History and Physical Examination Findings
A 9-year-old 17.2-kg (37.8-lb) spayed female Shetland Sheepdog was referred to a veterinary dental center for evaluation of an oral mass affecting the left maxilla. The dog had been treated for a similar, although much smaller, lesion at the same location 14 months prior to this examination. The previous lesion involved the left maxillary fourth premolar tooth. On physical and radiographic examination 14 months earlier, this tooth was presumed vital on the basis of an apparently normal periodontal ligament space, lack of a periapical lucency, and a pulp cavity that was similar in diameter to that of the contralateral maxillary fourth premolar tooth.1 A radiolucent lesion with a smooth, thin rim of sclerotic bone had been detected in the furcation of the left maxillary fourth premolar tooth, and the dog had been treated by surgical extraction of the left maxillary fourth premolar tooth and curettage of the apparently cystic lesion. The soft tissue lining of this lesion was submitted for histologic analysis. Histopathologic findings were consistent with a keratinizing odontogenic cyst.
Oral examination of the awake patient 14 months after the previous treatment revealed a hard, smooth, 2.5- to 3.0-cm-diameter mass on the buccal aspect of the left maxilla at the site of the previously extracted left maxillary fourth premolar tooth. Gentle palpation of the mass did not elicit signs of pain. Visual examination of the palatal mucosa revealed no noticeable abnormalities. A calculus index of 2 and generalized, mild inflammation of the marginal gingiva were noted.2 Results of general physical examination and hematologic evaluation (a CBC and serum biochemical analysis) were unremarkable. The dog was anesthetized, and lateral bisecting angle and occlusal intraoral radiographs of the left maxilla were obtained (Figure 1).
Left lateral bisecting angle (A) and occlusal (B) intraoral radiographs of the affected region of the maxilla in a 9-year-old Shetland Sheepdog evaluated because of an oral mass at the former site of the left maxillary fourth premolar tooth, which had been surgically extracted as part of treatment for a cystic lesion 14 months earlier. The occlusal radiographic image in panel B has been cropped to highlight the left maxilla.
Citation: Journal of the American Veterinary Medical Association 248, 11; 10.2460/javma.248.11.1241
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Diagnostic Imaging Findings
Examination of the lateral radiographic images revealed that the left maxillary fourth premolar tooth had been completely extracted, with no root elements remaining (Figure 2). There was a large, well-demarcated, radiolucent area at the previous extraction site. This area extended from the distal root of the left maxillary third premolar tooth to the alveolar margin mesial to the left maxillary first molar tooth. A well-defined cortical border surrounded the radiolucent area; this thin, sclerotic rim of bone extended approximately 2.5 to 3.0 cm palatally and buccally. A loss of the lamina dura from the apical third of the distal root of the left maxillary third premolar tooth was evident; however, the periodontal ligament space appeared normal in that location. There was no evidence of external root resorption affecting the left maxillary first molar tooth or the distal root of the left maxillary third premolar tooth.
On the occlusal view, the lesion was also well demarcated and observed to extend palatally to approximately the level of the palatal root of the left maxillary first molar tooth (Figure 2). The formation of a well-defined corticated border (characterized by a fairly uniform, thin, radiopaque line) and geographic bone loss were consistent with a slowly expansile growth.3,4 The radiographic appearance of the lesion supported a presumptive diagnosis of a recurrence of the previously treated keratinizing odontogenic cyst, which was suspected on the basis of the history and physical examination findings. A CT scan was recommended to more clearly define the borders of the lesion and aid in surgical planning but was declined by the client because of financial constraints.
Same radiographic images as in Figure 1. A large, unilocular radiolucent area with a well-defined, thin, sclerotic rim of bone (arrowheads), consistent with a slowly expansile cystic lesion, is present between the distal root of the left maxillary third premolar tooth and the alveolar margin mesial to the left maxillary first molar tooth. Notice the loss of the lamina dura associated with the apical portion of the third premolar tooth (arrows). There is no evidence of root resorption of the left maxillary third premolar tooth.
Citation: Journal of the American Veterinary Medical Association 248, 11; 10.2460/javma.248.11.1241
Treatment and Outcome
On the basis of the presumptive diagnosis, the client elected treatment by wide local excision with curative intent. Lactated Ringer solution (5 mL/kg/h [2.3 mL/lb/h]) was administered for supportive care. Buprenorphine (0.02 mg/kg [0.009 mg/lb], IM) and midazolam (0.2 mg/kg [0.09 mg/lb], IM) were administered for analgesia and mild sedation 20 minutes prior to anesthesia. The patient was anesthetized, and a left caudal maxillary nerve block was performed. Clindamycin (5.5 mg/kg [2.5 mg/lb]) was administered IV. A partial maxillectomy was performed; the excision extended from the furcation of the left second premolar tooth to the furcation of the left first molar tooth (Figure 3). After surgery, buprenorphine was administered (0.01 mg/kg [0.005 mg/lb], IM) and a fentanyl patch (25 μg/h) was placed on the thorax. The dog was discharged from the hospital on the same day with an Elizabethan collar and clindamycin (5.9 mg/kg [2.68 mg/lb], PO, q 12 h for 7 days). The client was given instructions to return the patient in 2 weeks for reexamination and removal of the Elizabethan collar, and reexamination and intraoral radiography under anesthesia was scheduled to be performed in 6 months.
Intraoperative image of the cyst as it was removed en bloc with a section of the left maxilla. A smooth, white rim of bone is visible on the palatal aspect of the cyst within the ostectomized segment. This rim of bone corresponds to the sclerotic border seen on the radiographic images.
Citation: Journal of the American Veterinary Medical Association 248, 11; 10.2460/javma.248.11.1241
On histopathologic examination, the lesion consisted of a cyst surrounded by a rim of remodeled, compressed, lytic bone and lined by well-differentiated stratified epithelium undergoing keratinization with small areas of parakeratinization (Figure 4). The cyst lumen was filled with keratin. Evidence of mild, chronic inflammation was present, with a predominance of macrophages surrounding the cyst wall. This histopathologic appearance was identical to that of the lesion excised 14 months earlier and confirmed recurrence of the previous keratinizing odontogenic cyst. With clean surgical margins (6 to 9 mm) on histopathologic examination, the cyst was considered completely excised by the second surgery. At follow-up 10 months later, there was no evidence of cyst recurrence. Continued monitoring of the surgical area was recommended.
Photomicrograph of a section of the cyst in Figure 3 showing a small area of parakeratinization (arrow) of the epithelial lining. Most of the lining is composed of stratified orthokeratotic squamous epithelium. H&E stain; bar = 100 μm.
Citation: Journal of the American Veterinary Medical Association 248, 11; 10.2460/javma.248.11.1241
Comments
It is important for veterinarians to recognize the radiographic appearance of cystic lesions in the bones of the oral cavity. These are usually round or oval; the common radiographic features include a periphery that is well-defined and corticated.3 Cyst contents can be totally radiolucent or have evidence of dystrophic calcification.3 Cysts may appear radiographically to have a scalloped border or internal septae.3 Cysts in the bones of the oral cavity typically grow slowly and can cause displacement or resorption of adjacent teeth. Evidence of root resorption commonly includes a very sharp, curved radiographic appearance of the affected tooth root.3 Cysts can grow within the cortical borders of the bone, or they can expand the cortical border lingually, buccally, or in both directions.3
Odontogenic cysts stem from remnants of epithelium of odontogenic origin. These can be developmental or can result from chronic inflammation.5 There have been a number of different types of odontogenic cysts identified in veterinary medicine; dentigerous (follicular) cysts, radicular cysts, lateral periodontal cysts, odontogenic keratocysts, and odontogenic parakeratinized cysts have all been reported in dogs.5 The nomenclature and description of odontogenic cysts are often extrapolated from human medicine and can be confusing for many practitioners owing to the continually evolving nature of our understanding of these conditions. Additionally, a variety of odontogenic and nonodontogenic neoplasias can appear radiographically as cystic lesions in the bones of the oral cavity. The most commonly encountered odontogenic cyst in dogs is the dentigerous cyst, which accounted for 29 of 41 (71%) identified cases in 1 study.5 Dentigerous cysts typically affect unerupted or impacted canine and first premolar teeth.5 In the dog of the present report, a form of cyst was identified that differed substantially in appearance and biological behavior from the more common dentigerous cyst.
The cyst identified in our patient partly resembled a canine odontogenic parakeratinized cyst because of the presence of areas of parakeratinized epithelium.5 However, the more prominent areas of orthokeratinized epithelium and the keratin-filled cyst lumen were distinctive in this case, and there were some features that are typically associated with orthokeratinizing odontogenic cysts in human patients. Some pathologists consider orthokeratinizing odontogenic cysts to be a variant of odontogenic keratocysts.6 Similar to the lesion seen in this patient, orthokeratinizing odontogenic cysts typically are not associated with resorption of adjacent tooth roots and are frequently characterized by prominent buccal bone expansion.6 The clinical and histopathologic findings for the dog of this report may have most closely resembled those of an orthokeratinizing odontogenic cyst but did not entirely match any previously described cystic lesion. The areas of chronic inflammation and parakeratinized epithelium seen in this case have not typically been described for patients with orthokeratinizing odontogenic cysts. An important feature of this case was the recurrence following treatment by surgical extraction of the left maxillary fourth premolar tooth and enucleation with curettage. The difficulty in categorization of the lesion in this patient highlights the need for additional study regarding these rare forms of odontogenic cyst. As more cases are reported, our body of knowledge will expand and potentially shed light on this unusual entity.
During the course of treatment, it is critical to obtain samples for histopathologic assessment to differentiate among the various lesions that have a cystic appearance radiographically. While all such entities have the potential for severe destruction of bone, some have a greater tendency to recur locally with incomplete resection. In rare cases, epithelial cysts have been known to convert to ameloblastoma or malignant squamous cell carcinoma.7 Appropriate treatment and monitoring is dependent upon the histopathologic diagnosis.
Previous surgical treatment of this dog was unsuccessful. Similar conservative treatment has been shown to be associated with a high recurrence rate for some forms of odontogenic cysts in humans.8 The radiographically apparent, sclerotic rim of bone around this lesion was critical in determining the surgical borders for peripheral ostectomy of the entire cystic lesion, which was considered curative in this case. Although declined by the owner of the dog of the present report, additional diagnostic imaging by CT would likely have added to the presumptive diagnosis in this patient prior to surgery. The high-contrast resolution of CT imaging is useful for diagnosing and determining the extent of lesions in the maxillofacial region3 and is a useful tool for surgical planning.
References
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4. Dobson HFriedman L. Radiologic interpretation of bone. In: Fackelman G, ed. Bone in clinical orthopedics. New York: Thieme, 2002;175–202.
5. Verstraete FJMZin BPKass PH, et al. Clinical signs and histologic findings in dogs with odontogenic cysts: 41 cases (1995–2010). J Am Vet Med Assoc 2011;239:1470–1476.
6. MacDonald-Jankowski DSLi TK. Orthokeratinized odontogenic cysts in a Hong Kong community: the clinical and radiological features. Dentomaxillofac Radiol 2010;39:240–245.
7. Barnes LEveson JWReichart P, et al., eds. World Health Organization classification of tumors. Pathology & genetics head and neck tumours. Lyon, France: IARC Press, 2005.
8. Chamberlain TVerstraete FJM. Clinical behavior and management of odontogenic cysts. In: Oral and maxillofacial surgery in dogs and cats. Oxford, England: Saunders-Elsevier, 2012;481–486.
