Neurol Med Chir (Tokyo) 40, 472 ~ 475, 2000 Giant Aneurysm of the Azygos Anterior Cerebral Artery —Case Report— Yukihide KANEMOTO, Yoshihiro TANAKA, Masahiro NONAKA, and Yasuo HIRONAKA Department of Neurosurgery, Nara Prefectural Gojo Hospital, Gojo, Nara Abstract A 77-year-old female presented with a giant aneurysm of the azygos anterior cerebral artery (ACA) manifesting as acute onset of akinetic mutism caused by enlargement of the aneurysm resulting from rapid thrombus formation within the aneurysmal sac. Thrombus removal to obtain decompression of the aneurysmal bulk and tension was performed before parent artery occlusion to prevent throm- boembolic events. The aneurysmal neck was completely clipped with preservation of the parent artery and all branches. This strategy for direct neck clipping of a giant thrombosed distal ACA aneurysm can reduce the possibility of ischemic sequelae. Key words: giant aneurysm, azygos artery, distal anterior cerebral artery, neck clipping Introduction Giant aneurysms of the distal anterior cerebral ar- tery (ACA) are extremely rare, with only 10 cases reported.’”*5*") The clinical symptoms at onset vary, in contrast to small aneurysms of the distal ACA which usually manifest as intracranial hemor- rhage.” Giant aneurysm of the distal ACA is likely to be misdiagnosed as a space-occupying lesion be- cause of the rarity, radiological findings, and the clinical presentation.”*"? Treatment by direct neck clipping may be challenging because of the size, the broad neck, and frequent association with thrombo- sis of the aneurysmal sac. Neck clipping has been performed in only three cases,’”” but the strategy and detailed technical aspects were not described. Here, we describe direct neck clipping of a giant thrombosed distal ACA aneurysm to reduce ischemic sequelae, and discuss the clinical presen- tation. Case Report A 77-year-old female began to behave bizarrely, and became careless in matters of daily life according to her family 7 days before admission. The patient was rushed to our hospital after suffering acute onset of Received February 17,2000; Accepted June 9, 2000 472 consciousness disturbance with urinary inconti- nence. The patient exhibited akinetic mutism on admis- sion. Neurological examination 2 days after admis- sion found that the patient could obey simple com- mands and move all extremities symmetrically following infusion of glycerol, but detailed neuro- logical examination could not be performed because of the patient’s akinetic algera. Computed tomography (CT) demonstrated a well-demarcated, 5-cm diameter mixed density lesion with slight rim- like enhancement in the frontal interhemispheric fissure, and surrounded by severe edema (Fig. 1). Magnetic resonance (MR) imaging showed a large globoid lesion consisting of two parts (Fig. 2). The dorsal part was hyperintense on both T,- and T.- weighted images, which suggested hematoma con- taining free methemoglobin, whereas the ventral part was inhomogeneously hyperintense on Tj- and inhomogeneously hypointense on T,-weighted im- ages, which suggested old thrombus containing hemosiderin and flow void signal. Left carotid an- giography revealed partial filling of the giant aneurysm, which arose at the point where the azy- gos artery branched into two pericallosal arteries displaced laterally and posteriorly (Fig. 3). A bifrontal craniotomy was performed. The dura was opened bilaterally and both the sagittal sinus and falx were incised at the most anterior part. The Giant Aneurysm of the Azygos Artery 473 Fig. 1 Computed tomography scan with contrast medium demonstrating a well-demarcated, 5-cm diameters mixed density lesion with slight rim-like enhancement in the frontal interhemispheric fissure, and surrounded by severe edema. Fig. 2 Magnetic resonance images showing a large globoid lesion consisting of two parts. The lower part was hyperintense on both T,- (left) and T,-weighted (right) images, which suggested a hematoma containing free methemoglobin, whereas the upper part was inhomogeneously hyperintense on T,- and inhomogeneously hypointense on T,-weight- ed images, which suggested old thrombus containing hemosiderin and flow void sig- nal. interhemispheric fissure was exposed widely. After the azygos artery and bilateral pericallosal arteries were identified, the aneurysmal wall was exposed. Neurol Med Chir (Tokyo) 40, September, 2000 Fig. 3 Left anteroposterior (left) and lateral (right) carotid angiograms revealing partial filling of the giant aneurysm, which arose at the point where the azygos artery branched into two pericallosal arteries displaced laterally and posteriorly. Fig. 4 Postoperative left anteroposterior (left) and lateral (right) carotid angiograms showing compiete disappearance of the aneurysm with preservation of all branches. The aneurysmal sac was opened. At first, only old thrombus far from the patent region of the aneurysm was removed to obtain shrinkage of the sac without temporary occlusion of the parent artery. Tempora- ry occlusion of the parent artery was performed af- ter bleeding occurred. Thrombus near the aneurys- mal neck was then completely removed to obtain space for neck clipping. The aneurysmal neck was completely clipped with four types of clips. The aneurysmal sac was subtotally extirpated. The period of temporary occlusion of the parent artery was 10 minutes. After surgery, the preoperative mutism resolved. Neurological examination 10 days after surgery showed no abnormal findings. Postoperative CT 474 Y. Kanemoto et al. demonstrated resolution of the frontal edema on both sides. Postoperative carotid angiography showed complete disappearance of the aneurysm with preservation of all branches (Fig. 4). The patient was discharged in excellent condition. Discussion The clinical presentation of cerebral giant aneurysms is usually the manifestation of either hemorrhage or chronic mass signs, or rarely throm- boembolic ischemia." However, in the 11 reported cases of giant aneurysms of the distal ACA, includ- ing our case, clinical symptoms at onset varied, in- cluding hemorrhage in three cases,'*’) chronic mass signs in two,*®) thromboembolism from thrombi within the sac in one,” and acute deterio- ration of mass signs due to a thrombic event within the aneurysmal sac in five.?*"°"” Small aneurysms of the distal ACA usually cause intracranial hemor- rhage.” In our case, fresh clot formation continuing from the patent region of the aneurysm was con- firmed on MR imaging and during surgery. In par- ticular, MR imaging 4 days after onset indicated clot formation in the subacute stage associated with old thrombus. The characteristic clinical presentation of these aneurysms is acute onset of clinical symptoms caused by enlargement of the aneurysm resulting from rapid thrombus formation within the aneurysm, which was seen in five of the 11 cases, including our case. This onset pattern lead to mis- diagnosis of a giant aneurysm of the distal ACA as a tumor associated with hemorrhage, especially in the case of a completely thrombosed aneurysm.”*" Direct neck clipping of a giant aneurysm involves two significant problems besides actual clip appli- cation: Hemodynamic ischemia during temporary occlusion of the parent artery, because direct neck clipping is usually impossible without decompres- sion of the aneurysmal bulk and tension; and thromboembolic ischemia, because all giant aneurysms of the distal ACA were partially or com- pletely thrombosed. Hemodynamic ischemia can be reduced by shortening the period of temporary oc- clusion of the parent artery, using various brain protective drugs, induced hypertension, and inher- ent collateral circulation. In particular, the period of temporary occlusion of the parent artery should be reduced. Our procedure for direct neck clipping of the thrombosed giant aneurysm was intended to prevent both hemodynamic and thromboembolic ischemia. The temporary clip was applied after the bleeding occurred to shorten the temporary occlusion time. Moreover, temporary clipping of the parent artery prevented thromboembolic ischemia caused by thrombi within the sac, and allowed assessment of the degree of collateral circulation by retrograde flow via the distal arteries: Tentative clipping of the aneurysmal sac before complete removal of the thrombus near the neck should be avoided to pre- vent thromboembolic ischemia, even if the parent artery is temporarily occluded. The tolerance time for temporary occlusion of the distal ACA is obscure, particularly for the azygos artery. The tolerance time for the ACA might be similar to that of the middle cerebral artery (MCA), because flow rates in the distal ACA (120 ml/min) are comparable to those of the MCA. No new neu- rological deficits appeared after 45 minutes of oc- clusion in one patient” or with permanent occlu- sion of the feeding vessel for giant aneurysms of the distal ACA in three patients (not including cases involving the azygos artery).*") Ten new infarcts, involving perforator territories in seven cases, oc- curred among 30 cases of direct neck clipping of giant aneurysms of the anterior circulation using temporary clipping of the parent artery.) However, there was no correlation between infarct and the duration of temporary clipping. We consider that hemodynamic ischemia may be avoided, despite the azygos artery, and may be less important than thromboembolic ischemia if the temporary occlu- sion time is limited to a reasonable period. References 1) Drake CG: Giant intracranial aneurysms: Experience with surgical treatment in 174 patients. Clin Neu- rosurg 26: 12-95, 1979 2) Farias JP, Trindade AM: Giant distal anterior cerebral artery aneurysm not visualized on an- giography: case report. Surg Neurol 48: 348-351, 1997 3) Gewirtz RJ, Awad IA: Giant aneurysms of the an- terior circle of Willis: Management outcome of open microsurgical treatment. Surg Neurol 45: 409-421, 1996 4) Hayashi M, Kobayashi H, Kawano H, Handa Y, Kabuto M: Giant aneurysm of an azygos anterior cerebral artery: Report of two cases and review of the literature. Neurosurgery 17: 341-344, 1985 5) Maiuri F, Corriero G, D’Amico L, Simonetti L: Giant aneurysm of the pericallosal artery. Neurosurgery 26: 703-706, 1990 6) Nornes H, Wikeby P: Cerebral arterial blood flow and aneurysm surgery. Part 1: Local arterial flow dy- namics. J Neurosurg 47: 810-818, 1977 7) Ohno K, Monma S&S, Suzuki R, Masaoka H, Matsushima Y, Hirakawa K: Saccular aneurysms of the distal anterior cerebral artery. Neurosurgery 27: 907-913, 1990 Neurol Med Chir (Tokyo) 40, September, 2000 8) 9) 10) 11) Giant Aneurysm of the Azygos Artery O’Neill M, Hope T, Thomson G: Giant intracranial aneurysms: diagnosis with special reference to com- puterized tomography. Clin Radiol 31: 27-39, 1980 Pia HW, Zierski J: Giant cerebral aneurysms: Problem in treatment, in Pia HW, Langmaid C, Zierski J (eds): Cerebral Aneurysms. Advances in Di- agnosis and Therapy. Berlin, Heidelberg, New York, Springer-Verlag, 1979, pp 336-342 Pozzati E, Nuzzo G, Gaist G: Giant aneurysm of the pericallosal artery. Case report. J Neurosurg 57: 566- 569, 1982 Preul M, Tampieri D, Leblanc R: Giant aneurysm of the distal anterior cerebral artery: Associated with an Neurol Med Chir (Tokyo) 40, September, 2000 12) 4715 anterior communicating artery aneurysm and a dural arteriovenous fistula. Surg Neurol 38: 347-352, 1992 Smith RR, Parent AD: End-to-end anastomosis of the anterior cerebral artery after excision of a giant aneurysm. Case report. J Neurosurg 56: 577-580, 1982 Address reprint requests to: Y. Kanemoto, M.D., Depart- ment of Neurosurgery, Nara Prefectural Gojo Hospital, 197 Nohara-cho, Gojo, Nara 637-0034, Japan.