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never visited HYPOPLASIA OF A1 SEGMENT OF ACA
Contributed by: antonio aguiar, Radiologist, Real Hospital Português De Pernambuco - Realimagem, Brazil.
Patient: 59 year old female
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Findings: The first part of the left anterior cerebral artery is hypoplastic. The left A2 segment fills with the aid of the anterior communicating artery (fig 1 and fig 2).
Diagnosis: Hypoplasia of left A1 segment of anterior cerebral artery.
Discussion: The circle of Willis, located at the base of the brain, is a potential collateral pathway through which adequate distribution of cerebral blood flow can be maintained in case of decreased flow through one or more of its feeding vessels. Its ability to redistribute blood flow depends on the presence and size of the component vessels. The following vessels comprise the circle of Willis: - two internal carotid artery (ICA); - two precommunicating or horizontal or A1 segments of both anterior cerebral arteries (ACA); - one anterior communicating artery (ACoA); - one basilar artery (BA); - two precommunicating or horizontal or P1 segments of both posterior cerebral arteries (PCA); - one posterior communicating artery. The distal internal carotid arteries (ICA) usually terminates by bifurcating into the anterior cerebral arteries(ACA) and middle cerebral arteries(MCA). The posterior cerebral arteries(PCA) typically arise from the basilar artery. The posterior communicating cerebral arteries(PCoA) interconnects the anterior and posterior circulation. The ICA, A1 segments of ACA and ACoA form the anterior part of the circle of Willis. The BA, P1 segments of PCA and both PCoA are termed the posterior circulation. The ACA has several major segments, each of which has important branchs. The first part of the ACA, A1 segment, extends medially from the ACA origin to its junction with the ACoA. A1 segment lies above the optic chiasm or optic nerves and is usually convex upward. Near the midline it is joined by the ACoA to its fellow on the opposite side. Beyond the ACoA, the ACA is called A2 segment, which turns fowards and upwards in the interhemispheric fissure. It passes around the anterior aspect of the corpus callosum and terminates by bifurcating into the pericallosal and callosomarginal arteries. Anatomic variations in the ACA-ACoA complex are very common. Hypoplastic A1 segment is seen in about 10% to 20% of anatomic dissections (fig 1 and fig 2). The true absent of A1 segment is found only in 1% to 2% of cases. When there is hypoplastic/absent A1 segment on one side, A2 segment on this side fills from the other side with the aid of the ACoA.
References: 1. Osborn AG. Diagnostic Neuroradiology. 1st ed. St. Louis, MO: Mosby - Year Book, Inc. 1994. 2. Osborn AG. Angiografia Cerebral - Diagnóstica. 2nd ed. Rio de Janeiro,RJ: Livraria e Editora Revinter Ltda. 2002. 3. Monique j, Krabbe-Hartkamp, Grond JVD, Leeuw FE, Gront JC, Algra A, Hillen B, Breteler MMB, Mali WPTM. Circle of Willis: Morphologic variation on three - Dimension Time-of-Flight MR angiogram. Radiology. 1998; 207: 103-111.
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Case Number: 30126126Last Updated: 08-09-2009
Anatomy: Cranium and Contents   Pathology: Normal/Variants
Modality: MRAccess Level: Readable by all users
Keywords: hypoplasia of a1 segment of acaACR: 178.1365

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