By John Lewis, VMD, DAVDC

Levi, a 12-year-old bloodhound, was recently presented to our practice for a right-sided facial swelling below the right eye (Figure 1). The swelling was not painful and was noted by the owners. Levi also had a history of a large, infiltrative lipoma over the left thorax. The lipoma was evaluated by a board-certified surgeon and mass removal surgery was scheduled for a later date after the facial swelling was addressed.

Oral examination was performed, which revealed generalized gingival enlargement, moderate plaque and calculus accumulation, and a fluctuant swelling measuring approximately 2.5 cm in diameter, centered over the furcation of tooth 108. Although the main cusp of tooth 108 showed very mild abrasion, no slab fractures or pulp exposure was evident.

A closer look

It would be understandable if you suspected an endodontic infection might be the etiology of Levi’s facial swelling, since tooth root abscesses are much more common than odontogenic cysts. However, Levi’s primary care vet suspected a cyst over the diagnosis of abscess for two reasons:

1) Degree of fluctuance. Although dental abscesses can be fluctuant, they are more commonly manifesting as a firm, diffuse swelling centered over the diseased tooth. Levi’s swelling was more focal and was palpable as an accumulation of fluid.

2) No evidence of tooth fracture/discoloration. If a tooth is abscessed, it shows signs of trauma, and with the maxillary fourth premolar, that is usually a slab fracture. Levi’s tooth 108 showed no signs of fracture or loss of vitality on conscious examination.

Levi was placed under general anesthesia, and dental radiographs revealed severe furcational bone loss (Figure 2). No gingival recession or furcation exposure due to periodontal disease was noted on probing in this area. A mucoperiosteal flap was raised (Figure 3), and in the process, a clear brown fluid escaped from the swollen area, and the swelling deflated.

After raising the flap, tooth 108 was extracted to obtain more visualization. A white, glistening lining was identified, and periosteal elevators were used to tease away the lining from the adjacent soft tissue structures. The site was closed with 4-0 poliglecaprone 25 in a single layer of simple interrupted sutures. The cystic lining was placed in a biopsy cassette and submitted for histopathology (Figure 4).

Different cysts

It’s hard to believe I have been writing the Dental Pearls column in Veterinary Practice News for 14 years! Over that span, I’ve dedicated at least two columns to dentigerous cysts; odontogenic cysts that arise due to lack of eruption of a tooth. Odontogenic cysts include dentigerous cysts, periapical cysts, lateral periodontal cysts, odontogenic parakeratinized cysts, and furcation cysts.

Submission of the cystic lining to the pathologist will help to rule out cyst-like neoplasias, but that will not commonly diagnose the type of cyst since most cysts have a similar cell type: stratified squamous epithelium.

Furcation cysts are seen in the furcation of erupted teeth, rather than the unerupted teeth associated with dentigerous cysts. The most common tooth affected by furcation cysts appears to be the maxillary fourth premolar tooth. I have seen furcation cysts most commonly in boxer dogs, but they are rare, so it is difficult to comment on breed predilection.

Until recently, furcation cysts did not have a name. A manuscript published in 2020 described 20 cases.¹ Mean body weight was 51.8 lbs, and mean age was 8.2 years. All 20 dogs had unilateral cysts located at the maxillary fourth premolar tooth, with 108 being affected almost twice as often as tooth 208.

The predominant clinical sign in this study was a fluctuant swelling of the buccal gingiva and mucosa overlying the maxillary fourth premolar tooth. Enucleation of the cyst lining, with or without extraction of the affected tooth, resolved the lesion in most dogs in that study.¹

Furcation cysts are also observed in humans, most commonly occurring on the buccal portion of the furcation of the mandibular first molar. In one study, the furcation cysts extended from the buccal furcation to the tooth apex in 81 percent, and a periosteal reaction on the lateral surface of the mandible adjacent to the cyst was noted in 69 percent of the cases. All of the 44 histologic reports were nonspecific, but they showed cyst lining of stratified squamous epithelium with chronic inflammation. In this study, microbiology consisted of mixed oral flora. Radiographic healing in all sites without recurrence was noted in a follow up two and a half years later. The periodontal pocket depth around all the involved teeth was normalized, and none of the mandibular first molars were extracted.

The human literature suggests extraction is not necessary for complete resolution, but since the cysts may be more advanced by the time they are noticed in our veterinary patients, I would not hesitate to extract the tooth the cyst is arising from and possibly adjacent teeth if that would provide better visualization of the entire cyst.

John Lewis, VMD, DAVDC, FF-AVDC OMFS practices and teaches veterinary dentistry and oral surgery at Veterinary Dentistry Specialists and Silo Academy Education Center, both located in Chadds Ford, Pa.

References

1. Soukup JW, Bell CM. The canine furcation cyst, a newly defined odontogenic cyst in dogs: 20 cases (2013-2017). J Am Vet Med Assoc. 2020 Jun 15;256(12):1359-1367.
2. Pompura JR, Sándor GK, Stoneman DW. The buccal bifurcation cyst: a prospective study of treatment outcomes in 44 sites. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 1997 Feb;83(2):215-21.