This is the first known report of the use of computerized tomography (CT) scanning to examine acute hydrocephalus in posterior fossa injury. Of the 1802 patients with acute head trauma treated at Funabashi Municipal Medical Center, 53 (2.9%) had suffered injury to the posterior fossa. Of these, 12 patients (22.6%) had associated acute hydrocephalus: nine patients with acute epidural hematoma (AEH) and three with intracerebellar hematoma and contusion (IH/C). There was a significant relationship between cases of AEH with hydrocephalus and supratentorial extension, hematoma thickness of 15 mm or more, and abnormal mesencephalic cisterns. In cases of IH/C, bilateral lesions and no visible fourth ventricle were significant causes of hydrocephalus. According to these results, possible mechanisms of acute hydrocephalus in posterior fossa injury may be as follow: in cases of AEH, hematoma that extends to the supratentorial area compresses the aqueduct posteriorly and causes hydrocephalus; in cases of IH/C, hematoma and contusional lesions may directly occlude the fourth ventricle and cause acute hydrocephalus. Seven patients suffering from AEH with acute hydrocephalus underwent evacuation of their hematoma without external ventricular drainage. In these cases, CT scanning showed that the hydrocephalus improved immediately after evacuation of the hematoma. Two patients suffering from IH/C with hydrocephalus underwent a procedure for evacuation of the hematoma and external ventricular drainage. The authors do not believe that ventricular drainage is necessary in treating posterior fossa AEH. However, both evacuation of the hematoma and ventricular drainage are necessary in cases of IH/C with hydrocephalus to provide the patient with every chance for survival. There was no significant difference in mortality rates when cases of AEH with acute hydrocephalus (0%) were compared with cases of AEH without hydrocephalus (7.7%). The observed mortality rates in cases of IH/C with hydrocephalus and those without hydrocephalus were 100% and 15.4%, respectively; this is statistically significant.

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Twenty operated cases of angiographically unrecognized microaneurysm (AUM) have been analysed with special reference to intra-operative observations and clipping-technique. Among the patients with intracranial aneurysms that the authors' facility has operated upon, the incidence of asymptomatic incidental AUM that was 2 mm or smaller amounted to 3.7%. Thirteen cases of AUM were found on the middle cerebral artery; four AUMs arose from the M1 portion, four from the bifurcation, and five from the second bifurcation. Sixty percent of AUMs were recognized on the parent arteries of ruptured aneurysms. In 90% of cases the AUMs were broad based in shape and in 70% of cases exhibited a thin-walled neck and a thin-walled fundus. Intra-operative findings revealed four reasons why AUMs were not visible in the pre-operative angiograms: (1) the AUM was sandwiched between two arteries; (2) the AUM was completely hidden by a contiguous large or giant aneurysm; (3) the AUM was diagnosed by pre-operative angiogram as a bleb of the contiguous aneurysm; (4) the AUM was not visible on angiograms because the height of the AUM was extremely low. Twelve cases of AUM were successfully clipped using four different clipping techniques; (1) clipping parallel to the bifurcation in four, (2) clipping parallel to the parent artery in four, (3) pinch-clipping in two of the cases, and (4) cross clipping in two of the cases. The other eight cases were wrapped and coated. AUMs may be present during the direct operation of intracranial aneurysms and in intravascular surgery. Neurosurgeons and neuroradiologists need to explain the possible existence of AUMs to patients and their families.

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