The authors report the case of a 15-year-old girl with a third ventricle colloid cyst. She presented with prolonged headache, nausea, vomiting, and loss of visual acuity with bilateral papilledema. Computed tomography and MRI revealed severe biventricular hydrocephalus with transependymal periventricular fluid and a minimally enhancing cystic mass of the third ventricle. The patient was diagnosed with a colloid cyst and obstructive hydrocephalus, and endoscopic resection with ablation of the cyst remnant was performed. While attempting to extricate the cyst from the patient's head, control of the cyst was lost and the cyst fell into the lateral ventricle beyond the surgeon's view. Postoperative imaging showed that the cyst had settled in the right occipital horn. After 3 years of follow-up, imaging suggests growth of the cyst in its new position without necrosis or displacement on prone imaging.
Keywords: colloid cyst; complication; endoscopy; oncology; third ventricle.