Cervical Arterial Collateral Network

A. Uchino

American Journal of Neuroradiology

Purkayastha et al¹ reported 3 cases of proatlantal intersegmental arteries of external carotid artery origin associated with Galen’s vein malformation; however, because of their configuration, I believe that the 3 cases do not demonstrate this rare arterial variation, but rather show collateral blood flow from the occipital artery (OA) to the vertebral artery (VA). In patients with a vein of Galen malformation, the intra-arterial blood pressure in the VA is lower than that in the OA because of blood steal phenomenon at the malformation. It is well known that there is a cervical arterial collateral network between OA, VA, and the deep cervical artery arising from the subclavian artery.² If one of these arteries is occluded, the remaining arteries and their branches are dilated and supply the distal segment of the occluded artery. The 3 cases reported by Purkayastha et al have a similar condition to proximal VA occlusion and therefore should not be considered proatlantal arteries.

References

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Purkayastha S, Gupta AK, Varma R, et al. Proatlantal intersegmental arteries of external carotid artery origin associated with Galen’s vein malformation. AJNR Am J Neuroradiol 2005;26:2378–83
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Bosniak MA. Cervical arterial pathways associated with brachiocephalic occlusive disease. AJR Am J Roentgenol 1964;91:1232–44

Reply:

The proatlantal artery of external carotid artery origin ascends lateral to the transverse processes of the first cervical vertebra in the neck up to the medial aspect of the mastoid process to join the vertebral artery as seen in the anteroposterior view. In the lateral view, it ascends obliquely posterosuperiorly and passes at the level of the foramen transversarium of the atlas. The type II proatlantal artery arising from the external carotid artery was also described as the first cervical intersegmental artery, which joins the vertebral artery before entering the foramen magnum. Proatlantal arteries also give rise to the occipital arteries. The proatlantal arteries of external carotid artery origin have a similar course to that of the occipital artery. It is doubtful whether the proatlantal artery of external carotid artery origin is merely a hypertrophied collateral occipital artery. This happens when the vertebral artery is hypoplastic. In our patients, however, in the presence of normal bilateral vertebral arteries it is the proatlantal arteries that gave rise to the occipital arteries on both sides. These occipital arteries are smaller in caliber than the proatlantal arteries. This finding also supports the view suggested by Lasjaunias et al¹ that the distal part of the occipital artery might be derived from the proatlantal artery.