An unusual ischaemic presentation of thrombosed intracranial mycotic aneurysm with subsequent subarachnoid haemorrhage

Background

Mycotic aneurysms are an unusual cause of subarachnoid haemorrhage but represent a potentially growing segment of haemorrhagic cerebrovascular disease as the opioid epidemic continues in the USA, with associated increased rates of bacterial endocarditis. Mycotic aneurysms may have varying presentations, including haemorrhagic, secondary to rupture, as well as ischaemic, secondary to thrombosis. Their endovascular management may be challenging due to frequent distal location, lesion friability, as well as occasional occult nature on angiographic studies. While the majority of these types of lesions currently develop in the setting of bacterial endocarditis often related to intravenous drug abuse, it is important to consider other causative factors such as dental or periodontal disease as well as metastatic aneurysm formation in diseases such as cardiac myxomas.

Case presentation

A late middle-aged male patient presented to the emergency department with the acute onset of left-sided facial and hemibody weakness, sensory neglect and dysarthria with National Institutes of Health (NIH) stroke scale of 9. He underwent CT and CT angiography demonstrating branch occlusion within the right M2 superior division with hypoattenuation of the associated vascular territory. A small rounded focus of associated hyperattenuation was noted distal to the site of vessel occlusion, initially interpreted as focal haemorrhagic transformation (figure 1). Given the concern for focal haemorrhagic transformation, the patient was not deemed a candidate for mechanical thrombectomy or intravenous thrombolytics.

The patient was transferred to the intensive care unit, where he subsequently developed a severe headache and decreased level of consciousness, Glasgow Coma Scale 13, with unchanged pattern of focal neurologic deficits. He was taken for follow-up CT which demonstrated diffuse sulcal and cisternal subarachnoid haemorrhage, centred predominantly within the right Sylvian fissure. CT angiography was repeated which demonstrated persistent occlusion of the right M2 superior division branch and no demonstrable source of subarachnoid haemorrhage (figure 2).

Neurointerventional service was consulted, with plan for angiographic evaluation and possible endovascular management. During preoperative assessment, the patient was noted to have profound dental and periodontal disease and endorsed self-extracting an abscessed tooth approximately 2 weeks prior to presentation. The patient and family denied any history of intravenous drug abuse. Toxicology screen was negative.

He was taken for angiography which demonstrated branch occlusion within the right M2 superior division and no angiographic demonstration of aneurysm or other haemorrhagic source. Given the provided history, underlying thrombosed mycotic aneurysm was considered to be the most likely differential consideration, and endovascular coil embolisation was performed at the level of the occlusion (figure 3). Postoperative CT head demonstrated localisation of the coil mass at the site of the hyperattenuating focus noted on the presentation head CT, suggestive of successful coil embolisation of angiographically occult mycotic aneurysm. Three-month follow-up CT head demonstrated well-developed infarction limited to the region of hypoattenuation seen on initial presentation (figure 4).

Differential diagnosis

Differential considerations for this case initially included haemorrhagic transformation of ischaemic stroke, thrombosed middle cerebral artery (MCA) aneurysm and thrombosed MCA mycotic pseudoaneurysm. The initial imaging with rounded hyperattenuating structure within the right Sylvian fissure represented an unusual morphology and location for haemorrhagic transformation, and as such early haemorrhagic transformation presenting in this manner would be considered very atypical. For these reasons, the alternative differential considerations were thought to be more likely. Cerebral aneurysms, particularly when thrombosed, may present with focal rounded hyperattenuation with Hounsfield units similar to that of acute blood products (approximately 60–90 HU). The subsequent development of cisternal subarachnoid haemorrhage further supported the diagnosis of thrombosed aneurysm or pseudoaneurysm. Given the history of recent dental abscess with self-performed tooth extraction, mycotic aneurysm became the leading differential consideration.

Treatment

Cerebral angiography was performed under general anaesthesia. A six French introducer sheath was placed in the right common femoral artery, and a five French angled tapered GlideCath (Terumo, Tokyo, Japan) was utilised to perform full diagnostic cerebral angiography, demonstrating occlusion of right M2 superior division branch and no other identifiable source of haemorrhage. Subsequently, an arrangement of a NavienTM (ev3, Plymouth, MN) 0.072″ support catheter with coaxial five French Sofia (Microvention, Aliso Viejo, California, USA) intermediate catheter and Headway Duo (Microvention) microcatheter was advanced over a Synchro-2 (Stryker, Kalamazoo, Michigan, USA) 0.014″ microwire. The occluded branch was accessed with the microcatheter and gentle microangiography was performed confirming branch occlusion. The microcatheter was distally navigated within the branch, and coil embolisation was carried out with Target (Stryker) detachable coils. Follow-up angiography was performed demonstrating occlusion of the segment and stable positioning of the coil mass with no contrast opacification distal to the coil mass.

Outcome and follow-up

The patient was transferred to the intensive care unit, where he recovered well with subsequent improvement in his stroke symptoms. Follow-up angiography was performed during his hospital stay demonstrating stable coil mass positioning with durable occlusion. He was discharged to home after recovery.

At 3-month clinic follow-up, the patient had resolution of stroke symptoms and was neurologically intact with NIH stroke scale 0. He had returned to work, and dental consult was obtained for further tooth extraction.