tumors with diameter of 20 mm, in dogs with body weight between 15 and 21 kg, were not visualized on survey radiographs, even though the gastrointestinal tract was completely empty in 1 of these dogs. Therefore, it was concluded that the visualization of adrenocortical tumors with di- ameter of 20 mm on survey radiographs is influ- enced by size of the dog, whereas larger tumors may be visualized regardless of size of the dog.
Tumor mineralization was found on survey ra- diographs in only 2 dogs. In one of these dogs, ra- diographic findings were considered inconclusive because only a small mineralized nodule was found without any evidence of a mass. Although miner- alization in an adrenal gland by itself is no evidence for adrenal gland neoplasia, the incidence of non- tumorous adrenal gland mineralization in dogs is low.34,35 Therefore, detection of unilateral adrenal gland mineralization on survey radiographs may,
even in the absence of a soft tissue mass, contrib- ute to the decision to undertake surgery in dogs with a biochemical diagnosis of hyperadrenocorti- cism attributable to adrenocortical tumor.3,18
Results indicate that survey radiography can provide the presurgical localization of adrenocor- tical tumors in a considerable number of dogs. X-ray computed tomography is not needed in these instances.
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