Benign aqueductal cyst causing bilateral internuclear ophthalmoplegia after external ventricular drainage. Case report.

The introduction of magnetic resonance (MR) imaging to the field of neuroimaging has allowed detection of various lesions that cause aqueductal stenosis. The authors report the case of a 3-year-old boy in whom a benign ventricular cyst developed in the aqueduct. The patient became drowsy after having complained of headache and vomiting; MR imaging revealed mild triventricular dilation and a normal-sized fourth ventricle. Repeated MR imaging performed 1 week later revealed an aqueductal cyst that had markedly enlarged during the intervening period. An external ventricular drainage system was installed, but recovery of consciousness in the child was unsatisfactory and a new bilateral internuclear ophthalmoplegia developed. Fenestration of the cyst wall and placement of a ventriculocisternostomy in the third ventricle were performed simultaneously by using a flexible neuroendoscope. By 2 weeks postsurgery, the patient's neurological symptoms had completely resolved. This case illustrates that simple rerouting of ventricular cerebrospinal fluid (CSF) can aggravate the symptoms of this rare lesion by causing severe compression of periaqueductal structures by a cyst that maintains a high intracystic pressure. Endoscopic surgery was an excellent choice of treatment to achieve both cyst fenestration and normalization of intracranial CSF pressure by creating a ventriculocisternostomy.