RESUMEN
BACKGROUND: Cowden syndrome is characterized by multiple hamartomas and accompanied by a germline mutation of the phosphatase and tensin homolog gene. Cowden syndrome has been described to be associated with vascular anomalies such as arteriovenous malformation and developmental venous anomalies with high frequency. However, the association of cerebral aneurysms with this syndrome has not been reported yet. CASE DESCRIPTION: A 39-year-old Japanese man presented with a subarachnoid hemorrhage due to a ruptured giant fusiform middle cerebral artery aneurysm. We diagnosed him with Cowden syndrome by clinical presentations as outlined in the National Comprehensive Cancer Network's criteria. As the ruptured fusiform aneurysm involved a middle cerebral artery bifurcation, we prepared for extracranial-intracranial bypass surgery. We successfully performed a surgical clipping using multiple tandem clipping techniques and suction decompression techniques. Bypass surgery was not performed as reconstruction of the M2 trunks was successfully completed. CONCLUSIONS: We present this rare case that potentially indicates an association between cerebral aneurysms and Cowden syndrome. Because vascular anomalies are not included in the diagnostic criteria for Cowden syndrome, intracranial vascular anomalies may be underestimated. We therefore recommended a careful search of vascular diseases, including cerebral aneurysms, in cases of Cowden syndrome.