Clear Cell Meningioma: A Clinicopathologic Study of 18 Tumors and Examination of the Use of CD10, CA9, and RCC Antibodies to Distinguish Between Clear Cell Meningioma and Metastatic Clear Cell Renal Cell Carcinoma

Clear cell meningiomas (CCM) can be difficult to distinguish from metastatic clear cell renal cell carcinomas by standard light microscopy. Distinction is important in deciding patient management and establishing prognosis. The purpose of this study is to evaluate the use of immunomarkers CA9, CD10, and RCC in differentiating between CCM and clear cell renal cell carcinoma. The study retrospectively reviewed the clinicopathologic features of 18 patients with CCM (9 females, 9 males; age range at the time of surgery 16 to 86 y) including immunostaining results with antibodies to CA9, CD10, and RCC. Immunostaining results were compared with those found in 26 cases of clear cell renal cell carcinoma. The most common sites of origin for the CCM included the meninges overlying the frontal lobe (n=7), cavernous sinus (n=3), and cerebellopontine angle/posterior fossa (n=2). All tumors had at least a 10% clear cell component (mean 41%). All tumors showed a sheet-like growth pattern. Other commonly observed morphologic features included increased cellularity (n=12), nucleolation (n=8), small cell change (n=6), microcalcifications (n=5), and necrosis (n=5). A mean of 1.9 mitotic figures per 10 high-power fields and a mean Ki-67 labeling index of 12.1% were observed. Seven tumors (38.9%) showed CA9 immunoreactivity, 5 tumors (27.8%) CD10 staining, and 0 cases showed RCC staining. Immunostaining results observed in the clear cell renal cell carcinoma group included 93.8% CA9 staining (15/16 cases evaluated), 100% CD10 staining (15/15 cases), and 36.4% RCC staining (4/11 cases). Follow-up was available in 16 CCM patients (mean follow-up of 58.9 mo); 10 patients (62.5%) developed at least 1 recurrence requiring surgical intervention. In conclusion, meningiomas with at least a 10% clear cell component tend to behave in a more aggressive fashion with increased risk of recurrence. Immunohistochemical staining with antibodies to CA9, CD10, and RCC are potentially useful in differentiating CCM from metastatic renal cell carcinoma. In the majority of cases in which immunostaining was observed in meningiomas, staining was focal (involving < 5% of neoplastic cells) in comparison with CA9 and CA10 immunostaining in renal cell carcinomas in which more than 50% of tumor cells stained the majority of cases.