Clinical importance of the supra-isthmic anastomosis between the superior thyroid arteries in six cases of occlusion of the common carotid artery.

In six cases of occlusion of a single common carotid artery, antegrade blood flow was demonstrable in the ipsilateral internal carotid artery by doppler ultrasonography. Antegrade blood flow was also observed in the intracranial portion of the internal carotid artery, comparatively reduced and irregular with respect to that of the corresponding contralateral artery. Studies by color doppler ultrasound and digital subtraction angiography revealed the presence of a collateral arch that passed through the supra-isthmic anastomosis between the superior thyroid arteries. All six subjects examined had presented with neurological deficits that subsequently almost completely regressed. The regression of symptomatology indicates the clinical importance of the collateral circle.