A 28-year-old male patient with a VP shunt suffered a fall from his wheelchair, for which he became progressively lethargic during the following 2 days. On evaluation, his neurological examination showed a Glasgow Coma Scale of 12. Eight years prior, he was diagnosed with a left cerebellar arteriovenous malformation during workup for headaches []. The patient had multiple embolization with N-butyl cyanoacrylate and coils followed by staged Gamma Knife radiosurgery. He developed symptomatic radionecrosis with acute obstructive hydrocephalus, and a VP shunt had to be placed in addition to chronic steroids and hyperbaric chamber treatment. As the patient had a VP shunt, it was believed that the acute lethargic presentation was due to malfunctioning of the VP shunt or a traumatic brain injury secondary to the fall. Manual palpation of the shunt valve showed good pumping and refill. A radiological workup for the shunt malfunction was ordered. The skull X-rays showed abundant air inside the ventricles, and we thought that it could be the source of his symptoms []. The axial head CT scan confirmed the initial radiographic impression of tension pneumoventricle without evidence of an acute traumatic brain injury. Coronal and sagittal head CT reconstructions were performed later by the neuroradiologist and showed a left ethmoidal meningoencephalocele with a fistulous air tract extending into the ventricle, which was not identified on the initial axial images []. We thought that the air inside the ventricle might have produced malfunctioning of the valve mechanism and brought the patient to the operating room to inspect the shunt system and, at the same time, remove some of the air inside the ventricles. During the surgery, it was found that the ventricular catheter was patent, and the valve had good distal flow, although a substantial amount of air inside the valve chamber. Air bubbles were observed draining together with a clear CSF when the valve was disconnected from the ventricular catheter. A new valve was placed, and the patient was admitted to the intensive care unit. No improvement was observed during the following 2 days, and a repeated head CT scan still showed a significant amount of pneumoventricle. He was returned to the operating room, and a frontal EVD was placed to remove the air trapped inside the ventricles. After 1 day, the EVD was kept closed to monitor the intracranial pressure. A subsequent head CT scan 6 days later showed resolution of the pneumoventricle and the EVD was removed when the second CSF culture was negative. No active evidence of a CSF leak was observed during the hospitalization. In our investigation toward the etiology of the pneumoventricle, a review of previous head CT scans and MRIs showed that the patient had a small left frontonasal meningoencephalocele extending into the ethmoid which had been previously unnoticed []. A small left frontal skull base defect produced migration of the meningoencephalocele into the ethmoid sinus. He did not present symptoms related to the meningoencephalocele on any of the prior admissions. The otolaryngology department was consulted to repair the meningoencephalocele and frontal skull base defect. The patient underwent endoscopic endonasal removal of the meningoencephalocele with a reconstruction of the frontal skull base defect using an underlay cartilage patch placed at the defect and a vascularized nasoseptal mucosal graft placed in an overlay fashion. No postoperative lumbar drainage was used. The patient did not present any CSF leak postoperatively, and the head CT scan showed small-sized ventricles with no pneumoventricle. Six months after the resection of the meningoencephalocele and reconstruction of the skull base defect, he continues asymptomatic without evidence of a CSF leak.