Endovascular coil embolization for ruptured cerebral aneurysms generally yields favorable outcomes; however, concerns regarding long-term recurrence persist. We report a rare case of a ruptured middle cerebral artery aneurysm treated with coil embolization that exhibited rapid enlargement over several months, accompanied by progressive thrombus formation. The clinical course and imaging findings are presented together with a review of the relevant literature. A 32-year-old woman presented with a sudden-onset headache and was diagnosed with subarachnoid hemorrhage. Angiography revealed a 2-mm saccular aneurysm in the right middle cerebral artery, for which endovascular coil embolization was performed. The postoperative course was uneventful. Follow-up angiography performed 13 days after treatment demonstrated only a small residual neck, and outpatient surveillance was planned. Although her clinical status remained stable, follow-up magnetic resonance imaging obtained four months later revealed recurrence of the aneurysm, which had enlarged to 10 mm with partial intraluminal thrombosis and associated perianeurysmal edema. Given the rapid enlargement, urgent preoperative cerebral angiography was performed, followed by surgical clipping. Subsequent follow-up demonstrated no further recurrence. Several factors have been identified as risks for recurrence after endovascular coiling of cerebral aneurysms, including large aneurysm size, low coil packing density, and a history of rupture. As illustrated by the present case, even aneurysms that are initially small may undergo substantial enlargement over a short period when associated with intraluminal thrombosis. These findings underscore the necessity of rigorous postoperative imaging surveillance.
Matsushita et al. (2026) studied this question.