Ectopic retinoblastoma within the 3rd ventricle: case report. Ectopic intracranial retinoblastomas are rare. These tumors usually occur in the pineal, parasellar, or suprasellar regions several years after the successful treatment of ocular retinoblastomas with no evidence of direct extension or distant metastasis. We report here a case of ectopic retinoblastoma occurring within the third ventricle. The tumor was surgically excised by the transventricular approach. Ectopic retinoblastomas exhibit greater differentiation than one would expect to observe in a metastatic lesion of this tumor. The distinction of ectopic retinoblastomas and metastasis from ocular retinoblastomas is important, since ectopic retinoblastomas, unlike metastasis, can be successfully managed by intensive therapy including radical excision. 