"The importance of being external": review of the literature of the rare phenomenon of common carotid occlusion with bulb reverse-crossed stenosis and external collaterals activation. Is still correct speaking about carotid steal?

Abstract

Common carotid artery occlusion (CCAO) is a rare phenomenon associated with the development of neurological symptoms. In CCAO, diversion of blood flow from the external carotid artery (ECA) to the internal carotid artery (ICA) via the carotid bulb (CB) may occur. This pathway activation has been called "carotid steal". Starting from a particular case we describe the ECD finding of a complete occlusion of CCA with patency of ICA and ECA. In case of occlusion of CCA, inversion of the ECA flow may occur, towards the ICA, and it can be damped by a significant stenosis crossed in retrograde direction that may concur to maintain the pressure balance between the two circulations. Usually, this particular compensation can guarantee normal flow velocities in middle cerebral arteries without signs of activation of anterior collateral pathways. In this review we underline the protective role of ECA and we propose a new definition for this phenomenon. The ECA may provide blood to the cerebral circulation through several anastomotic secondary channels. Finally, only with an extensive knowledge of hemodynamic information of all intracranial and extracranial arteries, including ECA, we can estimate cerebral ischemic risk of the patient and choose the correct management of this occlusion.

Keywords: Carotid steal; Collateral pathway; Common carotid occlusion; External carotid artery.

Fig. 1

A Complete occlusion of common carotid artery up to the carotid bulb and presence of color signal in internal carotid artery and external carotid artery with opposite flow directions in their proximal segments; B external carotid artery with antegrade flow (red) in the distal segment and retrograde flow (blue) in the proximal segment; C acceleration of the inverted flow coming from external carotid artery (PSV 160 cm/s) at the carotid bulb level due to the presence of an intimal lesion causing stenosis; D internal carotid artery’s velocitometric profile with tardus-parvus waveform; E bidirectional flow in the external carotid artery supplied by superior thyroid artery; F 3D reconstruction of supra-aortic trunks showing complete occlusion of left common carotid artery (yellow arrow), stenosis of the left carotid bulb and presence of flow in omolateral external carotid artery and internal carotid artery (red arrow)

Fig. 2

A Widespread increase in flow velocity (PSV 114 cm/s) of basal artery. B Segmental increase of speed of the basal artery at the origin (PSV 230 cm/s at a depth of 8 cm) indicative for severe stenosis. C Left vertebral artery with an increased calibre and elevated flow velocities (PSV 145 cm/s in the V2–V3 tracts). D Signs of posterior collateral pathways activation with increased speed flow in the posterior cerebral arteries. E 3D reconstruction of vertebrobasilar circulation confirming basal artery severe stenosis (red arrow), increased calibre of the left vertebral artery

Scheme 1

External Carotid Artery circulation and collateral anastomoses with Internal Carotid artery