To describe a case of spontaneous lobar intracerebral hemorrhage (sICH) that uncovered a ruptured mycotic aneurysm secondary to Streptococcus sanguinis infective endocarditis (IE), and to highlight the importance of considering infectious vascular etiologies in non-traumatic sICH.

Infective endocarditis (IE) can present atypically with neurological complications such as sICH, ischemic stroke, and CNS infections. Mycotic aneurysms, caused by septic embolization and arterial wall infection, account for <1% of sICH and are identified in <5% of IE cases. CTA and MRA have limited sensitivity, while digital subtraction angiography (DSA) remains the gold standard for diagnosis.

A 52-year-old woman with hypertension, recent venous thrombosis on apixaban, presented with sudden severe headache, nausea, and vomiting. CT revealed a large right temporoparietal ICH with subarachnoid extension and 7–9 mm midline shift. After anticoagulation reversal, she underwent emergency decompressive hemicraniectomy. Intraoperatively, diffuse subarachnoid hemorrhage and absent right hemispheric pulsation were noted. DSA demonstrated a distal right MCA (M4) pseudoaneurysm, consistent with a mycotic origin. Due to persistent bleeding, microsurgical aneurysm obliteration, hematoma evacuation, and right anterior temporal lobectomy were performed. Blood cultures yielded Streptococcus sanguinis, and transesophageal echocardiography identified a mitral valve vegetation with severe regurgitation, confirming IE. She completed a six-week course of intravenous ceftriaxone. Cardiothoracic surgery recommended medical management with interval TEE. At discharge to inpatient rehabilitation, she exhibited residual left hemiparesis and left visual field deficit.

This case illustrates that spontaneous ICH without clear vascular risk factors should prompt evaluation for infectious etiologies such as IE. Mycotic aneurysm rupture, although rare, can be the initial presentation of endocarditis and requires high diagnostic suspicion.