Figure 1
DWI
Azygos ACA
SectionNeuroradiology
Case TypeAnatomy and Functional Imaging
AuthorsAnirudh V Nair
Connected authors
53 years, female
Clinical History
Patient presented early morning to ER with history of acute onset of left lower limb weakness and aphasia.
Imaging Findings
Bilateral anterior cerebral artery (ACA) territory diffusion restriction with corresponding hypointense signal changes in ADC suggestive of acute infarct (Fig. 2 a, b). TOF image showing a single trunk arising after the joining of bilateral A1 (Fig. 3).
Discussion
Definition:
Bilateral A1 segment of ACA fuse to form a single trunk, instead of forming an ACOM and distal A2 segments. The prevalence of azygos anterior cerebral arteries is 0.2%–4.0% [3]
Embryology:
Azygos ACA represents persistence of median artery of corpus callosum [1]
Imaging perspective
Variations of cerebral circulation, in particular of the circle of Willis, are common. While assessing the angiographic images of the cerebral circulation, it is vital to understand the appearance of these normal variants and their clinical relevance [2]. Cerebrovascular accidents involving azygos ACA present with bilateral ACA territory involvement, which can sometimes mimic an underlying space-occupying lesion.
Azygos ACAs also often accompany other malformations, such as agenesis of the corpus callosum, hydranencephaly, saccular aneurysm and arteriovenous malformation (AVM). An azygos ACA has twice the blood flow and haemodynamic pressure of a normally paired A2 region of the ACA, which increases its susceptibility to aneurysm formation [4].
Bilateral A1 segment of ACA fuse to form a single trunk, instead of forming an ACOM and distal A2 segments. The prevalence of azygos anterior cerebral arteries is 0.2%–4.0% [3]
Embryology:
Azygos ACA represents persistence of median artery of corpus callosum [1]
Imaging perspective
Variations of cerebral circulation, in particular of the circle of Willis, are common. While assessing the angiographic images of the cerebral circulation, it is vital to understand the appearance of these normal variants and their clinical relevance [2]. Cerebrovascular accidents involving azygos ACA present with bilateral ACA territory involvement, which can sometimes mimic an underlying space-occupying lesion.
Azygos ACAs also often accompany other malformations, such as agenesis of the corpus callosum, hydranencephaly, saccular aneurysm and arteriovenous malformation (AVM). An azygos ACA has twice the blood flow and haemodynamic pressure of a normally paired A2 region of the ACA, which increases its susceptibility to aneurysm formation [4].
Differential Diagnosis List
1) Azygous ACA 2) Acute infarct involving bilateral frontal paranchymal ACA territory.
Underlying space-occupying lesion
Occlusion of one of the two A2 branches
Final Diagnosis
1) Azygous ACA 2) Acute infarct involving bilateral frontal paranchymal ACA territory.
References
[1] Osborn AG (1999) Diagnostic cerebral angiography. 2nd ed. Philadelphia. Lippincott Williams & Wilkins
[2] Simon J. Dimmick, Kenneth C. Faulder (2009) Normal Variants of the Cerebral Circulation at Multidetector CT Angiography. RadioGraphics 29, 1027-1043 (PMID: 19605654)
[3] Cinnamon J, Zito J, Chalif D, et al (1992) Aneurysm of the azygos pericallosal artery: diagnosis by MR imaging and MR angiography. AJNR Am J Neuroradiol 13: 280–282 (PMID: 1595459)
[4] Jun Suk Huh, Sang Keun Park, Jun Jae Shin, Tae Hong Kim (2007) Saccular Aneurysm of the Azygos Anterior Cerebral Artery: Three Case Reports. J Korean Neurosurg Soc 42(4): 342–345 (PMID: 2588199)
Case information
| URL: | https://www.eurorad.org/case/10971 |
| DOI: | 10.1594/EURORAD/CASE.10971 |
| ISSN: | 1563-4086 |
Figure 3
TOF
Time of flight image showing bilateral ACA joining to form a single trunk, azygos ACA (arrow).
DWI
Hyperintense signal in DWI, in bilateral ACA territory involving frontal paranchyma with corresponding hypointense signal changes in ADC.
Department of Radiology, Amrita institute of medical science, kochi, India.
Department of Radiology, Amrita institute of medical science, kochi, India.
ADC showing hypointense signal changes involving the ACA territory bilaterally.
Department of Radiology, Amrita institute of medical science, kochi, India.
Department of Radiology, Amrita institute of medical science, kochi, India.
Normal ACA
Pictogram showing normal ACA anatomy. A1 segments joining to form ACOM and distally continuing as A2 segment.
Department of Radiology, Amrita institute of medical science, kochi, India.
Department of Radiology, Amrita institute of medical science, kochi, India.
Pictogram showing azygos ACA. The two A1 segment are joining to form a single common trunk.
Department of Radiology, Amrita institute of medical science, kochi, India.
Department of Radiology, Amrita institute of medical science, kochi, India.
TOF
Time of flight image showing bilateral ACA joining to form a single trunk, azygos ACA (arrow).
Department of Radiodiagnosis, Amrita institute of medical science, Kochi, India.
Department of Radiodiagnosis, Amrita institute of medical science, Kochi, India.