[A case of trapped fourth ventricle which developed after a surgery of AVM (author's transl)]

We represent a case of cystic dilatation of the fourth ventricle resulted from obstruction of the foramina of Luschka and Magendie and of the aqueduct of Sylvius which developed after a surgery of AVM. A 42-year-old woman was admitted to our clinic for the operation of AVM located at the trigone of lateral ventricle and the lateral wall of midbrain. VPS had been performed previously because of acute hydrocephalus resulted from several attacks of ventricular hemorrhage. Total removal of the AVM was performed. The patient was stuporous after the surgery, and CT scan showed marked distension of the fourth ventricle with shifted third ventricle and slightly dilated supra-tentorial ventricular system. Although a revision of the abdominal side of VPs performed and the lateral and the third ventricles were shunted effectively, the fourth ventricle continued to show remarkable distension. Since it was considered that the occlusion of the foramina of Luschka and magendie due to previous episodes of ventricular hemorrhage and the blockage of the aqueduct of Sylvius 'trapped' the fourth ventricle, suboccipital craniotomy and re-opening of the foramen of Magendie was performed. The arachnoid membrane around the cisterna magna was strongly adhered to the dura mater. When incision was made on the arachnoid membrane between the cerebellar tonsils, slightly turbid and xanthochromic CSF spurted out and some old clots were also aspirated from the opened fourth ventricle. The size of the fourth ventricle returned normal on CT scan ten days after the operation, and the patient recovered progressively afterwards.