Studies of the carotid rete and its associated arteries

Abstract

This work records an investigation of the anatomy of the cranial blood supply in various species of mammal. The findings were based on a study of radiographs of specimens injected with a radioopaque mass and of casts of the vessels made by injection of neoprene latex, and on dissections of injected preparations. A well-developed carotid rete was found to be present in the cat, sheep, goat, ox and pig, and a rudimentary form of this structure was found in the dog. In the cat the rete is situated extracranially, but in the other species it lies within the cranium in the cavernous sinus. There is no carotid rete in the rabbit or the rat. The carotid rete consists of a compact network of intertwined, freely anastomosing arteries, and is related to the branches of the trigeminal nerve. When the rete is situated intracranially there is a variable degree of communication across the mid-line with the rete of the opposite side. W hether situated intracranially or extracranially the rete lies within a venous lake. The presence of a well-developed carotid rete was associated with the non-persistence of, or a degenerating internal carotid artery. A thin fibrous cord was the only rem nant of this artery found in the cat. In the goat, sheep and pig the internal carotid artery was absent proximal to the rete, but the large trunk which connected the rete with the circle of Willis was identified as representing the still persisting distal segment of this artery. In the ox (a young animal) a similar trunk connecting the rete with the circle of Willis formed the continuation of a still persisting but relatively narrow proximal segment of the internal carotid artery. The main vessels which may supply the carotid rete are the internal maxillary artery (usually via the ramus anastomoticus and the arteria anastomotica), the ascending pharyngeal artery, and the occipital artery. In the cat, sheep, goat and ox the chief vessel of supply is the internal maxillary artery, but in the pig it is the ascending pharyngeal artery. In the ox a substantial contribution is provided by the occipital artery. Both the ramus anastomoticus and the arteria anastomotica form connexions between the external and internal carotid systems and they join one another within the cavernous sinus. It is at his site that the intracranial carotid rete is developed, but the extracranial carotid rete, seen in the cat, is situated around the internal maxillary artery at the site of origin of the arteria anastomotica of the artiodactyls. The variations in the situation of the carotid rete in different species is along the line of the arteria anastomotica. It is suggested that the arteria anastomotica and the ramus anastomoticus respectively are homologous with the recurrent meningeal and the middle meningeal arteries of the rabbit and man. The arteries which supply the orbital and the ethmoidal regions are described and the homologies of the external ophthalmic artery are discussed. The great variability in the supply of these territories which was seen in the cat is thought to be associated with the presence of an extracranial carotid rete. In spite of variations in different species of animal a basic pattern can be discerned in the major arteries supplying the head. It is suggested that this basic pattern is related to a primitive stapedial artery, and that the variations seen are due to modifications of the branches of this earlier vessel. The circle of Willis was found to derive its blood supply from one or more of five sources: the internal carotid artery, the external carotid arterial system, the ascending pharyngeal artery, the vertebral artery (via the basilar artery) and the occipital artery. In the absence of an internal carotid artery the greatest contribution of blood passes to the circle of Willis through the carotid rete. An occipito-vertebral anastomosis seems to be of some importance in supplying the circle of Willis in the cat, pig, dog and rabbit. In the sheep, goat and ox the direction of the flow of blood in the basilar artery would appear to be away from and not towards the circle of Willis. In the pig the two anterior cerebral arteries anastomose in the mid-line and continue forward as a single vessel. The peculiar structure of the vessels which compose the carotid rete suggests that this compact network has a haemodynamic significance, and since the rete lies in the pathway of the major artery or arteries which supply the brain, its existence and possible influence should be borne in mind when problems of the cerebral circulation are considered in species in which this structure is present.

Cerebral blood flow and cerebrovascular reactivity after inhibition of nitric oxide synthesis in conscious goats

“…In this species, each internal maxillary artery, a branch of the external carotid artery, provides the total blood flow to each cerebral hemisphere via the rete mirabile; the vertebral arteries do not contribute to brain blood flow, and the extracranial internal carotid artery is absent (Daniel et al, 1953;Reimann et al, 1972). The circle of Willis in the goat is similar to that in man except that the blood flows in a caudal direction in the basilar artery (Daniel et al, 1953;Reimann et al, 1972).…”

“…However, obliteration of the extracerebral vessels from the internal maxillary artery does not cut off vascular supply to half of the face. The areas supplied by the ethmoidal, buccinator, dental, and temporal arteries are nourished by anastomotic channels that are normally in a state of dynamic balance but in which the direction of blood flow can be quickly changed, depending on the pressure differential from one side of the union to the other (Daniel et al, 1953;Reimann et al, 1972). There is no necrosis, and the functions related to these areas such as eating, drinking, and rumen are intact.…”

“…In this species, each internal maxillary artery, a branch of the external carotid artery, provides the total blood flow to each cerebral hemisphere via the rete mirabile; the vertebral arteries do not contribute to brain blood flow, and the extracranial internal carotid artery is absent (Daniel et al, 1953;Reimann et al, 1972). The circle of Willis in the goat is similar to that in man except that the blood flows in a caudal direction in the basilar artery (Daniel et al, 1953;Reimann et al, 1972). Analysis of the distribution of radioactively labelled microspheres in the cerebral circulation of the goat after the surgical procedure described by Reimann et al (1972) indicates that nearly all of the blood carried by the internal maxillary artery passes directly to cerebral tissue (Miletich et al, 1975).…”

Pathophysiology and pathological findings of heatstroke in dogs

“…66 Pleural bloodtinged effusion may be occasionally detected, whereas the lungs frequently appear to be heavy, due to hyperemia and edema, with large volumes of frothy hemorrhagic fluid in the trachea and bronchial tree. 12,66 Pulmonary infarction has been rarely recorded. 5 Heart examination typically reveals mild to severe endocardial, myocardial, and epicardial hemorrhages (Figure 2), which can be associated with hemopericard.…”

Local transfer of substances between the blood vessels at the base of the brain

“…Various authors have comprehensively described the structure and function of the vascular complex of cavernous sinus and carotid rete (Daniel et al, 1953;Godynicki et al, 1981;Ghoshal and Khamas, 1985;Simoens et al, 1987). Therefore, only information relevant to the understanding of the morphological and physiological factors affecting the transfer will be provided in the review.…”