Objective: The objective of this study was to assess the collateral circulation and blood flow velocity in arteries forming collateral circulation in patients with cerebral aneurysms and the occlusion of the brachiocephalic vessels.
Methods: Between 1989 and 2004 we examined a group of seven consecutive patients with diagnosed cerebral aneurysm and occlusion of the extracranial artery by means of cerebral angiography, transcranial color-coded sonography (TCCS) and color Doppler sonography of extracranial arteries. The Doppler examination results achieved in this group were compared with the Doppler results of 40 healthy subjects from a control group.
Results: Three patients were diagnosed with an occluded innominate artery. In four other cases an occlusion of the extracranial segment of the internal carotid artery was found. The aneurysms were located on intracranial arteries of collateral flow. The innominate artery occlusion resulted in a hemodynamic effect which was a complete vertebral steal and systolic deceleration (in one case) or alternating flow (in two cases) in the right common carotid artery. An additional route of collateral circulation in all these cases led from extracranial carotid branches through the right external carotid artery to the ipsilateral internal carotid artery. In all seven patients, 13 intracranial collateral pathways were examined. In eight of them, including four cases with cerebral aneurysms, an increase in blood flow velocity was observed. In the remaining five cases, including three cases with cerebral aneurysms, the mean blood velocity was within the normal range. The anterior communicating artery (AComA) formed the main intracranial collateral pathway which was found in seven patients, including three patients with diagnosed AComA aneurysm. Blood flow velocity in ipsilateral (on the obstructed side) and contralateral (on the unobstructed side) anterior cerebral artery, as well as pulsatility and resistance indexes in contralateral anterior cerebral and middle cerebral arteries were higher compared with healthy control subjects. In the ipsilateral middle cerebral artery a relative, insignificant decrease of pulsatility and resistance indexes was detected. Ipsilateral and contralateral middle cerebral artery blood flow velocities were lower compared with the control group.
Conclusion: Occlusion of the brachiocephalic vessels leads to formation of collateral circulation through the circle of Willis and the extracranial collaterals connecting the external and internal carotid arteries. An increase in blood flow velocity is commonly observed in intracranial arteries forming a collateral pathways. In some cases, not excluding arteries with a cerebral aneurysm, the increase in blood flow velocity is insignificant or none at all. This study shows that formation of a cerebral aneurysm is not always related to an increase in the flow velocity of collateral arteries.