A6-year-old Appaloosa mare in good physical condition was referred to the University of Florida Veterinary Medical Center because of acute onset of inappetence and difficulty eating. The mare had undergone prophylactic dentistry 3 months prior to referral. The mare was reported to be 27 days in gestation and was being treated with orally administered altrenogest.a Flunixin meglumine had been administered before referral.
On arrival at the medical center, the right eye had a moderate volume of mucopurulent discharge, and the conjunctiva was hyperemic and swollen. Ophthalmologic examination revealed a fibrotic scar and a small superficial corneal ulcer in the right eye. A CBC and serum biochemical analysis revealed no important findings. Gastroscopic examination revealed no abnormal findings, and results of a reproductive tract examination were consistent with a 23- to 24-day pregnancy.
The mare was treated with flunixin meglumine (1.1 mg/kg [0.5 mg/lb], IV) and housed in a stall overnight for observation. Physical examination on the following morning again revealed no abnormalities except that a large quantity of hay was held in the mouth and the mare grew agitated when examination of the oral cavity was attempted.
Endoscopic examination of the upper portion of the respiratory tract and auditory tube diverticula (guttural pouches) revealed the right stylohyoid bone to be abnormally thick, consistent with THO (Figure 1). In the caudomedial portion of the roof of the left guttural pouch, a yellow and white plaque on the internal carotid artery was detected (Figure 2). Radiography revealed moderate right-sided otitis media, consistent with mild to moderate right-sided THO. On the basis of these findings, THO in the right guttural pouch and mycosis in the left guttural pouch were diagnosed. Medical and surgical treatment options were discussed with the owner, and the horse underwent unilateral ceratohyoidectomy (right side) and surgical occlusion of the left internal carotid artery.
Preoperative treatment included administration of single doses of potassium penicillin G (22,000 U/kg [10,000 U/lb], IV), gentamicin sulfate (6.6 mg/kg [3 mg/lb], IV), and tetanus toxoid (IM). Flunixin meglumine and altrenogesta treatment were continued, and the corneal ulcer was treated with 1 dose (0.2 mL) of topically administered atropine solution and neomycin-polymyxin-gramicidin ophthalmic solutionb (0.2 mL, q 4 h). The mare was sedated with xylazine hydrochloride (200 mg, IV), and anesthesia was induced with diazepam (12 mg, IV) and ketamine hydrochloride (1.2 g, IV) and maintained with isoflurane in oxygen. An electrolyte solution (5 mL/kg/h [2.3 mL/lb/h], IV) was administered during anesthesia. The horse was positioned in dorsal recumbency and prepared for aseptic surgery.
Ceratohyoidectomy was performed on the right side through a 10-cm incision medial to the right linguofacial vein and centered over the basihyoid bone in a method that has been described.1 The right hypoglossal nerve and lingual branches of the right mandibular and glossopharyngeal nerves were retracted with Penrose drains to protect them during dissection and removal of the ceratohyoid bone. Incisional closure was routine.
With the horse still in dorsal recumbency, a sufficient length of the left internal carotid artery (6 cm) was exposed through a 10-cm-long incision parallel and cranial to the wing of the atlas to locate aberrant branches, a finding that has been reported.2–4 No arterial branches were found; the artery was ligated close to its origin from the common carotid artery, and a small arteriotomy was made distal to the ligature. A 6-F single-end-hole nylon catheterc was introduced rostrally into the internal carotid artery through the arteriotomy and advanced approximately 13 cm. A polyethylene terephthalate fiber–covered, stainless-steel occluding spring embolization coil (5-mm diameter and 5 cm long)c was inserted in the catheter, and a 0.038-inch guidewire was used to push the coil into the artery at the sigmoid flexure. A second embolization coil of the same size was inserted in the same manner until backflow of blood through the arteriotomy ceased. The catheter was withdrawn, and the absence of backflow confirmed arterial occlusion.3,5,6 The artery was ligated distal to the arteriotomy site, and the incision was closed routinely.
The mare recovered from anesthesia without complications and was treated postoperatively with orally administered phenylbutazone (2.2 mg/kg [1.0 mg/lb], q 24 h) and altrenogesta during hospitalization. All physical examination variables remained within reference range. Clinical signs of difficult prehension and mastication were not observed, and the mare was discharged 3 days after surgery. During the 3 weeks after surgery, the owner reported that the mare continued to improve and was able to eat without difficulty.
Fifty-three days after surgery, the mare was returned to the medical center with a 3-week history of dysphagia (including discharge of food material and water from the nostrils) and weight loss. Endoscopy revealed left laryngeal hemiplegia and persistent displacement of the soft palate. The mycotic plaque in the left guttural pouch was more extensive than on the previous examination but had not invaded the structures or vasculature of the lateral compartment (Figure 3). The mare had left-sided Horner syndrome and atrophy of the right side of the tongue (Figure 4) but no tongue protrusion. Because of the worsening clinical condition and unfavorable prognosis, the mare was euthanatized, and necropsy was performed.
The most important gross abnormality was the finding of gray to yellow flocculent material adhered to the roof of the medial compartment of the left guttural pouch and overlying the left internal carotid artery. The left internal carotid artery contained a complete and mature thrombus from the level of the ligature to the cerebral arterial circle, and the 2 microcoils were found incorporated in the thrombus at the first bend of the sigmoid flexure in the internal carotid artery. There was no evidence of an aberrant branch from the internal carotid artery. The right stylohyoid bone was moderately thick close to and involving the articulation with the temporal bone, and the right side of the tongue was atrophied. The right hypoglossal nerve was intact and was surrounded by fibrous tissue at the ceratohyoidectomy site.
Histologic examination of the plaque revealed complete mucosal necrosis with overlying neutrophils; fibrin; bacteria; necrotic debris; and septate, branching fungal hyphae. Histologic examination also revealed extensive inflammation and nerve injury characterized by swollen myelin sheaths, swollen axons, and axonal and myelin degeneration that was extensive and advanced with complete necrosis in some nerve sections. No attempt had been made beforehand to identify specific nerves for histologic examination. A mature and extensive thrombus with areas of fibrous connective tissue filled the lumen of the left internal carotid artery. The right half of the tongue was severely atrophied, and the left half was moderately atrophied, characterized by different degrees of myocyte atrophy within myocyte bundles. Histologic examination confirmed incorporation of the right hypoglossal nerve in the area of fibrosis and granulation tissue at the ceratohyoidectomy site. Mild to moderate atrophy of the left laryngeal muscles was observed, and chronic diffuse and marked bone proliferation of the right stylohyoid bone was detected.
Regu-mate solution 0.22%, Intervet Inc, Millsboro, Del.
Neopolygram, Bausch & Lomb Pharmaceuticals Inc, Tampa, Fla.
Embolization coils, Cook Inc, Bloomington, Ind.
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