Invisible Until It Burst: Unexpected Subarachnoid Hemorrhage From a Rapid-Onset Infectious Aneurysm in a Patient With Endocarditis

Abstract

Infective endocarditis (IE) can lead to serious neurological complications, including septic embolism and infectious intracranial aneurysms (IIAs). Although IIAs are rare, their rupture often results in catastrophic outcomes. Predicting their formation, especially within a short period, remains a clinical challenge. We present the case of a man in his 70s who was newly diagnosed with colon cancer. During preoperative evaluation, transthoracic echocardiography revealed vegetations on the aortic and mitral valves, leading to a diagnosis of IE caused by Streptococcus sanguinis. On the third day of hospitalization, the initial brain magnetic resonance imaging (MRI) revealed asymptomatic cerebral infarction, but magnetic resonance angiography (MRA) did not show any aneurysms. Despite appropriate antibiotic therapy, the patient developed sudden left hemiparesis and impaired consciousness on day 6. Emergent computed tomography (CT) and computed tomography angiography (CTA) revealed a subarachnoid hemorrhage and a newly formed ruptured aneurysm in the M1 segment of the middle cerebral artery. Given the patient's overall prognosis, neurosurgical intervention was deemed inappropriate, and best supportive care was initiated. The patient passed away shortly thereafter. This case highlights the unpredictable nature of IIAs in IE. Although imaging performed just three days prior showed no aneurysms, a rapidly formed and ruptured IIA resulted in fatal subarachnoid hemorrhage. It underscores the challenge of predicting the rupture of infectious aneurysms in IE and emphasizes the importance of frequent imaging follow-up, even when initial imaging findings are normal.

Keywords: brain mri; cerebral infarction; colon cancer; infectious intracranial aneurysm; infective endocarditis; rapid aneurysm formation; streptococcus sanguinis; subarachnoid hemorrhage; vegetation.

Figure 1. Abdominal contrast-enhanced CT.

(A) Cardiomegaly with right-sided pleural effusion is observed (arrow). (B) An irregular hypodense area in the spleen is noted, suggestive of splenic infarction (arrow). (C) A localized wall thickening is observed in the sigmoid colon, with heterogeneous post-contrast enhancement, suggestive of sigmoid colon cancer (arrowhead). (D) A small protruding lesion is noted on the left wall of the rectum, consistent with rectal cancer (arrowhead).

Figure 2. Lower gastrointestinal endoscopy.

(A) A 20 mm protruding lesion is seen in the rectum. (B) Circumferential colon cancer is observed in the sigmoid colon, with narrowing of the lumen. (C) A self-expanding metal stent has been placed.

Figure 3. Echocardiography.

(A) A club-shaped mass is observed on the aortic and mitral valves (arrow). (B) A mass is observed in the aortic valve annulus (arrow).

Figure 4. Head MRI and MRA.

DWI (A, B) and FLAIR (C, D) show high signal areas in the left corona radiata and frontal lobe, consistent with acute to subacute ischemic infarction. MRA (E) reveals no significant aneurysms. DWI, diffusion-weighted imaging; FLAIR, fluid-attenuated inversion recovery; MRI, magnetic resonance imaging; MRA, magnetic resonance angiography

Figure 5. Head CT and CTA.

(A, B) Subarachnoid hemorrhage is observed from the basal cistern to the suprasellar cistern, along the bilateral Sylvian fissures, and in the right hemisphere sulci. A subcortical hemorrhage is noted in the right temporal lobe. There is significant compression of the right lateral ventricle with a midline shift to the left. (C, D) A 12 x 3 mm contrast-enhancing mass is observed protruding dorsally from the proximal M1 segment of the right middle cerebral artery, consistent with a pseudoaneurysm (arrow). CTA, computed tomography angiography; CT, computed tomography