A 5-year-old, 520 kg Standardbred mare was admitted for an osteosarcoma of the right premaxilla. Two horizontal incisions of the labial mucosa and lingual surface were made 1 cm around the ulceration from the canine tooth to the premaxillary symphysis. The premaxilla and rostral portion of the maxilla were transected 1 cm caudal to the canine tooth with an oscillating saw. The maxillary symphysis was transected using an oscillating saw and a hammer. The wound was closed by primary intention and healed without complication. The cosmetic appearance of the mare was good. The mare was able to prehend hay and grain and grazed without difficulty and the tongue did not protrude. The neoplasm had not recurred 18 months after the surgery. A premaxilla and rostral portion of the adjacent maxilla can be resected to treat horses for a unilateral lesion of the premaxilla but care must be taken to avoid the palatine and incisive arteries which lie within the interincisive canal.
Proliferative, fibro-osseous lesions of the mandible and premaxilla have been previously reported in horses (Barber et al. 1983; Orsini et al. 1991; Richardson et al. 1991; Schumacher et al. 1996; Auer 2005; Bush et al. 2007). Ossifying fibroma is the most common neoplasm encountered (Richardson et al. 1991; Auer 2005). Fibroma (Barber et al. 1983), fibrosarcoma (Auer 2005), osteosarcoma (Bush et al. 2007) and squamous cell carcinoma (Orsini et al. 1991) are the other neoplasms which can be encountered. Exuberant granulation tissue (Auer 2005) and phaeohyphomycosis are non-neoplastic lesions which produce fibrous proliferation (Schumacher et al. 1996). Phaeohyphomycosis has been previously reported on the premaxillae of the horse (Schumacher et al. 1996).
Osteosarcoma of horses is rarely reported. Based on the majority of reports, the tumour most commonly occurs on the head and, more commonly, in the mandible of young horses (Bush et al. 2007). Osteosarcomas have also been described at the scapula (Zaruby et al. 1993; Bush et al. 2007), proximal aspect of the radius of a donkey (Kilcoyne et al. 2010), proximal aspect of the tibia (Bush et al. 2007) and at the tarsus (Jenner et al. 2003).
As proliferative fibro-osseous lesions are most commonly encountered at the rostral aspect of the mandible than the premaxillae, rostral mandibulectomy has previously been well described (Richardson et al. 1991; Auer 2005). This procedure can also be performed with the horse standing (Schumacher 2011). However, the resection of premaxilla(e) and maxilla(e) has not been described extensively. One case report describes the resection of the premaxillae and rostral portions of the maxillae in a horse with squamous cell carcinoma (Bush et al. 2007) and another describes treatment of a horse infected with phaeohyphomycosis (Schumacher et al. 1996). In these reports, maxillae were resected and all incisive teeth removed because the lesions were extensive. To our knowledge, resection of one premaxilla and the rostral portion of the adjacent maxilla of a horse has not previously been reported.
In this article we report resection of a premaxilla and the rostral portion of the adjacent maxilla of a horse to remove an osteosarcoma. The contralateral incisors were preserved.
A 5-year-old, 520 kg Standardbred mare was presented at the Clinique Equine de Livet for a proliferative lesion adjacent to the right upper incisor teeth. Radiographic examination showed bone proliferation of the right premaxilla. The right intermediate incisor (Triadan 102) was slightly displaced labially and the corner incisor (Triadan 103) was severely displaced labially (Fig1). The lesion, thought to be exuberant granulation tissue, was resected and the corner incisor excised, with the horse anaesthetised. The wound could not be closed by primary intention.
Histological examination of the excised tissue showed a tumoural proliferation into the osseous tissue. A dense background of blood, including associated white blood cells, was present. A variable number of cells occurring singly or in clusters with indistinct cell boundaries were seen. Nuclei were round to slightly oval with several nucleoli. Macronucleoli were seen occasionally and mitotic figures seen rarely. Occasionally, binucleation and, uncommonly, multinucleation were seen. At the surface of the mass, inflammatory cells were seen. These findings were consistent with an osteosarcoma.
After this procedure, the mucosa healed well but a recurrence of the lesion occurred progressively 5 months after the surgery. The mare re-presented at the hospital 6 months after the first surgery.
At physical examination, the mass was firm and ulcerated rostrally and caudally to the 102. The mass was slightly smaller than at the first presentation. The mass extended dorsally on the gingiva, ventrally to the mucosa of the hard palate, rostrally 1 cm to the premaxillary symphysis and caudally 2 cm to the canine tooth (104) (Fig2). Radiographic examination revealed bone proliferation with extensive osteolysis around the right, intermediate, premaxillary incisor (Triadan 102), which was displaced labially. An island of dystrophic mineralisation was present ventrally (Fig3). After discussion with the owner, it was decided to perform a resection of the right premaxilla and rostral portion of the maxilla from the premaxillary symphysis to the canine tooth (104).
Prior to surgery, the mare received procaine penicillin G (22,000 iu/kg bwt i.m. b.i.d.) and flunixin meglumine (1.1 mg/kg bwt i.v. s.i.d.). Following sedation with romifidine (0.08 mg/kg bwt i.v.), anaesthesia was induced with ketamine (2.2 mg/kg bwt i.v.) and diazepam (0.2 mg/kg bwt i.v.) and maintained with isoflurane and i.v. infusion (romifidine [5 μg/kg bwt/min], ketamine [20 μg/kg bwt/min], butorphanol [5 μg/kg bwt/min]). The mare was placed in left lateral recumbency. The endotracheal tube was placed through the left nasal passage to facilitate access to the mouth. A wedge was placed between the left maxillary and mandibular check teeth to hold the mouth open. The upper lip was retracted and secured to the nostril with a suture. The oral cavity was washed using a povidone iodine solution. The infraorbital nerves were anaesthetised with 3 ml of 2% lidocaine into the infraorbital foramen to maintain a lighter depth of anaesthesia.
A horizontal incision of the labial mucosa was made 1 cm dorsally to the ulceration from the canine tooth to the premaxillary symphysis. A horizontal incision of the lingual surface was made from the canine tooth to the premaxillary symphysis. Both ends of the incisions were joined 1 cm caudally to the canine tooth and maxillary symphysis. Care was taken to avoid the major palatine artery. The gingiva was elevated with a periosteal elevator to expose normal bone. The junction of the gingiva to the mucosa of the hard palate is firmly attached to the premaxilla and a sharp incision had to be performed before elevating the flap.
An oscillating saw was used to cut the right premaxilla and rostral portion of the right premaxilla 1 cm caudally to the canine tooth (Triadan 104). The palatine process of the premaxilla was also transected using an oscillating saw. The bone edges were smoothed with a curette and care taken to avoid inadvertent incision of the oral mucosa. The ventral part of the maxillary symphysis was transected using an oscillating saw and the dorsal part carefully transected using an osteotome and a hammer to avoid the incisive artery contained within the interincisive canal. It was possible to resect more than 1 cm around the lesion.
An intraoperative radiographic examination showed no debris around the bone edges (Fig4). The soft tissues of the lingual surface were apposed to the labial side using a cruciate suture using a polydiaxonone USP 0 (PDS). A Penrose drain was placed at the premaxillary symphysis between the bone and soft tissue.
After surgery the mare received procaine penicilline G (22,000 iu/kg bwt i.m. b.i.d.) and phenylbutazone (2.2 mg/kg bwt i.v. b.i.d) for 4 days. No bilateral nasal collapse following infraorbital nerve block occurred post operatively. The mouth was washed with a chlorhexidine solution (Hextril)1 twice daily for 10 days. The Penrose drain was removed 2 days after the surgery. Grain was withheld to prevent awns from penetrating the incision. Hay was given for 3 days and grain was then reintroduced. The mare was able to prehend and masticate hay and grain correctly. No sign of pain was present. The tongue did not protrude. The mare was discharged 3 days after surgery.
The wound healed by first intention. Six weeks after surgery, the mucosa was completely healed and there were no signs of recurrence of neoplasia (Fig5). The appearance of the mare was completely normal and she was able to prehend hay and grain and to graze without difficulty. The tongue did not protrude.
Six months after surgery, the appearance was still normal. No signs of recurrence of the neoplasm were observed during radiographic examination of the head (Fig6). The mare became a broodmare and foaled successfully.
Two years after surgery, the mare was examined and the appearance of the mucosa was still normal.
Osteosarcomas are primary malignant bone tumours that arise in the medullary cavity and are characterised by the production of osteoid and/or immature bone by malignant osteoblasts . Very few cases have been reported within the equine species (Zaruby et al. 1993; Thompson and Pool 2002; Jenner et al. 2003; Kilcoyne et al. 2010). The aetiology and pathogenesis of osteosarcomas are unknown but possible predisposing factors may include trauma, viral infection and exposure to radiation (Jenner et al. 2003). Some horses may be genetically predisposed to developing osteosarcoma. In a large case series, the majority occurred in male horses aged 7 years or older with a lack of metastasis identified in any horse (Bush et al. 2007). However, osteosarcomas have also previously been described in foals (Thompson and Pool 2002). In this report, the mare was only 5-years-old.
Treating horses for osteosarcoma is difficult. Inability to completely excise the tumour and progression of disease typically result in euthanasia (Bush et al. 2007). Surgical excision was found to be effective if it does not recur within 14 months following surgery (Bush et al. 2007). Adjuvant chemotherapy is commonly employed when treating human osteosarcoma. The most common chemotherapeutic agents used to treat man are methotrexate, doxorubicin and cisplatin (Withrow et al. 1991). Longer disease-free intervals and survival in the dog have been demonstrated with cisplatin or cisplatin/doxorubicin combination following amputation (Withrow et al. 1991). In this case, as it was possible to resect more than 1 cm around the lesion, chemotherapy was not performed. The other reason was that no data for treating horses for osteosarcoma with chemotherapy are available.
Rostral mandibulectomy of the horse is most commonly performed to remove a neoplastic lesion from the region and the most commonly encountered neoplasm found at this site is the juvenile ossifying fibroma (Richardson et al. 1991). Indications for premaxillectomy of the horse are identical to those for rostral mandibulectomy but the procedure is not performed as commonly as is rostral mandibulectomy because juvenile ossifying fibroma is less commonly encountered on the premaxillae than it is on the mandible (Schumacher 2011). With rostral mandibulectomy to treat ossifying fibroma, there were no surgical complications or recurrences and the cosmetic and functional results were good (Auer 2005). Mandibulectomy can also be performed with the horse standing (Schumacher 2011). During anaesthesia, the endotracheal tube can be inserted nasally so that the tube does not interfere with surgery (Schumacher 2011). To resect both premaxillae, the horse is positioned in dorsal recumbency but because the lesion in our horse was located on only one premaxilla, the horse was positioned in lateral recumbency.
In rostral mandibulectomy, the most caudal portion of the mandibular symphysis should be preserved to maintain stability (Richardson et al. 1991). The ability to prehend feed can be preserved despite the loss of a row of incisors and marked shortening of the mandible (Auer 2005). However, some horses can encounter problems grazing short grass but can prehend longer grass with their lips (Auer 2005). With resection of the premaxilla, stability is naturally maintained with the support of the nasal bones and maxillae. In this case, the 3 left incisive teeth were maintained and the mare was able to prehend short grass. Overgrowth of the opposite incisors occurred but no problem to prehend food was associated with these changes (Auer 2005). Partial rostral hemimandibulectomy has been shown to cause degenerative changes in the temporomandibular joints of dogs (Umphlet et al. 1988) but such degenerative changes have not been recognised in horses (Auer 2005).
The main difference between performing premaxillectomy and performing mandibulectomy is the care that must be taken in preserving large vessels during premaxillectomy. The major palatine artery (Arteria palatina major) is bilateral and is located about 1 cm axial to gingival margins of the palate (Collin 1993). Care must be taken when the mucosa is elevated to avoid damaging this artery.
At the level of the premaxillary incisors, both major palatine arteries anastomose to form the incisive artery (Fig7a), which enters the interincisive canal (Canalis interincisivus). Dorsally, the incisive artery divides into 2 lateral branches connected to the superior labial artery (Arteria labialis superior) and lateral nasal artery (Arteria lateralis nasi) (Collin 1993) (Fig7b). Care must be taken when excising a premaxilla to avoid traumatising the incisive artery when the premaxillary symphysis is separated.
The premaxilla (and the adjacent rostral portion of the maxilla, if necessary) can be excised to remove a neoplastic, osseous lesion on the premaxilla. Care must be taken to avoid the major palatine and incisive arteries at the level of the interincisive canal.
Authors’ declaration of interests
No conflicts of interest have been declared.
Hextril, Johnson and Johnson, Issy les Moulineaux, France.