Is the rupture of cerebral berry aneurysms influenced by the perianeurysmal environment?

Purpose: To evaluate contact between cerebral berry aneurysms and the perianeurysmal environment and to study the influence this contact has on aneurysm rupture. Materials and Methods: In a series of 76 consecutive patients, pre- and post-contrast CT images of 87 aneurysms were evaluated. Aneurysm locations were identified and aneurysms were divided into two different groups depending on whether they had ruptured or not. Contact between aneurysms and the perianeurysmal environment was studied when present, and considered to be balanced or unbalanced according to symmetry of contact and type of contact interface, i, e. with bone, dura, etc. Results: Rupture occurred in 47 aneurysms at an average maximum dome size of 7.4 mm. There was contact with elements of the perianeurysmal environment in 38 (81%) of ruptured cases and no evidence of contact in 7 (15%). The nature of contact was unclear in 2 (4%) ruptured aneurysms. In the aneurysms with contact, the nature of contact was unbalanced in 34 (72%) and balanced in 4 (9%). Unbalanced aneurysms ruptured at significantly smaller sizes (average: 7.7 mm) than balanced aneurysms (average: 11.4 mm). Seven aneurysms of small size (3.3-6.9 mm, average: 4.8 mm) were found to have ruptured, despite the fact that they were too small to exhibit contact with the perianeurysmal environment. In 40 unruptured aneurysms (average size: 6.3 mm), contact with the perianeurysmal environment was found in 15 aneurysms, for which balanced contact was found in 11 (27.5%) and unbalanced contact in 4 (10%), and no contact in 25 (62.5%). The average size of the aneurysms without contact (3.7 mm) was significantly smaller than that with balanced contact (10.3 mm) or with unbalanced contact (11.3 mm). Conclusion: Aneurysms exhibit contact with their perianeurysmal environment as soon as they reach a size that exceeds their allowance given by the local subarachnoid space. The contact with the environment was found to be an additional determinant parameter in the evolution of cerebral berry aneurysms and their risk to rupture.