Accurate mycotic aneurysm diagnosis remains a clinical challenge because these lesions often mimic other neurosurgical emergencies. While most mycotic aneurysms (MAs) cause intracranial hemorrhage, they rarely present as a subdural hematoma (SDH). Specifically, clinicians must maintain high suspicion in patients with ventriculoatrial shunts (VASs). These shunts carry a higher risk of bacteremia compared to ventriculoperitoneal shunts. Consequently, a long-standing shunt can serve as a source for subacute bloodstream infections.

A recent illustrative case involved a 61-year-old female presenting with an acute-on-chronic SDH. Interestingly, she did not show signs of endocarditis. However, cultures from her blood and cerebrospinal fluid grew Cutibacterium acnes. Imaging revealed a fusiform distal left middle cerebral artery MA. Because C. acnes is a low-virulence organism, the infection likely progressed silently over many years. This unique presentation underscores the need for thorough investigation in shunt patients.

Challenges in Mycotic Aneurysm Diagnosis

Early mycotic aneurysm diagnosis is vital to prevent catastrophic rupture and improve patient survival. Physicians traditionally link MAs to infective endocarditis or intravenous drug use. However, this case highlights how a long-term VAS predisposes individuals to rare complications. Because the VAS drains directly into the venous system, it facilitates persistent bacterial seeding. Moreover, the distal location of these aneurysms often requires specialized surgical or endovascular management.

In addition to imaging, clinicians should prioritize multiple culture samples. Cutibacterium acnes often requires extended incubation periods. Therefore, laboratories must hold cultures for at least 10 to 14 days. If an MA is suspected, angiography remains the gold standard for confirmation. Ultimately, a multi-disciplinary approach involving neurosurgeons and infectious disease specialists ensures the best outcome.

FAQs about Shunt-Related Infections

What are the common causes of mycotic aneurysms?

Most cases arise from infective endocarditis. Other causes include intravenous drug use, bacterial meningitis, and infections related to neurosurgical hardware like shunts.

Why are ventriculoatrial shunts more prone to these infections?

VAS systems provide a direct path into the bloodstream. This configuration increases the risk of systemic bacteremia compared to shunts that drain into the peritoneum.

Which imaging modality is best for detecting these lesions?

While CT and MRI identify associated hemorrhage, digital subtraction angiography remains the most sensitive tool for identifying small or distal mycotic aneurysms.

Disclaimer: This content is for informational and educational purposes only. It does not constitute medical advice or establish a doctor-patient relationship. Always seek the advice of a qualified healthcare provider regarding any medical condition. Refer to the latest local and national guidelines for clinical practice.

References

Amaral-Nieves N et al. Mycotic aneurysm presenting in a patient with a ventriculoatrial shunt with positive CSF cultures for Cutibacterium acnes: illustrative case. J Neurosurg Case Lessons. 2026 May 04. doi: undefined. PMID: 42081835.

Zhu G et al. Infectious intracranial aneurysms: a review of the literature. Frontiers in Neurology. 2019;10:498.