Managing challenging oral cases in dogs: part II (Proceedings)

Unusual oral lesions that may require surgical treatment include: osteomyelitis and bone sequestra, dentigerous cyst, mucoceles, lip avulsions inability to open or close the mouth, management of electrical cord injuries and severe tongue lesions requiring partial glossectomy.

Osteomyelitis and bone sequestra occur infrequently in dogs and cats and may be a complication of advanced periodontal disease, extraction complications or maxillofacial fractures. Several cases of severe osteomyelitis with secondary necrosis of bone have occurred in Cocker Spaniels and less frequently in other breeds. These animals are usually presented for examination because of fetid breath, severe oral pain, facial swelling, reluctance or inability to eat and have severe purulent nasal discharge if the osteomyelitis or bone sequestra are located in the maxilla. Dental radiography is performed to assist in the diagnosis. All necrotic bone and teeth in necrotic bone must be removed and the surrounding bone must be curettaged to the level of healthy, bleeding bone. Intraoperative samples should be collected and submitted for bacterial culture and sensitivity testing. Samples of tissue should also be submitted for histopathologic examination to rule out the possibility of an underlying neoplasia. The surgical site should be liberally flushed with sterile saline and closed with a mucoperiosteal flap using 3-O PDS in a simple interrupted pattern.

Dentigerous cysts occur infrequently in dogs, however, the diagnosis of dentigerous cysts should be a primary consideration in young dogs presenting with fluid filled oral swellings. Additionally, the possibility of an iatrogenic dentigerous cyst must be considered in those dogs in which a deciduous tooth was extracted or a traumatic episode had occurred in a puppy and subsequently the permanent tooth fails to erupt. Definitive diagnosis of a dentigerous cyst is based on history, physical examination, radiography, and histopathologic examination. Dentigerous cysts arise from the cellular components of the developing dental follicle. The cyst contains one or more embedded teeth and usually surrounds the coronal aspect of the tooth. As the tooth bud continues to develop but fails to erupt, the cyst becomes filled with fluid. Fluid pressure within the cyst results in a smooth-bordered radiolucent cavity typically adjacent to the cementoenamel junction as viewed radiographically. The treatment of a dentigerous cyst usually involves surgical extraction of the affected tooth and thorough removal of the entire epithelial lining of the cyst wall which is submitted for histopathologic examination. Complete excision of the tooth and the cystic epithelium is curative.

There are four pairs of major salivary glands in the dog and cat. The major salivary glands are: the parotid, mandibular, sublingual, and zygomatic salivary glands.

The parotid salivary gland is located at the base of the auricular cartilage. The parotid duct is formed by 2 or 3 short radicles and passes lateral to the masseter muscle. It enters the oral cavity opposite the maxillary fourth premolar. The mandibular salivary gland is located at the junction of the maxillary and linguofacial veins. It is covered by a dense capsule. The mandibular duct leaves the medial surface of the gland and courses between the masseter muscle and mandible laterally and the digastricus muscle medially and then passes over the digastricus muscle laterally. The mandibular duct enters the mouth on a papilla lateral to the rostral end of the frenulum. The sublingual salivary glands consist of a caudal portion located at the rostral pole of the mandibular gland and a rostral portion which lies directly below the oral mucosa lateral to the tongue. The sublingual salivary duct originates at the caudal portion of the gland and accompanies the mandibular duct to a common or separate opening on the papilla at the rostral end of the frenulum. The zygomatic salivary glands are located ventral to the zygomatic arch. They are found only in carnivores. The major zygomatic duct opens about one centimeter caudal to the parotid papilla on a ridge of mucosa and minor ducts open on this ridge caudal to the major duct. In addition to the major salivary glands, there are small clusters of seromucus secretory units in the submucosa of the oral cavity known as minor salivary glands. These minor salivary glands are named according to their location (lingual, labial, buccal, palatine).

Salivary mucoceles or sialoceles result from damage to the duct or gland with leakage of saliva into the surrounding tissues. Salivary mucoceles are lined by inflammatory connective tissue and do not have an epithelial lining that is present in cysts. The cause of salivary mucoceles is rarely identified, although blunt trauma (choke chains), foreign bodies, and sialoliths have been suggested. Saliva tends to take the path of least resistance, most commonly accumulating in the cranial cervical or intermandibular region and less frequently accumulating in the sublingual area, pharyngeal tissues, and retrobulbar space. The most common sites for mucoceles include: cervical mucoceles and ranulas, and less commonly pharyngeal and zygomatic mucoceles. Ranulas are located in the sublingual tissues on the floor of the mouth on one side of the tongue.

The clinical signs associated with cervical mucoceles depend on the location of the mucocele. Animals with cervical mucoceles are presented because of a soft, fluctuant, nonpainful swelling in the cervical area. An animal with a ranula will often be presented because of abnormal tongue movements, reluctance to eat, dysphagia, or blood-tinged saliva. Animals with pharyngeal mucoceles usually are presented because of difficulty breathing or swallowing. Animals with zygomatic mucoceles present because of exophthalmos, divergent strabismus and a fluctuant non-painful swelling in the orbital area.

Diagnosis of mucoceles are usually based on palpation and aspiration of a clear, viscous blood-tinged to light brown fluid. Aspiration of mucoceles should be performed under aseptic conditions to prevent the development of an infected mucocele. Aspirated fluid reacts postitively with a mucus-specific stain such as periodic acid-Schiff, confirming the diagnosis. Sialography can also be utilized to evaluate the patency of a salivary duct and can help confirm the diagnosis of mucoceles. Sialography however is utilized infrequently because general anesthesia is required to perform the necessary duct cannulation for injection of the water-soluble radiopaque dye and cannulation of the duct can be difficult to perform and it is usually not necessary for diagnostic purposes.

Various types of treatment of mucoceles have been recommended including: aspiration, resection of the mucocele, surgical excision of involved glands and drainage of the mucocele, and marsupialization. Aspiration alone of the mucocele is inadequate since the mucocele will reoccur. Resection of the mucocele is inappropriate since the lining of the mucocele is nonsecretory and the mucocele will reoccur.

Surgical excision of the involved salivary glands and drainage of the mucocele is the treatment of choice for mucoceles since this prevents recurrence of the mucocele. Cervical mucoceles are the most commonly occurring mucoceles and they are treated by removing the mandibular and sublingual salivary glands on the affected side. Mucoceles are usually unilateral, however, in some cases ventrally located cervical mucoceles may be difficult to determine which side is affected. Positioning of the animal in dorsal recumbency usually results in shifting of the mucocele to one side. Gentle manual pressure on the mucocele may result in expansion of the swelling ventral to the ear or next to the tongue on the affected side. If after thorough examination the affected side can still not be determined the mucocele can be incised and evaluated from the inside at the time of sialadenectomy. The affected side usually has a tunnel or tract extending dorsally towards the affected salivary gland while the unaffected side is rounded and smooth. If the affected side can not be determined bilateral removal of the sublingual and mandibular salivary glands is recommended. Removal of these glands bilaterally does not result in clinically significant reduction of saliva production.

Removal of the mandibular and sublingual salivary glands is achieved through a lateral approach. After the affected side is determined a skin incision is made from the junction of the maxillary and linguofacial veins to the angle of the mandible. The mandibular gland is located and an incision is made in the capsule of the mandibular and caudal sublingual gland. The mandibular salivary gland is then bluntly dissected from the capsule ligating and severing arteries and veins that enter the dorsomedial aspect of the gland. The dissection of the sublingual gland is continued rostrally between the masseter and digastricus muscles. The gland and ducts are clamped and ligated as far rostrally as possible with 3-0 PDS. The capsule and the subcutaneous tissue and skin are closed routinely. A penrose drain should be placed in the most ventral aspect of the mucocele.

A sublingual mucocele or ranula is a collection of saliva in the sublingual tissues caudal to the openings of the sublingual and mandibular salivary ducts. Ranulas may be treated by marsupialization which involves removal of an elliptical, full thickness section of the mucocele wall and suturing the granulation tissue lining to the sublingual mucosa to encourage drainage. If the ranula recurs removal of the mandibular and sublingual salivary glands is recommended.

Pharyngeal mucoceles are treated by resection of the mandibular and sublingual salivary glands and excision of redundant pharyngeal tissue with marsupialization to prevent airway obstruction after evacuation of the mucocele.

Zygomatic salivary gland excision is recommended for the treatment of zygomatic mucoceles. The zygomatic salivary gland is excised through an incision along the dorsal aspect of the zygomatic following removal of the dorsal aspect of the zygomatic arch using rongeurs. The globe is retracted dorsally to expose the zygomatic salivary gland beneath the periorbital fat. The gland is retracted dorsally, the vessels supplying the gland are ligated and the gland is removed. The palpebral fascia is sutured to the periosteum of the zygomatic arch and the subcutaneous tissues and skin are closed routinely.

Complications associated with sialadenectomy include recurrence of the mucocele that is caused by incomplete removal of the affected salivary gland. Treatment includes removal of residual glandular tissue.

Dogs with pharyngeal mucoceles typically are presented because of difficulty breathing or swallowing. Confirmation of pharyngeal mucoceles is made on oral examination and aspiration of a clear or blood-tinged, ropey fluid that is consistent with saliva. The animal should be preoxygenated if possible prior to induction and entubated rapidly to prevent anoxia secondary to obstruction of the upper airway by the pharyngeal mucocele. Pharyngeal mucoceles are treated by marsupialization of the mucoceles and removal of the ipsilateral mandibular and sublingual salivary glands.

Lip avulsions can occur secondary to trauma. Lower lip avulsions occur more frequently then upper lip avulsions. They are treated by surgical preparation, flushing and liberal debridement of the wound prior to closure with absorbable monofilament suture (Monocryl) in a simple interrupted pattern between the teeth. Incorporation of the periosteal layer while placing sutures can strengthen the repair. Sutures may be placed through a interdentally preplaced hypodermic needle. Collars or basket muzzles placed postoperatively may help prevent postoperative dehiscence.

Several pathologic conditions in the dog can cause a dog to be unable to open the mouth. These conditions include masticatory muscle myositis, adhesion of the zygomatic arch to the ramus of the mandible following trauma or other adhesion between the maxilla and mandible, neoplasia in the region of the temporomandibular joint and craniomandibular osteopathy.

Several pathologic conditions in the dog can cause a dog to be unable to close the mouth. These conditions include idiopathic trigeminal neuropathy also known as canine dropped jaw syndrome and displacement of the coronoid process lateral to the rostral part of the zygomatic arch in dogs with dysplastic temporomandibular joints. Displaced teeth maloccluding with the opposite dental arch may prevent proper closing of the mouth. Foreign bodies wedged over the teeth may also prevent proper closing of the mouth.

Chewing on electrical cords is the most common cause of electrical injuries in dogs and cats. Electrical burns occur primarily on the lips, gingiva, palate and tongue. Initially affected areas may appear charred, pale gray or tan. Edema occurs one to 2 days following the injury. The full extent of the injuries may not be apparent for 2 to 3 weeks. Treatment of patients with electrical injuries includes assessment for pulmonary edema and treatment with diuretics, aminophylline and morphine. Repair of damaged tissues should be delayed until the full extent of the injuries is firmly established. Minor injuries often heal by second intention. Oronasal fistulas should be repaired with appropriate mucoperiosteal flaps. Necrotic bone must be debrided and teeth affected by electrical injuries should be appropriately treated.

Partial glossectomy may be necessary in dogs with extensive tongue trauma or tongue tumors. A type of trauma that may necessitate a partial glossectomy includes trauma caused by paper shedders. The most common malignant tongue tumor in dogs is a squamous cell carcinoma. A previous report in which major partial glossectomies were performed in five dogs demonstrated that major partial glossectomies were well tolerated by dogs and partial glossectomies may be viable treatment options for aggressive tongue tumors and other conditions that render the tongue unsalvageable. Performance of a partial glossectomy involves amputation of the tongue caudal to the lesion and in the cases of lingual squamous cell carcinomas up to 2cm caudal to the lesion to help insure clean surgical margins. To perform a partial glossectomy a surgical marker is used to mark the proposed glossectomy site. A Doyen clamp may be placed cranial to the resection site to help prevent backbleeding during the surgical procedure. The amputation is begun on one side of the tongue and vessels are ligated as they are encountered advancing the incision across the tongue while closing the suture site intermittently. The mucosa of the dorsal aspect of the tongue is sutured to the mucosa of the ventral aspect of the tongue in a simple interrupted pattern. Adjunctive therapy should be considered in these cases because of the possibility of lymphatic and vascular invasion associated with lingual squamous cell carcinomas.

References:

Manfra Marretta S. Maxillofacial surgery. Vet Clin North Amer (Small Anim Pract) 28(5):1285-1296, 1998.

Hedlund CS. Surgery of the oral cavity and oropharynx. In: Fossum TW, ed. Small Animal Surgery; 2nd ed, St. Louis: Mosby; 274-306, 2002.

Harvey CE, Emily PP. Oral surgery. In: Harvey CE, Emily PP, eds. Small Animal Dentistry. St. Louis, Mosby; 312-377, 1993.

Manfra Marretta S. Dentistry and diseases of the oropharynx. In: Birchard SJ, Sherding RG, eds. Saunders Manual of Small Animal Practice, 2nd ed, Philadelphia: WB Saunders; 702-725, 2000.

Dvorak LD, Beaver DP, Ellison GW, Bellah JR, Mann FA, Henry CJ. Major glossectomy in dogs: A case series and proposed classification system. Jour Amer Anim Hosp Assoc 40:331-337, 2004.