Evolution of Giant P2-Posterior Cerebral Artery Aneurysm over 16 Years: Saccular to Serpentine

Giant intracranial aneurysms account for only about 5% of all intracranial aneurysms. Giant intradural aneurysms are associated with severe natural history, yet remain potentially curable. These aneurysms cause symptoms due to their mass effect, and only 14–35% of cases present with subarachnoid haemorrhage (SAH). The present case report is an imaging evolution of a giant posterior cerebral artery (PCA) aneurysm in a patient who was lost on follow-up from 1992 to 2008 giving insight into the natural history and morphologic evolution of giant serpentine aneurysms. Attempted surgery 16 years previously for a saccular PCA aneurysm produced encephalomalacia and created a more spacious perianeurysmal environment, preventing any mass effect on vital structures in its vicinity. This allowed the patient to have a long symptom-free period and also allowed the aneurysm to follow a morphologic evolution over a long period without causing symptoms which would have called for intervention. This unusual development gave a unique opportunity to study the evolution of a gaint serpentine aneurysm from a saccular aneurysm and also the clinical and morphologic changes in an aneurysm if it can be prevented from producing mass effect. The Coanda effect, or boundary wall effect, has been considered responsible for the development of the serpentine channel in the original globular aneurysm. However many Authors conclude that giant serpentine aneurysms are not derived from saccular aneurysms.