Arteriovenous Fistula inthe Orbit of a Calf. CHRISTOPHER R. LAMB AND JONATHAN M. NAYLOR. Veterinary Teaching Hospital, Western College of Veterinary ...
CASE REPORT
Arteriovenous Fistula in the Orbit of a Calf CHRISTOPHER R. LAMB AND JONATHAN M. NAYLOR
Veterinary Teaching Hospital, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan S7N 0 WO
Abstract plexus avait provoque l'erosion de l'os An Ayrshire calf with a protruding frontal. left eye and a fluctuant swelling dorsal to the orbit was examined. A diagnosis Mots cles: fistule arterio-veineuse, of arteriovenous fistula was made veau, exophthalmie. based on the findings of pulsation, a palpable thrill and a machinery-like Introduction bruit on auscultation over the swelling. An arteriovenous (A-V) fistula is a Arteriography failed to outline the full communication between an artery and extent of the fistula. The calf was vein that bypasses the capillary network. euthanized and the fistula dissected. They have previously been reported in An enlarged superficial temporal the dog (1,2,3,4,5,6,7), cat (8,9,10) and artery communicated with a branch of horse (11). Clinical signs depend on the the maxillary vein by way of a tortuous location, size, duration and etiology of mass of vessels. The frontal bone was the fistula (12). eroded by this plexus. Arteriovenous fistulas may arise as a result of congenital anomalies (6,7,13), Key words: Arteriovenous fistula, calf, trauma (1, 14), as complications of surgiexophthalmos. cal procedures (I 5,16,17) and with medial arteriosclerosis, Ehlers-Danlos syndrome and renal carcinomas in man (16). Resume Fistule arterio-veineuse, au-dessus de Peripheral A-V fistulas are classil'orbite d'un veau cally described as painless swellings, Les auteurs ont procede a l'examen with a continuous palpable thrill and clinique d'un veau Ayrshire dont l'oeil pulsation. A machinery-like bruit can gauche faisait protrusion, tandis be detected on auscultation. When qu'une tumefaction fluctuante se pressure is applied over the artery situait au-dessus de l'orbite de cet oeil. proximal to an A-V fistula, the conIls conclurent que cette tumefaction tinuous bruit and thrill cease. Occlusion of a large fistula correspondait a une fistule arterioveineuse, parce qu'ils y percevaient des decreases the venous return to the pulsations, et des fremissements vibra- heart and this reduces cardiac output toires, tandis que son auscultation and may result in a temporary drop in permettait d'entendre un bruit sembla- heart rate (14). This has been referred ble a celui d'une machinerie. L'arterio- to as Branham's bradycardia sign. graphie ne reussit pas a delimiter completement l'etendue de cette fistule. History and Clinical Findings Les auteurs procederent a 1'euthanasie A 16 month old Ayrshire heifer was du veau et A la dissection de la tumefac- presented to the Large Animal Clinic tion orbitale. Ils constaterent que l'ar- at the Western College of Veterinary tere temporale superficielle etait dilatee Medicine (W.C.V.M.) with the comet communiquait avec une branche de plaint of protrusion of the left eye. la veine maxillaire, au moyen d'une This had been noticed six months premasse tortueuse de vaisseaux. Ce viously and was reported to be getting
progressively larger. The animal had never stopped eating, but was not growing as well as its contemporaries. There was no history of previous illness or injury. The body temperature, pulse and respiratory rates were within normal limits. The hematology was normal. The left eye exhibited exophthalmos, excessive lacrimation, and episcleral congestion (Figure 1). The eye moved in and out of orbit with the pulse. Direct and consensual pupillary reflexes were present though slow. The menace response was sluggish. The animal had no other neurological deficits. Dorsal to the orbit, the frontal bone was partially overlayed by a soft, warm, fluctuant swelling in which a pulse could be palpated. Between the lateral border of the orbit and the base of the ear another soft, easily compressible swelling was present. This exhibited a continuous palpable thrill and pulsation. Auscultation of this swelling revealed a machinery-like bruit, which could be greatly reduced by applying digital pressure rostral to the base of the ear in a position corresponding to the course of the superficial temporal artery. During this procedure, the heart rate remained constant. The left jugular vein also pulsated and filled very rapidly when manually occluded at the base of the jugular groove. A tentative diagnosis of arteriovenous fistula involving the blood supply to the orbit was made. Blood gas determinations were made on heparinized samples drawn from the right and left jugular veins.
Reprint requests to Dr. J.M. Naylor.
Can Vet J 1985; 26: 105-107.
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and external maxillary arteries and the trunk were opacified by this method. Dorsally, numerous large vessels of varying size were visible caudal to the orbit, superimposed over the cranium. These represented a net of tortuous vessels associated with the fistula. Even though three separate injections of contrast were made, the vessels feeding the fistula could not be determined. Because of the calf s stunted growth and the difficulties in surgically excising the fistula the calf was euthanized. A mixture of red latex and radiopaque dye was infused into the left common carotid artery. This was designed to facilitate dissection and further angiographic studies. A postmortem radiograph showed that the main artery feeding the A-V fistula was the superficial temporal, a branch of the maxillary artery. Perfusion of the head was incomplete, however, and the tangled net of vessels seen
liguofacial
FIGURE 1. Exophthalmos, scleral congestion and swelling dorsal and caudal to the orbit were visible in this calf.
on
FIGURE 2. Drawing of the arterial supply to the arteriovenous fistula, its locations and venous drainage. ST = superficial temporal artery, P = plexus of blood vessels feeding the fistula, AV = aneurysmal varix in caudal orbit, MV = enlarged maxillary vein. Inset shows spatial relation of inflow and outflow tracts of the fistula.
An elevated oxygen tension in the left jugular was detected (80.6 mm Hg, compared with 41.0 mm Hg in the right jugular). Radiography of the skull revealed that the left frontal sinus was expanded dorsally, and the roof was
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partially destroyed. There was overlying soft tissue swelling. Angiography was performed in the anesthetized calf. The left common carotid artery was exteriorized and dye was injected under pressure into the vessel. The carotid and internal
angiography was not opacified.
The skin was removed from the head. There was a tortuous mass of veins dorsal to the frontal bone. Three arterial branches fed this plexus, these arose from an enlarged superficial temporal artery at the level of the root of the supraorbital process. The frontal bone was eroded by this plexus. The plexus drained into a large aneurysmal varix situated in the frontal sinus and, by replacement of the floor of the frontal sinus, the medial orbit. Drainage of this chamber was via a grossly distended branch of the maxillary vein, which passed caudally and ventrally over the masseter to drain into the external jugular vein, which was also enlarged (Figure 2). In addition, a network of veins penetrated the temporal part of the frontal bone to enter the cranium and compress the olfactory tract and temporal lobes of the left side of the brain. Discussion Normal venous drainage of the orbit comprises several fine veins which pass deep to the rectus muscles and form a plexus near the apex of the orbit. This then drains into the maxillary vein (18). In the present case, the position and size of the varix and its drainage into the maxillary vein suggests that venous blood flow from the eye would be restricted. This would account for
the episcleral congestion seen in this case. Exophthalmos was the result of enlarged veins in the caudodorsal orbit. The elevated oxygen tension in the left jugular vein was helpful in making the diagnosis. Since the oxygen tension of venous blood varies, a sample taken from only one vein is of limited value. However, when blood from the other side of the body was taken for comparison, an elevated oxygen tension is indicative of an arteriovenous shunt (13,16). Angiography of an A-V fistula, to outline its exact topography and extent, is essential for the assessment of operability (12). Ideally, several radiographs should be made in rapid sequence to outline the arterial, capillary, and venous phases. Though great variability of the morphology of A-V fistulas and the flow of contrast medium may be observed, premature filling of veins and the absence of a normal capillary phase are typical
findings. In this calf angiography failed to outline the vessels feeding the fistula. This is probably related to difficulties in rapidly injecting sufficient contrast material into a large calf and to the timing of radiographs. The fistula was represented by a net of tortuous vessels. These are seen in long standing A-V fistulas, or in diffuse congenital cases, where many small collateral channels have developed. Small arteriovenous fistulas need not compromise the animal. Large fistulas allow blood to be diverted from normal capillary perfusion through the shunt. This calf had a large fistula which was supplied by an enlarged superficial temporal artery. This may have diverted blood from the carotid artery and reduced the flow to the brain. In addition the fistula had
eroded through the frontal bone into the cranium. The olfactory tract and temporal lobe of the left side of the brain were compressed. Malaise from cerebral compression and reduced perfusion of the brain may have interfered with the ability of the calf to forage and resulted in stunted growth. Surgical removal of the fistula (19) would have been difficult because the vascular network was deep in the caudal orbit and frontal sinus. The calf was euthanized because of its stunted growth and the inability to remove the fistula. Arteriovenous fistulas are rare in cattle. Diagnosis of this case was based on the presence of a pulsating, fluctuant, swelling. There was a palpable thrill and a machinery-like bruit on auscultation over the swelling.
Acknowledgments Dr. Tom Kasari helped with the initial work-up of this case. We would also like to thank Dr. Jerry Bailey for advice, and Denise Dunlap and Dr. Hilary Clayton for help with the dissection. Dr. John Pharr interpreted the radiographs. Wilfred Hein kindly donated the calf to the Western College of Veterinary Medicine.
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