Acta Neurochir (Wien) (2005) 147: 1283–1286 DOI 10.1007/s00701-005-0615-2 Neurovascular Observation Surgical treatment of a basilar perforator aneurysm not accessible to endovascular treatment W. Hamel1 , U. Grzyska2 , M. Westphal1 , and U. Kehler1 1 2 Klinik f€ ur Neurochirurgie, Universit€atsklinikum Hamburg-Eppendorf, Hamburg, Germany Klinik f€ ur Neuroradiologie, Universit€atsklinikum Hamburg-Eppendorf, Hamburg, Germany Received December 16, 2004; accepted July 14, 2005; published online August 29, 2005 # Springer-Verlag 2005 Summary Aneurysms originating from perforatoring branches of the midbasilar artery are extremely rare. Rupture of such an aneurysm resulted in a subarachnoid hemorrhage with a prepontine clot in a 44 year old male who presented with an acute confusional state. After coil embolization had failed, the partially thrombosed aneurysm was wrapped and coagulated via a combined supra-=infratentorial subtemporal presigmoid approach in prone position. The postoperative course was complicated by a tension pneumatocephalus and liquorrhea. Additional aneurysms of the anterior communicating artery and right middle cerebral artery were clipped several months later. The patient recovered well, and except for slight gait ataxia no other deficit remained. Keywords: Aneurysm; basilar artery; microsurgery; subarachnoid hemorrhage. Introduction Aneuryms of the vertebro-basilar system comprise approximately 10–15% of all intracranial aneurysms and most occur at the bifurcation of the basilar artery [8]. In contrast, aneurysms arising from perforating branches of the basilar artery have hardly been observed [2]. With regard to treatment, it is widely agreed on that for most aneurysms of the posterior circulation endovascular coiling is a safer treatment than clipping (e.g. 5). Since most of these aneurysms are readily accessible to the endovascular route and suitable for such treatment only few aneurysms remain to be treated by microsurgery. Case report A 44 year old male who stayed away from work for two days was admitted to the Department of Psychiatry of another hospital because of confusion and a deteriorated level of consciousness. The previous history was unremarkable except for regular consumption of alcohol. Upon admittance of the disoriented patient slight anisocoria with relative widening of the left pupil and slight neck rigidity was found. No other focal deficit was elicited. Blood alcohol was negative. A cranial CT scan (performed at Diakoniekrankenhaus Rotenburg=W€umme, Germany) revealed a subarachnoid hemorrhage with a large prepontine clot according to Fisher Grade III (Fig. 1A). A CT angiograpy revealed three aneurysms at the following locations: midbasilar artery perforator, anterior communicating artery, right middle cerebral artery (Fig. 1B, C). The following day the patient was referred to our hospital in an unchanged neurological condition. Because of the prepontine blood clot the origin of the hemorrhage was suspected to be the basilar artery perforator aneurysm which revealed slow filling during angiography. At first, endovascular treatment was attempted. Although, a microguide could be placed into the aneurysm a microcatheter could not be advanced into the aneurysm allowing for insertion of coils. A CT scan after the intervention showed progressive hydrocephalus, and external ventricular drainage was instituted. Two days later the aneurysm was operated on using a combined supra- and infratentorial subtemporal presigmoid approach in the prone position. Following removal of the hematoma from the basilar artery dissection was continued towards the superior cerebellar artery (SCA). The prepontine hematoma had displaced the pons slightly dorsally giving some additional space for dissection. The aneurysm could be located almost 10 mm below the SCA. The aneurysm was found to be partially thrombosed and opened which resulted in some minor bleeding which was controlled by coagulation. One of two perforators in contact with the aneurysm were dissected off the aneurysm wall. However, an aneurysm clip could not be placed without compromising the perforator. Therefore, the coagulated aneurysm was wrapped with tachocomb. The bone flap was reinserted after the dura was closed with tachocomp and mastoid cells were sealed with bone wax. Immediately after the operation the patient developed a left sided mydriasis. An emergency CT scan revealed a tension pneumatocephalus with severe midline shift (Fig. 1G). The anisocoria vanished promptly after the air had been evacuated through a small frontal burr hole in the ICU. Postoperative angiography revealed complete elimination of the aneurysm (Fig. 1H–J). 1284 W. Hamel et al. Fig. 1. (A) Preoperative CT scan revealing the large prepontine clot with minimal subarachnoid blood. The temporal horn is dilated indicating enlargement of the ventricular system. (B) Preoperative CT angiography revealing the aneurysm (black arrow) in proximity to the midbasilar artery (white arrow) within the blood clot. (C) 3D reconstruction of the CT angiography revealing all three aneurysm originating from a basilar perforator artery (white arrow), the right middle cerebral artery (open arrowhead), and the anterior communicating artery (asterisk). (D–F) Preoperative angiogram depicting the location and slow filling of the basilar perforator aneurysm (indicated by arrows); (D and E) oblique projections obtained for the endovascular treatment attempted; (E) lateral projection. (G) Severe pneumocephalus with extensive midline shift and signs of transtentorial herniation in a CT scan obtained immediately after the operation. The postoperative angiogram (H) anterior-posterior; (J) lateral view- confirmed complete elimination of the aneurysm 1285 Surgical treatment of a basilar perforator aneurysm The patient remained sedated, and a moderate triple H therapy was initiated maintaining a MAP of 80–90 mmHg. Transcranial Doppler examination revealed a mean flow velocity of 200 cm=sec in both MCA, and nimodipine was added. The patient developed rhinoliquorrhea, although, open mastoid cells had been carefully waxed. On postoperative day 3 operative revision was performed. The dura was re-adapted as best as possible and sealed with tachocomb, muscle, and fibrin glue in sandwich technique. Thereafter, sedation could be reduced. The external ventricular drainage was removed 14 days after aneurysm surgery. A mild arm-accentuated hemipareses resolved completely, and at the time the patient was sent to a rehabilitation hospital he was formally oriented. Mobilization had been achieved into the wheelchair and he could stand with some support. Seven months later the patient was readmitted for clipping of both other aneurysms which was performed using a standard right pterional approach. Upon admittance the fully oriented patient complained of some fatigue and revealed some residual psychomotor slowing. There was no focal motor or sensory deficit except for mild gait ataxia which had remained. A hydrocephalus could be ruled out. The postoperative course after aneurysm clipping was uneventful and the patient was discharged in an unchanged neurological condition. Discussion To our knowledge, only one case of a basilar perforator aneurysm has been reported to date [2]. Thus, basilar artery aneurysm originating from small collateral arteries or perforating branches appear to be extremely rare. The middle basilar artery gives rise to five to nine perforators of 210 to 940 um (average 250 um in diameter) which originate directly from the basilar artery or from a common trunk together with the superolateral or inferolateral pontine artery [1, 6]. Similarly, Rhoton observed that the distal centimeter of the basilar artery is the origin of on average 8 perforating arteries usually arising from the posterior and lateral surface [8]. In our case, the aneurysm most probably originated from one of the two long pontine arteries mentioned above or from a perforator arising directly from the middle basilar artery. It is self explanatory that these arteries which supply the brain stem, mesencephalon, and thalamus must be preserved during surgery. Similar to our case, Ghogawala observed slow filling of an aneurysm originating from the distal basilar artery [2]. In general, small vessel aneurysms appear to be characterized by a rather reduced flow which may be due to narrow aneurysm necks. This may facilitate spontaneous partial or complete thrombosis which, in our case, may have been further promoted by the initial endovascular approach. Aneurysms originating from small arteries may also be found on other cerebral vessels, e.g. lenticulostriate arteries [3]. Such aneurysms may or may not be associated with arterial hypertension, and in most cases the etiology cannot be solved. The basilar perforator aneurysm as well as both other aneurysms could clearly be visualized on the CT angiography (CTA) performed at a general hospital before the patient was referred to our institution. This underscores the usefulness of this technique for early detection of aneuryms. An acute confusional state as seen in our case may be the presenting symptom in 1–2% of SAH [7]. Tension pneumatocephalus following surgery for basilar trunk aneurysms has been reported previously [4]. In that case, the patient had been operated on in the sitting position using a right lateral suboccipital craniectomy resulting in a prepontine tension pneumatocephalus with fatal outcome [4]. Tension pneumatocephalus as a complication of posterior fossa approaches has always to be considered, in particular when overdrainage of cerebrospinal fluid from a ventricular catheter may have occurred. In our case, sufficient air could be evacuated through a twist burr hole performed on the ICU after which anisocoria resolved. In the foreseeable future, surgical treatment of posterior circulation aneurysms will be rather the exception. Nevertheless, surgery remains the only other option for treatment of such aneurysms if endovascular treatment fails as illustrated here. Due to the location of the aneurysm at the middle=upper basilar artery a combined supra- and infratentorial approach was chosen giving convenient access to the aneurysm. The prepontine hematoma with dorsal displacement of the pons made this combined approach even more comfortable. However, the decision for a certain route is also influenced by the experience of the surgeon, and, as an alternative, the anterior transpetrosal approach could have been chosen. Acknowledgments We thank Dr. Festring, Director, Radiologische Abteilung, Diakoniekrankenhaus Rotenburg=W€umme, Germany, for making the CT angiography available for this report. References 1. Caruso G, Vincentelli F, Giudicelli G, Grisoli F, Xu T, Gouaze A (1990) Perforating branches of the basilar bifurcation. J Neurosurg 73: 259–265 2. Ghogawala Z, Shumacher JM, Ogilvy CS (1996) Distal basilar perforator artery aneurysm: case report. Neurosurgery 39: 393–396 3. Herb E, Kehler U (1992) Macro-aneurysm in the basal ganglia region. 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Neurosurgery 51: 121–158 Correspondence: Wolfgang Hamel, Neurochirurgische Klinik, Universit€atsklinikum Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany. e-mail: w.hamel@uke.uni-hamburg.de