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Cystic renal tumours are a diagnostic challenge. Both benign and malignant tumours may have cystic features. Oncocytoma is a benign epithelial tumour that can present focal central microcystic features, but oncocytoma with a multilocular cystic presentation is very rare, and is often misdiagnosed as renal carcinoma with a cystic component.1,2,3,4,5 Here, we report two consecutive cases of multilocular cystic renal oncocytoma.
A 67 year old man presented with a sudden pain in his left back. He had no relevant medical history. Physical examination showed a microscopic haematuria.
Ultrasonography, computed tomography (CT) scan and magnetic resonance imaging (MRI) uncovered a large heterogeneous tumour in the left kidney. The tumour measured 7 cm in its greatest diameter, and was largely cystic with multilocular septa. Enhancement of the septa and the nodular central component showed up well on MRI (fig 11).). A radical nephrectomy was performed. After a follow up of 26 months, the patient is well without recurrence or metastasis.
A 47 year old woman without relevant antecedents presented with diffuse abdominal pain. A CT scan and MRI studies were performed and showed a small 3.5 cm multilocular cystic tumour in the upper pole of the left kidney. Multiple thickened septa were more easily seen on the MRI than the CT scan. Septa and wall were well enhanced on contrast imaging. A partial nephrectomy was performed, and eight months later the patient is well.
On gross examination, both tumours were predominantly cystic, multilocular, with thickened septa, and with no central scar. Microscopically, septa were covered by cuboidal or columnar eosinophilic cells ((figsfigs 2, 33).). The cytoplasm was abundant and granular. The nuclei were round with one or several nucleoli. No severe atypia or necrosis was noted. No hobnail cells were found. Mitotic activity was low (less than one mitotic figure/10 high power fields). A small area of classic solid tubulocystic oncocytoma was identified in each case. In the first case, tumour cysts focally invaded the perinephric fat. No vascular invasion was seen. On immunohistochemistry, tumour cells were diffusely positive for epithelial membrane antigen and pancytokeratin and focally positive for cytokeratin 7. Staining for cytokeratin 20, high molecular weight cytokeratin, and CD10 was negative.
Oncocytoma is a renal adenoma that makes up 5–7% of all renal tumours.1,2 Classically, oncocytoma is a solid mass that develops in the renal parenchyma with a central fibrous scar. Oncocytoma with prominent macroscopic cystic features is very unusual and should be distinguished from other renal cystic tumours, such as multilocular clear cell carcinoma or cystic nephroma.3,4,5 Preoperatively, in our cases, no distinction was possible by imaging studies; in particular, no central scar was seen. Therefore, these tumours were classified as suspected cystic tumours, Bosniak's class 3.
Only microscopic examination can identify the characteristic oncocytic cells covering the tumour septa. However, a minor component of usual oncocytoma is also often seen.
In the first case, focal invasion of the perinephric adipose tissue was present. This unusual feature is seen in less than l0% of oncocytomas in large series, and has no effect on the prognosis.1,2 Oncocytomas may present limited central microcystic degeneration but a prominent multicystic presentation is very unusual. Only isolated cases have been reported in the English literature.3,4,5,6 The diagnosis cannot be made radiologically. In the literature, one case resembled a haemorrhagic cyst on imaging.6 In a recent series of 28 cases of atypical renal cystic tumours evaluated by imaging guided biopsy, one case of cystic oncocytoma was diagnosed.7
The prognosis of this variant is excellent; metastasis has not been reported. The clinical course appears to be very similar to that of usual oncocytoma and these tumours may be managed by partial nephrectomy.8