[A case of isolated fourth ventricle in the early postoperative period of subarachnoid hemorrhage].

An adult case of isolated fourth ventricle which developed in the early postoperative period of SAH is reported. A 72-year-old male with Hunt & Kosnik Grade 4 subarachnoid hemorrhage (SAH) underwent emergent neck-clipping of an anterior communicating artery aneurysm along with setting of external ventricular drainage (EVD) and cisternal drainage (CD). The lamina terminalis (LT) was opened. Preoperative study had showed diffuse SAH with intraventricular hemorrhage (IVH), and mild dilatation of the whole ventricular system on CT scan (Fisher Group 4). Twelve hours after surgery, both of the drainages were opened with the pressure setting of 20 cm H2O for EVD and 10 cm H2O for CD. Although his neurological state had been improving, 2 hours after the opening of the drainages he suddenly fell into respiratory arrest and coma, when 20 ml of CFS through CD was drained. On CT scan, isolated fourth ventricle was recognized. The patient died on the ninth postoperative day. In case of severe SAH with diffuse IVH, we should be careful when setting the pressure of EVD or CD with the LT opened, because of the possibility of occlusion of the fourth ventricle outlet and aqueduct, that results in fourth ventricle isolation.