Click on Images for Enlarged View

Findings: Figure I: Axial CT (without contrast) images of the head at 8 mm intervals. A rounded 2.5 cm high attenuating lesion is seen extending from suprasellar cistern to the head of the left caudate nucleus. There is a mass effect on the frontal horn of the left lateral ventricle but no herniation.

Figure II: Left carotid angiogram demonstrates a giant saccular aneurysm (with a thin rim of clot) at the distal ICA without evidence of bleeding.

Diagnosis: Giant aneurysm with rim of clot and no sign of subarachnoid hemorrhage.

Discussion: Intracranial aneurysms are most commonly saccular (berry) outpouchings of the arterial wall at vascular bifurcations. Approximately 3-5% of the general population is thought to have aneurysms. These malformations are products of congenital and acquired influences. For example, there is increased incidence of such aneurysms in patients with polycystic kidney disease, aortic coarctation, and connective tissue diseases (Marfan Syndrome). Also hypertension and smoking seem to predispose one to aneurysm formation. Greater than 90% of aneurysms are in the anterior circulation at the following bifurcations: ACA/ACOM, ICA/PCA bifurcation, and MCA bifurcation.

Rupture of aneurysms leads to subarachnoid hemorrhage (SAH) causing the patient severe headaches, nauchal rigidity, and neurologic deficits. As the intracranial pressure rises, brainstem compression can occur leading to death. The neurologic status of a SAH patient can be assessed by the Hunt-Hess grading scale. The risk of rupture is substantial for a greater than 10 mm aneurysm versus a less than 3 mm aneurysm. Unruptured aneurysms have a 1-2% yearly risk of rupture while ruptured aneurysms have a 3-4% yearly risk of rupture.

Diagnosis of aneurysms begins with a non-contrast CT of the head which could reveal a clot, blood in the ventricles, or SAH (all of which show high attenuation). If CT is negative, then lumbar puncture should be performed to look for RBC degradation products. When these exams reveal a probable aneurysm, then angiography needs to be performed to better localize the malformation. To decrease probability of bleeding, the aneurysm can be surgically clipped or endovascularly coiled.

References:
Hart B, Benzel E, Ford C. Fundamentals of Neuroimaging.
W. B. Saunders Company, Philadelphia.

Grossman R, Loftus C. Principles of Neurosurgery.
Lippincott-Raven, Philadelphia; 1999.

Return to Interventional Imaging Page