Giant renal oncocytoma with classic stellate scar.

To cite: Sussman RD, Kowalczyk KJ. BMJ Case Rep Published online: [please include Day Month Year] doi:10.1136/bcr-2016218944 DESCRIPTION A middle-aged man with poor access to medical care presented with shortness of breath and 3 years of abdominal distention. On physical examination, he was found to have a palpable mass in the left upper quadrant. He was found to have undiagnosed congestive heart failure with dilated cardiomyopathy, and a CT scan of the abdomen and pelvis revealed a left renal mass. An MRI performed to further characterise the lesion demonstrated a large exophytic mass with a central scar and segmental enhancement originating from the lateral aspect of the left kidney with no evidence of renal vein or caval thrombus (figure 1). Owing to the possibility of renal malignancy, the patient underwent an open left radical nephrectomy through a hemi-chevron incision. The patient recovered well with no complications and was discharged home in good condition. Gross pathology demonstrated a 26 cm well-circumscribed mahogany brown tumour with intervening fibrous tissue and central scarring (figure 2). Histology was consistent with oncocytoma (figure 3). Immunohistochemical staining showed diffuse positivity for CD117 and E-cadherin, negativity for vimentin and only patchy positivity for CK7, all of which further supported the diagnosis. Renal oncocytomas are the most common benign renal tumours accounting for 3–7% of kidney tumours. As demonstrated in this case, they typically appear as an enhancing renal mass on crosssectional imaging and are presumed to be renal cell carcinoma (RCC) until surgical excision. Common imaging characteristics include a central stellate scar with segmental enhancement, and a spoke-wheel pattern of feeding arteries. Unfortunately, imaging