Disproportionately Large Communicating Fourth Ventricle: Report of Two Cases occurring after Suboccipital Craniectomy

An isolated fourth ventricle or “disproportionately large communicating fourth ventricle” (DLCFV) is a clinical entity characterized by marked dilatation of the fourth ventricle isolated from other cerebrospinal fluid pathways, producing various brain stem and/or cerebellar symptoms. In some cases, the aqueduct is reported patent. Two patients with a DLCFV developed after suboccipital craniectomy are reported. Both cases had previously undergone a ventriculo-peritoneal shunting procedure (V-P shunt) for hydrocephalus secondary to suboccipital craniectomy. Following the malfunction of the V-P shunt, the entire ventricular system was found to be markedly dilated, the fourth ventricle being disproportionately large. The aqueduct was found to be patent. Both cases have had several revisions of the V-P shunt, but they failed to reduce the size of the fourth ventricle and worsened neurological symptoms. Therefore, a fourth ventriculo-peritoneal shunt (IVth-P shunt) was performed. At the time of shunting in one case, pressure monitoring of the fourth ventricle was performed, and revealed large compliance. It is speculated that one of the mechanisms producing the DLCFV is altered cerebellar compliance due to suboccipital craniectomy. IVth-P shunt is proposed as treatment of DLCFV, if it is not relieved by revision of the V-P shunt.