Rapid Development and Rupture of an Infected Intracranial Aneurysm Caused by Streptococcus salivarius Meningitis: A Case Report

The clinical manifestation of intracranial mycotic aneurysms (ICMAs), which are rare but carry high risks of rupture and early mortality, remains poorly understood. We present a case of an ICMA that rapidly developed and ruptured after the diagnosis of meningitis caused by <i>Streptococcus salivarius </i>(<i>S. salivarius</i>), which rarely causes bacterial meningitis. A 54-year-old man presented with a headache that worsened on coughing, without altered consciousness or vomiting. He was diagnosed with pneumocephalus due to a meningoencephalocele, which was detected on contrast-enhanced magnetic resonance imaging; no arterial abnormalities were identified. The day after admission, his headache worsened and the level of consciousness decreased. The cerebrospinal fluid analysis confirmed <i>S. salivarius</i> meningitis. On day 2, the patient suddenly became comatose. Head computed tomography revealed subarachnoid hemorrhage; the patient subsequently died. The autopsy revealed a ruptured 10 mm aneurysm in the right vertebral artery. ICMA is a rare but potentially fatal complication of bacterial meningitis. This case highlights the rapid progression of aneurysm formation during treatment, despite improvement of clinical symptoms and normal findings on initial imaging.