Published Online
on August 19, 2004

A more recent version of this article appeared on October 1, 2004

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Submitted on February 23, 2004
Revised on April 2, 2004
Accepted on May 9, 2004

Remodeling of Saccular Cerebral Artery Aneurysm Wall Is Associated With Rupture. Histological Analysis of 24 Unruptured and 42 Ruptured Cases

Juhana Frösen MD^*; Anna Piippo MB; Anders Paetau MD, PhD; Marko Kangasniemi MD, PhD; Mika Niemelä MD, PhD; Juha Heresniemi MD, PhD; and Juha Jääskeläinen MD, PhD

From the Neurosurgery Research Group (J.F., A. Piippo, A. Paetau, M.K., M.N., J.H., J.J.), Biomedicum Helsinki, Helsinki, Finland; the Departments of Neurosurgery (J.F., A. Piippo, M.N., J.H.) and Pathology (A. Paetau), and the Medical Imaging Center (M.K.), Helsinki University Central Hospital, Helsinki, Finland; and the Department of Neurosurgery (J.J.), Kuopio University Hospital, Kuopio, Finland.

^* To whom correspondence should be addressed. E-mail: juhana.frosen{at}hus.fi.

Background and Purpose--The cellular mechanisms of degeneration and repair preceding rupture of the saccular cerebral artery aneurysm wall need to be elucidated for rational design of growth factor or drug-releasing endovascular devices.

Methods--Patient records, preoperative vascular imaging studies, and the snap-frozen fundi resected after microsurgical clipping from 66 aneurysms were studied. Immunostainings for markers of smooth muscle cell (SMC) phenotype, proliferation, and inflammatory cell subtypes and TUNEL reaction were performed.

Results--Unruptured (24) and ruptured (42) aneurysms had similar dimensions (median diameter in unruptured 6 mm; median in ruptured 7 mm; P=0.308). We identified 4 basic types of aneurysm wall that associated with rupture: (1) endothelialized wall with linearly organized SMCs (17/66; 42% ruptured), (2) thickened wall with disorganized SMCs (20/66; 55% ruptured), (3) hypocellular wall with either myointimal hyperplasia or organizing luminal thrombosis (14/66; 64% ruptured), and (4) an extremely thin thrombosis-lined hypocellular wall (15/66; 100% ruptured). Apoptosis, de-endothelialization, luminal thrombosis, SMC proliferation, and T-cell and macrophage infiltration associated with rupture. Furthermore, macrophage infiltration associated with SMC proliferation, and both were increased in ruptured aneurysms resected <12 hours from rupture, suggesting that these were not just reactive changes.

Conclusions--Before rupture, the wall of saccular cerebral artery aneurysm undergoes morphological changes associated with remodeling of the aneurysm wall. Some of these changes, like SMC proliferation and macrophage infiltration, likely reflect ongoing repair attempts that could be enhanced with pharmacological therapy.

Key words: cerebral aneurysm • inflammation • intracranial aneurysm • rupture

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