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NEURORADIOLOGY Table of Contents   
Year : 2007  |  Volume : 17  |  Issue : 3  |  Page : 153-155
Case series: Saccular aneurysm of the azygos anterior cerebral artery: Report of 2 cases and review of literature


1 Department of Radiodiagnosis, Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh, India
2 Department of Neurosurgery, Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh, India

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Keywords: Azygos anterior cerebral artery, intracranial aneurysm, subarachnoid hemorrhage

How to cite this article:
Bapuraj JR, Ojili V, Khandelwal N, Kaza RK, Shanbhogue AK, Chabbra R. Case series: Saccular aneurysm of the azygos anterior cerebral artery: Report of 2 cases and review of literature. Indian J Radiol Imaging 2007;17:153-5

How to cite this URL:
Bapuraj JR, Ojili V, Khandelwal N, Kaza RK, Shanbhogue AK, Chabbra R. Case series: Saccular aneurysm of the azygos anterior cerebral artery: Report of 2 cases and review of literature. Indian J Radiol Imaging [serial online] 2007 [cited 2020 Jul 3];17:153-5. Available from: http://www.ijri.org/text.asp?2007/17/3/153/34719
The azygos anterior cerebral artery (ACA) is a rare variation in the circle of Willis, in which the distal (A 2 ) segments of both ACAs are represented by a single common vessel, from which arise all the major vessels supplying most of the medial aspects of both anterior cerebral hemispheres and the corpus callosum. [1] Aneurysms of the azygos or unpaired ACA are extremely rare and only a few cases have been reported in literature. [1],[2],[3],[4],[5] This is a report of two cases of saccular aneurysm of the azygos ACA, diagnosed by angiography, the findings of which were confirmed at the time of surgical clipping. The clinical significance of the azygos ACA is highlighted.


   Case Reports Top


Case 1

A 45-years-old woman presented to the emergency department with acute onset of severe bifrontal headache, dizziness, and neck pain. There was no history of seizures or loss of consciousness. There was no past or family history of hypertension or diabetes. Blood pressure was 120/80 mmHg and the patient was afebrile. Though the patient was lethargic, her memory functions were intact. The patient was able to move all her extremities, cranial nerve functions were normal, and there was no impairment of brain stem reflexes. Noncontrast CT scan of the brain showed anterior interhemispheric and intraventricular hemorrhage. Digital subtraction angiography (DSA) showed an azygos ACA, with a saccular aneurysm arising at its bifurcation [Figure - 1] A-C. In addition, the patient had another aneurysm from the basilar artery, between the left posterior cerebral artery and the left superior cerebellar artery. The anterior circulation aneurysm had ruptured and, hence, this was operated. The azygos state was confirmed at surgery.

Case 2

A 40-years-old hypertensive, nondiabetic woman developed severe headache and meningismus associated with transient loss of consciousness. A lumbar puncture at a private hospital revealed bloody CSF and the patient was referred to our institute for further evaluation. CT of the brain showed diffuse subarachnoid hemorrhage. DSA revealed a saccular aneurysm arising at the ramification of an azygos ACA; this was confirmed at surgery [Figure - 2]A and B.


   Discussion Top


The ACA and the anterior communicating artery complex are an important division of the circle of Willis. Variations of the ACA deserve attention because they govern the distribution of blood to the two cerebral hemispheres, and certain clinical syndromes of cerebral vascular occlusive disease will be a function of their specific anatomic arrangement. The azygos ACA is a rare variation of the circle of Willis in which the distal (A 2 ) segments of both ACAs are represented by a single common vessel, from which arise all the major vessels supplying most of both anterior cerebral hemispheres as well as the corpus callosum. [1]

A brief phylogenetic review of the ACA was presented by LeMay and Gooding in 1966, where they had stated that among the lower mammals there was no anterior communicating artery. In chimpanzees, the ACAs unite at the entrance of the longitudinal cerebral fissure and course forward to the rostrum of the corpus callosum, where the trunk then divides. This description resembles that of an azygos ACA. [2]

Lesem stated that in the human fetal and infantile brains which he had examined, he could make out the sequential changes marking the transition of the ACA from a single artery to two arteries. In 22 out of 33 human fetuses (68%) and in 18 out of 24 infant brains (75%), the two ACAs united to form a single artery within the longitudinal fissure. [6] DeVriese hypothesized that since there was a higher incidence of azygos ACA in fetuses than in adults, in early embryonic life either one or three ACAs may exist. If only one existed, a single stem would duplicate and in case three vessels were present, one would degenerate. [7]

According to Baptista's review of the literature, 23 of 2153 adult brains (1.0%) had unpaired ACAs. [1] Baptista described three types of anomalies occurring in the distal ACA:

a) a true azygos artery, from which all major branches are given off to both cerebral hemispheres; b) a bihemispheric ACA, where both right and left ACAs are present, but one is rudimentary and most of the major branches to both hemispheres arise from the other ACA; c) a triple ACA, with the accessory ACA arising from the anterior communicating artery. [1] Our cases were judged to belong to type (a).

The clinical significance of the azygos ACA is threefold: 1) Its association with other congenital anomalies such as holoprosencephaly; 2) The existence of an azygos ACA can explain the presence of bilateral ischemic changes in the setting of occlusion of the vessel and; 3) The high incidence of associated berry aneurysms. [2]

Aneurysms of the azygos ACA, either ruptured or unruptured, are extremely rare and only a few cases have been previously reported in the literature: three by Pool et al., three by Latinen et al., and one each by Baptista, LeMay et al., Katz et al., and Kondo et al. [1],[2],[3],[4],[5] Abnormal medial and intimal elements in the vessel wall of this developmental variant may account for the increased prevalence of associated saccular aneurysms.

Though these aneurysms can be noninvasively imaged either by CT angiography or MR angiography, DSA plays an important role in identifying saccular aneurysms of the azygos ACA and it is the gold standard for diagnosis. An exact preoperative diagnosis is important because extra precautions have to be taken during the surgical clipping of these aneurysms, since injury to this common arterial trunk can lead to devastating complications. [3]

 
   References Top

1.Baptista AG. Studies on the arteries of the brain. II. The anterior cerebral artery: some anatomic features and their clinical implications. Neurology 1963;13:825-35.  Back to cited text no. 1    
2.LeMay M, Gooding CA. The clinical significance of the azygos anterior cerebral artery (A.C.A.). Am J Roentgenol Radium Ther Nucl Med 1967;98:602-10.  Back to cited text no. 2    
3.Katz RW, Horoupian DS, Zingesser L. Aneurysm of azygous anterior cerebral artery. A case report. J Neurosurg 1978;48:804-8.  Back to cited text no. 3    
4.Laitinen L, Snellman A. Aneurysms of the pericallosal artery: A study of 14 cases verified angiographically and treated mainly by direct surgical attack. J Neurosurg 1960;17:447-58.  Back to cited text no. 4  [PUBMED]  
5.Kondo A, Koyama T, Ishikawa J, Iwaki K, Yamasaki T. Ruptured aneurysm of an azygos anterior cerebral artery. Neuroradiology 1979;17:227-9.  Back to cited text no. 5  [PUBMED]  
6.Lesem WW. Comparative anatomy of ACA. Postgrad Med 1905;20:455-65.  Back to cited text no. 6    
7.DeVriese B. Sur la signification morphologique des arteres cerebrales. Arch Biol 1905;21:357-457.  Back to cited text no. 7    

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Correspondence Address:
Jayapalli Rajiv Bapuraj
Department of Radiodiagnosis, PGIMER, Chandigarh - 160 012
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0971-3026.34719

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