Histopathological Characteristics of an Ossifying Fibroma Formed in the Maxilla of a Racehorse

A 1-year-old male thoroughbred racehorse experienced swelling of the left upper lip. The swelling was attributable to enlargement around the incisive bone of the interdental space posterior to the third incisor in the left maxilla. Even after two operations to reduce the bulk of the mass, it continued to increase in size. Dyspnea caused by stenosis of the nasal cavity forced us to perform euthanasia, and a pathological examination was conducted. Macroscopic examination of a section of the mass revealed the formation of multiple areas of solid fibrous tissue, and trabeculae within the incisive bone which had displaced the cortical bone. On histology, the mass was composed of trabecular bone-like structures due to the proliferation and aggregation of fibroblasts. Therefore, we diagnosed it as an ossifying fibroma. Equine ossifying fibroma is characterized by development in the mandible, but was formed in the maxilla in this case. Equine ossifying fibroma has not been reported previously in Japan. This is the first case of equine ossifying fibroma identified in Japan.     

Mandibular ossifying fibroma in a dog

An aged mongrel dog was admitted for hemimandibulectomy as treatment for a mandibular mass that had been diagnosed as osteosarcoma. The fibro-osseous mass that surrounded the first molar tooth and replaced alveolar and cortical bone was reclassified as ossifying fibroma on the basis of anatomic location and histologic features. The tumor was composed of isomorphic fusiform cells with few mitotic figures. Tumoral stroma contained trabeculae of woven bone that were bordered by a single layer of osteoblasts. Excision was deemed complete with no evidence of extension or metastasis by computed tomography of the skull or thoracic and abdominal radiography. The dog was reportedly healthy 6 months after initial presentation. Though far less common than osteosarcoma as a primary canine bone tumor, ossifying fibroma should be included in the differential diagnosis for fibro-osseous proliferations, especially those of the jaw. Although benign, en bloc excision may be necessary for surgical cure.     

Urinary obstruction secondary to an ossifying fibroma of the os penis in a dog

A 13-year-old, 25-kg, castrated male border collie was referred for evaluation of pollakiuria, stranguria, and a decreased urine stream. A calcified periurethral mass near the caudal aspect of the os penis was identified on survey abdominal radiographs. A retrograde contrast urethrocystogram demonstrated that the mass was compressing the penile urethra. The mass was surgically resected. A histopathological diagnosis of an ossifying fibroma of the os penis was made. This report describes an atypical presentation of a rare tumor, an ossifying fibroma, that caused a urinary obstruction in a male dog. A review of the incidence, histopathological features, and behavior of ossifying fibromas is included.     

Ossifying fibroma in a miniature rex rabbit (Oryctolagus cuniculus)

In humans and animals, ossifying fibroma is a benign neoplasm that most frequently affects the mandible, often resulting in cosmetic deformities and malocclusion. It is considered rare in animals and most frequently affects young horses. A surgical biopsy of a solitary mass located beneath the gingiva in the right maxillary region, which had overgrown teeth and expanded the adjacent hard palate from a 6-year-old miniature Rex rabbit was submitted for light microscopic examination. The submitted incisional biopsy specimen was pale pink, firm, and nodular. Histopathologically, the neoplasm was composed of fibroblastic cells separated by abundant collagen. The neoplastic cells were interwoven with osteoblasts surrounding islands of mineralized, bony matrix containing few, widely spaced, often empty, lacunae. Minimal inflammation was present. Based on the histopathologic features, the tumor was diagnosed as an ossifying fibroma. To our knowledge, this is the first report of an ossifying fibroma in a rabbit.     

Multiple mandibular ossifying fibromas in a yearling Belgian Draught horse filly

A yearling Belgian Draught horse filly was presented with a history of bilateral, progressive, painful swelling of the mandible, fever and anorexia. Radiographs and computed tomographic images showed an expansile lesion with a coalescing, well‐defined cystic pattern at the level of the horizontal ramii of the mandible. The histopathological findings confirmed the diagnoses of bilateral, multiple ossifying fibroma. This report indicates that ossifying fibroma should be included in a differential diagnosis if multiple expansile lesions of the jaw are present.     

Ossifying fibroma in a llama.

A 4.5-year-old llama was admitted for evaluation of a firm mass rostral and ventral to the medial canthus of the left eye. Mucopurulent nasal discharge and absence of airflow through the left nostril were noted. Radiographs of the skull revealed a sharply demarcated soft tissue mass with faint mineralization. Endoscopy of the nasal passages revealed a mucosa-covered mass originating in the area of the second premolar, extending to the edge of the soft palate, and obstructing the airway. Examination of the oral cavity revealed a missing second molar and a mass protruding 2-cm from the empty alveolus. An ossifying fibroma, a previously unreported tumor in llamas, was diagnosed at postmortem examination.     

Computed tomographic appearance of equine sinonasal neoplasia

The computed tomography (CT) features of tumors involving the nasal cavity and/or paranasal sinuses of 15 horses were reviewed. The 15 tumors included five neuroendocrine tumors/neuroblastomas, two undifferentiated carcinomas, two myxosarcomas, and one each of nasal adenocarcinoma, hemangiosarcoma, chondroblastic osteosarcoma, anaplastic sarcoma, myxoma, and ossifying fibroma. All tumors except the ossifying fibroma were iso- or hypoattenuating relative to masseter muscle. Thirteen of the fifteen tumors exhibited moderate or marked osteolysis of adjacent cortical bone and 14/15 were characterized by destructive changes of the nasal turbinates, nasal septum, and/or infraorbital canal. Ten horses had moderate or marked involvement of the cribriform plate and six had clear intracranial extension of the mass. CT features were compared to radiographic findings for 10 horses. A mass was observed in 10/10 radiographic studies and mass within the caudal maxillary sinus (7/8) and rostral maxillary sinus (6/7) was identified correctly in most horses. The radiographs were least sensitive for identifying masses within the sphenopalatine sinus (0/5), cranium (0/4), and retrobulbar space (1/7) compared to CT. The radiographs also underestimated potential features of malignancy, such as severity of osteolysis or osseous production. While radiographs are a useful screening tool for identification of sinonasal masses, CT provides greater information regarding mass extent, features of malignancy, and important prognostic indicators.     

Use of a titanium mesh for cranioplasty following radical rostrotentorial craniectomy to remove an ossifying fibroma in a dog

CASE DESCRIPTION: A 6-year-old Australian Terrier was evaluated for surgical removal of an ossifying fibroma of the left calvarium of 7 months' duration. CLINICAL FINDINGS: Computed tomography revealed invasion of the mass through the left parietal bone and extension into the epidural space of the brain. TREATMENT AND OUTCOME: A left rostrotentorial and frontal bone craniectomy was performed, and the mass was removed, along with a 1-cm margin of grossly normal bone. Cranioplasty was performed with a combination of porcine submucosa, titanium mesh, and screws. The dog recovered from surgery without complications and was discharged 3 days later. The dog was followed up for 24 months after surgery and has remained clinically normal. CLINICAL RELEVANCE: Findings suggested that rostrotentorial craniectomy is a viable option for removal of benign tumors affecting the parietal bones in dogs. Reconstruction of the resulting defect in the calvarium is possible with a combination of porcine submucosa and rigid titanium mesh.     

Fibro‐osseous tumour of the second metacarpal bone in a Thoroughbred filly

A 7‐month‐old Thoroughbred filly was evaluated because of an enlarging mass present on the proximomedial aspect of the left metacarpus. The mass was first noticed at age 2 months and had continued to increase in size. The mass was firm, nonpainful to palpation, covered with normal haired skin and had never been associated with lameness. Radiographs obtained at ages 2 and 7 months revealed an enlarging and partially mineralised mass associated with the second metacarpal bone. Based on the clinical and radiographic progression, as well as the location of the mass, a poor prognosis for future athletic soundness was given and the filly was subjected to euthanasia. The mass had histological features of both an ossifying fibroma and osteoma.     

Use of a free cortical ulnar autograft following en bloc resection of a mandibular tumor

A dog was presented for the en bloc resection of a previously irradiated mandibular ossifying epulis. A central hemimandibulectomy was performed, and the mandibular defect was stabilized by the use of a free cortical ulnar autograft and rigid internal fixation. The dog had normal mastication and left forelimb function two weeks after surgery. Radiographic evaluation of the surgical site at three and 10 months after surgery showed normal bony healing.     

Ameloblastic odontoma in the mandible of a llama

A 4-year-old llama had an aggressive, multiloculated, expansile bone lesion involving the rostral mandible. The mandibular lesion was imaged using radiography and computed tomography. Antemortem diagnosis of an ossifying fibroma was made histologically. Postmortem findings showed the lesion to be limited to the mandible. Final diagnosis was ameloblastic odontoma.     

Radiotherapy of a recurrent ossifying fibroma in the paranasal sinuses of a horse

A 7-year-old female Thoroughbred was admitted with a history of labored breathing, stridor, and exercise intolerance. Examination revealed a mass in the left paranasal sinuses that was determined to be an ossifying fibroma. Initial treatment consisted of surgical removal of the mass alone; however, the mass recurred 9 months after surgery. The mass was again removed, and adjunctive radiotherapy consisting of 3,000 cGy of cobalt radiation was administered. This time, the tumor did not recur for > 6 years. A third surgery was performed to remove the mass, and adjunctive radiotherapy consisting of 4,000 cGy of photon beam radiation from a linear accelerator was administered. The mass did not recur during the subsequent 3 years. Ossifying fibromas are uncommon tumors that frequently recur if incompletely excised. Results in this horse suggest that adjunctive radiotherapy may delay or prevent tumor recurrence in affected horses.     

Surgical management of ameloblastic fibroma in the cat

A 14-month-old spayed female domestic short-haired cat was presented for evaluation of a rostral mandibular mass diagnosed from biopsy as an ameloblastic fibroma. Radiographs of the mandible demonstrated marked osteolysis and cortical expansion. A rostral mandibulectomy was performed extending from the caudal edge of the second premolar on the right side to the caudal edge of the canine tooth on the left side. Histological evaluation of the excised mass confirmed the diagnosis of ameloblastic fibroma. Follow-up evaluation at eight months revealed normal oral function with the exception of occasional saliva soiling of the chin. The owner was satisfied with the cosmetic result.     

Rostral mandibulectomy in five horses.

Rostral mandibulectomy with primary gingival closure was performed in 5 horses with rapidly growing or bleeding mandibular tumors. The technique involved preservation of the most caudal portion of the mandibular symphysis to maintain stability. There were no surgical complications or recurrences, and the cosmetic and functional results were good. The histopathologic diagnosis of all the tumors was ossifying fibroma. Rostral mandibulectomy affords a simple and effective technique of treating tumors of the rostral portion of the mandible in horses.     

Fibro‐osseous tumour of the fourth metacarpal bone in a horse: Clinical,radiographic and long‐term post operative findings

This case study describes a rare case of a fibro‐osseous tumour in the distal part of the fourth metacarpal bone of a 13‐year‐old horse. The tumour was surgically removed and wound healing occurred without complications. A specific diagnosis was reached by considering the clinical and histological features of the mass. However, the process was complicated by the different classification systems for this type of tumour. When classified according to the veterinary literature, ossifying fibroma is the appropriate diagnosis, whereas in human medicine this term has been replaced.     

Ossifying fibroma as a cause of blindness in a 5-year-old Quarter Horse gelding

A 5-year-old Quarter Horse gelding presented to Texas A&M University Veterinary Medical Teaching Hospital with a several week history of bilateral blindness. Neurological deficits included an absent menace response and severe atrophy of the optic nerve head in the left eye (OS) as well as decreased vision in the right eye (OD). Advanced imaging consisting of computed tomography (CT) and magnetic resonance imaging (MRI) confirmed a large mass in the base of the skull invading the sinuses and asymmetrically compressing the optic nerves rostral to the optic chiasm. Due to the size and location of the mass as well as severity of associated neurological signs, humane euthanasia was elected. Necropsy examination identified a large mass effacing the sphenopalatine sinuses and compressing the optic nerves. Histologically, the mass was identified as an ossifying fibroma (OF) and degeneration of the optic nerves was confirmed. As an OF in this location has never been described in a horse, this case demonstrates a new differential for blindness in horses.     

Equine juvenile mandibular ossifying fibroma

Benign proliferative fibro-osseous lesions of the rostral mandible in six young horses are classified as equine juvenile mandibular ossifying fibroma. Histologically there is a characteristic abrupt transition from subgingival fibroblastic stroma to a zone of proliferating osteoblasts that form irregular spicules of osteoid. The layer of proliferating osteoblasts blends with a deeper zone of bony trabeculae rimmed by osteoblasts and separated by intertrabecular spaces of moderate cellular density. Incomplete surgical excision resulted in local recurrence, while rostral mandibulectomies resulted in no recurrence. The predilection for the rostral mandible of young horses coupled with the similar clinical, radiographic, and histological characteristics supports the classification of this lesion as a distinct entity.     

Resection of the incisive bone and rostral maxillae for removal of an ossifying fibroma in an 18‐year‐old Warmblood gelding

A 510 kg, 18‐year‐old Warmblood gelding used for high level dressage was presented with a 6 week history of a growing mass at the rostral aspect of the incisive bone. Radiographic examination of the maxillae showed an osteolytic lesion between the left maxillary central and intermediate teeth spreading caudally into the hard palate. Biopsy of the mass was consistent with an aggressive oral fibrosarcoma. Diagnostic work‐up ruled out metastatic lesions. An amputation of the incisive bone and part of the rostral maxillae was performed with the intent of removing the mass in healthy margins. However, the neoplastic tissue extended to the rostral aspect of the ventral nasal conchae and a resection in healthy margins was not performed to avoid surgical complications due to communication with the nasal conchae. After surgery, the horse's appetite and food uptake were not impaired and cosmetic appearance was excellent. Active drains were used in order to prevent any submucosal collection of fluids. Histopathological examination of the surgical margins of the removed maxillae confirmed the presence of tumoural tissue. Even though excision of the tumour was not complete, no macroscopic local recurrence was reported post operatively at 36 months' follow‐up. Based on histological re‐evaluation of the removed tissue and the absence of recurrence a definitive diagnosis of ossifying fibroma was made.     

Multiple myeloma in a horse

Multiple myeloma was diagnosed in a horse on the basis of clinical signs, protein electrophoresis pattern, Bence-Jones proteinuria, and radiographic changes in bone. The horse had mild depression, weight loss, edema of the distal portion of the left hind limb, anemia, hyperproteinemia, and monoclonal gammopathy in the beta 2 region. Radiographically, punctate cortical lysis of bone was seen. Specific treatment for the multiple myeloma was not attempted and the horse was euthanatized.