Presentation Penny, a five-year-old female spayed beagle, was presented for evaluation of periodontal disease and an abnormal lucency noted on dental radiographs in the rostral maxilla. Penny’s primary care veterinarian first noted this lucency during a routine dental cleaning and radiographs. Periodontal bone loss was seen across multiple teeth during that time, and a widened pulp chamber was appreciated on a radiograph of the right maxillary first incisor (tooth 101) with an expansile periapical lucency surrounding the tooth, causing displacement of 101 and adjacent teeth (Figure 1). Due to anesthetic concerns, extractions were limited to tooth 101, and a biopsy was then performed. Biopsy results of the area around tooth 101 showed inflammation and mixed bacteria, with no evidence of neoplasia. Penny was reported to be eating, drinking, urinating, and defecating normally. Figure 1. Intraoral radiograph of the rostral maxilla of a five-year-old beagle. Note the nonvital (as evidenced by wide canal) tooth 101, which has been displaced mesially by a cystic structure with a sclerotic or corticated border, which is a classic radiographic finding of a cyst. Photo courtesy Dr. John R. Lewis Diagnosis Penny was presented for a consultation with my colleague, Kirk Herrmann, DVM, DAVDC. Dr. Herrmann’s exam showed a firm 1 cm x 1 cm x 0.7 cm swelling apical to the mucogingival line in the area of missing teeth 101-102. The palatal mucosa caudal to the incisors normally has a “spongy” feel to it due to the large venous plexus between the mucosa and the bone of the hard palate, but Penny’s palate in this area felt fluctuant, suggestive of a cyst. This, coupled with the history of a nonvital tooth 101 in the area, raised Herrmann’s suspicion of a periapical cyst. A cone-beam CT scan supported the cyst diagnosis as evidenced by an increased density of bone (cortication) immediately adjacent to the cystic structure (Figure 2). Figure 2. Cone-beam CT scan of the maxilla showed a spherical cyst-like lesion with cortication and expansion toward adjacent incisor teeth. Photo courtesy Dr. John R. Lewis The umbrella term “odontogenic cyst” refers to any cyst that arises from epithelium involved in the formation and development of the tooth or periodontal structures. These include dentigerous cysts, periapical cysts, lateral periodontal cysts, odontogenic parakeratinized cysts, and furcation cysts. Dentigerous cysts, which arise due to a tooth's lack of eruption, are the most common type of odontogenic cyst. In our hospital, the next most common type of cyst is likely the furcation cyst, which occurs in the furcation of the maxillary carnassial tooth.1 One study that described 41 cases of odontogenic cysts in dogs found dentigerous cysts to be the most common odontogenic cysts, with no mention of periapical cysts. Submitting the cystic lining to the pathologist will help rule out cyst-like neoplasia, but that will not typically diagnose the type of cyst since most cysts have a similar cell type: stratified squamous epithelium. One exception to this might be keratinized cysts, which also look different clinically. These keratinized cysts contain a thicker (almost caseous in appearance) fluid instead of the straw-colored or brownish-clear fluid of most other odontogenic cysts. Findings Penny’s cyst was enucleated (cystic lining was removed) after extraction of adjacent incisors and lifting a mucogingival flap to expose a white-blue glistening lining (Figure 3). The lining was submitted for histopathology, which showed stratified squamous epithelium consistent with an odontogenic cyst. Figure 3. Intraoperative photograph of the cystic structure of the rostral maxilla. Note the glistening appearance of the cyst lining. Photo courtesy Dr. Kirk Herrmann Periapical lucency seen on dental radiographs can be due to various physiologic or pathologic processes. A physiologic process that is a normal anatomic variation is what has been referred to as a “chevron lucency,” considered to be a normal finding most commonly associated with mandibular first molar teeth and canine teeth. Unlike true periapical pathology, chevron lucencies are not wider than the apex of the root and taper as they traverse further from the apex. The most common cause for a truly pathologic periapical lucency is a granuloma of a nonvital tooth. Granulomas and periapical abscesses differ from a periapical cyst in that the former results in a loss of radiographically perceptible periapical periodontal ligament space in the area of the lucency, whereas the periapical cyst results in prominent periapical sclerosis or cortication (Figure 4). Figure 4. Radiograph of a different patient showing a suspected periapical cyst at the mesial root of tooth 409. The sclerotic or corticated border of the cyst is very pronounced in this patient. When this appearance is noted, exploration at the time of tooth extraction is warranted to remove any cystic lining at the apex to try to prevent cyst recurrence. Photo courtesy Dr. John R. Lewis John R. Lewis, VMD, DAVDC, FF-OMFS, practices and teaches at Veterinary Dentistry Specialists and Silo Academy Education Center in Chadds Ford, Pa. References https://www.veterinarypracticenews.com/seize-and-de-cyst-canine-furcations/ Verstraete FJ, Zin BP, Kass PH, Cox DP, Jordan RC. Clinical signs and histologic findings in dogs with odontogenic cysts: 41 cases (1995-2010). J Am Vet Med Assoc. 2011;239(11):1470-1476.
