Delayed Spontaneous Rupture of a Posterior Inferior Cerebellar Artery Aneurysm Following Treatment with Flow Diversion: A Clinicopathologic Study

Lateral projection from an angiogram obtained immediately after successful deployment of a single 4 × 20 mm PED construct across the aneurysm neck. Contrast material is stagnant within the aneurysm fundus, persisting into the venous phase of angiography. Contrast material was noted to washout from the aneurysm fundus into the PICA, which also remained faintly opacified throughout the venous phase.

A, Maximum intensity projection from an MRA performed on POD 9 demonstrates near-complete thrombosis of the aneurysm fundus. The left PICA remains patent, filling from a tiny niche of residual flow in the region of the aneurysm neck (arrow). B, Axial postcontrast T1-weighted sequence demonstrates linear enhancement of the aneurysm wall marginating the intra-aneurysmal thrombus. A focal niche of enhancement corresponds to the small neck remnant, which allows the patency of the PICA (arrow).

Noncontrast head CT scan obtained on POD 20 demonstrates aneurysmal rupture with dissection through the brain stem and into the fourth ventricle. A small amount of subarachnoid hemorrhage is noted within the prepontine cistern.

A, Base of the brain stem showing a large saccular aneurysm arising from the midportion of the left vertebral artery and embedded in the cerebellopontine angle, compressing the ipsilateral cranial nerves VII and VIII. Note that postdissection remnants of acute subarachnoid hemorrhage surround the aneurysm. Note distention of the segment of the artery at the base of the aneurysm by the stent. Cranial nerves are designated by Roman numerals. Lines with numbers indicate the plane of section of whole mounts of the aneurysm and vertebral artery as illustrated in B (Masson trichrome). B, Cross-sections of the aneurysm show incorporation of the vertebral artery into its wall (levels 1 and 2) and exit (level 1). Location of the stent (asterisk) is outlined by the luminal thrombus that partially fills the aneurysm. Fresh blood tracks along a lateral wall to the rupture through the dome (arrow). Boxes with letters represent microscopic fields shown in Fig 6.