A case of adrenal oncocytoma: reviewing the literature of radiological finding

Abstract

Oncocytoma is a tumour that predominantly occurs in the kidneys and salivary glands. Only approximately 200 cases have been reported to be of adrenal origin to date, and only a few reports about its radiological findings have been published so far. Herein, we present the CT and MRI findings of an adrenal oncocytoma observed in a patient suspected of having mitochondrial abnormalities, along with the pathological findings. The tumour was roughly classified into three areas: a hypercellular region, a region containing fibrous tissue, and an oedematous region. These corresponded to the restricted diffusion area on the apparent diffusion coefficient map, the gradually enhanced area at the secretory phase on contrast-enhanced CT scan, and the obvious hyperintensity on the T2-weighted image, respectively. We also discuss these findings in the context of previously reported radiological findings in the literature. Diagnosing adrenal oncocytoma through imaging is challenging, and it is crucial to consider the possibility of malignancy while making the differential diagnosis. Small-sized homogenous tumours may be hard to differentiate from lipid-poor adenomas, while larger inhomogeneous ones are hard to distinguish from adrenal cancer.

Keywords: CT; MRI; adrenal adenoma; adrenal oncocytoma; oncocytoma.

Figure 1.

(A) Pre-contrast, (B) early arterial, (C) late arterial, and (D) equilibrium-phase CT. On pre-contrast CT, the tumour is isodense compared to the muscle, and there is no calcification. The dorsal portion of the tumour has a peak of contrast in the late arterial phase, with washout in the equilibrium phase. The ventral portion of the tumour gradually enhanced until the equilibrium phase.

Figure 2.

MRI of the tumour. (A) out-of-phase, (B) in-phase, (C) T2WI, (D) DWI b = 800, and (E) ADC images. The lesion is almost isointense to muscle on T1WI, without the fat component. It has a slightly higher intensity than muscle on T2WI; however, the dorsal portion of the tumour is slightly lower in signal than the ventral one. The central portion has the highest T2 intensity. The ADC of the dorsal portion is lower than that of the ventral portion. Abbreviations: ADC = apparent diffusion coefficient; T1WI = T1-weighted imaging; T2WI = T2-weighted image.

Figure 3.

Pathological findings: H-E stain (A) peripheral portion of the tumour, (B) high-power field, (C) ventral portion of the tumour, and (D) dorsal portion of the tumour. (A) The tumour was a well-circumscribed mass encapsulated by a thick fibrous capsule. Compressed non-neoplastic adrenal tissue was seen around the tumour. (B) The tumour cells had eosinophilic cytoplasms and relatively uniform, small round nuclei. (C) The gradually enhanced areas on the equilibrium phase of the enhanced CT revealed fibrosis (black arrows) surrounding the tumour nests (white arrows). (D) In the area with a high signal intensity on T2WI, eosinophilic tumour cells (arrows) were scattered within the oedematous tissues with a low cellular density. Abbreviations: H-E = haematoxylin-eosin; T2WI = T2-weighted image.