The aspect ratio between ruptured aneurysms and unruptured aneurysms was found to be statistically significant, and almost 80% of the ruptured aneurysms showed an aspect ratio of more than 1.6, whereas almost 90% of the unruptured aneurysms showed an aspect ratio of less than 1.6. This study therefore suggests that the aspect ratio may be useful in predicting imminent aneurysmal ruptures.

A 42-year-old man suffered subarachnoid hemorrhage manifesting as sudden severe headache one month before admission. On admission, his headache had subsided and he had no neurological deficits. Cerebral angiography demonstrated an aneurysm originating from the bifurcation of the right middle cerebral artery. The aneurysm was irregular, with a snowman-like shape. Neck clipping of the aneurysm was carried out through a right pterional approach. Intraoperatively, a red, pulsating sac mimicking a blood clot (the snowman's``head'') was located over the yellowish, thick-walled portion of the aneurysm. Exploration around the aneurysm detached the red sac from the thick-walled portion of the aneurysm. There was a small tear in the apex of the thick-walled aneurysm sac. A Sugita clip was applied to the neck of the true aneurysm. The postoperative course was uneventful and he was discharged one month later without neurological deficits. Histological examination of the red-colored sac showed the features of pseudoaneurysm. The red sac may have been a pseudoaneurysm covering the rupture site of the true aneurysm.

The pathogenesis of sudden death during subarachnoid hemorrhage (SAH) still remains to be eluci dated. A new rat common carotid artery-prechiasmal extracorporeal shunt model was designed to study the effect of different severities of SAH on intracranial pressure (ICP), regional cerebral blood flow (rCBF), and mortality. Different severities of SAH were induced by controlling the bleeding period (from 30 to 90 sec) and number of bleedings (one or three times). SAH caused a dramatic increase in ICP and immediate depression of rCBF, which recovered slowly to a certain extent. ICP increased sharply within the first 30 seconds and reached a plateau concomitant with nearly zero rCBF, which suggested the occurrence of cerebral circulation arrest. Bleeding of more than 60 seconds and increased ICP over 80 mmHg were directly correlated with the mortality. Respiratory arrest was the first sign of death, immediately followed by cardiac depression resulting in sudden death. This model combines arterial bleeding with systemic blood pressure and controlled bleeding time to simulate the acute period of SAH.

A 42-year-old woman presented with a ruptured aneurysm of the distal posterior inferior cerebellar artery (PICA), which had a rare extracranial and extradural origin. Medial suboccipital craniectomy and C-1 laminectomy were performed. The aneurysm had adhered to the right cerebellar tonsil, but was successfully clipped without difficulty. Intraoperatively, the PICA origin was recognized in the extracranial and extradural space between the dorsal roots of the C-1 and C-2 nerves. The origin of the PICA from the vertebral artery (VA) may occur at any portion of the VA from the site of penetration of the dura to the vertebrobasilar junction, but an extradural origin is uncommon. A ruptured aneurysm of the PICA branching from the VA at a site proximal to the vertebrobasilar junction and below the foramen magnum may be overlooked by three-vessel angiography if the contrast medium cannot reflux to the contralateral PICA origin.

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