History and Physical Examination Findings
An approximately 11-year-old female spayed Labrador Retriever was presented to the Dentistry and Oral Surgery Service at an academic institution for periodontal treatment.
Historical problems included a grade III/VI left apical systolic heart murmur secondary to mitral and tricuspid degenerative valve disease without cardiac enlargement on echocardiogram. Other historical problems included obesity, atopic dermatitis managed with caninized monoclonal anti–IL-31 antibody injections, and a chronic urinary tract infection without an underlying cause identified on abdominal ultrasound but resolved with amoxicillin and clavulanate potassium tablets by the time of the periodontal treatment. There were no other recent or chronic medications aside from parasite control. Complete blood count and serum biochemistry were both unremarkable.
Anesthetized oral examination revealed calculus index of 3/3 (heavy calculus covering > two-thirds of the buccal tooth surface), plaque index of 3/3 (abundant plaque covering > two-thirds of the buccal tooth surface), and gingival index of 1/3 (mild gingivitis with no bleeding on probing). There were no abnormal periodontal probing depths. Other findings included generalized abrasion and absent teeth (historically extracted or confirmed absent). There was also a supernumerary right maxillary first premolar (modified Triadan system 105).
Full-mouth radiographs (CR 7 Vet Image; iM3 Inc) and cone beam CT (CBCT) scan of the skull (VetCAT; Xoran Technologies LLC; window width, 5,507 HU; window level, 896 HU; 0.3-mm slice thickness) were acquired and revealed an incidental left mandibular lesion. Select images are provided below (Figure 1).
A select intraoral radiograph (A) and transverse cone beam (CBCT) slice (B) at the furcal area of 307 and the right mandibular third molar (modified Triadan system 407) of an approximately 11-year-old female spayed Labrador Retriever with an incidental left mandibular lesion. The transverse CBCT slice just begins to include the mesial aspect of the distal roots of 307 and 407.
Citation: Journal of the American Veterinary Medical Association 261, 4; 10.2460/javma.22.09.0410
Diagnostic Imaging Findings and Interpretation
Full-mouth radiographs revealed a single ovoid area of increased mineral opacity with a mildly irregular margin present in the apical furcal area of the left mandibular third premolar (modified Triadan system 307; Figure 2). The lesion extended further ventrally than the apices of 307. There was also a thin region of increased radiolucency surrounding the mesial and coronal aspects of the lesion.
The same images as in Figure 1. A—The lesion (arrowhead) was a single ovoid area of increased mineral opacity with a mildly irregular margin present in the apical furcal area of 307 and extending further ventrally than the apices. There was also a thin region of increased radiolucency surrounding the mesial and coronal aspects of the lesion. B—The lesion (arrowhead) was positioned lingual to 307, between the buccal and lingual cortical plates of the mandible within the cancellous bone, and extended ventrally to the level of the caudal mental foramen within the mandibular canal. Additionally, the right maxillary third premolar (modified Triadan system 107) and the left mandibular second premolar (modified Triadan system 306) were absent, and there was mild generalized external replacement tooth resorption.
Citation: Journal of the American Veterinary Medical Association 261, 4; 10.2460/javma.22.09.0410
CBCT confirmed the radiographic description of the lesion, which measured 6.6 mm dorsoventral X 4.8 mm mesiodistal X 3.2 mm linguobuccal (Figure 2). Additional details revealed on CBCT included that the lesion was positioned lingual to 307, between the buccal and lingual cortical plates of the mandible within the cancellous bone, and extended ventrally to the level of the caudal mental foramen within the mandibular canal.
Retrospectively, this same lesion was apparent on full-mouth radiographs from 2 and 3 years prior (Figure 3). It was of similar radiographic appearance, except for size. Initially, 3 years prior, the lesion did not extend further ventrally beyond the apex of the mesial root of 307. The radiolucency on the mesial and coronal aspects of the lesion was also absent.
The lesion (arrowhead) at the time of presentation (A), 2 years prior (B), and 3 years prior (C). The lesion changed in size and appearance over that period. Initially, 3 years prior, the lesion did not extend ventrally beyond the apex of the mesial root of 307. The radiolucency on the mesial and coronal aspects of the lesion was also absent. Notably, radiographs B and C are not appropriately centered on the lesion. Additionally, 306 was absent and there was mild generalized external replacement tooth resorption.
Citation: Journal of the American Veterinary Medical Association 261, 4; 10.2460/javma.22.09.0410
Differential diagnoses considered on the basis of the diagnostic images included bony proliferation secondary to trauma or idiopathic (exostosis), idiopathic osteosclerosis, condensing osteitis secondary to endodontic disease of 307, proliferative fibro-osseous disease including fibrous dysplasia or ossifying fibroma, or, lastly, neoplasia including osteoma, osteochondroma, or low-grade osteosarcoma.
Treatment and Outcome
Left inferior alveolar nerve block was performed (0.3 mL total volume, comprising 1.5 mg bupivacaine and 15 mcg buprenorphine). A mucogingival flap was raised to expose the caudal mental foramen as a landmark. A buccal bone window was created over the lesion with a piezoelectric surgical unit (Piezosurgery Inc). The bony lesion was gently elevated off of the lingual cortex and out of the mandibular canal (Figure 4). The mucogingival flap was closed with 4-0 poliglecaprone 25 in a simple interrupted pattern. The lesion was submitted for histopathology.
The mandible at the level of the lesion (arrowhead) before (A) and after (B) surgical excision. Additionally, 306 was absent and there was mild generalized external replacement tooth resorption.
Citation: Journal of the American Veterinary Medical Association 261, 4; 10.2460/javma.22.09.0410
Histopathology described lobules of dense, poorly cellular bone with compact lamellar organization including occasional circular osteons. There were no remarks on mitotic activity or atypia. There was no evidence of tooth substance. The histologic diagnosis was an intraosseous mandibular lesion composed of a lobular mass of dense bone consistent with an endosteal osteoma.
Postoperative healing was uncomplicated. The patient did not experience any grossly apparent recurrence but did not receive any further intraoral or skull imaging prior to humane euthanasia for unrelated reasons 5 months later.
Comments
In the present case, full-mouth radiographs led to the identification of an incidental endosteal osteoma of the left mandible. An osteoma is a benign primary bone neoplasm.1–4 It is uncommon, and oral osteomas are often nonpainful incidental findings.1–4 They occur most commonly in senior to geriatric, medium- to large-breed dogs but have also been reported in cats.1,4 They arise most commonly from the periosteum (periosteal or peripheral osteoma) but can also arise from the endosteum (endosteal or central osteoma) or extraskeletal soft tissue.2 While there is no reported malignant transformation or metastatic potential, within the oral cavity an osteoma can interfere with occlusion and surrounding structures, such as displacing adjacent dentition or impeding temporomandibular joint motion.2 Radiographically and on CT scan, an osteoma appears as a well-circumscribed area of mineral opacity with bone proliferation/expansion and occasionally areas of bone lysis.3 Since an endosteal osteoma is essentially “bone within bone,” it has been suggested that continuous growth, expansion, or displacement is necessary to support a diagnosis of endosteal osteoma rather than an exostosis, idiopathic sclerosis, or condensing osteitis. Treatment is surgical removal, and recurrence is not expected following complete excision.3,4 For asymptomatic patients, active surveillance with serial oral exams and imaging every 6 to 12 months to monitor expected slow growth for clinical changes, and the development of symptoms would be prudent based on expert opinion. In some cases, osteoma growth will cease, resulting in quiescence.2
In the present case, surgical removal was performed after retrospectively recognizing an increase in size and change in radiographic appearance over the 3 years prior. Since there was no grossly apparent lesion, imaging was essential for not only identification of the lesion but also localization. While it is possible to use a radiopaque marker as a radiographic guide, CBCT provided more specific qualitative and quantitative directional information. Specifically, CBCT allowed diagnosis that the lesion was lingual to 307 within the mandibular canal at the level of the caudal mental foramen, as well as for measurement from the buccal approach to the lesion (Figure 2).
This information was valuable for creating an appropriately positioned and sized bone window with a piezoelectric surgical unit for treatment of the osteoma. An alternative approach is to use powered bone cutting with a bur on a high-speed handpiece to create this bone window. However, the piezoelectric surgical unit uses high frequency vibration of a metallic tip to selectively cut bone while sparing soft tissue.5 This was particularly useful given the proximity of the inferior alveolar neurovascular bundle within the mandibular canal. Other advantages of piezoelectric bone surgery compared with powered bone cutting include reduced bleeding with improved visibility and reduced risk of thermal damage.5 Piezoelectric bone surgery can also be faster than using powered bone cutting.5
In the present case, a histologic diagnosis was achieved after complete surgical excision of the lesion as an excisional biopsy. Biopsy was recommended over continued monitoring because the lesion was gradually increasing in size and changing in radiographic appearance, which was concerning for a more aggressive lesion such as a low-grade osteosarcoma. Radiographically and on CT, low-grade osteosarcomas can appear as well-circumscribed or ill-defined areas of mineral opacity or mixed mineral and soft tissue opacity and can include areas of bone lysis and bone proliferation/expansion.3 Excisional biopsy was considered most practical since the lesion was able to be elevated off of the lingual cortex and out of the mandibular canal as a single unit without expanding the margins of a revision surgery if it were to be needed. However, for faster progressing, more aggressive appearing, or grossly apparent oral lesions, incisional biopsy is often the more appropriate initial diagnostic. An incisional bone biopsy can be collected using rongeurs, with or without first scoring the bone with a bur on a high-speed handpiece. If the lesion in the present case had been an osteosarcoma, or there was significant concern for recurrence, a definitive intent revision surgery in the form of a segmental mandibulectomy would have been recommended following complete staging.
In conclusion, oral masses can be of benign or malignant etiology. Valuable diagnostics include an oral examination, imaging with radiographs or CT scan, and a biopsy for definitive diagnosis. One differential diagnosis for a bony oral mass is an osteoma. Osteomas are benign, can be treated definitively with surgery, and with complete margins are not expected to recur.
Acknowledgments
The authors received no financial support for the research, authorship, or publication of this article. The authors declare no potential conflict of interest with respect to the research, authorship, or publication of this article.
The authors are very thankful for the excellent histopathology performed by Cynthia M. Bell, DVM, DACVP, through Specialty Oral Pathology for Animals LLC. The authors are very thankful for the excellent veterinary technician support provided by Emily Metz Quandt, AAS, CVT.
References
- 1.↑
Fiani N, Arzi B, Johnson EG, Murphy B, Verstraete FJ. Osteoma of the oral and maxillofacial regions in cats: 7 cases (1999-2009). J Am Vet Med Assoc. 2011;238(11):1470–1475. doi:10.2460/javma.238.11.1470
- 2.↑
Murphy B, Bell C, Soukup J. Tumors of the jaw: osteoma. In: Veterinary Oral and Maxillofacial Pathology. John Wiley & Sons; 2020.
- 3.↑
Soltero-Rivera M, Engiles JB, Reiter AM, Reetz J, Lewis JR, Sánchez MD. Benign and malignant proliferative fibro-osseous and osseous lesions of the oral cavity of dogs. Vet Pathol. 2015;52(5):894–902. doi:10.1177/0300985815583096
- 4.↑
Volker MK, Luskin IR. Oral osteoma in 6 dogs. J Vet Dent. 2014;31(2):88–91. doi:10.1177/089875641403100204
- 5.↑
Hennet P. Piezoelectric bone surgery: a review of the literature and potential applications in veterinary oromaxillofacial surgery. Front Vet Sci. 2015;2:8. doi:10.3389/fvets.2015.00008
