Computed Tomography and Magnetic Resonance Images of Adrenocortical Oncocytoma Cases
In June 2010, an incidentally detected left adrenal mass was found in a 54-yr-old man via CT performed at another hospital. Abdominal CT scans detected a lobulating contoured, well-demarcated, well-enhancing solid mass in the left adrenal gland, which contained the central necrotic portion.\nMR images were obtained with a 1.5 T unit using a contrast agent (Gadovist®, Bayer Healthcare, Germany). On a T2-weighted gradient echo image (TR/TE: 3.7/1.6), the mass was primarily of slightly high signal intensity with a hyperintense central portion. This mass primarily demonstrated hypointensity on T1-weighted gradient echo images (TR/TE: 175.0/5.0), without a definite signal drop (suggesting a fat component) on the opposed-phase correlated with the in phase. The previously highly hyperintense focus on T2-weighted images showed hypointensity on the T1-weighted images, suggesting a necrotic portion, and a central hemorrhagic component was revealed within the necrosis by demonstrating a hyperintense foci on a T1-weighted image and hypointense foci on a T2-weighted image (). Contrast-enhanced MR images heterogeneously demonstrated the enhancement of the solid tumor portion at the 1-min, peak enhancement at the 3-min, and slight washout at the 5-min delayed phases. Intratumoral hemorrhagic necrosis was not constantly enhanced (). The blood vanillylmandelic acid, total metanephrine, epinephrine, and norepinephrine were within the normal ranges.\nBased on these observations, adrenal carcinoma and metastasis were included with the differential diagnosis. The patient underwent meticulous examination for the primary origin, including colonoscopy, gastroscopy, and chest CT; there was no evidence of a primary focus. The most probable preoperative diagnosis was adrenal carcinoma. The patient underwent laparoscopic adrenalectomy, and histology suggested adrenal oncocytoma with uncertain malignant potential.\nThe tumor was a soft oval mass measuring 9×6×5 cm in dimensions and 116 g in mass. The outer surface was well encapsulated by a thin fibrous capsule, and it was focally attached to a normal adrenal gland. Upon sectioning, the mass showed a brownish-yellow, fish-flesh-like cut surface with a multifocal brownish hemorrhagic necrosis and focal cystic changes ().\nThe tumor was composed of epithelial cells with abundant acidophilic cytoplasm, with nuclear pleomorphism and a diffuse growth pattern, as shown using a light microscope (), and the oncocytic cytoplasm was filled with a large number of mitochondria, as well as some lysosomes, Golgi bodies, small lipid particles, and glycogen particles (), the histological features of which were consistent with adrenocortical oncocytoma. The tumor showed a low mitotic count (<5/50 HPFs), the absence of atypical mitosis, and venous invasion, but it also showed focal necrosis and inconspicuous capsule invasion, the histological features of which were consistent with uncertain malignant potential (borderline) behavior. Electron microscopy showed that microscopic and immunohistochemical findings were compatible with an adrenocortical oncocytoma. Because of this finding, we performed a careful follow-up study to exclude the possibility that the adrenal tumor was malignant over a three-year follow-up period. This workup included multiple abdominal ultrasounds examinations, as well as chest and abdominal CT scans. All of the imaging findings were unremarkable. We concluded that the final diagnosis in this case was primary adrenocortical oncocytoma.