anterior medial surface of both cerebral hemispheres originate. The first two patterns are not uncommon, amounting to 25 % of 381 dissected brains (1), but the third pattern was found in only one specimen. Congenital anomalies associated with azygos arteries include alobar holoprosencephaly, agenesis and lipomas of the corpus callosum, porencephaly, and cerebral and spinal dysraphic states manifested by occipital and lumbar meningoceles. Persistent carotid-basilar anastomoses (persistent trigeminal, otic, and hypoglossal arteries) are associated with congenital aneurysms, with the aneurysm occurring on the artery itself or elsewhere on the circle of Willis (2). In the former case, the findings would be consistent with the theory that congenital cerebral aneurysms arise from incompletely involuted embryonic vessels. These areas, characterized by deficiencies in the elastica and media, may exist when a primitive vessel does not develop into a mature artery (3) but persists into adulthood. A single ACA represents persistence of a common fetal pattern into adulthood, and aneurysms of this vessel should therefore be expected. Although mention has been made of the higher incidence of pericallosal artery aneurysms with azygos arteries (3), the angiography of this condition has never been published to our knowledge. The " proximal azygos artery aneurysm" described by LeMay and Gooding (4) appears to be an anterior communicating artery aneurysm arising from a bihemispheric ACA. A true azygos artery requires fusion of both horizontal or A 1 portions of the anterior cerebral arteries to form a large single ACA (Figs. 1, Band 2). The case described here suggests an association between these primitive arteries and congenital aneurysms along their course.

Aneurysm of the Azygos Artery 1 Robert M. Quencer, M.D., and Edward V. Cox, III, M.D. A saccular aneurysm of the azygos artery is reported . The relationship between (a) this aneurysm and the primitive vessel from which it arises and (b) the aneurysms which are frequently seen involving pers istent carotid-basilar anastomoses is described. INDEX TERMS: Aneurysm. cerebral (Anter ior cerebral artery. congen ital aneurysm. 1[73] .736) • Arteries. azygos. Cerebral blood vessels. anatomy Radiology 125:724. December 1977

SINGLE midline anterior cerebral artery, also known as an azygos artery, is unusual. Congenital aneurysms along the course of this vessel are rare, and their angiography has not been reported previously. Such a case is presented below.

A

CASE REPORT A 42-year-old woman was found unconscious at home. A CT scan showed bloody cerebrospinal fluid and ventricular enlargement with intraventricular hemorrhage. On awakening several hours later, only bilateral papilledema was present. Cerebral angiograms (Figs. 1 and 2) showed filling of a single anterior cerebral artery with an irregular saccular aneurysm at its bifurcation into pericallosal and callosomarginal arteries . The submentovertex view clearly showed fusion of the two horizontal anterior cerebral arteries to form the azygos artery. No other aneurysms were present and the findings ruled out absence of the corpus callosum. Angiographic features of obstructive hydrocephalus were present, presumably due to previous subarachnoid hemorrhage. Four days after placement of a right ventriculo-peritoneal shunt, the aneurysm was clipped via a right frontal interhemispheric approach. Angiograms confirmed obliteration of the aneurysm. The patient was asymptomatic and neurologically normal one month after surgery.

Department of Radiology University of Miami/Jackson Memorial Medical Center Miami , Fla. 33136

REFERENCES 1. Baptista AG: Studies on the arteries of the brain. II. The anterior cerebral artery: some anatomic features and their clinical implications. Neurology 13:825-835, Oct 1963 2. Wolpert SM: The trigeminal artery and associated aneurysms. Neurology 16:610-614. Jun 1966 3. Pool JL. Potts DG: Aneurysms and Arteriovenous Anomalies of the Brain. Diagnosis and Treatment. New York, Harper & Row, 1965,

DISCUSSION Variations involving the vascular pattern of the anterior cerebral artery (ACA) distal to the anterior communicating artery show three basic patterns: (a) bihemispheric, with a single dominant ACA supplying a large portion of the medial surface of the opposite cerebral hemisphere; (b) an accessory ACA arising from the anterior communicating artery; and (e) an unpaired ACA or azygos artery from which all branches to the

1A

18

P 463 4. LeMay M. Gooding CA: The clinical significance of the azygos anterior cerebral artery (A.C.A.). Am J Roentgenol 98:602-610, Nov 1966

2

t t

Fig. 1. Right carotid arteriogram, lateral (A) and AP (B) views . The azygos artery (arrowheads) is formed by fusion of the horizontal portions of the right and left ACAs (straight arrows) , clearly seen on the AP view . At the genu of the corpus callosum, the azygos artery bifurcates into callosomarginal and pericallosal arteries. A saccular aneurysm .with an irregularity along its superior surface (curved arrow) is present. Stretching of the pericallosal artery is due to obstructive hydrocephalus. Fig . 2. Right carotid arteriogram (basal view). Repeat right carotid injection in the submentovertex position shows the azygos artery in three dimensions as well as fusion of the two ACAs (arrows) to form an azygos artery (arrowheads).

1 From the Departments of Radiology (R.M.a.) and Neurosurgery (E.V.C.), University of Miami/Jackson Memorial Medical Center, Miami , Fla . Revised version accepted for publication in September 1977. sjh

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