The Perianeurysmal Environment: Influence on Saccular Aneurysm Shape and Rupture

A 47-year-old man with chronic headache. A left, unruptured middle cerebral artery (MCA) aneurysm was suspected during routine CT, which motivated high-resolution CT angiography (HCRTA). HRCTA revealed a 6-mm MCA aneurysm, which pointed inferiorly and was embedded in the temporal lobe (A–D). The whole circumference of the aneurysm was surrounded by brain tissue, resulting in a balanced contact constraint (A–C). This aneurysm had regular contours.

A–C, Sequential, coronal plane, multiplanar reconstructions of HRCTA. arrows, balanced contact constraint with surrounding temporal lobe parenchyma.

D, Three-dimensional reconstruction of HRCTA, left superior view. A, MCA aneurysm; asterisk, posterior clinoid process.

Ruptured, right-sided giant middle cerebral artery (MCA) bifurcation aneurysm with right, intraparenchymal temporal lobe hematoma. On noncontrast CT, the aneurysm was seen as a round structure that was hypoattenuated compared with the temporal lobe hematoma (A). Postcontrast high-resolution CT angiography (HCRTA) showed an unbalanced contact constraint with the frontal and temporal lobes (B) and with the greater sphenoid wing (C–E). The aneurysm had a regular shape with no blebs. This case showed how the trajectory and growth of the aneurysm could have been influenced by the contact constraints it developed with the perianeurysmal environment. As it grew, this aneurysm was probably canalized laterally and outward by the adjacent frontal and temporal lobes that delimitate the sylvian fissure, and then, when it developed a contact constraint with the sphenoid greater wing, it grew caudally toward the middle cranial fossa.

A, Axial, noncontrast enhanced, HRCT. A, aneurysm; H, hemorrhage.

B and C, Axial, postcontrast HRCTA. H, hemorrhage.

D, 3D reconstruction of HRCTA, superior view.

E, 3D reconstruction of HRCTA, posteroanterior view.

Axial noncontrast CT. Ruptured anterior communicating artery (AcomA) aneurysm with Fisher IV subarachnoid hemorrhage (SAH). The SAH delineates the cisternal portion of both occulomotor nerves (white arrows), which appear as a “negative print” within the blood clot. In such cases, contact constraints between an aneurysm with the occulomotor nerve could readily be identified.

High-resolution CT angiography (HCRTA) of a ruptured right posterior communicating artery (PcomA) aneurysm with Fisher IV SAH. This aneurysm is highly irregular with multiple blebs (A–C). Axial HRCTA images show unbalanced contact constraints with the mediotemporal lobe (A) and the free border of the tentorium cerebelli (B). Coronal plane reconstructions show the occulomotor nerve as a round nonenhancing structure and the free edge of the tentorium as an enhancing, linear, slitlike structure (D–L). The contours of the aneurysms are clearly deformed by the imprint of these 2 structures on its inferior surface. The PcomA is visualized medially to the aneurysm.

A and B, Axial HRCTA images. White arrow, PcomA aneurysm; asterisk, contact with the mesiotemporal lobe; arrowhead, contact with the free border of the tentorium cerebelli.

C, 3D reconstruction of HRCTA, posteroanterior view. Arrow, imprint from free border of tentorium cerebelli and right occulomotor nerve.

D–L, Coronal plane, sequential, back to front, thin section multiplanar reconstruction of the PcomA aneurysm. Double arrowhead, free border of the tentorium cerebelli; white arrowhead, PcomA; red arrow, right occulomotor nerve; white arrow, PcomA aneurysm; red arrowhead, cisternal internal carotid artery (ICA); blue arrow, ICA-PcomA aneurysm junction.