A 26-year-old female presented with an acute febrile illness, bilateral flank pain, and breathlessness. She was admitted to the medical intensive care unit (ICU) and started on non-invasive ventilation (NIV). Initial investigations revealed bilateral lung infiltrates and consolidations. Blood culture showed growth of Klebsiella pneumoniae. Ultrasonography (USG) and subsequent CT scans identified a large adrenal mass (10.3 x 8.9 x 8.6 cm) with thrombosis extending into the left renal vein and inferior vena cava (IVC).

USG-guided biopsy confirmed an oncocytic neoplasm. Hormonal characterization of the tumor showed elevated DHEAS and testosterone levels. Imaging characteristics suggested a neoplastic etiology with probable superadded infection. The patient underwent left adrenalectomy with thrombectomy due to the diagnosis of adrenocortical carcinoma with tumor thrombus involving the adrenal vein and IVC. Intraoperatively, a large mass (14 x 12 cm) arising from the left adrenal gland with tumor thrombus adherent to adrenal and renal veins was identified. HPE revealed features consistent with adrenocortical carcinoma, oncocytic variant. The tumor exhibited eosinophilic cytoplasm, marked nuclear pleomorphism, low mitotic activity, and tumor necrosis. Lymphovascular invasion was not identified. The tumor was staged as pT4 due to renal vein invasion.

1-year followup showed no metastases.

Adrenal oncocytomas are extremely rare, often non-functioning tumors that present as incidental findings. Diagnosis of oncocytomas is challenging with imaging alone. Histological analysis is essential for an accurate diagnosis due to similarities in appearance with malignant lesions. Treatment involves adrenalectomy and thrombectomy in cases with tumor thrombus extension Follow-up for at least 5 years post-surgery is advised due to potential recurrence in malignant cases.