Metastatic melanoma of the septum pellucidum mimicking a colloidal cyst of the third ventricle. A novel case.

We report the first case in the literature of a solitary metastatic melanoma of the septum pellucidum, mimicking a colloidal cyst of the third ventricle. In a 22-year-old man clinical and radiological examination revealed regional left inguinal, bilateral suprarenal and left broncho-pulmonary parailar nodular masses. Immunohistochemical staining on bronchoscopic, lymph nodes and neuroendoscopic biopsy confirmed the diagnosis of metastatic melanoma, in spite of extensive workup failed to detect a primary cutaneous or systemic tumor site. The clinical course was progressive and lethal. The neuroendoscopic approach to the septal lesion, performed before stereotactic radiosurgery, was extremely useful to obtain biopsy of the tumor and, by means of septum pellucidotomy, to treat biventricular hydrocephalus by monoventriculo-peritoneal drainage, in the same seat. Even if metastases can occur anywhere within the central nervous system, the novelty in this report is their intracranial localization, as they have been detected in the septum pellucidum, a case never reported previously.