A 13-year-old 130-kg (286-lb) female Miniature Horse with a 3-week history of progressive unilateral exophthalmia was evaluated at the veterinary medical teaching hospital of The Ohio State University. The horse had been treated by the referring veterinarian with an ophthalmic corticosteroid preparation applied topically every 8 hours, but there had been no improvement in the condition. The horse was considered to be current on vaccinations, and the medical history was otherwise unremarkable.
Results of an initial physical examination at our facility were unremarkable, except for exophthalmus of the left eye. To facilitate ocular examination, xylazine hydrochloride (0.30 mg/kg [0.14 mg/lb], IV) was administered. Examination of the left eye identified exophthalmia with rostral and lateral displacement of the globe, mild conjunctival hyperemia, and blepharedema. There was complete resistance to retropulsion, and evaluation of globe size and ocular motility revealed no abnormalities. A positive result for the menace response and normal direct and consensual pupillary light reflexes were detected. Corneal and intraocular examinations were performed with biomicroscopy and indirect ophthalmoscopy and yielded no abnormal findings. Evaluation of the right eye revealed no abnormalities.
The primary differential diagnosis was orbital neoplasia. Other considerations included nonneoplastic orbital lesions and extension of an extraorbital disease. Nonneoplastic orbital lesions described in horses include orbital cellulitis,1 retrobulbar abscess,2,3 orbital fracture,4,5 retrobulbar hematoma,6 retrobulbar dermoid cyst,7 and hydatid cyst.8 Described extraorbital disorders causing exophthalmus in horses include bacterial or fungal sinusitis,9–11 ethmoid hematoma,12 meningitis,13 neoplasia of the paranasal sinuses (adenocarcinoma14,15 or osteoma16), sinonasal cyst,17 and myonecrosis of the muscles of mastication.18
Initial diagnostic evaluation included hematologic and serum biochemical analyses, thoracic radiography for evaluation of evidence of metastatic disease, and CT imaging of the head. Results of a CBC were unremarkable, except for hyperfibrinogenemia (459 mg/dL; reference range, 193 to 422 mg/dL). Serum biochemical analysis revealed increases in activity of alkaline phosphatase (276 U/L; reference range, 80 to 187 U/L), J-glutamyltransferase (41 U/L; reference range, 7 to 20 U/L), sorbitol dehydrogenase (15.1 U/L; reference range, 4 to 13 U/L), creatine kinase (464 U/L; reference range, 150 to 360 U/L), and hypertriglyceridemia (71 mg/dL; reference range, 10 to 60 mg/dL). Results of thoracic radiography were unremarkable, and there was no evidence of pulmonary metastasis.
The horse was anesthetized for CT imaging of the head. Preanesthetic medications administered included potassium penicillin (22,000 U/kg [10,000 U/lb], IV), gentamicin (7 mg/kg [3.2 mg/lb], IV), and flunixin meglumine (0.6 mg/kg [0.27 mg/lb], IV). Tetanus toxoida was administered IM. Anesthesia was induced by IV administration of xylazine (0.75 mg/kg [0.34 mg/lb]), diazepam (0.10 mg/kg [0.045 mg/lb]), and ketamine hydrochloride (1.9 mg/kg [0.86 mg/lb]). The horse was intubated, and anesthesia was maintained with inhaled isoflurane.b The horse was positioned in dorsal recumbency, and CT imaging of the head was performed by use of a single-slice helical scanner.c Slice thickness was 5 mm, and the image plane was perpendicular to the hard palate.
Computed tomography revealed a large, clearly demarcated mass within the left caudal maxillary and left conchofrontal sinuses. Lysis of the sphenoid and palatine bones of the medial left orbit and left infraorbital canal was apparent. Extension into the left retrobulbar space was identified, with rostral and lateral displacement of the left globe (Figure 1). Contact with the cribriform plate was also evident.
Computed tomographic image of the head of a 13year-old Miniature Horse with unilateral exophthalmia of the left globe of 3 weeks' duration. A large mass is evident within the left conchofrontal sinus (asterisk). Bony lysis and proliferation of the sphenoid and palatine bones of the medial left orbit are apparent (arrowhead). Retrobulbar extension of the mass is evident with exophthalmus of the left globe.
Citation: Journal of the American Veterinary Medical Association 233, 2; 10.2460/javma.233.2.285
Rhinoscopy and sinus trephination were conducted to establish an etiologic diagnosis and formulate a treatment plan. Anesthesia was maintained, and the horse was positioned in right lateral recumbency. Rhinoscopy was performed with a flexible endoscope.d Hyperemia of the nasal turbinates with mild distortion of the nasal cavity was visible, but no other abnormalities could be identified. Trephination of the left caudal maxillary sinus was performed by use of a Steinmann pin and Jacobs chuck, as described elsewhere.19 Copious amounts of turbid, yellow fluid immediately flowed from the trephination site, and a sample was aspirated. Anesthesia was discontinued, and the horse recovered without incident. Treatment was initiated with sulfamethoxazole-trimethoprim (15 mg/kg [6.8 mg/lb], PO, q 12 h) and flunixin meglumine (0.6 mg/kg, IV, q 12 h).
Analysis of fluid obtained from the mass revealed a specific gravity of 1.035, total protein concentration of 10.5 g/dL, and WBC count of 1,320 cells/μL. Cytologic examination revealed a proteinaceous background with nondegenerate neutrophils and vacuolated macrophages, some of which contained RBCs and hemosiderin. Findings were compatible with a diagnosis of sinonasal cyst. Less likely differential diagnoses were a necrotic, fluid-containing neoplastic lesion or the possibility that fluid samples had been obtained from the obstructed sinus.
Surgical excision of the mass was recommended and was performed 4 days after the initial examination at our facility. Anesthesia was as previously described, and the anesthetized horse was positioned in right lateral recumbency. An oscillating saw was used to create a large frontonasal osteoplastic flap in the left frontal bone, as described in another report.20 A thick lining, consistent with a sinonasal cyst, was identified within the maxillary and conchofrontal sinuses. The lining of the cyst was removed by digital manipulation combined with use of a rongeur and curettage. Excision was incomplete because of the extensive nature of the lesion, involvement of the cribiform plate, and moderate intraoperative hemorrhage. The sinus cavity was packed with gauze and the osteoplastic flap was pressed back into place. Skin margins were apposed with 2-0 polydioxanone.e Because of intraoperative blood loss, 1 L of plasma was administered IV during the procedure. The horse recovered from anesthesia without complication; however, mild hemorrhage persisted after surgery. Postoperative hemorrhage was controlled by the application of ice, administration of epsilonaminocaproic acidf (30 mg/kg [13.6 mg/lb], IV), and insertion of a suture to close the left naris. Two days after surgery, the suture was removed from the naris and the gauze packing was extracted from the sinus cavity without incident.
Histologic examination of the excised tissue revealed a ciliated, pseudostratified columnar epithelium with mucus-producing goblet cells. A thick fibrous capsule was evident, and spicules of trabecular bone were detected (Figure 2). Extensive hemorrhage and edema were evident within the subepithelial tissues, with evidence of a mild inflammatory response. Aerobic and anaerobic culture of the fluid sample obtained from the sinus yielded no growth after 7 days. These findings confirmed the diagnosis of a sinonasal cyst.
Photomicrograph of a section of a sinonasal cyst obtained from the horse in Figure 1. The cyst wall has pseudostratified columnar epithelium and a thick fibrous capsule. Spicules of trabecular bone and extensive hemorrhage are evident within the subepithelial tissue (arrowhead). Mucinous and hemorrhagic content of the cyst are evident within the epithelial lining (arrow). H&E stain; bar = 300 Pm.
Citation: Journal of the American Veterinary Medical Association 233, 2; 10.2460/javma.233.2.285
Forty-eight hours after surgery, there was a reduction in the degree of exophthalmia and slight improvement in retropulsion of the left globe. Conjunctival hyperemia of the left eye was persistent but diminished. Complete physical and ophthalmic examination findings were otherwise unremarkable. The horse was discharged from the hospital 3 days after surgery. Medications prescribed at the time of discharge included phenylbutasone (2 mg/kg [0.9 mg/lb], PO, q 24 h for 2 days) and sulfamethoxazole-trimethoprim (15 mg/kg, PO, q 12 h for 10 days).
Four months after surgery, evaluation by the referring veterinarian revealed complete resolution of the exophthalmus and blepharedema, and the left eye appeared normal. There was no evidence of recurrence of the sinonasal cyst, and no postsurgical complications were identified.
Discussion
Sinonasal cysts have been described with some frequency in horses, accounting for approximately 13% of all paranasal sinus disease in horses.21 However only 1 report17 describing exophthalmus associated with sinonasal cyst disease was identified by the authors. In that report, exophthalmus was evident in addition to more typical signs of sinonasal cyst disease, such as distortion of the facial bone. Other commonly reported findings include unilateral nasal discharge, obstruction of nasal airflow, obstructive respiratory noise, epiphora, and submandibular lymphadenopathy.17,21,22 In the horse described here, exophthalmia was the only clinical finding identified.
Similarities between sinonasal cysts in horses and sinus mucoceles in humans have been described. Both are expansile, mucus-filled cavities within the paranasal sinuses and are capable of bone destruction.23 Histologically, both possess a mucus-secreting epithelial lining, which is typically accompanied by a mild inflammatory response.23 Orbital extension of sinus mucoceles in humans has been verified. Exophthalmus is most commonly reported in these patients, although enophthalmus related to bone destruction has also been described.24,25 The apparent lower incidence of orbital extension in sinonasal cysts in horses may reflect a paucity of reports in the literature. It is also possible that differences in comparative anatomy, specifically the physical proximity of the sinus ostia to the orbit, may make sinonasal cysts in horses less prone to orbital extension.
The cause of these conditions has not been elucidated. However, the development of sinus mucoceles in humans has been associated with obstruction of the sinus ostium, which can be congenital or may be caused by persistent inflammation, trauma, scarring, repeated infection, or previous surgery.26–28 A higher incidence of exophthalmia has been described in primary sinus mucoceles in humans, relative to mucoceles secondary to trauma or maxillofacial surgery.24 Whether the specific cause of sinonasal cysts in horses similarly influences their potential for orbital extension remains to be determined, but certainly the horse reported here had no known history of trauma or previous surgical intervention.
Computed tomography was chosen for imaging the head of the horse reported here. In a study29 of orbital disease in dogs, investigators found diagnostic value to be similar for CT and ultrasonography; however, CT more frequently revealed extraorbital involvement. Magnetic resonance imaging is an alternative imaging modality, and the superior soft tissue detail of MRI may be more sensitive for distinguishing a sinonasal cyst from neoplasia.30 However, MRI has limited value in assessing bone erosion and sinus configuration.30
The location of the sinonasal cyst in this Miniature Horse was typical (ie, within the conchofrontal and caudal maxillary sinuses). Extension into the orbit reflected the potential of sinonasal cysts for bone destruction. This has been correlated with direct pressure of the cyst wall on bone.31 Increased concentrations of prostaglandin E2, interleukins, and tumor necrosis factor within the mucosa of sinus mucoceles in humans may also contribute to the invasive nature of these conditions.32,33
Results of rhinoscopy are typically not specific for sinonasal cyst disease, which was true for the horse reported here. Abnormal respiratory tract secretions and nasal cavity distortion are commonly reported and support imaging findings of sinus disease.17,34 Direct endoscopic examination of the paranasal sinuses may be of greater diagnostic value.19 For the horse reported here, evaluation of a biopsy specimen of the mass yielded similar results without the benefit of gross examination. Fluid obtained from the cyst in this horse had negative results for bacterial culture and had cytologic evidence of chronic inflammation and erythrophagocytosis, which are findings consistent with previous reports.23,35 Bacterial colonization of sinonasal cysts has been described,23 but this appears to be atypical.
Sinonasal cysts typically require surgical excision because of their tendency for bone destruction and continued expansion. Although complete extirpation is advocated, this is rarely achieved because of the sensitivity of associated anatomic structures (such as the cribriform plate) and the potential for hemorrhage. In the horse reported here, excision of the sinonasal cyst was performed through a large frontonasal osteoplastic flap, as described elsewhere.20 This technique provided access to the conchofrontal and maxillary sinuses and enabled maximal debridement of the extensive lesion. Endoscopic surgery is an alternative and has been advocated for treatment of humans that have sinus mucoceles with orbital involvement.25 Endoscopic debridement and lavage performed in 3 standing, sedated horses with sinonasal cysts indicated that this is a technique best reserved for selected horses with small cysts.36
In the horse reported here, surgical excision was curative, with complete resolution of the exophthalmus without complication or recurrence by 4 months after surgery. This outcome was consistent with that in other reports17,21,22 of horses with sinonasal cyst disease. Cyst recurrence appears to be a rare event; however, a persistent mucoid nasal discharge has been described in a small percentage of patients.17,21,22 Transient postoperative nasal discharge is a more commonly reported sequela but is of minimal importance.
The information reported here should make equine practitioners aware of sinonasal cysts as a cause of retrobulbar disease in horses. Additionally, exophthalmia may be the only clinical finding in horses with sinonasal cyst disease. Diagnosis is aided by use of CT, and the prognosis for resolution after subtotal surgical excision via a frontonasal osteoplastic flap is good.
ABBREVIATIONS
| CT | Computed tomography |
| MRI | Magnetic resonance imaging |
Tetanus toxoid, Fort Dodge, Wyeth, Overland Park, Kan.
Isoflurane, Abbott Animal Heath, Chicago, Ill.
Picker PQS, Philips, Bothwell, Wash.
Endoscope, Olympus, Center Valley, Pa.
Polydioxanone, Ethicon Inc, Piscataway, NJ.
Epsilon-aminocaproic acid, Abbott Laboratories, Abbott Park, Ill.
References
- 1.↑
Wilkie DA. Equine ophthalmology. In: Reed SM, Bayly WM, Sellon DC, eds. Equine internal medicine. 2nd ed. London: WB Saunders Co, 2004;995–1024.
- 2.
Homco LD, Ramirez O. Ultrasonographic diagnosis retrobulbar abscesses. Vet Radiol Ultrasound 1995;36:240–242.
- 3.
Hubert J, Williams J, Hamilton HL, et al. What is your diagnosis? Chronic retrobulbar abscess in a horse. J Am Vet Med Assoc 1996;209:1703–1704.
- 4.
Caron JP, Barber SM, Bailey JV, et al. Periorbital skull fractures in five horses. J Am Vet Med Assoc 1986;188:280–284.
- 5.
Blogg JR, Stanley RG, Phillip CJ. Skull and orbital blow-out fractures in a horse. Equine Vet J Suppl 1990;10:5–7.
- 6.↑
Boroffka SA, van de. Belt AJ. CT/ultrasound diagnosis—retrobulbar hematoma in a horse. Vet Radiol Ultrasound 1996;37:441–444.
- 7.↑
Muñoz E, Leiva M, Naranjo C, et al. Retrobulbar dermoid cyst in a horse: a case report. Vet Ophthalmol 2007;10:394–397.
- 8.↑
Barnett KC, Cottrell BD, Rest JR. Retrobulbar hydatid cyst in the horse. Equine Vet J 1988;20:136–138.
- 9.
Freeman DE. Paranasal sinuses. In: Beech J, ed. Equine respiratory disorders. Philadelphia: Lea & Febinger, 1991;275–303.
- 10.
Scott EA, Duncan JR, McCormack JE. Cryptococcosis involving the postorbital area and frontal sinus in a horse. J Am Vet Med Assoc 1974;165:626–627.
- 11.
Johnson GR, Schiefer B, Pantekoek JF. Maduromycosis in a horse in western Canada. Can Vet J 1975;16:341–344.
- 12.↑
Barnett KC. Globe and orbit. In: Barnett KC, Crispin SM, Lavach JD, et al, eds. Equine ophthalmology: an atlas and text. St Louis: Mosby Co, 2004;51–58.
- 13.↑
Gough MR, Mayhew IG, Munroe GA, et al. Purulent basilar empyema and meningitis associated with exophthalmos in a pony. Equine Vet Educ 1998;10:58–62.
- 14.
Davis JL, Gilger BC, Spaulding K, et al. Nasal adenocarcinoma with diffuse metastases involving the orbit, cerebrum, and multiple cranial nerves in a horse. J Am Vet Med Assoc 2002;221:1460–1463.
- 15.
Hill FW, Moulton JE, Schiff PH. Exophthalmos in a horse resulting from an adenocarcinoma of the frontal sinus. J S Afr Vet Assoc 1989;60:104–105.
- 16.↑
Scotty NC, Ford M, Williams F, et al. Exophthalmia associated with paranasal sinus osteoma in a Quarterhorse mare. J Vet Diagn Invest 2004;16:155–160.
- 17.↑
Woodford NS, Lane JG. Long-term retrospective study of 52 horses with sinunasal cysts. Equine Vet J 2006;38:198–202.
- 18.↑
Step DL, Divers TJ, Cooper B, et al. Severe masseter myonecrosis in a horse. J Am Vet Med Assoc 1991;198:117–119.
- 19.↑
Ruggles AJ, Ross MW, Freeman DE. Endoscopic examination of normal paranasal sinuses in horses. Vet Surg 1991;20:418–423.
- 20.↑
Freeman DE, Orsini PG, Ross MW, et al. A large frontonasal bone flap for sinus surgery in the horse. Vet Surg 1990;19:122–130.
- 21.↑
Tremaine WH, Dixon PM. A long-term study of 277 cases of equine sinonasal disease. Part 1: details of horses, historical, clinical and ancillary diagnostic findings. Equine Vet J 2001;33:274–282.
- 22.
Lane JG, Longstaffe JA, Gibbs C. Equine paranasal sinus cysts: a report of 15 cases. Equine Vet J 1987;19:537–544.
- 23.↑
Tremaine WH, Clarke CJ, Dixon PM. Histopathological findings in equine sinonasal disorders. Equine Vet J 1999;31:296–303.
- 24.↑
Fu CH, Chang KP, Lee TJ. The difference in anatomical and invasive characteristics between primary and secondary paranasal sinus mucoceles. Otolaryngol Head Neck Surg 2007;136:621–625.
- 25.↑
Khong JJ, Malhotra R, Wormald PJ, et al. Endoscopic sinus surgery for paranasal sinus mucocoele with orbital involvement. Eye 2004;18:877–881.
- 26.
Lund VJ. Anatomic considerations in the aetiology of frontoethmoidal mucoceles. Rhinology 1987;25:83–88.
- 27.
Busaba NY, Salman SD. Ethmoid mucocele as a late complication of endoscopic ethmoidectomy. Otolaryngol Head Neck Surg 2003;128:517–522.
- 28.
Chobillon MA, Jankowski R. Relationship between mucoceles, nasal polyposis and nasalization. Rhinology 2004;42:219–224.
- 29.↑
Boroffka SA, Verbruggen AM, Grinwis GC, et al. Assessment of ultrasonography and computed tomography for the evaluation of unilateral orbital disease in dogs. J Am Vet Med Assoc 2007;230:671–680.
- 30.↑
Branstetter BF, Weissman JL. Role of MR and CT in the paranasal sinuses. Otolaryngol Clin North Am 2005;38:1279–1299.
- 31.↑
Kass ES, Fabian RL, Montgomery WW. Manometric study of paranasal sinus mucoceles. Ann Otol Rhinol Laryngol 1999;108:63–66.
- 32.
Lund VJ, Harvey W, Meghji S, et al. Prostaglandin synthesis in the pathogenesis of fronto-ethmoidal mucoceles. Acta Otolaryngol 1988;106:145–151.
- 33.
Lund VJ, Henderson B, Song Y. Involvement of cytokines and vascular adhesion receptors in the pathology of fronto-ethmoidal mucoceles. Acta Otolaryngol 1993;113:540–546.
- 34.
Beard WL, Hardy J. Diagnosis of conditions of the paranasal sinuses in the horse. Equine Vet Educ 2001;13:265–273.
- 35.
Trotter GW. Paranasal sinuses. Vet Clin North Am Equine Pract 1993;9:153–169.
- 36.↑
Ruggles AJ, Ross MW, Freeman DE. Endoscopic examination and treatment of paranasal sinus disease in 16 horses. Vet Surg 1993;22:508–514.
