An angiographic test of collateral circulation through the anterior segment of the circle of Willis.

This communication is concerned with the angiographic estimation of collateral circulation through the anterior segment of the circle of Willis. The collateral circulation, which may be present between the ophthalmic artery and the branches of the external carotid artery and the posterior segment of the circle of Willis carrying blood from the vertebral circulation, is outside the scope of this discussion. This angiographic test of the collateral circulation has been carried out sporadically in neurosurgical services all over the world. Personal experience of it extends over 13 years. The estimation of its adequacy through the anterior cerebral arterial complex is of great practical importance to neurosurgeons if it is proposed to treat certain intracranial aneurysms by ligating the internal carotid artery or the anterior cerebral artery. In recent years general physicians and neurologists have been interested in its role, as spontaneous or traumatic thrombosis of the internal carotid artery has become a well established diagnosable entity. The many and variable clinical symptoms and signs of that condition (which is sometimes symptomless) can be largely explained by the anatomical and dynamic state of the collateral circulation through the anterior segment of the circle of Willis. Other possible collateral channels may also be brought into play later. The stimulus to employ this angiographic test in a larger number of patients was provided by the observation that some elderly subjects possessed an excellent collateral circulation. Two questions were posed: (1) Can angiography substantiate or refute the belief that collateral circulation deteriorates with age so that thrombosis or ligation of the internal carotid artery becomes excessively hazardous after the age of 50 ? (2) To what extent can the collateral circulation be disturbed by other factors ? In an attempt to elucidate the answer to these questions, the test was performed on patients subjected to diagnostic angiography in the Regional Neurosurgical Centre at Liverpool from 1954 to 1957. At first digital compression was carried out on each case. Unfortunately at the beginning of 1956 the two surgeons carrying out this experiment were warned that dangerous amounts of radiation were being received on their hands. In view of this the routine performance of the test was discontinued. Thus only 712 patients had the collateral circulation tested. The view held here is that angiography is the safest method of investigation in cerebral contrast radiography. Its technique and the reasons why it is considered safe have been discussed at length in a previous communication (Sedzimir, 1955). The series is now close to 2,000 angiograms without death, with one case of transient hemiparesis, two transient supranuclear facial palsies, and one case of infection of the neck which resolved without surgical intervention.