Clinical features of clear cell meningioma: a retrospective study of 36 cases among 10,529 patients in a single institution

Clear cell meningioma (CCM) is a rare subtype of meningioma. We present the largest series of 36 CCMs and evaluate several prognostic factors of patient's clinical outcome. Thirty-six patients with pathologically confirmed CCM among a total of 10,529 meningioma patients were retrospectively reviewed. CCM constituted 0.3 % of the intracranial meningiomas and 1.4 % of the intraspinal meningiomas. The male-to-female ratio (36 vs 64 %) for CCMs was similar to that for total meningiomas (28 vs 72 %) patients (chi-squared test, p = 0.3). The mean age at diagnosis of CCM patients (29.3 +/- 18.4 years) was significantly younger than that of total meningiomas (49.8 +/- 11.9 years) patients (t-test, p = 0). During the follow-up, 15 patients (42 %) suffered from tumor recurrence. The recurrence time ranged from 10 months to 12 years, with a median time of 29 months. Kaplan-Meier survival analysis showed that patients after total resection (Simpson grades I and II) had significantly longer progression-free survival (PFS) time than those after subtotal resection (Simpson grades III and IV) (log-rank test, p = 0.006). However, age (a parts per thousand currency sign20 years or > 20 years, p = 0.9), gender (p = 0.3), postoperative radiotherapy (p = 0.4), progesterone receptor staining (positivity or negativity, p = 0.2), and Ki-67 index (a parts per thousand currency sign5 % or > 5 %, p = 0.4) did not have significant effects on patients' PFS time. The proportion of CCM in spinal meningiomas is likely to be much larger than that in intracranial meningiomas. CCMs should be resected totally when possible to decrease the risk of recurrence or prolong patient's PFS time.