Abstract
Adrenal tumors with invasion into the inferior vena cava (IVC) are typically malignant. Here, we present a case of adrenocortical adenoma with protrusion into the IVC. A 70-year-old man was referred to our hospital after his magnetic resonance imaging scan of the abdomen coincidently revealed a right adrenal tumor invading the IVC. We suspected an aggressive adrenal carcinoma and tumor resection was performed. However, all 3 existing pathological criteria (Weiss, modified Weiss, and Helsinki) suggested the tumor was benign. Immunohistochemistry for CD31 showed the tumor inside the central adrenal vein (CAV), right adrenal vein (RAV), and IVC was entirely covered with CD31-positive vascular endothelial cells. The CAV is known to sometimes lack smooth muscle in its walls and normal adrenocortical cells covered by endothelial cells sometimes protrude into the CAV from this gap. These findings suggest that this tumor likely protruded into the IVC by pushing against the CAV wall, rather than by invasion into the vascular wall. In the case with adrenal tumors protruding into the IVC, the fact that the tumor surface was covered by vascular endothelial cells was considered supportive of its benign nature.