Endoscopic resection of a giant colloid cyst in the velum interpositum: illustrative case

BACKGROUND: Colloid cysts are an unusual differential diagnosis for lesions in the lateral ventricles. Microsurgery is usually recommended for the treatment of giant colloid cysts. This case is the largest reported colloid cyst in this unusual location treated with an endoscope. OBSERVATIONS: A 39-year-old woman with a history of pulsing headaches presented with nausea, vomiting, vision blurring, and paresthesia of the left leg. On the brain computed tomography, a huge, well-defined homogeneous hyperdense intraventricular lesion with hydrocephalus was observed. Magnetic resonance imaging showed a spherical lesion over the third ventricle inside the lateral ventricles, obstructing the Sylvius aqueduct. There was no enhancement and no diffusion restriction on diffusion-weighted images. Endoscopic third ventriculostomy was undertaken for hydrocephalus treatment. Then the lesion was resected grossly. The cyst wall was resected as much as it was safe. There was no clot or bloody product inside the lesion. LESSONS: Colloid cyst is rarely encountered in the velum interpositum and lateral ventricles, but the authors’ giant colloid cyst case along with similar cases led to considering it out of the third ventricle. According to their experience, endoscopic removal is a safe and efficient method for colloid cyst surgery, even in giant cases.