Acta Neurochir (Wien) (2001) 143: 837±843 Acta Neurochirurgica > Springer-Verlag 2001 Printed in Austria Spontaneous Total Thrombosis of Distal Superior Cerebellar Artery Aneurysm H. Ohta, N. Sakai, I. Nagata, H. Sakai, A. Shindo and H. Kikuchi Departments of Neurosurgery, National Cardiovascular Center, Osaka, Japan Summary We report the case of an aneurysm of the distal segment of the superior cerebellar artery (SCA) which showed complete spontaneous thrombosis. Initial angiography performed in another institution showed 3 non-ruptured aneurysms located on the right distal SCA, C3 segment of the right internal carotid artery (ICA) and left basilar artery (BA) ± SCA bifurcation. The patient had two episodes of transient cerebellar ataxia of the right hand before admission to our hospital, but no neurological signs were noted on admission. Computed tomography (CT) and magnetic resonance image (MRI) showed a thrombosed mass on the right cerebellar peduncle, and angiography showed no ®lling of the right SCA from its origin. A follow up angiogram 9 month after endovascular surgery for other aneurysms showed no recanalization of SCA or the aneurysms. There are no previous reports of total spontaneously thrombosed non-giant aneurysms of the distal segment of the SCA. crural cistern compressing the cerebellar peduncle (Fig. 1). On June 23, 1999, cerebral angiography showed multiple sacular aneurysms on the anterior pontine segment of the right SCA, at the left basilar artery (BA) ± SCA bifurcation (Fig. 2a), and on right C3 segment of the internal carotid artery (ICA) (Fig. 2b). At that time, there was no intra-aneurysmal thrombosis of the distal SCA aneurysm visible on the angiogram. On July 24 and August 2, 1999, she experienced episodes of transient cerebellar ataxia of her right hand which continued for several hours, then improved spontaneously. Follow-up CT scan showed partial thrombosis of the aneurysm on August 4, 1999 (Fig. 3a). She was then referred to our hospital for treatment of all aneurysms by endovascular surgery. On August 21, 1999, she was admitted to our hospital. On admission she had no neurological signs or abnormal haematological ®ndings including coagulation time. CT scan demonstrated a moderately high density mass in the right crural cistern. There were no infarctions in the right SCA territory. On magnetic resonance Keywords: Distal superior cerebellar artery; spontaneous total thrombosis; aneurysm. Introduction Aneurysms of the distal segment of the superior cerebellar artery (SCA) are quite rare. About 30 cases of distal SCA aneurysms have been reported to our knowledge [4±7, 10, 11, 13±20, 22, 23, 25, 26, 29±32, 35]. On the other hand, there are many reports of spontaneous thrombosis of aneurysms in several intracranial areas [1±3, 8, 21, 27, 28, 33, 34], but they are usually giant aneurysms. We describe here a case of total spontaneous thrombosis of a non-giant aneurysm on the distal segment of the SCA. Case Report A 47-year-old female experienced sudden transient double vision in June, 1999. She was found to have a right oculomotor nerve palsy by an ophthalmologist and went to neurosurgery clinic for further examination. CT scan showed an isodense round mass in the right Fig. 1. Initial CT scan showing an isodense round mass on the right crural cistern. The cerebellar peduncle was compressed posteriorly by the mass 838 H. Ohta et al. Fig. 2. (a) Vertebral angiogram showing sacular aneurysms on the anterior pontine segment of the right SCA and at the left BA ± SCA bifurcation. (b) Right carotid angiogram showing a sacular aneurysm on the C3 segment Fig. 3. (a) Follow-up CT scan showing a high density mass considered to be a total thrombosis of the aneurysm in the crural cistern. (b) MRI on T1 weighted images showing high intensity signal changes of the aneurysms imaging (MRI), the aneurysm was seen as a high intensity mass on T1 and T2 weighted images, which indicates a subacute phase of thrombosis (Fig. 3b). Spontaneous total thrombosis of the aneurysm was suspected. Angiography was perfomed on August 25, 1999, and showed a ®lling defect of the right SCA at its origin (Fig. 4). Angiographic collateral ¯ow from the right anterior inferior cerebellar artery (AICA) and from the posterior inferior cerebellar artery (PICA) was enough to supply the right SCA territory. The remaining two aneurysms did not show any thrombosis, and were treated with aneurysmal embolization with Guglielmi detachable coils (GDCs) on September 1, 1999. The post-operative course was uneventful and she was discharged without any neurological de®cits. Follow-up angiography 9 months after the endovascular surgery showed no recanalization of the right SCA or other aneurysms. Discussion Aneurysms arising in the distal portion of the SCA are very rare, accounting for less than 0.2% of all intracranial aneurysms [24, 35]. About 30 cases of distal SCA aneurysms have been reported [4±7, 10, 11, 13± 20, 22, 23, 25, 26, 29±32, 35]. The reported cases are summarized in Table 1. They are comprised of 18 males and 13 females ranging in age from 7 to 69 years (mean, 36.6 years). Most cases (24 cases) showed subarachnoid haemorrhage (SAH), and 11 patients had Spontaneous Total Thrombosis of Distal Superior Cerebellar Artery Aneurysm Fig. 4. Follow-up vertebral angiogram showing no ®lling of the right SCA from its origin on wards intracranial nerve palsies. According to Hardy's and Ho¨mann's classi®cation of the SCA segment [9, 12], 14 cases were located at the cortical segment, one at the quadrigeminal segment, 5 at the ambient segment, and 8 at the anterior pontine segment. The locations of the other three cases were not exactly speci®ed (Case No. 3, 22, 23). Four cases had multiple cerebral aneurysms, 2 of which showed associated cerebral arterio-venous malformation (AVM). Intra-aneurysmal thrombosis was observed in 8 of 31 (25.8%) cases (Table 2). One case was a traumatic false aneurysm, another case was a dissecting aneurysm associated with ®bromuscular dysplasia, and the other 6 cases seemed to be true aneurysms. Seven of 8 cases showed partial thrombosis and only our case had total thrombosis of the aneurysm. All 8 patients had symptoms and signs, 4 of diplopia and 4 of SAH. Three cases were located on the cortical segment and 3 cases were on the ambient segment, and only our case was located on the anterior pontine segment. Neck clipping was done in only 2 patients, another 4 patients were treated with parent artery occlusion with or without STA-SCA bypass. Thus, it seems to be di½cult to perform neck clipping for a thrombosed aneurysm. Spontaneous intra-aneurysmal thrombosis is a well documented phenomenon that has been noted in approximately 50% of giant intracranial aneurysms [33]. Pozzati et al. reported that the incidence of total thrombosis in giant aneurysms is between 13% and 20% [27], but there were no reports of non-giant (large 839 or small) aneurysms. This high incidence of thrombus formation within giant intracranial aneurysms is related to the ratio between aneurysmal volume and aneurysmal neck size. In aneurysms with a relatively small neck, intra-arterial thrombosis may occur. Although other biophysiological and dynamic parameters contribute to the delicate balance between thrombogenesis and thrombolysis within the aneurysm (vide infra), the volume: ori®ce ratio would appear to be the major factor [1]. In our case, the dome size of the distal SCA aneurysm was about 12 mm and the neck size was about 3 mm on the initial angiogram, thus the volume: ori®ce ratio was larger than in other aneurysms (ICA and BA-SCA aneurysms). In addition, the right SCA had a narrow diameter and blood ¯ow was too small to supply the distal aneurysm. The narrow neck of the aneurysm and poor blood supply from the parent artery may have caused the spontanous total thrombosis. A follow-up angiogram showed no recanalization of the SCA trunk or aneurysms, but a more long term follow-up might be necessary to see the spontaneous recanalization of the thrombosed aneurysm. The surgical approaches for distal SCA aneurysms have been described in many reports [4±7, 10, 11, 22± 26, 29±32, 35]. With the advances in microcatheter technology, endovascular surgery such as GDC embolization can be considered as an alternate treatment. Most distal SCA aneurysms were treated with neck clipping, but some aneurysms such as dissecting or fusiform aneurysms were treated by trapping or proximal occlusion of the parent artery with or without a bypass procedure. To prevent post-operative ischaemia in the SCA territory from sacri®ce of the parent artery, a preoperative balloon occlusion test should be done by the endovascular technique. Tolerance of SCA occlusion when treating a fusiform or dissecting aneurysm can be better assessed with a proximal test balloon occlusion of the SCA while the patient is awake. Based on the ®ndings of this endovascular testing, decisions should then be made as to whether the bypass is necessary. Surgical treatment carries risks of temporal lobe contusion, venous infarction and cranial nerve palsy, and such complications sometimes lead to negative outcomes. On the other hand, endovascular surgery is less invasive than direct surgery despite the possibility of recanalization due to coil compaction. Endvascular treatment will become a useful and mainstream treatment for distal SCA aneurysms. Cockrill et al. (1977)4 Collins et al. (1992)5 Dimsdale et al. (1959)6 Gacs et al. (1983)7 " " " " " Hidaka et al. (1989)10 Hirose et al. (1989)11 Itoyama et al. (1990)13 Kalyan-Raman et al. (1983)14 Kubota et al. (1994)15 Logue (1964)16 Mabuchi et al. (1992)17 Matricali et al. (1986)18 Murtagh et al. (1981)19 Nagasawa et al. (1995)20 Orz et al. (1995)22 Papo et al. (1977)23 Poppen (1959)25 " Pozzati et al. (1980)26 Sherman et al. (1977)29 Sugita (1985)30 Uede et al. (1986)31 Vincent et al. (1980)32 Yasargil et al. (1984)35 " Present case 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 15/M 23/M 56/F 59/F 53/F 21/M 50/M 69/M 10/M 37/F 25/F 64/M 38/M 40/F 56/F 65/M 45/F 27/M 21/M 48/M 23/F 49/M 53/M 40/F 13/F 47/M 51/M 7/M 62/F 51/M 47/F Age/sex diplopia diplopia SAH SAH SAH SAH SAH SAH SAH SAH SAH SAH diplopia SAH SAH CH SAH SAH SAH SAH SAH SAH SAH SAH SAH SAH tinnitus SAH SAH SAH diplopia TIA Clinical symptom Rt. ambient segment Lt. ambient segment Rt. ant.-pont. segment Lt. cortical segment Bil. cortical segment Lt. cortical segment Lt. cortical segment Rt. cortical segment Lt. cortical segment Lt. cortical segment Rt. ant.-pont. segment Rt. cortical segment unknown Rt. cortical segment Rt. ant.-pont. segment Rt. cortical segment Rt. cortical segment Lt. cortical segment Lt. ambient segment Lt. ant.-pont. segment Rt. ambient segment unknown unknown Lt. ant.-pont. segment Lt. ambient segment Lt. ant.-pont. segment Rt. quad. segment Lt. ant.-pont. segment Lt. cortical segment Rt. cortical segment Rt. ant.-pont. segment Site of aneurysms 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1 2 1 1 1 3 Number of aneurysms partial partial ± ± ± partial ± ± ± ± ± ± partial ± ± ± partial ± partial ± ± ± ± ± ± ± ± ± ± partial total Intraaneurysmal thrombosis proximal occlusion trapping trapping trapping occlusion occlusion clipping resection resection clipping proximal occlusion clipping ± clipping trapping resection clipping clipping trapping clipping clipping trapping trapping clipping trapping clipping clipping clipping clipping clipping ± Treatment traumatic false aneurysm 4th CN palsy 5th and 6th CN palsy 3rd CN palsy ± 4th CN palsy ± AVM AVM ± 6th CN palsy ± FMD ± 5th and 6th CN palsy AVM ± ± 4th CN palsy ± 4th CN palsy ± ± 3rd CN palsy Rt. hemiplegia ± 7th and 8th CN palsy 3rd N palsy AVM ± ± Complications M Male, F female, SAH subarachnoid haemorrhage, CH cerebellar haemorrhage, Rt. right, Lt. left, ant.-pont. anterior-pontine, ± nothing, CN cranial nerve, AVM arterio-venous malformation, TIA transient ischemic attack, FMD ®bromuscular dysplasia. Author (year) Case no. Table 1. Summary of Reported Cases of Distal SCA Aneurysms 840 H. Ohta et al. Cockrill et al. (1977)4 Collins et al. (1992)5 Gacs et al. (1983)7 Kalyan-Raman et al. (1983)14 Matricali et al. (1986)18 Nagasawa et al. (1995)20 Yasargil et al. (1984)35 Present case 1 2 3 4 5 6 7 8 38/M 45/F 21/M 51/M 47/F 23/M 21/M 15/M Age/sex diplopia SAH SAH SAH diplopia TIA diplopia SAH diplopia Clinical symptom unknown Rt. cortical segment Lt. ambient segment Rt. cortical segment Rt. ant.-pont. segment Lt. ambient segment Lt. cortical segment Rt. ambient segment Site 1 1 1 1 3 1 1 1 Number of aneurysms partial partial partial partial total partial partial partial Intra-An. thrombosis proximal occlusion trapping proximal occlusion ± clipping trapping clipping ± Treatment dissection (FMD) ± 4th CN palsy ± ± diplopia (traumatic An.) 4th CN palsy 4th CN palsy Complications (comments) D excellent excellent excellent excellent fair excellent good Outcome Intra-An. Intra-aneurysmal, M male, F female, SAH subarachnoid haemorrhage, TIA transient ischaemic attack, Rt. right, Lt. left, ant.-pont. anterior-pontine, traumatic An. traumatic aneurysm, CN cranial nerve, FMD ®bromuscular dysplasia, D died. Author (year) Case no. Table 2. Summary of Reported Cases of Distal SCA Aneurysms with Intra-Aneurysmal Thrombosis Spontaneous Total Thrombosis of Distal Superior Cerebellar Artery Aneurysm 841 842 References 1. Black SPW, German WJ (1960) Observation on the relationship between volume and size of the or®ce of experimental aneurysms. J Neurosurg 17: 984±990 2. Cantore G, Santoro A, Pian RD (1994) Spontaneous occlusion of supraclinoid aneurysms after the creation of extraintracranial bypasses using long grafts: report of two cases. Neurosurgery 44(1): 216±220 3. Carlson DH, Thomson D (1976) Spontaneous thrombosis of a giant cerebral aneurysm in ®ve days: report of a case. Neurology 26: 334±336 4. 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Thieme-Stratton, Stuttgart, pp 260± 280 Comments Ohta et al. present a case of spontaneous total thrombosis of distal superior cerebellar artery aneurysm with associated intra-arterial thrombosis of the proximal segment. The patient presented with two episodes of ataxia as an ischaemic sign before complete thrombosis was documented with angiography. Spontaneous thrombosis has been described for giant aneurysms, but intra-arterial thrombosis is apparently an uncommon phenomenon. In their case the authors treated with GCD two associated incidental aneurysms, but the symptomatic right distal SCA was left untreated due to its spontaneus thrombosis. The natural history of thrombosed aneurysms and eventual embolic complications is unknown. Some cases of recanalization and even rupture of thrombosed aneurysms have been reported (1, 2). Thus, failure to exclude the aneurysm from the circulation places the patient at risk not only of new embolic complications, but also of recanalization and even rupture. This morbimortality of a continuous follow up period with serial angiography is not negligible. Besides, the anti-agregation that may be indicated to Spontaneous Total Thrombosis of Distal Superior Cerebellar Artery Aneurysm prevent embolic events can accelerate the recanalization process. Finally, we do not agree with the authors conclusion that an endovascular procedure is a ``safe and less invasive'' approach to this lesion. The embolization with coils of a distal aneurysm of the SCA carries the risk of arterial dissection, arterial occlusion, distal emboli and the possibility of long term complications of coil compactation, wire protrusion and embolic events. In experienced hands, microsurgical techniques can minimize the eventual complications of parenchymal contusion, venous infarction or cranial nerve palsy. Nevertheless the authors have done a good review of the literature and as a rare case it should be published in the Acta. 843 1. Atkinson J, Lane J, Colbassani H, Llewellyn M (1993) Spontaneus thrombosis of posterior cerebral artery aneurysm with angiographic reappearence. J Neurosurg 79: 434±437 2. Andrews B, Edwards M, Gannon P (1984) Acutely thrombosed aneurysm of the middle cerebral artery presenting as intracranial hemorrhage in a 3 year old child. J Neurosurg 60: 1303±1307 J. Mura, H. Tedeschi and E. de Oliveira Correspondence: Hajime Ohta, M.D., Department of Neurosurgery, National Cardiovascular Center, 5-7-1 Fujishirodai, Suita, Osaka 565-8565, Japan.