Metastatic chromophobe renal cell carcinoma in cerebellum.
Renal cell carcinoma (RCC) is the commonest neoplasm of the kidney. Chromophobe renal cell carcinoma (chRCC) accounts for 5-10% of all RCC . Although a wide range of histomorphologic prognostic parameters have been investigated for RCC, those that really matter to the patient are very limited. Tumour morphology is one of the most important of prognostic parameters with chRCC documented to have a better prognosis than the other subtypes. Other time tested parameters include Fuhrman nuclear grade, sarcomatoid and rhabdoid differentiation. Interestingly, chRCC is an exception to the rule, as it is the only variant amongst the other subtypes, for which the International Society of Urological Pathologists (ISUP) has recently agreed upon not grading this subtype . A vast majority of chRCC are indolent, present at a low stage and are associated with a more favourable outcome. Only a few behave aggressively with a higher stage. The most common metastatic sites are liver, lung and lymph nodes [1,2]. To the best of our knowledge, unequivocal brain metastasis is reported in only 2 cases of chRCC [2,3]. Our case is unique in several aspects: 1) first documented case of chRCC with a solitary cerebellar metastasis, 2) rarity of chRCC presenting with brain metastasis compared to other variants of RCC especially, clear cell RCC,3) existing controversies regarding the management and outcome of such patients.
Until date, the following issues remain unaddressed with respect to chRCC metastasis localized to the cerebellum:
Differential diagnoses of cerebellar lesions include hemangioblastoma, microcystic meningioma, clear cell RCC and rarely low grade gliomas. Neoplastic cells express immunoreactivity with inhibin in hemangioblastoma while meningiomas are diffusely positive with EMA and vimentin. Immunoreactivity with glial fibrillary acidic protein helps in distinguishing low grade gliomas from other lesions arising within cerebellum. Neoplastic cells in clear cell RCC characteristically show immunoreactivity with CD10, besides being positive for CK, EMA and PAX8.
The postoperative period of the index case was uneventful and a radical nephrectomy is anticipated provided the performance status permits.
Contributed by Balan Louis Gaspar, MD, Kirti Gupta, MD, Apinder Preet Singh, MS, M Ch, Pravin Salunke, MS, M Ch