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Giant serpentine aneurysms are rare and have distinct angiographic findings. The rarity, large size, complex anatomy and hemodynamic characteristics of giant serpentine aneurysms make treatment difficult. We report a case of a giant serpentine aneurysm of the right middle cerebral artery (MCA) that presented as headache. Treatment involved a superficial temporal artery (STA)-MCA bypass followed by aneurysm resection. The patient was discharged without neurological deficits, and early and late follow-up angiography disclosed successful removal of the aneurysm and a patent bypass graft. We conclude that STA-MCA bypass and aneurysm excision is a successful treatment method for a giant serpentine aneurysm.
Giant serpentine aneurysms were first documented by Segal and McLaurin14). The distinctive neuroimaging features of these aneurysms are a large size (> 25 mm), and a twisted vascular course within the aneurysm with multiple entrance and exit points. Giant serpentine aneurysms contain a thrombus, show peripheral calcification, have a mass effect including a midline shift, and have adjacent edema mimicking a brain tumor in computed tomography (CT)1,3,5). Patients with giant serpentine aneurysm usually show symptoms associated with the mass effect, including headache, hemiparesis and seizure4,15). Aggressive treatment is generally recommended for giant serpentine aneurysms since conservative measures often result in continual aneurysm growth, neurological deterioration and poor outcomes11,12,15). Prior to the use of revascularization surgery in the neurosurgical field, surgical treatment of giant serpentine aneurysms was associated with unacceptable morbidity and mortality rates as high as 33%1,7). However, the application of bypass surgery has resulted in satisfactory outcomes16). Treatment of giant serpentine aneurysms should be individualized due to the complex and varied hemodynamics and morphological features6).
The present report describes a case of a giant serpentine aneurysm of the middle cerebral artery (MCA). Treatment involved a superficial temporal artery (STA)-MCA bypass and resection of the aneurysm. Neurological and angiographic studies two years after postoperatively indicated the treatment was successful.
A 43-year-old woman presented at the emergency department complaining of severe headache. She had a two year history of intermittent headache which had gradually worsened over the past several months. She also experienced transient left hand weakness that persisted for ten minutes and left facial numbness. Her past medical history was unremarkable, and she did not take any regular medication. Neurological examinations at admission revealed no focal deficits. CT showed a 7 × 8 × 5 cm mass with an approximately 10 mm midline shift, and adjacent edema. There was peripheral calcification and mixed density within the mass (Fig. 1A). Contrast enhancement showed that the mass had a heterogeneous enhancing pattern, and a large and tortuous blood vessel passed through the mass. Magnetic resonance image (MRI) scans showed different stages of organizing hematoma within the mass, and continuity with the right MCA (Fig. 1B). A diagnosis of a giant aneurysm was made. Angiography showed the right MCA was displaced upward, and demonstrated an eccentric vascular course through the aneurysm with multiple entrance and exit points that differentiated the mass from a regular saccular giant aneurysm. The morphology of the vascular course within the aneurysm was snake-like and serpiginous. Flow stagnation resulted from a long transit time that was attributed to the formation of a thrombus within the aneurysm (Fig. 2).
The patient was treated surgically. The parietal branch of the STA was prepared for anastomosis. A wide sylvian dissection was performed and the whole length of the aneurysm and proximal and distal MCA were identified. End-to-side bypass surgery was performed between the STA and the efferent M4 branch. After bypass, permanent clips were placed at the proximal and distal artery of the aneurysm and the aneurysm excised. Several perforators from the aneurysm were coagulated and cut. The postoperative course was uneventful and the patient was discharged without any neurological problems. A postoperative CT scan revealed complete removal of the mass and normalized midline shifting (Fig. 3A). A one week postoperative angiography demonstrated good patency of the bypass graft with sufficient distal perfusion (Fig. 3B), and a two year follow-up CT angiography revealed the same findings.
The origin and pathogenesis of giant serpentine aneurysms remain uncertain. They may represent the expansion of a fusiform aneurysm with partial thrombosis and repeated intramural hemorrhage through a weak point in the arterial wall10). Christiano et al.4) reported that giant serpentine aneurysms most commonly occur in the MCA circulation (50%) followed by the PCA circulation (18%) and vertebrobasilar artery (15%). The MCA circulation has no barriers such as dural or bony structures to prevent aneurysm growth, and this anatomical characteristic is thought to favor development of serpentine aneurysms.
Fanning et al.7) suggested that the lower force of jet blood flow of the MCA brought about the flow stagnation within the aneurysm which was attributed to the formation of thrombus. Additionally, giant serpentine aneurysms have the different eccentric vascular channels, resulting the Coanda effect, describing jet blood flow forces are stronger in the deflected surface of the wall rather than central portion of the aneurysm which makes thrombus within central portion of the aneurysm.
In computed tomography, the giant serpentine aneurysm looks like brain tumor in several aspects, well circumscribed mass lesion with edema and midline shifting. Therefore, it may be often misdiagnosed as a brain tumor, initially. In contrast enhancing CT scan, the giant serpentine aneurysm demonstrates as hererogenous enhancing mass with peripheral calcification and thick, wavy vessel within the mass. These findings imply that the thrombus is located within the aneurysm and the formation of the giant serpentine aneurysm has been taken a long time. There are no consistent findings associated with MRI resulting from coexistence of different stages of thrombus10).
The natural history of giant serpentine aneurysms has not been established due to their rarity and severity. The few reports on giant serpentine aneurysms contain only a small number of cases. While some authors reported spontaneous occlusion of the aneurysm12), the majority reported rapid neurological deterioration leading to death after ischemic stroke, or recanalization of the spontaneously occluded aneurysm9,11,14). Suzuki et al.15) followed 39 giant serpentine aneurysm cases and reported that angiographic enlargement occurred in 12 of those patients over the follow-up period. They suggested that this enlargement was the result of repetitive intramural hemorrhage and accumulation of the thrombus. Sari et al.12) reported a case of spontaneous, complete thrombosis of a giant serpentine aneurysm. Mahadevan et al.11) reported on a giant serpentine aneurysm that caused rapid neurological deterioration and death due to ischemic stroke. The neurological deterioration in that case resulted from stretching or compression of the parent cortical vessels or acute occlusion of the vascular channel due to thrombosis accumulation. Lee et al.9) reported a case where a giant serpentine aneurysm recanalized after spontaneous occlusion. Therefore, monitoring and further treatment should always be considered even after spontaneous occlusion. Although subarachnoid hemorrhage (SAH) is not considered a common presentation of giant serpentine aneurysms, Suzuki et al.15) reported 28% of giant serpentine aneurysm patients initially presented with SAH.
Surgery appears to be the optimal treatment for most giant serpentine aneurysm cases. Suzuki et al.15) documented outcomes following conservative or aggressive management of 18 cases of MCA giant serpentine aneurysm. Of the six conservatively treated patients, five suffered neurological deterioration or death, while one showed no neurological change. Of the 12 surgically treated patients, all showed neurological improvement and preserved distal cortical blood flow. These findings indicate that aggressive treatments should be considered.
Important issues to consider in aneurysm surgery include accessibility, aneurysm morphology and perforators. In the past, carotid artery ligation was used to treat giant serpentine aneurysms, but was associated with poor outcomes and ischemic stroke rates as high as 33%13). Surgical wrapping or coating was attempted, but resulted in the deaths of two of 18 patients15). Horowitz et al.8) reported that occlusion of the distal outflow only was an effective surgical management, but this approach has yet to be established. Prior to the introduction of bypass surgery, giant serpentine aneurysm surgery resulted in overall morbidity and mortality rates of 30-35%1). Outflow from the giant serpentine aneurysm feeds distal cortical vessels, and occlusion or narrowing of those vessels results in stroke7). Amin-Hanjani et al.2) reported a case of a giant serpentine aneurysm treated using an STA-MCA bypass and proximal MCA clipping. The patient was neurologically intact, and follow-up angiography revealed no aneurysm and a patent bypass 13 years later2). Recently, endovascular approaches have been used to treat giant serpentine aneurysms, especially those in surgically inaccessible areas, and successful results have been reported6,16). However, endovascular approaches do not immediately relieve the mass effect and cannot be performed in cases of insufficient collateral distal blood flow. The present patient suffered headache and ipsilateral compressive trigeminal neuropathy due to the severe local mass effect of the aneurysm, making a key goal of treatment the immediate elimination of the mass effect.
Bypass surgery is indispensable for avoiding ischemic complications after aneurysm resection. When performing an STA-MCA bypass to provide distal blood flow, it is easier to create the anastomosis at the surface of the brain rather than deep in the sylvian fissure. However, it is sometimes difficult to identify the correct recipient vessel on the brain surface. Cerebral angiographs do not provide sufficient information regarding the correct distal vessel for bypass, especially near the sylvian point where MCA branching is maximal and the course of branches is complex and crowded. Therefore, we used a microvascular Doppler on the cortical artery to detect loss of arterial sound when we applied a temporary clip to the MCA just distal to the aneurysm, and the return of sound after removal of the temporary clip. After a successful bypass, the aneurysm can be excised and the perforators from the aneurysm to the insular cortex can be sacrificed as they appear to be non-functioning.
We found that STA-MCA bypass and aneurysm excision was a successful treatment method for a giant serpentine aneurysm. This approach immediately relieved symptoms related to the mass effect, and provided distal blood flow.