Carotid Rete Mirabile in Man

Since the time of Galen, anatomists have been aware of a compact network of intertwined, freely anastomosing arteries in certain lower vertebrates (1). This network corresponds to the intracranial extradural portion of the internal carotid artery in man. It re-forms within the cavernous sinus into one or two short trunks which are the major source of blood supply to the circle of Willis. This network, termed either the “rete mirabile” or the “carotid rete,” is associated with a nonpersisting or hypoplastic internal carotid artery. In man and in those animals in which the internal carotid artery is present in adult life, no carotid rete exists. Daniel, Dawes, and Prichard's (2) studies of carotid circulation in animals revealed a well developed carotid rete in the cat, sheep, goat, ox, and pig. The internal carotid artery was either poorly developed or nonexistent in these animals. In the dog, in which the internal carotid artery is present, a rudimentary rete could be identified. The principal arteries that supply the carotid rete are the internal maxillary, the ascending pharyngeal, and the occipital. The internal maxillary artery provides the greatest contribution in most mammals. In the pig and ox, however, the ascending pharyngeal artery and the occipital artery, respectively, are the major suppliers to the rete. A recent arteriographic examination in a 43-year-old man revealed the presence of a carotid rete. As far as we are aware, such an occurrence in man has not been previously reported. Case Report A 43-year-old Caucasian male was admitted to the Veterans Administration Hospital, San Francisco, with a history of progressive lack of balance and unsteadiness of the lower extremities for six months. A transient loss of balance and unsteadiness twenty years previously had cleared spontaneously. Transient double vision and peripheral field loss were noted eleven months prior to admission. No loss of mental function had been apparent. The patient was intelligent and alert. Marked impairment of balance and a slow, wide-based gait were noted. Nystagmus was present, as were also underactivity of the right facial nerve and slight right-sided weakness. A Babinski sign on the right and hyperactive deep tendon reflexes generally, without clonus, were observed. The physical examination otherwise was unremarkable. High cervical and foramen magnum myelography, as well as pneumoencephalography, revealed no abnormality. A right common carotid arteriogram showed an unusually large external carotid artery and hypoplastic internal carotid artery (Fig. 1). A selective external carotid arteriogram demonstrated multiple small arterial channels arising from the internal maxillary artery filling the distal portion of the right carotid siphon (Fig. 2). Selective internal carotid arteriography disclosed a small internal carotid artery which formed a plexus of small arterial channels in the petrous portion (Fig. 3).