Progressive ossifying paranasal sinus mass of suspected traumatic origin in a mare: Surgical treatment and follow-up

Abstract

This report describes a case of a multilobular, osseous mass including parts of the right orbit, concho frontal sinus and right ventral and dorsal conchal sinuses that developed after a traumatic insult to the right maxillary sinus 4 years prior to presentation. Surgical removal of the mass including parts of the bony orbit and long-term outcome are reported.

Benign fibro-osseous tumors such as osteoma, ossifying fibroma, or fibrous dysplasia are uncommon in domestic animals, but seem to occur more frequently in cattle and horses (1). All of these tumors show various stages of osteogenous differentiation and ossification and are therefore suspected to originate from the same basic pathology and eventually form osteomas (1–4). In contrast, fibrous dysplasia is not defined as a true bony neoplasia, as it consists of a cellular fibro-vascular stroma with thin, poorly mineralized osteoid or bone spicules (2). Only a limited number of case reports and case series have been published describing treatment and outcome in horses with bone-associated tumors of the paranasal sinuses. In a previous published report of 256 cases with sinonasal disorders, 22 cases were diagnosed with neoplasia (5). Amongst these, only 1 was an osteoma and a fibroma (5). Dixon and Head (3) described 5 cases with neoplasia originating from bony sinus structures. Osteomas are usually suitable for surgical removal due to their small pedunculated attachment; however, the complex anatomy of the equine paranasal sinus makes complete removal without massive injury to adjacent structures challenging (6), especially if the bony portion of the orbital floor is involved. So far only 2 reports describe multilobular sinus tumors in horses (7,8). To the authors’ knowledge the current case is the first report that suggests an association between a traumatic insult to the sinus system and the subsequent development of an osseous sinus mass.

We describe diagnosis and treatment of a multilobular ossified mass extending from the right orbit to the right concho frontal, dorsal and ventral, conchal sinus of suspected traumatic origin.

Case description

A 6-year-old, 548-kg Swedish warmblood mare was admitted to the reporting clinic because of a progressive, right-sided facial swelling and right serous ocular discharge. At 1.5 y old, the mare had sustained a perforating injury by a tree branch in the area of the right concho frontal and caudal maxillary sinus. The wound had been treated but subsequently a bony swelling rostroventral to the right eye developed and the patient started to show right-sided ocular discharge. At the age of 4 y an osseous mass was partly removed from the right caudal maxillary and concho frontal sinus in a standing procedure at an equine clinic. According to the surgical report approximately 40% of the mass was removed during this surgery. Histopathological examination of the resected mass revealed dense osseous tissue with trabeculae of mineralized lamellar bone and a normal amount of osteocytes. Due to the histologic appearance and extreme density of tissue specimens submitted, a presumptive diagnosis of an osteoma was made.

Progressive regrowth of the mass within 1 y after the surgical intervention resulted in a right-sided facial swelling rostroventral to the right eye and unilateral serous ocular discharge.

On initial examination at the reporting clinic, the horse was in good body condition and vital parameters were within normal limits. Abnormal findings included a 5-cm long, 6-cm wide, and 2-cm thick bony convexity in the area of the right caudal maxillary sinus and concho frontal sinus rostoventral to the right eye and mild, right-sided serous ocular discharge (Figure 1). A computed tomography (CT) examination performed before admission revealed a mass with bone attenuation (~1000 Houndsfield units) originating from the right orbit and zygomatic arch occupying approximately 2/3 of the right concho frontal sinus, extending into the right ventral and dorsal conchal sinuses. Osteolytic changes and thinning of bony lining was observed at the entire bony orbital floor as well as in the part of the maxillary bone that covered the osseous mass (Figure 2).

Figure 1.

Bone dense right-sided facial swelling rostroventral to the right eye.

Figure 2.

Pre-surgical CT images showing the most rostral (A) and caudal (D) extension of the bone dense mass. B and C — Note the osteolytic changes and thinning of bony lining at the entire bony orbital floor as well as in the right maxillary bone covering the osseous mass (white arrows).

Surgical removal of the osseous mass was recommended. The horse was anesthetized and placed in left lateral recumbency. A right maxillary nerve block was performed during general anesthesia under aseptic conditions with 10 mL of mepivacaine (Mepinaest; Gebro Pharma GmbH, Fieberbrunn, Austria) (9) and 10 mL of ropivacaine (Naropin; AstraZeneca Gmbh, Vienna, Austria) using the extraperiorbital fat body insertion (EPFBI) technique. A modified right maxillary bone flap was created with the skin incision starting 1 cm rostral and 1 cm ventral to the medial canthus of the right eye, extending in a caudoventral direction towards the zygomatic arch. The skin incision was extended for 10 cm in a rostral direction about 1 cm dorsal to the zygomatic arch and facial crest (Figure 3). One centimeter caudal to the rostral end of the facial crest, the incision was directed in a dorsal direction for 7 cm. Subcutaneous tissue and periosteum were incised in the same plane and 3 mm of periosteum were elevated on either side of the incision using a sharp periosteal elevator. The exposed maxillary bone was cut with an oscillating saw in bevelled fashion and the bone flap was subsequently elevated with a pair of chisels and fractured along its dorsal aspect as previously described (10). While the rostral half of the maxillary bone flap appeared slightly irregular and thickened, the caudal half was extremely thin.

Figure 3.

A — Skin incision for the modified right maxillary bone flap. B — Exposed fraction of the bony mass after elevation of the bone flap.

Elevation of the bone flap exposed a fraction of the bony mass emanating from the right orbit and zygomatic arch. The exposed surface of the mass appeared smooth and harder than normal bone (Figure 3). The mass was gradually reduced by chipping off fragments of varying sizes with straight and curved chisels and a mallet. In the caudal direction the mass merged into the orbital process and the temporal process of the zygomatic bone. The periorbital fascia was dissected bluntly from the orbital process of the zygomatic bone and elevated with blunt tissue retractors to facilitate further removal of the pathological bony overgrowth. Following removal of most of the bony floor of the orbit, more pathologically changed bone extending into the temporal process of the zygomatic bone was removed. In order to avoid transection or fracture of the zygomatic arch and subsequent instability, a small portion of sclerotic bone was left in place. Finally, the peg-shaped rostral portion of the mass extending into the ventral and dorsal conchal sinuses was removed with intraoperative radiographic control. This portion was well-delineated and had no contact with other facial bones. Further radiographs confirmed complete removal of the rostral portion of the mass.

All visible bone fragments were removed and the sinuses were subsequently flushed with sterile Ringer’s solution. Intraoperative inspection of the periorbital tissues after resection of the mass revealed an 8-mm fascial rent and a small prolapse of retro-bulbar fat. A Board-certified ophthalmologist was consulted immediately to evaluate the right eye. Based on his recommendations and the fact that the right globe appeared only minimally sunken we decided to preserve the right eye. The frontal trephination portal from the first surgery was reopened to gain access to the concho frontal sinus.

The right ventral conchal sinus was perforated into the nasal cavity using long-handled (35 cm), bent dressing forceps. An elastic net bandage with iodine-impregnated gauze was passed through the opening into the nasal passage exiting at the right nostril using a flexible urinary catheter. The packing material was sutured to the nostril. Additional gauze packing was inserted into the concho frontal sinus through the frontal trephination portal.

The thin caudal half of the bone flap was resected because it had fractured along the junction with the thicker part and the remaining bony portion together with the skin and subcutaneous tissues of the flap were repositioned. Closure was completed in 3 layers (periosteum, subcutaneous tissue, skin). Total surgery time was 300 min and total estimated blood loss was 3 to 4 L.

Before and after surgery and continuing for 7 d post-surgery the horse received penicillin (Penicillin G Natrium; SANDOZ GmbH, Kundl, Austria), 30 000 IU/kg body weight (BW), IV, q6h, gentamicin (Gentavan; VANA GmbH, Vienna, Austria), 6.6 mg/kg BW, IV, q24h, flunixin meglumine (Finadyne; MSD Animal Health, Walton, Milton Keynes, Buckinghamshire, UK), 1.1 mg/kg BW, IV, q12h, and omeprazole (GastroGard; Merial GmbH, Hallbergmoos, Germany), 4 mg/kg BW, PO, q24h. Additional analgesia was provided by administering morphine hydrochloride (Vendal; G.L. Pharma GmbH, Lannach, Austria), 1 mg/kg BW, IV, q6h for 2 d. Subsequently, meloxicam (Metacam; Boehringer Ingelheim Vetmedica GmbH, Ingelheim, Germany), 0.6 mg/kg BW, PO, q24h and omeprazole (GastroGard; Merial GmbH), 4 mg/kg BW, PO, q24h were administered for 3 d.

The horse developed no major complications after surgery, only a mild left-sided facial nerve paralysis and a very mild left-sided triceps myopathy; both were attributed to the left lateral recumbency during surgery and resolved within 12 h after surgery.

The sinus packing was removed 3 d after surgery. Control radiographs on the fifth day after surgery indicated that no remnants of the mineralized mass remained in the right paranasal sinuses. For the next 4 wk, endoscopic examinations and lavages of the paranasal sinuses with sterile Ringer’s solution were performed under sedation at 3- to 4-day intervals. Endoscopic examinations revealed progressive, uncompromised wound healing. Multiple small bony fragments were identified during endoscopy and removed with endoscopic forceps.

The right globe showed a slight enophthalmos but no loss of vision could be detected during hospitalization. Histopathological examination of the resected mass revealed mature reactive fibrous tissue without any evidence of neoplasia or inflammation. Small isolated areas of mature bone within the fibrous tissue were detected. The histological findings were interpreted as being consistent with a chronic lesion and very likely the result of a former trauma to the area.

Nineteen days after surgery a second CT examination was performed under general anesthesia. Two small bony fragments were identified in the caudal maxillary sinus near the roots of the last molar. Another small bony fragment was located close to the trephination site of the frontal bone. The maxillary bone showed marked thickening of the caudal part of the bone flap. The area of the temporal process of the zygomatic bone, where a remnant of the mass was left in place, appeared sclerotic (Figure 4). The fragments were subsequently removed under endoscopic control and the horse was discharged 50 d after surgery.

Figure 4.

Computed tomographic images 19 days after surgery of the areas of the most rostral (A) and caudal (B) extension of the bone dense mass. B — There is an area of sclerotic bone (black arrow) at the temporal process of the zygomatic bone where a remnant of the mass was left in place. C and D — The thinned and osteolytic areas of bony lining covering the mass in the area of the bony orbital floor and maxillary bone were removed together with the mass (white arrow). D — There is a slight propulsion of periorbital fat in the maxillary sinus (white arrow).

Follow-up telephone calls to the owner were made over a 2-year period. The horse had an episode of facial swelling 3 mo after surgery that was treated with oral antibiotics by the referring veterinarian. The swelling subsided after a few days of treatment and did not recur when antimicrobials were discontinued. No other complications or signs of regrowth were reported by the owner. At the time of writing, 2 y and 3 mo after removal of the mass, no clinical signs were reported by the owner and the horse was successfully performing at her previous level of performance. The owner also reported satisfaction with the overall cosmetic outcome.

Discussion

Histopathological findings of the paranasal sinus mass found in the case described herein revealed the mass to be composed predominantly of chronic fibrous tissue infiltrated with areas of bone. This histological appearance was more consistent with an ossifying fibroma than a typical osteoma. Histologically benign fibro-osseous masses are composed of fibrous tissue, cells, and mineralized cancellous and compact bone in various proportions (1). In contrast, osteomas form well-differentiated areas of bone within a fibrous stroma. Even areas of well-developed Haversian systems may be found. Chronic ossifying fibromas possess features of both osteomas and fibrous dysplasia. Well-differentiated osteoids within a fibrous stroma can be detected next to poorly mineralized bone spicules (2). In the current case, however, gross pathology, and radiographic and CT findings were indicative of an osteoma. Histopathological examination revealed chronic fibrous tissue around the areas of well-differentiated mature bone, features that would be consistent with an ossifying fibroma. However, no signs of malignant growth or metastatic activity could be found in the excised tissue. Therefore, considering all results, the presumptive diagnosis of an osteoma was made. Osteomas are characterized by a smooth surface, lobulated shape, and an expansive, noninvasive growth pattern. They consist of bone with abnormal density but normal architecture (3).

Osteomas are expansive and are typically found in the maxillary sinus in horses (3,6). This feature was expressed as swelling and deformation of the facial bones in the case reported. Although osteomas are usually amenable to surgical removal, the complex anatomy of the equine sinus system may impede complete resection (6). Regrowth after surgical excision was not associated with incomplete resection (11). The overall outcome after surgical resection of sinus osteomas is reported to be good with no signs of reoccurrence in 3 of 5 cases between 18 mo and 10 y after surgery (12–14). In contrast, ossifying fibromas seem to have a more guarded prognosis compared with osteomas since all reported cases showed signs of regrowth (15,16). In the case described in this study the osteoma was found in the right concho frontal sinus, extending into the right ventral and dorsal conchal sinuses as well as the right orbital floor. The bony orbital floor had undergone pressure resorption and thinning and was subsequently removed.

Complications after fractures of the orbit in which the integrity and supportive function of the bony part of the orbital floor are disrupted, as in our case, include traumatic uveitis, lacerations of the globe, herniation of the retro-bulbar fat and globe into the sinus system, changes in position of the globe, and loss of vision (17).

In human medicine various techniques for orbital floor reconstruction after orbital floor fractures or surgical excision after tumor removal are described. Allogenic implants commonly used are made of high-density polypropylene poly-L-lactic acid or polyglycolic acid and titanium (18–20). Another method for reconstruction is the use of autologous bone grafts (19,20). In these studies, the 2 most common clinical signs described after orbital floor fractures and herniation of orbital soft tissues into the sinus system are diplopia and enophthalmos. Diplopia is mainly caused by impaired function of the extra-ocular muscles (21–23). Usually these symptoms can be alleviated by performing orbital floor reconstruction and restoration of support for orbital soft tissues (24). In our case orbital floor reconstruction with any kind of implants was not considered due the fact that the mare had concurrent sinusitis of the right maxillary and concho frontal sinus and therefore was at an increased risk of implant infection. Mild enophthalmos was detected in our case. Whether the horse was suffering from diplopia or other impairments of vision would have been difficult to determine. All ophthalmologic examinations performed after surgery revealed no pathologies and no behavioral changes were observed during hospitalization that would have indicated impairment in vision. In summary, resection of the bony part of the orbital floor might be possible without major impairments in certain cases. However, to the authors’ knowledge, this is the first report to describe this procedure and further documentation of similar cases will be necessary to determine possible complications and drawbacks.

In human medicine osteoma formation after trauma to the facial bones has been documented in a few case reports (25–27). The most common site for osteoma formation was the mandible (26). However post-traumatic osteomas were also associated with the orbit or the maxillary sinus (25,27). The etiopathogenesis of these osteomas is still not completely elucidated, but a reactive neoplastic transformation of the periosteum or bone itself is suspected (25–27). Therefore in the case reported herein, the osteoma most likely developed as a result of trauma (tree branch injury) to the maxillary sinus before presentation. CVJ