Maxillectomy and mandibulectomy in the horse: Indications and necessity of post operative adjunct therapy
Version of Record online: 12 MAR 2013
© 2013 EVJ Ltd
Equine Veterinary Education
Volume 26, Issue 5, pages 274–279, May 2014
How to Cite
Witte, S. (2014), Maxillectomy and mandibulectomy in the horse: Indications and necessity of post operative adjunct therapy. Equine Veterinary Education, 26: 274–279. doi: 10.1111/eve.12024
- Issue online: 7 APR 2014
- Version of Record online: 12 MAR 2013
- ossifying fibroma;
- fibrous dysplasia
Resection of the rostral mandible, incisive bone and maxilla has previously been described (Auer 2005). Although the equine literature consists primarily of case reports, such procedures are performed routinely in small animal cancer patients (Arzi and Verstraete 2010). With adequate knowledge of the regional anatomy and the prerequisite of adequate margins, resection can be performed with relative ease and good success. Mandibulectomy was recently described in the standing horse (Schumacher 2011). Case reports and this author's personal experience suggest that horses cope remarkably well, showing minimal post operative discomfort and minimal loss of function (with appropriate modifications in feed) following removal of the rostral jaw. In general, cosmetic outcome also seems favourable to good (Richardson et al. 1991) (Fig 1).
In order to avoid confusion, a common (and anatomically correct) classification should be used to describe resection of the jaw bone: mandibulectomy procedures are classified according to the portion of mandible removed. A ‘rim excision’ or partial segmental resection leaves the ventral border of the mandible intact (Brown et al. 2002). The terms unilateral or bilateral mandibulectomy state whether one or both mandibles are removed. Resection may be rostral, central, caudal or total. Maxillectomy can also be performed uni- or bilaterally. Incisivectomy of the upper jaw refers to excision limited to the incisive bone (premaxilla). Rostral maxillectomy removes the rostral aspect of the maxillary bone and the incisive bone (Verstraete 2005). Central, caudal and total maxillectomy are terms that are less likely to be relevant to the equine patient. In the accompanying case report Cousty and Tricaud (2014) describe a unilateral rostral maxillectomy.
A single report has previously described partial maxillectomy for treatment of infection with a dermatiaceous fungi causing phaeohyphomycosis (Schumacher et al. 1996). Tumours are a more common indication for surgery and will be the focus of the remainder of this discussion. Tumours of the equine jaw can be classified as those coming from the dental tissue, of epidermal origin and originating from bone (Knottenbelt 2005).
Tumours originating from dental tissues (odontogenic tumours) are rare. Those most commonly referred to in the literature are ameloblastoma, cementoma and odontoma. Reference to oral adamantinoma can be found in earlier literature (Wahl 1936; Vaughan and Bartels 1968; Hanselka et al. 1974; French et al. 1984). Based on human classification and their odontogenesis, these tumours should possibly be grouped together with the ameloblastoma (Ivey and Churchill 1930). Ameloblastomata show clinical and radiographic signs consistent with other oral tumour types. Differentiation relies on histopathological evaluation of biopsy specimens demonstrating the presence of odontogenic (specifically enamel producing) epithelium. This tumour has previously been described in foals (Roberts et al. 1978; Summers et al. 1979; Jones and Brumbaugh 1991). Reports of early intervention and wide surgical margins suggest that surgery alone can be curative (French et al. 1984; Rosol et al. 1994). This is consistent with the treatment of human patients with ameloblastoma in which no adjunct therapy is recommended (Franca et al. 2012; Tortorici et al. 2012). While metastasis is unlikely, hypercalcaemia as a sign of paraneoplastic syndrome has been described with this tumour type (Rosol et al. 1994). Cementoma is the most common term used to describe ‘hyperplastic cement accumulation’. The terms cementosis and cementicles are also found in the literature. The nomenclature of this group of cement accretions will likely need refining as their aetiology and pathophysiology become clearer (J. Easley, personal communication). The masses are mesenchymal in origin and may be present during tooth development. They are formed of reactive tissue rather than representing a true neoplasm (Freeman 1991). Location of these tumours, at the tooth root, makes early recognition unlikely. Any disease creating periapical inflammation, such as tooth fracture, periodontitis and dental impaction can cause cementoma formation. Their radiographic appearance is very characteristic (Fig 2) (Kreutzer et al. 2007; Schaaf et al. 2007). Tooth removal is hampered by expansion in the region of the root through the obstructive presence of the mass. This benign lesion can, however, be resolved with tooth extraction or local resection and currettage alone. Odontomas are hamartomas which contain well differentiated dental tissues. The adjectives complex and compound can be used to further differentiate tumours histologically into those which display relative organisation of the 3 tooth components (compound) and those with a chaotic (complex) structure (Figs 3 and 4). There is no apparent age predisposition for this tumour which may present as painless swellings over the root regions of any of the teeth of the jaw and can extend into the paranasal sinuses (Dubielzig et al. 1986; Heufelder et al. 1994; Schumacher et al. 1997; Rubio-Martinez et al. 2011). Depending on location, partial resection of the rostral upper or lower jaw may be indicated. In the past repeat surgeries have been necessary, giving a fair prognosis for resolution of disease (Dillehay and Schoeb 1986; Dubielzig et al. 1986; Brounts et al. 2004; Knottenbelt 2005). Adjunct therapy is not warranted.
While osteosarcomas are rarely reported in the horse, most of those recorded have been located in the region of the head (Thorp and Graham 1934; Barber et al. 1983; Livesey and Wilkie 1986; Bush et al. 2007). This malignant mesenchymal tumour causes bone lysis (Fig 5) and the haphazard deposition of reactive trabecular new bone by neoplastic cells. A biopsy should be taken and evaluated in order to clearly differentiate it from other tumours (ameloblastoma, ossifying fibroma and fibrous dysplasia). Neoplastic osteoblasts (and a variable number of osteoclasts) show a characteristic high mitotic index. Attempts at surgical excision have been previously described but failed due to inadequate surgical margins (Bush et al. 2007). To the author's knowledge, Cousty and Tricaud (2014) are the first to describe the successful surgical management of an osteosarcoma affecting the equine skull. Through their novel approach of unilateral rostral maxillectomy they were able to minimise morbidity and improve post operative case management by preserving the mare's ability to prehend grass. Surgery and systemic chemotherapy are the current standard of care for osteosarcoma in small animals, with radiation generally only providing tumour control or palliation (Coomer et al. 2009). In man surgical excision remains the mainstay of treatment for osteosarcoma of the jaw, with both chemo- and radiation-therapy being of questionable value (Clark et al. 1983; Kassir et al. 1997; Jasnau et al. 2008). As stated by Cousty and Tricaud (2014), systemic use of chemotherapy is poorly described in the equine literature (Mair and Couto 2006). Local use of platin-based drugs are, however, effective in the management of cutaneous neoplasms (Theon et al. 1999, 2007) and implantation of cisplatin beads might be considered prior to gingival closure (Hewes and Sullins 2006).
Squamous cell carcinoma can affect any of the structures within the equine oral cavity, pharynx and larynx. As with any mass-lesion, presence and extent of disease must be assessed as early and as thoroughly as possible, ideally through advanced imaging such as computed tomography (Witte and Perkins 2011), prior to any form of intervention. This tumour shows aggressive behaviour which is infiltrative, destructive and ulcerative. Chronic irritation of the mucosa, as seen in chronic periodontitis, has been proposed as a cause of squamous cell carcinoma of the oral cavity (Knottenbelt 2005). While a high index of suspicion is justified based on prevalence and appearance, histopathological confirmation through the identification of the characteristic irregular cords of downward-invading neoplastic keratinocytes and keratin ‘pearls’ should be performed before committing to treatment. Incisivectomy (Orsini et al. 1991) has been reported for the successful management of squamous cell carcinoma. Figures 6-8 show this author's experience with bilateral rostral maxillectomy in an 11-year-old Tennessee Walking Horse presented for treatment of a squamous cell carcinoma. Based on the apparent sensitivity of this tumour type to gamma radiation, (Walker et al. 1998) and in order to decrease the likelihood of recurrence, surgical intervention was followed at 6 weeks with weekly radiation. A total dose of 32 Gray was delivered in 4 treatments. On the basis of the potentially beneficial effects of nonsteroidal anti-inflammatory medication in controlling squamous cell carcinoma (Moore et al. 2003; Elce et al. 2007; Thamm et al. 2008) this horse was also discharged on oral piroxicam. Adjunct local chemotherapy (e.g. cisplatin beads) might also be indicated and practical in such cases (Theon et al. 2007; Barabas et al. 2008). The horse in Figure 1 showed no signs of local recurrence and was being used for pleasure riding at 6 year follow-up.
Ossifying fibroma is a proliferative, fibro-osseus, tumour-like lesion that most commonly develops in the rostral mandible causing distortion of the lip and adjacent teeth (Fig 9). Most cases occur in horses less than one year of age (Morse et al. 1988). Dense tissue is seen on radiographs with variable degrees of calcification. Unilateral rostral maxillectomy and bilateral rostral mandibulectomy have been described with adequate margins being the prerequisite for curative surgery (Richardson et al. 1991; Kawcak et al. 1996). Radiation alone has also been reported to be successful (Robbins et al. 1996) and may be helpful as an adjunct therapy in the case of incomplete surgical resection (Orsini et al. 2004).
Fibrous dysplasia presents as a smooth contoured bone deformity arising from loss of bone structure with extensive formation of fibro-osseus matrix (Fig 10). A well demarcated radiolucent cavity is visible radiographically (Fig 11). The tumour becomes evident through its progressive expansile growth. Most lesions are monostotic (involving only a single bone), asymptomatic and identified incidentally. They can be treated with clinical observation alone. Should the expansile growth impinge upon adjacent structures, surgical excision may be warranted. Use of bisphosphonates, to reduce pain and initiate bone deposition, has been previously described in human patients and could be considered in the equine patient (Wirth 2012).
The described mass lesions are those more commonly encountered in the equine oral cavity, affecting the jaw. Additional differential diagnoses include osteomas, exuberant granulation tissue, epulis, myxomatous tumours of the jaw, haemangiosarcoma, lymphosarcoma and aneurismal bone cysts (Knottenbelt 2005). Imaging and biopsy should always be performed prior to undertaking any form of management (Witte and Perkins 2011). Surgical resection, through mandibulectomy or maxillectomy, can be considered in cases of diseases affecting the jaw if adequate surgical margins can be achieved.
Author's declaration of interests
No conflicts of interest have been declared.
- 2010) Mandibular rim excision in seven dogs. Vet. Surg. 39, 226-231. and (
- 2005) Craniomaxillofacial disorders. In: Equine Surgery, Eds: J.A. Auer and J.A. Stick , W.B. Saunders, St Louis. pp 1341-1362. (
- 2008) Cisplatin: a review of toxicities and therapeutic applications. Vet. Comp. Oncol. 6, 1-18. , , and (
- 1983) Fibroblastic tumor of the premaxilla in two horses. J. Am. Vet. Med. Assoc. 182, 700-702. , and (
- 2004) Surgical management of compound odontoma in two horses. J. Am. Vet. Med. Assoc. 225, 1423-1427. , , , , and (
- 2002) Factors that influence the method of mandibular resection in the management of oral squamous cell carcinoma. Br. J. Oral Maxillofac. Surg. 40, 275-284. , , , , and (
- 2007) Equine osteosarcoma: a series of 8 cases. Vet. Pathol. 44, 247-249. , and (
- 1983) Osteosarcoma of the jaw. Cancer 51, 2311-2316. , , and (
- 2009) Radiation therapy for canine appendicular osteosarcoma. Vet. Comp. Oncol. 7, 15-27. , , , , and (
- 2014) Resection of a premaxilla and rostral portion of the maxilla in a horse. Equine Vet. Educ. 26, 269-273. and (
- 1986) Complex odontoma in a horse. Vet. Pathol. 23, 341-342. and (
- 1986) Complex odontoma in a stallion. Vet. Pathol. 23, 633-635. , , and (
- 2007) Expression of cyclooxygenase-1 and -2 in naturally occurring squamous cell carcinomas in horses. Am. J. Vet. Res. 68, 76-80. , and (
- 2012) Ameloblastoma demographic, clinical and treatment study: analysis of 40 cases. Braz. J. Otorhinolaryngol. 78, 38-41. , , , , and (
- 1991) Paranasal sinuses. In: Equine Respiratory Disorders, Ed: J. Beech , Lea and Febiger, Philadelphia. pp 275-303. (
- 1984) Mandibular adamantinoma in a horse; radical surgical treatment. Vet. Surg. 13, 165-171. , and (
- 1974) Adamantinoma of the equine mandible, a case report. Vet. Med. Small Anim. Clin. 69, 157-160. , and (
- 1994) [Case report of a complex odontoma in a horse – clinical picture, radiography, ultrasonography and computed tomography]. Tierarztl. Prax. 22, 155-158. , , and (
- 2006) Use of cisplatin-containing biodegradable beads for treatment of cutaneous neoplasia in equidae: 59 cases (2000-2004). J. Am. Vet. Med. Assoc. 229, 1617-1622. and (
- 1930) The need of a standardized surgical and pathological classification of tumors and anomalies of dental origin. Am. Assoc. Dent. Sch. Trans. 7, 240-245. and (
- 2008) Craniofacial osteosarcoma experience of the cooperative German-Austrian-Swiss osteosarcoma study group. Oral Oncol. 44, 286-294. , , , , , , and (
- 1991) What is your diagnosis? Polycystic osteolytic lesion of the rostral portion of the mandible. J. Am. Vet. Med. Assoc. 199, 630-631. and (
- 1997) Osteosarcoma of the head and neck: meta-analysis of nonrandomized studies. Laryngoscope 107, 56-61. , , , , and (
- 1996) Treatment of ossifying fibroma in a horse by hemimaxillectomy. Equine Pract. 18, 22-25. , and (
- 2005) Oral and dental tumors. In: Equine Dentistry, 2nd edn., Eds: G. Baker and J. Easley , Elsevier, Philadelphia. pp 127-148. (
- 2007) Dental benign cementomas in three horses. Vet. Pathol. 44, 533-536. , , , , and (
- 1986) Focal and multifocal osteosarcoma in two foals. Equine Vet. J. 18, 407-410. and (
- 2006) The use of cytotoxic drugs in equine practice. Equine Vet. Educ. 18, 149-156. and (
- 2003) Long-term control of mucocutaneous squamous cell carcinoma and metastases in a horse using piroxicam. Equine Vet. J. 35, 715-718. , , and (
- 1988) Equine juvenile mandibular ossifying fibroma. Vet. Pathol. 25, 415-421. , , and (
- 2004) Radiotherapy of a recurrent ossifying fibroma in the paranasal sinuses of a horse. J. Am. Vet. Med. Assoc. 224, 1483-1486, 1454. , and (
- 1991) Excision of oral squamous cell carcinoma in a horse. Vet. Surg. 20, 264-266. , , and (
- 1991) Rostral mandibulectomy in five horses. J. Am. Vet. Med. Assoc. 199, 1179-1182. , and (
- 1996) The use of megavoltage radiation to treat juvenile mandibular ossifying fibroma in a horse. Can. Vet. J. 37, 683-684. , and (
- 1978) Ameloblastic ondontoma in a foal. Equine Vet. J. 10, 91-93. , and (
- 1994) Humoral hypercalcemia of malignancy associated with ameloblastoma in a horse. J. Am. Vet. Med. Assoc. 204, 1930-1933. , , , , and (
- 2011) What is your diagnosis? A large heterogeneous mass containing small enameldensity circular opacities with central radiolucencies is evident within the right maxillary sinus. J. Am. Vet. Med. Assoc. 238, 695-696. , and (
- 2007) Calcified tumours of the paranasal sinuses in three horses. Aust. Vet. J. 85, 454-458. , and (
- 2011) Surgeries of horses that appear difficult but are not. In: Proceedings of the 20th Annual Scientific Meeting of ECVS. Ghent, Belgium. pp 96-99. (
- 1997) What is your diagnosis? Well-circumscribed osseous or enamel opacities associated with the caudal root of the mandibular third premolar and rostral root of the fourth premolar. Odontoma. J. Am. Vet. Med. Assoc. 211, 851-852. , and (
- 1996) Removal of the premaxillae and rostral portions of the maxillae of a horse. J. Am. Vet. Med. Assoc. 209, 118-119. , , and (
- 1979) Ossifying ameloblastoma in a horse. Aust. Vet. J. 55, 498-500. , and (
- 2008) Cyclooxygenase-2 expression in equine tumors. Vet. Pathol. 45, 825-828. , , and (
- 1999) Comparison of perioperative versus postoperative intratumoral administration of cisplatin for treatment of cutaneous sarcoids and squamous cell carcinomas in horses. J. Am. Vet. Med. Assoc. 215, 1655-1660. , , , , and (
- 2007) Long-term outcome associated with intratumoral chemotherapy with cisplatin for cutaneous tumors in equidae: 573 cases (1995-2004). J. Am. Vet. Med. Assoc. 230, 1506-1513. , , , , and (
- 1934) A large osteosarcoma of the mandible. J. Am. Vet. Med. Assoc. 84, 118-119. and (
- 2012) Management of primary ameloblastoma of the jaw: a 15 years' experience. Minerva Stomatol. 61, 175-182. , , and (
- 1968) Equine mandibular adamantinoma. J. Am. Vet. Med. Assoc. 153, 454-457. and (
- 2005) Mandibulectomy and maxillectomy. Vet. Clin. N. Am.: Small Anim. Pract. 35, 1009-1039. (
- 1936) Adamantinoma polycysticum ossificans am Unterkiefer eines Pferdes. Dtsch Tierarztl. Wochenschr. 46, 113-117. (
- 1998) Cobalt 60 radiotherapy for treatment of squamous cell carcinoma of the nasal cavity and paranasal sinuses in three horses. J. Am. Vet. Med. Assoc. 212, 848-851. , , , , , , , , , , , and (
- 2012) [Fibrous dysplasia]. Orthopade 41, 993-1006. (
- 2011) Early diagnosis may hold the key to the successful treatment of nasal and paranasal sinus neoplasia. Equine Vet. Educ. 23, 441-447. and (