Answers to Case 1-2-3
1. Figure 1-2-3.1 is an axial CT showing multiple well-demarcated solid enhancing
masses in both kidneys. The largest in the left kidney contains a central low
attenuation scar. The appearances are non-specifi c and the differential diagnosis
includes multiple renal cell carcinomas, renal metastasis, renal lymphoma and
multiple oncocytomas. Multiple angiomyolipoma are unlikely because of the
absence of fat. Bilateral pyelonephritis can rarely present with multiple focal
areas of altered enhancement, but there would be a history of infection. The
central stellate scar within the largest mass suggests oncocytoma but this is not
diagnostic.
2. There are no fi rm diagnostic features of oncocytoma. Oncocytomas are benign
tumours in which the predominant cell, the ‘oncocyte’ has deeply eosinophilic,
copious glassy cytoplasm containing numerous mitochondria with a dearth of
other organelles. Pre operative biopsy may not aid the diagnosis because welldifferentiated
renal carcinomas may contain eosinophilic cells, and up to 30% of
tumours that are predominantly oncocytomas contain foci of clear cells, typical
of some renal carcinomas.
3. Angiography typically demonstrates a ‘spoke-wheel’ confi guration of radiating
vessels, but is now rarely used. MRI does not provide any additional
information.
4. Figure1-2-3.2 is the cut surface of a nephrectomy specimen containing a well
circumscribed brown tumour with a central scar expanding the lower pole. Light
and electron microscopy showed the typical features of oncocytoma, as described
in answer 2.