Cyst of the velum interpositum treated by endoscopic fenestration

BACKGROUND The cavum veli interpositi is a not infrequent radiologic finding in both children and adults, as confirmed by computed tomography (CT) and magnetic resonance (MR). A moderate enlargement of the cavum may sometimes be observed; on the other hand, a true large cyst may be considered exceptional, with only one reported case. CASE HISTORY This 9-year-old boy with psychomotor retardation and epileptic seizures had a large CSF cyst in the region of the cavum veli interpositi, diagnosed by CT and MR. The patient was treated by endoscopic surgery, with introduction of the endoscope into the occipital horn of the right lateral ventricle and multiple fenestrations from the right ventricle to the cyst, and then from the cyst to the left lateral ventricle. The surgery resulted in decrease in the size of the cyst and reduction of the frequency of seizures. DISCUSSION AND CONCLUSIONS Children with dilated or cystic cavum veli interpositi present with a large head, mental retardation, seizures, and hydrocephalus. On CT and MR, the cyst shows a typical triangular configuration on the axial plane and lies on the roof of the third ventricle in the coronal plane. Endoscopic ventricular fenestration is the treatment of choice for these as well as all other intraventricular and intracerebral CSF cysts, because it ensures communication between the cyst and the ventricular system and avoids definitive shunting of the cyst.