Subarachnoid hemorrhage secondary to internal carotid artery aneurysm.

A 72-year-old woman who presents a short disorientation episode. In cranial CT images is showed a saccular dilatation in the supraclinoid segment of the right carotid artery. Two days later the patient presented intense headache, nausea and vomiting. Contrast-enhanced cranial CT shows an extensive bleeding diffusely fills the suprasellar and central basal cisterns and extends to the cerebral convexities.

The images corresponds to spontaneous subarachnoid hemorrhage (SAH) grade IV (modified Fisher's scale) secondary to aneurysm in the supraclinoid segment of the right internal carotid artery. Spontaneous subarachnoid hemorrhage is secundary to the rupture of an intracranial aneurysm, in 80% of the cases mostly in the carotid bifurcation and in the anterior communicating artery. Unenhanced CT is the best initial test for patients clinically suspected to have SAH. When unenhanced CT findings are positive, or when clinical suspicion for aneurysm rupture is high, CT angiography or digital subtraction angiography is performed to exclude underlying saccular aneurysm. The epicenter of SAH occasionally suggests the location of an underlying ruptured saccular aneurysm. SAH can be classified into at least three distinct patterns by location on initial unenhanced CT. 1. SAH is centered in the suprasellar or central basal cisterns and extends in a diffuse manner, it's characteristic of saccular aneurysm rupture 2. SAH is centered in the perimesencephalic or low basal cisterns and does not extend peripherally, characteristic of idiopathic perimesencephalic hemorrhage 3. SAH is localized to the cerebral convexities alone, infrequent pattern, and may be secondary to reversible cerebral vasoconstriction syndrome, cerebral amyloid angiopathy, later reversible encephalopathy syndrome, cerebral venous thrombosis.

Saccular aneurysm rupture is the most common cause of SAH that diffusely fills the suprasellar and central basal cisterns and extends to the cerebral convexities. The imaging findings on initial unenhanced CT can help focus on the differential diagnosis and guide the subsequent imaging evaluation.

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