Korean Journal of Cerebrovascular Surgery 2009;11(4):145-149.
Published online December 1, 2009.
"Occult" Ruptured Infectious Aneurysm of the Distal Anterior Cerebral Artery: Case Report.
Ahn, Duck Hyung , Kim, Dae Won , Kang, Sung Don
Department of Neurosurgery, School of Medicine, Institute of Wonkwang Medical Science, Wonkwang University, Iksan, Korea. kangsd@wku.ac.kr
Abstract
A 58-year-old man who underwent mitral valve replacement for mitral valve prolapse that was complicated by severe mitral regurgitation was referred to our department due to his sudden onset of drowsiness. Brain computed tomography revealed a hemorrhage in the anterior interhemispheric fissure and left frontal lobe. Cerebral angiography demonstrated a saccular aneurysm at the angular branch of the middle cerebral artery (MCA), but there was no evidence of vascular abnormalities at the hemorrhagic area. End-to-end anastomosis of the angular branch was performed after resection of the friable aneurysm and the perianeurysmal parent artery segment. Follow-up cerebral angiography after three weeks showed an aneurysm in the distal anterior cerebral artery (ACA) in the previously hemorrhagic area. This ruptured aneurysm was successfully clipped. An infectious aneurysm was confirmed on the histopathological examination.
Key Words: Infectious aneurysm, Occult

Introduction

Infectious aneurysms, although rare, are probably under recognized due to a lack of prospective studies. Infectious aneurysms constitute approximately 2.5~6.5% of all intracranial aneurysms according to a hospital-based retrospective analysis.6) In a recent report that was one of the largest series from any single center, it accounted for only 1.44% of all intracranial aneurysm.9) The term ¡°infectious aneurysm¡± is probably more appropriate than the other terms used to denote this condition because infectious aneurysms can be caused by bacteria, tuberculous bacilli or fungi.

The failure rate of initial angiography for demonstrating any causative lesion is 6~30% in subarachnoid hemorrhage (SAH) patients.8) We describe here a case of ¡°occult¡± ruptured infectious distal anterior cerebral artery (ACA) and unruptured distal middle cerebral artery (MCA) infectious aneurysms with a review of the literature.

 

Case Report

A 58-year-old man who underwent mitral valve replacement for mitral valve prolapse complicated by severe mitral regurgitation was referred to our department for sudden onset of headache and drowsiness 10 days after the operation. At the time of presentation, the patient was receiving anticoagulant therapy. Six weeks before admission to our hospital, he was admitted to a local clinic for fever and pleural effusion. Since the echocardiogram showed severe mitral valve prolapse and mitral regurgitation, he was transferred to our hospital for mitral valve replacement. Brain computed tomography, magnetic resonance imaging, and magnetic resonance angiography after the ictus revealed a hemorrhage in the anterior interhemispheric fissure and left frontal lobe but no evidence of vascular abnormalities (Fig. 1 A, B, C, D). Digital subtraction angiography (DSA) demonstrated a 9-mm sized incidental saccular aneurysm at the angular branch but no evidence of vascular abnormalities in the hemorrhagic area (Fig. 1E). Because the patient had already been treated with antibiotics over the preceding 6 weeks, surgery was planned for treating the aneurysm. Aneurysmal excision and end-to-end anastomosis of the M4 segment were performed due to premature bleeding from the friable aneurysmal neck and parent artery despite careful dissection (Fig. 2). The aneurysm was excised because it was tightly adhered to the dura mater. End-to-end anastomosis was difficult to perform but was possible after resection of the perianeurysmal parent artery segment, which was very friable, making suturing difficult. After the operation, the patient developed Gerstmann syndrome. However, his condition improved completely after 1 week. Follow-up DSA after 3 weeks showed an aneurysm in the distal ACA (callosomarginal artery) in the previously hemorrhagic area (Fig. 3A). A second operation was performed for this aneurysm; follow-up DSA revealed no aneurysmal remnants or any other aneurysms (Fig. 3B). Blood culture reports for both aneurysms were negative. However, both aneurysms were confirmed to be infectious aneurysms on histopathological examination that showed chronic inflammation (Fig. 4). The patient was discharged without any neurological deficits.

 

Discussion

The definitive feature that distinguishes infectious aneurysms from other aneurysms is the infectious pathological process in the wall of the aneurysm. However, these findings are not always conclusive. In fact, Yamakawa et al.15) reported that histological examination demonstrated the infectious nature of the lesion only in 33% of cases. Little is known regarding the exact structural changes caused by antibiotics treatment; however, antibiotics possibly may cause histological changes because complete resolution of bacterial intracranial aneurysms has occurred after antibiotics treatment in certain cases.15) The incidence of positive blood or CSF cultures varies from 30~47% in infectious aneurysms.5)12)14)

Several institutions have recommended antimicrobial therapy as the first line of treatment for infectious aneurysms.6) Based on these observations, indications for surgical treatment are as follows: (1) rupture of infectious aneurysms, (2) presence of significant mass effect, (3) enlargement of infectious aneurysms during antibiotic treatment, and (4) persistence of infectious aneurysms on completion of antibiotics treatment.6) Recent studies have shown a higher chance of survival with surgical treatment, particularly for proximal infectious aneurysms.1)9) Kannoth et al.9) reported that infectious aneurysms related to meningitis tend to occur in the vertebro-basilar territory, are more proximal and bleed often, leading to SAH and death while under medical treatment. In contrast, those related to infective endocarditis are located more often in the carotid territory, tend to be distal, and are probably less prone to catastrophic bleeding. Therefore, they concluded that early surgical intervention may be considered in patients with infectious aneurysms in proximal locations, particularly in the vertebro-basilar territory secondary to meningitis.

With improvements in catheter technology, endovascular therapy is another option for patients with ruptured infectious aneurysms who do not have a hematoma that produces a mass effect. However, according to the literature, the parent artery was preserved only in 35% of the endovascularly treated aneurysms. In contrast, the preservation rate of the parent artery was 63% in the surgically treated group. It is noted that the fragile nature of these aneurysms and the surrounding vasculature may increase the risk associated with an endovascular procedure. Therefore they concluded that endovascular therapy should be halted if the aneurysm involves an eloquent parent artery, such as the angular artery in the dominant hemisphere, and these patients should be considered for surgery.4) As in our case, which involved the parent artery, infectious aneurysms, are very friable and necrotic, particularly in the acute stage, and are prone to fatal bleeding. Although neck clipping is performed successfully, the aneurysm can be ruptured if the clip is moved unintentionally. Surgical resection of the aneurysm along with a short segment of the parent vessel and end-to-end anastomosis is not always possible because the perianeurysmal parent artery is typically friable. Therefore, surgeons must be cautious while clipping infectious aneurysms with parent artery preservation and should plan the bypass or reconstruction of the parent artery if the aneurysm does incorporate an eloquent parent artery. An alternative technique such as an interposition graft can also be considered as a treatment option.

Mortality because of hemorrhage from an infectious aneurysm ranges from 12 to 46%.5)6)9)12)14) Kannoth et al.9) reported that the this overall mortality was 32%. In their series, mortality was significantly higher for those with older age, meningitis, and infectious aneurysms located in the vertebro-basilar territory. They concluded that the clinical features, imaging characteristics, and probably the natural history of infectious aneurysms related to meningitis differ from those of infectious aneurysms related to infective endocarditis.9) Fungal etiology has always carried a higher mortality, as reported earlier.10) Another study has shown better outcomes for infectious aneurysms associated with infective endocarditis (100% survival) in comparison to infectious aneurysms associated with meningitis or other causes (33% survival).1)

The pathogenesis of non-aneurysmal SAH is unknown. Prevailing explanations include rupture of a venous or capillary vessel, rupture of an occult aneurysm, and focal arteritis without frank aneurysm formation.3) Minor leaks from a mycotic aneurysm which may be undetected by angiography in ~10% of cases,16) or only found with repeated studies,2) may account for some cases of non-aneurysmal SAH. Cerebral angiography performed immediately after the onset of SAH commonly fails to reveal any causative lesion, and the rate of failure of cerebral angiography for detecting an aneurysm has been reported to be 6~30%.8) In most of these cases, the cause of SAH remains unknown even after repeat angiography. However, in a small percentage of such patients, repeated angiography discloses a lesion undetected in the initial angiography. The failure to detect some ruptured aneurysms in the initial angiography has been attributed to vasospasm, spontaneous thrombosis of the aneurysm, arterial dissection, microaneurysms that are too small to opacify, and interpretative errors.7,13) Previous studies have reported the rate of detection by a repeat angiography for aneurysms missed on the initial angiography to be 5~36%.8) This relatively high rate necessitates repeat angiography in patients with non-traumatic SAH in whom the initial angiography is negative.

 

Conclusion

The presence of an ¡°occult¡± aneurysm should be considered after SAH or intracerebral hemorrhage of unknown origin in specific sites such as the sylvian or anterior interhemispheric fissure; repeated angiography is recommended in such cases. Various treatments have been recommended for treating infectious aneurysm, but the principal goals should be to eliminate the aneurysm from the circulation and to preserve blood flow to the distal vasculature. Because the infectious aneurysm and the incorporated parent artery is typically very friable, surgeons must caution against clipping of infectious aneurysms with parent artery preservation and should plan for bypass or reconstruction of the parent artery if the aneurysm is located an eloquent parent artery.

 

REFERENCES

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9)              Kannoth S, Iyer R, Thomas SV, Furtado SV, Rajesh BJ, Kesavadas C, et al. Intracranial infectious aneurysm: Presentation, management and outcome. J Neurol Sci 256:3-9, 2007

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13)            Rinkel GJE, Wijdicks EFM, Hasan D, Kienstra GEM, Franke CL, Hageman LM, et al. Outcome in patients with subarachnoid haemorrhage and negative angiography according to pattern of haemorrhage on computed tomography. Lancet 338:964-8, 1991

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15)            Yamakawa H, Hattori T, Tanigawara T, Enomoto Y, Ohkuma A. Ruptured infectious aneurysm of the distal middle cerebral artery manifesting as intracerebral hemorrhage and acute subdural hematoma: Case report. Neurol Med Chir (Tokyo) 43:541-5, 2003

16)            Ziment I. Nervous system complications in bacterial endocarditis. Am J Med 47:593-607, 1969



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