Benign cyst of the paramedian pontine tegmentum.

A benign ovoid cyst, without an epithelial lining, localized in the paramedian pontine tegmentum, was examined by computed tomography (CT) and magnetic resonance imaging (MRI) (25 x 15 x 15 mm) and successfully operated upon. The one-and-a-half syndrome (horizontal gaze palsy to the right and paralysis of adduction of the right eye) and ipsilateral "peripheral" VII nerve palsy dominated the clinical picture. Fenestration, 5 mm in diameter, of the cyst wall through the floor of the IV ventricle was performed and 2.6 ml of clear, colorless fluid was evacuated. Inspection of the cyst, using the operating microscope, revealed a smooth, white, glistening cavity with no evidence of other pathological tissue. Duraplasty was performed with allogenic pericardium. Neurological symptoms improved immediately after surgery. Light and electron microscopy of the cyst wall revealed a fibrillar astroglial network and fragments of ependyma at the ventricular side of the biopsy.