Maxillary fibrous dysplasia in a yearling filly. John R. Field, F. Donald Horney. The paranasal sinuses of the equine skull are inter- connected and share a ...
Maxillary fibrous dysplasia in
John R. Field, F. Donald Horney The paranasal sinuses of the equine skull are interconnected and share a common nasomaxillary opening into the middle nasal conchae (1). Only two of these sinuses lend themselves to endoscopic examination and surgical intervention, these being the maxillary and frontal sinuses. Exploration of these sinuses may be required for diagnosis and/or treatment of neoplasia, inflammation, or trauma (2,3). Surgical techniques currently available include the Kral tap (4), trephination (5), and the rectangular bone flap (6). Recently, a new technique involving bone flap triangulation has been used (3). We describe herein the use of such a technique in the exploration of the frontal and maxillary sinuses of a yearling filly initially suspected of having a congenital mucoid cyst in either the maxillary or the frontal sinus or both.
CAUDAL ROSTRAL MAXILLARY SINUS
A unilateral swelling over the left maxillary sinus was present together with a mucopurulent discharge from the left nostril A one-year-old Thoroughbred filly was referred to the Ontario Veterinary College with a two-month history of unilateral facial swelling involving the left maxilla. Initially, a mucoid discharge was in evidence from the left nostril; this discharge later became mucopurulent with progression of the lesion. Oral trimethoprim - sulfadiazine had been used unsuccessfully. The respiration of the filly had become progressively more stridulous. Physical examination at the time of admission revealed fair body condition although the hair coat was poor. A unilateral swelling over the left maxillary sinus was present together with a mucopurulent discharge from the left nostril. Breathing was stridulous with no passage of air through the left nostril. Temperature and pulse were within normal limits. However, the respiratory rate was elevated at 80/min. Leukograms performed on two separate occasions over the period of hospitalization were within normal limits. Results of a fecal flotation for detection of parasitic ova were
negative. Lateral and oblique radiographs of the skull did not clearly elucidate any significant lesion in either the left maxillary or frontal sinus. Complete endoscopic examination using a fiberoptic endoscope was prevented by an apparent septal deviation into the ventral nasal meatus 10-15 cm caudal to the nasal opening.
Figure 1. Location of the caudal and rostral maxillary sinus compartments. Also depicted are the Kral tap sites (*). b. Frontal sinus location and orientating landmarks. Hatchmarked area represents the region encompassed by the triangulated bone flap.
With the filly sedated with xylazine, (Rompun, Chem Agro Ltd., Etobicoke, Ontario) at 1.0 mg/kg body weight in combination with butorphanol Can Vet J 1991; 32: 40-41 (Torbugesic, Ayerst Laboratories, Montreal, Quebec) Department of Clinical Studies, Ontario Veterinary College, at 0.02 mg/kg BW, and with the left maxillary sinus region aseptically prepared, a Kral tap was performed University of Guelph, Guelph, Ontario NIG 2W1. at three locations into both the rostral and caudal compartments of the maxillary sinus (Figure la). A watery, Reprints not available.
Can Vet J Volume 32, January 1991
Figure 2. Sagittal section of skull to show expansive maxillary mass and obstruction to nasal meatuses. Arrows indicate extension of mass into ventral nasal conchae.
honey-like fluid discharged from the sinus under pressure. A swab of this fluid was submitted for bacterial culture, but did not yield growth of either aerobic or anaerobic organisms. A 10 cm segment of sialastic tubing was implanted and secured in place through each of the three holes. This enabled recurrent flushing of the sinus with warm lactated Ringer's solution. It was hoped this procedure would reestablish the nasomaxillary opening thereby allowing drainage of the sinus. Such was not the case and a more aggressive approach was adopted. With the filly anesthetized in right lateral recumbency and the left frontomaxillary aspect prepared aseptically, the triangulated bone-flap technique (2) was performed (Figure lb). This approach gave good exposure of the frontal sinus and the frontomaxillary opening through which a multi-loculated, fluidfilled mass could be seen. Curettage of the mass was performed with segments placed in 1007 formol saline and submitted for histopathological examination. The nasomaxillary opening was cannulated, with the tubing left in situ to allow drainage through this opening. The bone edges were reunited by adjoining the periosteum using 2-0 polyglactin in a continuous pattern. The skin flap thus created was closed using 0 polypropylene in a simple interrupted pattern. Pre- and postoperative medication consisted of phenylbutazone and penicillin. Daily flushing with lactated Ringer's solution failed to resolve the condition to any extent, although drainage was evident through the left nostril implying a patent nasomaxillary opening. The filly was euthanized two weeks post-operatively because of continued respiratory distress, halitosis, and loss of condition. At necropsy, the left maxilla was seen to be enlarged by a 10 cm, expansive mass growing within the bone and causing its distortion (Figure 2). This filled the caudal and rostral maxillary sinuses. A small dorsal portion of the mass had been removed surgically. On cut section, the mass was mottled tan and red and varied in consistency from hard, where bone was included, to soft and fluctuant. Multiple cystic areas with mucoid contents were present. The mass was demineralized and examined histologically. From the tissues submitted for histopathology at the time of surgery, a diagnosis of hemorrhagic nasal polyp with marked sub-acute, erosive sinusitis was Can Vet J Volume 32, January 1991
made. Cyst-like structures were composed of loosely organized edematous strands of fibrin encircled by a hemorrhagic periphery and infiltrated by aggregates of neutrophils and bacteria. Within sections of turbinate, epithelial erosion with edematous stroma infiltrated by large numbers of neutrophils were observed. Dysplasia was not a feature nor were mitotic figures present. Histological examination of the demineralized maxillary mass revealed loosely woven, fibrous connective tissue containing large numbers of osteoid trabeculae rimmed by benign osteoblasts. Cystic areas contained amorphous necrotic material and were lined by well developed granulation tissue with an intense neutrophilic infiltrate. The lesion was diagnosed as maxillary fibrous dysplasia based on the typical histological findings of the expansive mass growing within the maxillary bone. Mucoid degeneration of the nasal conchae is a term which describes a variety of cyst-like lesions involving the nasal and paranasal sinuses of horses (7). Fibrous dysplasia in the horse is thought to develop due to secondary nutritional hyperparathyroidism (7). The consistent morphological manifestation of hyperparathyroidism is a generalized osteopenia due to excessive bone resorption and subsequent replacement with fibrous tissue (7,8). This case highlights the need for accurate radiographic, cytopathological, and bacteriological interpretation as an aid to diagnosis. These features, considered in combination, should narrow down the list of differential diagnoses when a young horse with unilateral facial swelling and associated dyspnea is presented for diagnosis. A frontal sinus approach (3) was chosen in this case to allow creation of drainage through the nasomaxillary opening, which is readily accessible through the exposed frontomaxillary aperture. The triangulated bone flap technique gave excellent visualization of all structures, including the dorsal margins of the maxillary mass, allowing partial resection of the mass. In contrast, a rectangular bone flap (6) created over the maxillary sinus only, while allowing good visualization of both rostral and caudal compartments, would not provide adequate exposure of the frontal sinus. cvi
References 1. Pascoe JR. Specific aspects of equine dental surgery. In: Surgery and diseases of the oral cavity and respiratory tract. Proc Aust Equine Vet Assoc, 1981: 20-26. 2. Baker GH. Sinusitis. In: Surgery and diseases of the oral cavity and respiratory tract. Proc Aust Equine Vet Assoc, 1981: 18-19. 3. Blackford JT, Goble DO, Henry RW, Geiser DR. Triangulated flap technique for nasofrontal surgery. Results in five horses. Vet Surg 1985; 14: 287-294. 4. Kral F. Equine sinusitis - a new therapeutic approach to equine sinusitis. J Am Vet Med Assoc 1954; 124: 373-375. 5. Wheat D. Sinus drainage and tooth repulsion in the horse. Proc Am Assoc Equine Pract 1973; 19: 171-176. 6. Milne DW, and Turner AS. An atlas of surgical approaches to the bones of the horse. Philadelphia: WB Saunders, 1979: 174-180. 7. Rubarth 5, Krook L. Etiology and pathogenesis of so-called mucoid degeneration of the nasal conchae in the horse. Acta Vet Scand 1964; 9: 253-267. 8. Jubb KVF, Kennedy PC, Palmer N, eds. Pathology of Domestic Animals. 3rd ed. Vol. 2. Toronto: Academic Press, 1985: 431.