Prediction of vascular invasion using a 7-point scale computed tomography grading system in adrenal tumors in dogs

Abstract

Background: Previous studies evaluating the accuracy of computed tomography (CT) in detecting caudal vena cava (CVC) invasion by adrenal tumors (AT) used a binary system and did not evaluate for other vessels.

Objective: Test a 7-point scale CT grading system for accuracy in predicting vascular invasion and for repeatability among radiologists. Build a decision tree based on CT criteria to predict tumor type.

Methods: Retrospective observational cross-sectional case study. Abdominal CT studies were analyzed by 3 radiologists using a 7-point CT grading scale for vascular invasion and by 1 radiologist for CT features of AT.

Animals: Dogs with AT that underwent adrenalectomy and had pre- and postcontrast CT.

Results: Ninety-one dogs; 45 adrenocortical carcinomas (50%), 36 pheochromocytomas (40%), 9 adrenocortical adenomas (10%) and 1 unknown tumor. Carcinoma and pheochromocytoma differed in pre- and postcontrast attenuation, contralateral adrenal size, tumor thrombus short- and long-axis, and tumor and thrombus mineralization. A decision tree was built based on these differences. Adenoma and malignant tumors differed in contour irregularity. Probability of vascular invasion was dependent on CT grading scale, and a large equivocal zone existed between 3 and 6 scores, lowering CT accuracy to detect vascular invasion. Radiologists' agreement for detecting abnormalities (evaluated by chance-corrected weighted kappa statistics) was excellent for CVC and good to moderate for other vessels. The quality of postcontrast CT study had a negative impact on radiologists' performance and agreement.

Conclusions and clinical importance: Features of CT may help radiologists predict AT type and provide probabilistic information on vascular invasion.

Keywords: CT; canine; carcinoma; pheochromocytoma; thrombus.

FIGURE 1

Illustration (A) and table (B) representing the grades of vascular invasion by the adrenal tumor

FIGURE 2

Decision tree obtained based on CT criteria differentiating pheochromocytoma from adrenocortical carcinoma. A tumor demonstrating a precontrast attenuation value <39 HU and a thrombus with a long‐axis dimension <49 mm has a probability of 97% to represent a carcinoma and associated with almost 32 times the risk of a wrong diagnosis, that is, pheochromocytoma based on histopathological report. A tumor demonstrating a precontrast attenuation value >48 HU has a probability of 95% to represent a pheochromocytoma. Note the gray zone where the precontrast attenuation value is in between 39 and 48 HU and where the size of the contralateral AG can help discriminate the two types of tumor but with a lesser level of probability (70%‐80%) in absence of vascular invasion

FIGURE 3

Transverse postcontrast CT images of seven different adrenal tumors (T) illustrating the 7 different scores according to the 7‐point scale CT grading system. The vessel is depicted by the letter V. Grade 1 represents an absence of contact between the vessel and the mass as a layer of adipose tissue is identified in between. Grade 2 shows contact between the two structures, affecting less than 90° of the vessel. Grade 3 represents contact affecting more than 90° of the vessel with a concave aspect of the tumor, encircling the vessel. Grade 4 depicts increased contact between the structures, affecting more than 90° of the vessel, with a convex aspect of the tumor against the vessel, the two structures having smooth regular margins. In grade 5, the tumor also has a convex aspect against the vessel; however, the margins are irregular and ill‐defined. A grade 6 represents a compression of the vessel by the tumor making it impossible to identify the contact point. Grade 7 describes a clear invasion of the vessel by the tumor

FIGURE 4

Postcontrast computed tomographic images of a pheochromocytoma invading the left adrenal gland in a 13‐year‐old Jack Russell Terrier. (A) Transverse postcontrast CT image illustrating the heterogeneously contrast enhancing tumor (white large arrowhead) deforming the contours of the left adrenal gland that is no longer recognizable A voluminous tumor thrombus (white small arrowhead) is seen invading the caudal vena cava (*) through the left phrenicoabdominal vein. (B) Sagittal multiplanar reformatted image illustrating the length of the tumor thrombus (small white arrowheads) in the caudal vena cava (*) and its continuity with the tumor (large white arrowhead). (C) Dorsal multiplanar reformatted image showing the close contact between the tumor (large white arrowhead) and the cranial mesenteric artery (white arrow). Note the contrast enhancement of the tumor thrombus that is similar to the main tumor. (D) Transverse multiplanar reformatted image showing the tumor encircling the abdominal aorta (#) and in close contact with the left renal vein (white arrow) without invading it. The cleavage between the tumor (large white arrowhead) and those structures is depicted by the black dotted line