By Andrew Goodman, DVM, DACVS
Mandibulectomy and maxillectomy are relatively common procedures in the canine patient, primarily for treatment of oral neoplasia. The ability for dogs to tolerate excision of large portions of the jaw allows for improved local control of disease. An understanding of tumor behavior enables owners to make informed decisions regarding care. An overview of common malignant canine oral tumors and their surgical treatment is provided.
Figure 1: Dr. Goodman outlines a mass to be excised.
The lower jaw is made up of right and left mandibles. The body of the mandible contains the teeth, the ramus is the vertical component that associates with the skull via the temporomandibular joint, and the two portions are connected via the angle of the mandible. The two mandibles are connected via a central fibrous symphysis. The inferior alveolar artery is the primary blood supply to the mandible which enters via the mandibular foramen on the medial aspect of the angle of the mandible and is a branch of the maxillary artery. This is the primary artery to be controlled during mandibulectomy and runs within the mandibular canal and exits the mental foramen rostrally (caudal to the canine tooth). The mandibular nerve is a branch of the trigeminal nerve and also runs within the mandibular canal. The sublingual papillae open midline caudal to the symphysis. The upper jaw is comprised of the maxilla, incisive, and nasal bones. The palatine arteries course on either side of the hard palate halfway between the midline and teeth. The infraorbital artery runs through the caudal nasal passage, through the infraorbital canal of the maxilla, and exits laterally through the infraorbital foramen near the upper fourth premolar. The infraorbital nerve courses adjacent to the artery. The parotid papilla is just lateral to the upper fourth premolar. Salivary ducts and papillae can be ligated without adverse consequences.
The most common oral tumors of dogs (in descending level of frequency) are malignant melanoma, squamous cell carcinoma, fibrosarcoma, osteosarcoma, and acanthomatous ameloblastoma. Ameloblastomas arise from odontogenic epithelium rather than the periodontal ligament; and although this tumor is a local disease, complete excision is necessary to prevent recurrence. Following are a selection of journal articles which provide review of oral neoplasia behavior which is helpful for understanding prognosis both for surgical planning and owner discussion.
Figures 2, 3, 4: Patient immediately following mass removal.
- Tuohy JAVMA 2014: MST Sx only 874d; Sx + chemo- 396d; Mets at dx- 131d after sx; no chemo benefit
- Boston JAVMA 2014- Sx + chemo- 335d; Sx alone- 352d; 1yr survival 29%; LN biopsy recommended vs. FNA; no chemo benefit
- Grosenbaugh AJVR 2011- Vx after sx: 464d vs. 156d w/o vx- VXS helpful
- Ottnod Vet Comp Onc 2013- MST 500d overall; No improvement with vaccine vs. sx alone
- Freeman JVIM 2008- Radiation (hypofractionated) and chemotherapy (carboplatin or cisplatin) for treatment for incompletely excised oral melanoma; MST 363d; 15% local recurrence median 139d; 51% metastasis median 311d
Malignant melanoma is an aggressive disease process with a tendency toward metastasis (local lymph nodes-mandibular, medial retropharyngeal, parotid- and lungs). Survival times have improved vs. previous literature with wide surgical resection. Chemotherapy seems to be less effective compared to other tumors. There is some controversy regarding efficacy of the melanoma vaccine, but one paper (Grosenbaugh) had a significant survival advantage with use. Radiation +/- chemotherapy may be indicated with incomplete excision. Sampling of local lymph nodes and appropriate staging is necessary, as significantly reduced outcomes have been noted with higher disease stage. Typically pigmented tumors, but can be amelanotic. Often older small breed dogs, but can be large breeds as well.
Squamous Cell Carcinoma
- Boria JAVMA 2004- Cisplatin + Piroxicam; MST 237d; 5/9 remission
- Fulton JAVMA 2013- 0% alive at 1yr without surgery; 29% metastasis; surgery decreased risk of death by 91.4%
- Riggs JAVMA 2018- Clean surgical excision MST not reached; dirty surgical excision MST 181d; dirty surgical excision with radiation MST 2,051d; 5% metastasis; 23% local recurrence
- Kosovsky Vet Surg 1991- Surgery alone (partial mandibulectomy); 91% alive at 1 year; medial progression-free interval 26 months (6-84 months)
- Theon JAVMA 1997- Radiation treatment alone; medial progression-free interval of 36 months; better outcomes with smaller tumors
Squamous cell carcinoma often affects older large-breed dogs and commonly has a flat/ulcerated appearance. The tumor may appear small but can extend significantly into underlying bone. In general, non-tonsillar oral SCC has a relatively low metastatic rate, but staging should still be completed as spread is possible. Aggressive surgical resection is recommended and can be possibly curative with clean excision. Radiation treatment can be considered for non-resectable masses or if incomplete excision has been obtained and second surgery declined. Chemotherapy, including Piroxicam, can be considered for non-resectable tumors or for palliation, however surgical excision should be considered if at all possible.
- Gardner VCOT 2013- Overall MST 488d; Sx + Rad- 505d; Sx only- 220d; Rad only- 204d; Golden Retreivers; 67% maxilla; caudal location common
- Frazier VCOT 2012- Overall 743d; Sx only- 1024d; Sx + rad- 576d; 24% mets; 24% local recurrence
- Martano The Veterinary Journal 2018- Improved outcome recent papers with MST of 247-743 days vs. 30-540 days papers before year 2000 (better surgical planning?); up to 57% local recurrence rate; late metastasis 10-14% cases
Fibrosarcoma is common in middle age to older large breed dogs, especially golden and Labrador retrievers. A caudal maxillary location is common. A variant is the histologically low-grade, biologically high-grade fibrosarcoma which is much more aggressive than biopsy would predict. In general, local recurrence is the most common complication, especially given difficulty in obtaining clean margins with more caudal locations. Metastasis is not uncommon and staging is important. Radiation treatment can be considered, especially as an adjunct to incomplete surgical excision. Chemotherapy is generally less indicated for this tumor as local control is the most common issue, however it may be considered in the face of metastatic disease.
- Selmic JAVMA 2014- Sx- 329d; Sx + Rad- 162d; Palliative care- 35d; 38.5% Met; 498d to met (usually lungs); improved outcome with tumor-free margins
- Sarowitz JSAP 2017- Sx- 209d; 22% met; 29.6% local recurrence
- Farcas V Comp Onc 2014- 4.6-64months MST (dep on study); better outcome with complete excision
- Coyle V Comp Onc 2013- MST 525d; w/ chemo 935d; 58% mets; Lower grade and chemo = better outcome
Osteosarcoma generally was a better outcome compared to appendicular osteosarcoma as decreased metastatic potential. The MST improves significantly with complete excision. Recurrence is more likely when the disease is in a location that precludes wide excision, such as the calvarium or caudal maxilla. Lower grade, complete surgical excision, use of chemotherapy have all been associated with improved outcome.
Radiographic imaging of the affected area is important to determine degree of bone involvement. Dental radiographs show evidence of lysis in 60-80% of oral tumors, however tend to underestimate the degree of bone involvement as a significant degree of mineral loss is required before lysis is evident. CT is more sensitive for detecting bone loss as well as the degree of tumor soft-tissue involvement. Dental radiographs may be more sensitive than CT for detecting pathology within individual teeth. CT can also be used for staging the thorax and abdomen concurrently (although thoracic radiographs +/- abdominal ultrasound can be considered). Dental radiographs can also be utilized after mandibulectomy or maxillectomy to determine whether tooth roots have been completely extracted. 3D reconstruction of CT images can be considered for masses in difficult-to -ccess locations for the purposes of surgical planning or specific implant creation. MRI is superior to CT for soft tissue imaging and may be especially helpful should the mass extend toward or invade important neurologic structures. Pre-operative wedge biopsy can be performed at the time of imaging and should occur in a location within the mass that will be excised at the time of definitive treatment. The regional lymph nodes include the mandibular, parotid, and medial retropharyngeal. FNA of regional lymph nodes can be performed, though only the mandibular is easily accessible. Enlarged size of the mandibular lymph nodes on palpation was only 70% sensitive and 51% specific in one study on malignant melanoma. When all three sets of nodes were removed concurrent with tumor excision in one study, only 54.5% of metastatic lymph nodes were the mandibular nodes. Advanced imaging (CT, MRI) is also helpful in determination of lymph node metastasis (i.e. contrast enhancement, size/asymmetry, etc…).
Through a combination of physical exam, signalment, pre-operative biopsy, and appropriate staging, the owner can be counselled about the prognosis, whether or not surgical excision is possible, what form of surgery would be required, and the likelihood of the need for ancillary treatment (i.e. radiation, chemotherapy). Advanced imaging has enhanced our ability to stage accurately and to plan an appropriate level of surgical excision, which has improved outcome.
Forms of mandibulectomy include unilateral rostral, bilateral rostral, segmental, complete, or combinations of the above. Local nerve blocks should be used as appropriate. The anatomic structures to be transected should be appreciated, especially the large vessels previously discussed. An attempt should be made to ligate the inferior alveolar artery prior to transection upon entry into the mandibular canal. Temporary or permanent ligation of the carotid arteries can be considered in the case of caudal mandibulectomy and maxillectomy where vascular control may be difficult and may result in significant hemorrhage. A step-by-step description of this technique has been published in the Journal of Veterinary Dentistry by Dr. Alice Ekerdt Goodman and myself (Goodman JVD 2016). Ancillary hemorrhage control can be achieved with the use of electrocautery and/or gelatin sponges. Bone should be transected with a Hall air drill, sagittal saw, or dental drill a minimum of 1cm for the edge of lysis on CT, although 2cm is recommended for aggressive neoplasia. As dental radiographs are likely less sensitive for identifying lysis compared to CT, a more aggressive approach may be indicated. Osteotomes are typically recommended only for finishing the ostectomy, as there is a risk of splitting the bone, especially in the mandible. Osteotomy should be completed through the root of a tooth already planned to be removed if possible — this decreases the likelihood of damage to the caudal tooth and the root remnant can be removed without difficulty after bone excision.
Rostral mandibulectomy includes either removal or sparing of the symphysis. If the symphysis remains intact, there may be a reduction in post-operative pain however this should only be elected based upon the biology of the mass being excised as dogs do well with excision of the symphysis as well. Stabilization of the mandibles is not indicated even with excision of the symphysis. Bone edges should be beveled prior to gingival closure and the tissue closed in a tension-free manner. Segmental or central mandibulectomy sites can typically be closed without tension, suturing the gingiva to the labial and sublingual mucosa. A mucosal flap can be elevated as necessary. For caudal excisions and complete mandibulectomy, incision of the lip commissure can be completed to improve visualization. Removal of the zygomatic arch can also be considered for this purpose. Care should be taken to keep in mind the soft tissues involved in the tumor and that appropriate margins are obtained in this manner as well. Some creativity in soft tissue reconstruction may be required in more advanced cases (skin flaps, commissure mobilization, etc…). Intra-oral suture type should be monofilament rapidly absorbable — typically 3-0 or 4-0 Monocryl is used.
Maxillectomy types can be similarly described. Bleeding vessels to be controlled include the major palatine arteries and the infraorbital arteries. Diffuse hemorrhage is common during transection of nasal turbinates. Caudal maxillectomies are especially at risk for severe hemorrhage and osteotomies of the caudal locations should be performed after all other transections. Bleeding is often best controlled after complete bone segment removal. Caudal maxillectomy visualization may be improved by combining the intraoral approach with a dorsal skin incision. A cantilever suture may be indicated to decrease nasal drooping with bilateral rostral maxillectomy. Closure of internal nasal tissues is not necessary after rostral maxillectomy.
Water and food can be offered the next day. Depending on the type and extent of bone excision, some degree of diet alteration may be indicated. Commonly, soft dog food is utilized for two weeks which may need to be hand fed as meatballs initially to aid in prehension. Owners should be warned that initially, eating and drinking often is messy, though this improves after the first 1-2 weeks. An e-collar is sometimes necessary if extra-oral sutures are present. Chew toys should be avoided for 4 weeks. Swelling under the tongue after a mandibulectomy is common and often resolves within 1-2 weeks after surgery. Aspiration of this swelling is unlikely to be helpful and it is also unlikely to represent a ranula. Common complications include mandibular drift for lateralized mandibulectomy, oronasal fistula, epistaxis, and nasal congestion after maxillectomy, dehiscence (especially after bilateral rostral mandibulectomy), and damage to nearby teeth which could require extraction at a later date. Trauma to tissues overlying a tooth could also require crown amputation or tooth extraction at a later date. Antibiotic use is controversial — these are contaminated procedures, but the likelihood of infection is low in the mouth given its impressive blood supply. If antibiotics are elected, common choices include Clindamycin (5.5-11mg/kg BID) and Clavamox (13.75mg/kg BID). Alternatively, antibiotics may be started only if there is any sign of infection during the recovery period. Consultation with an oncologist should be considered for cases of malignant disease. A plan/timeline for monitoring for local tumor recurrence and/or metastasis should be created with the owners. The appearance of the patient after surgery should be discussed with the owner beforehand. A helpful website that has many before and after images after various forms of oral surgery is www.animalcancersurgeon.com by Dr. Julius Liptak who is a veterinary oncologic surgeon.
Referral to Angell is always welcome for consultation. With specialists in surgery, dentistry, medical oncology, radiation oncology, and 24-hour emergency doctor coverage, we are well-equipped to provide treatment of even the most complicated cases.
References not included in above text:
- Tobias KM & Johnston SA (2012). Veterinary Surgery: Small Animal. St. Louis, Missouri: Elsevier Saunders
- Verstraete FJM & MJ Lommer (2012). Oral and Maxillofacial Surgery in Dogs and Cats. St. Louis, Missouri: Elsevier Saunders
- Bojrab RM (1983). Clinical Techniques in Small Animal Surgery (2nd ed.). Philidelphia, Pennsylvania: Lippincott Williams & Wilkins
- Pavletic MM (2010). Atlas of Small Animal Wound Management and Reconstructive Surgery (3rd ed.). Ames, Iowa: Wiley-Blackwell
- Liptak, Julius. http://www.animalcancersurgeon.com/ (2019, March 3rd).