Mycotic Aneurysm of the Brain

Figure 1. Brain MRA 3D-time-of-flight showing a 7mm x 5mm aneurysm in the pericallosal branch of the left anterior cerebral artery (asterisk).

Based on the arterial site of the aneurysm and underlying infection (pneumonia), it was believed to be a mycotic aneurysm. Due to the size and persistence of the mycotic aneurysm, conventional angiogram and endovascular embolization of the aneurysm was planned.

Figure 2. Cerebral angiogram, lateral view (top) shows contrast-enhancing mass on the left pericallosal branch suggestive of a mycotic aneurysm (asterisk).
3D-reconstruction, lateral and craniocaudal views (bottom), shows a saccular aneurysm with an irregular shape (lobulated) of about 6mm x 9mm x 3mm in dimensions.

Baseline cerebral angiogram found an irregularly shaped pericallosal saccular aneurysm that had increased in size over the past weeks (Figure 2). Although the aneurysm was asymptomatic, treatment was indicated due to the dynamic anatomy and mycotic nature of the aneurysm.

Embolization was performed with coils and resulted in near complete obliteration of the aneurysm (Figure 3). The patient had an uneventful course.

Figure 3. Post-coiling cerebral angiogram with near-complete embolization of the pericallosal branch aneurysm (circle, left). Coils can be seen within the aneurysm sack (circle, right).

Treatment Considerations

Mycotic aneurysms of the brain represent a minority (<5%) and may occur with systemic or local spread of an infection to a cerebral artery [1,2]. Most frequently, the cause is a bacterial infection (other causes include fungi and viruses). Infection and inflammation of the arterial wall lead to degenerative remodeling processes, thereby weakening the vessel wall integrity, ultimately allowing an aneurysm to form. Typically, mycotic aneurysms are located in the periphery unlike true aneurysms for which more proximal cerebrovascular junctions are predilection sites. Due to the infected, inflamed and weakened vessel wall, mycotic aneurysms are prone to rupture with likely detrimental outcome for most of the affected. The primary therapy is treatment of the underlying infectious cause with extended antibiotic treatment. Mycotic aneurysms should be closely watched with regular assessment of the risk of rupture and treated when size remains unchanged or increases [3,4]. The lack of randomized clinical trials have prevented a definition of a standard in practice. The identification and treatment of the infectious cause and careful observation of the mycotic aneurysm with timely effective intervention to eradicate the lesion appear prudent practice. References

1. Kannoth S, Iyer R, Thomas SV, et al. Intracranial infectious aneurysm: presentation, management and outcome. J Neurol Sci. 2007 May 15;256(1-2):3-9. https://pubmed.ncbi.nlm.nih.gov/17360002/
2. Allen LM, Fowler AM, Walker C, et al. Retrospective review of cerebral mycotic aneurysms in 26 patients: focus on treatment in strongly immunocompromised patients with a brief literature review. AJNR Am J Neuroradiol. 2013 Apr;34(4):823-7. https://pubmed.ncbi.nlm.nih.gov/23064596/
3. Zanaty M, Chalouhi N, Starke RM, et al. Endovascular treatment of cerebral mycotic aneurysm: a review of the literature and single center experience. Biomed Res Int. 2013;2013:151643. https://pubmed.ncbi.nlm.nih.gov/24383049/
4. Khan A, Waqas M, Nizamani WM, Bari ME. Ruptured mycotic aneurysms: Report and outcomes of two surgically managed patients. Surg Neurol Int. 2017;8:144. https://pubmed.ncbi.nlm.nih.gov/28781921/