History

A 4-year-old 3.8-kg female spayed domestic shorthair cat was referred to the veterinary teaching hospital for further workup and treatment of a slowly growing left rostral maxillary mass. The mass was reportedly excised 3 years prior by a shelter veterinarian before adoption. She subsequently presented to her family veterinarian at 2 years old for progressive swelling of the left rostral maxilla, dysphagia, and epiphora. Transgingival fine needle aspirate of the swelling showed blood and mild mixed inflammation. Over the next year the mass did not appear to grow, and the cat remained sub-clinical.

At 3 years old, the cat presented again to her veterinarian for anorexia. On dental radiographs there are marked bony lysis and cystic lesions around the left maxillary canine, premolars and first molar, which were previously extracted (Figure 1). On submitted bone and the third premolar tooth, histology is mild fibroplasia. The patient was then referred to an oncology service. The swelling centered over the left rostral maxilla measuring 1.8-cm X 1-cm X 0.5-cm causing unilateral facial asymmetry. No further treatments or diagnostics were performed at initial consultation, and the owner declined surgical consultation and treatment. Approximately 8 months later, the patient was represented for revaluation. The maxillary swelling measured 2-cm X 2-cm and was fluctuant on palpation. Complete blood count and serum biochemistry analyses were unremarkable.

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Ventrodorsal (A) and oblique (B) maxillary dental radiographs and postcontrast parasagittal (C) and transverse (D) CT images of the head of a 4-year-old 3.8-kg spayed female domestic shorthair cat evaluated for a slowly progressive left rostral maxilla swelling combined with dysphagia and epiphora. Radiographic images were provided by the referring veterinarian. C and D—The line across each represents the imaging plane of the other. Both images are presented in a bone window (window level, 350 HU; window width, 2,700 HU) with a 3-mm slice thickness. L = Left radiographic positional marker. Rostral = Rostral direction of the patient.

Citation: Journal of the American Veterinary Medical Association 262, 5; 10.2460/javma.24.01.0031

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Diagnostic Imaging Findings and Interpretation

The cat, now 4-years-old, underwent a contrast-enhanced CT scan of the head and neck (Figure 1; Toshiba Aquilion, 16-row multidetector scanner, 3-mm slices) using 6-mL of iohexol, an iodinated nonionic contrast medium (Omnipaque 300; GE Healthcare Inc). The mass is expansile, lobular, cystic, and measured 2.7-cm L X 1.5-cm W X 1.7-cm H, causing abaxial expansion and thinning of the surrounding bone (Figure 2). Fluid cytology of the mass was consistent with previous hemorrhage.

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Same radiographic and CT images as in Figure 1. A and B—Left maxillary dental arcade lateral to the incisors (left maxillary canine, premolars and first molar) are absent (star). C and D—Left lobular cystic maxillary mass causing thinning and expansion of the surrounding bone (arrow) measuring 2.7-cm L X 1.5-cm W X 1.7-cm H.

Citation: Journal of the American Veterinary Medical Association 262, 5; 10.2460/javma.24.01.0031

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Given the expansile, cystic, and bone thinning character of the mass in a young cat, working differential diagnoses were primary bone cyst or cystic tumor. Cytology of an intra-operative tissue impression smear noted benign epithelial proliferation suggestive of an odontogenic cystic tumor. Few plump polygonal nucleated, basophilic cells without malignancy features were seen in a tight cluster. Bacterial culture was negative for growth.

On histologic examination of excised tissue is a multilobulate mass of neoplastic odontogenic epithelium, characterized by peripheral palisading with prominent central stellate cells with long intracellular bridges (stellate reticulum). No mitoses are evident. Islands of neoplastic cells were separated by dense fibrous connective tissue (Figure 3). The large islands of odontogenic epithelium with central stellate reticulum and the lack of ectomesenchyme or amyloid-like material led to the diagnosis of conventional ameloblastoma (CA).

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Low- and high-magnification photomicrographs of excised tissue from the maxillar swelling. A—At low magnification there are multiple nodules of odontogenic epithelium (OE) surrounded by dense fibrous stroma (asterisk). H&E stain; bar = 100 µm. B—High magnification shows the odontogenic epithelium is predominantly comprised of stellate reticulum (SR) with peripheral palisading (P). H&E stain; bar = 100 µm.

Citation: Journal of the American Veterinary Medical Association 262, 5; 10.2460/javma.24.01.0031

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Treatment and Outcome

En bloc resection by hemimaxillectomy was declined by the owner in favor of surgical biopsy, cyst debridement, and bone graft application (Figure 4). The left lateral maxilla was approached via incision of the mucogingival junction and elevation of the buccal mucosa. The thin bone and cyst were easily opened via blunt probing. Approximately 5 mL of mucoid opaque liquid were aspirated, and the cyst tissue lining was removed by curettage. Collected tissue was submitted for cytologic and histologic analysis. Following complete debridement, the maxillary cavity was packed with injectable bone graft putty (Fusion Xpress; Veterinary Transplant Services Inc). The incision was closed routinely. Postoperatively the cat received transdermal buprenorphine (20 mg) analgesia. The patient recovered unremarkably and was discharged the following day with a soft food diet, oral gabapentin (10 mg/kg, PO, q 8 h), and robenacoxib (6 mg, PO, q 24 h).

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Intraoperative views of left maxillary cystic lesion. A—Preoperative swelling focused around previously extracted left maxillary canine tooth. B—The mass was debrided via an intraoral approach. C—Bone graft putty was inserted into the curettaged void. D—The wound was closed in routine fashion.

Citation: Journal of the American Veterinary Medical Association 262, 5; 10.2460/javma.24.01.0031

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At a 2-week recheck with the family veterinarian, the incision had healed. The patient was reportedly eating well, and no clinical concerns were expressed by the owners. In a 3-month postoperative phone conversation with the owners, the patient was continuing to do well. The swelling was reportedly reduced in size and lent to a more symmetrical facial appearance. Considering neoplastic tissue extended to the margins of all submitted tissue, regrowth is expected. The owners declined radiation and electrochemotherapy treatment options.

Comments

This case highlights the benefits of integrating clinical signs with radiologic findings to guide next steps in bringing the case to a histologic diagnosis. Marked bony lysis and cystic lesions on radiographs, with continuation of clinical signs and growth of the maxillary swelling, necessitated further imaging by CT to direct surgical treatment. Biopsy of intra-operative samples was required, especially considering the patient's young age, to correctly diagnose the tumor type and guide oncologic and palliative treatment options.

Though comprising only approximately 2% of all feline oral tumors, cystic odontogenic tumors and odontogenic cysts should be considered in all cystic oral lesions.¹ Odontogenic tumors arise from dental lamina epithelium resulting in multilocular cysts that commonly displace and resorb teeth, and deform bone outside regional cortical plates.^1,2 The expansive nature of these tumors creates a clinically apparent swelling that is frequently the cause of presentation.¹ In contrast, odontogenic cysts are typically incidentally found, unilocular fluid-filled cavities lined by odontogenic epithelium.¹ Odontogenic cysts are frequently constrained to the cortical plates and only result in tooth resorption, not displacement.¹ Both cystic lesions require careful differentiation between clinical, radiologic, and histologic characteristics for definitive diagnosis.¹ Based on radiologic and clinical findings, this present case was considered to likely be an odontogenic tumor.

The three most common feline cystic odontogenic tumors include CA, amyloid-producing ameloblastoma (APA), and feline inductive odontogenic tumor (FIOT), all of which prominently feature odontogenic epithelium.¹ Conventional ameloblastoma tumors are rarely reported in cats. In a retrospective study, the youngest cat reported with CA was 6 years old, and this tumor appeared to preferentially originate from the maxilla.² Histologically, CA is expansile and can incite osteolysis.² Its islands of odontogenic epithelium contain large centers of stellate reticulum-like cells; stellate reticulum can be seen in FIOT and APA, but CA lacks induced mesenchyme or extracellular amyloid.^1,2 Additional imaging, like that of histologic photomicrographs, can procure a definitive diagnosis that facilitates accurate discussion about prognosis and treatment options.

Common benign odontogenic cysts are dentigerous, periapical, periodontal, and gingival cysts with 9.7 years as the mean age of cats affected.¹ Histologically, cyst epithelium is variably stratified, non-keratinized and can encase mixed inflammatory or hemorrhagic cells, yet cyst classification by histology of their epithelium alone is rarely specific.¹ Other benign bony cystic lesions include aneurysmal and unicameral bone cysts, but these have not yet been reported in the feline maxilla.³

In diagnosing oral swellings, dental radiography is employed first to characterize the extent of osteolysis. Fine-needle aspirates are often unrewarding as oral tumors frequently have high instances of necrosis and inflammation.⁴ Like other neoplasms, staging of oral tumors includes evaluating regional lymph nodes and the thoracic cavity for metastases. Finally, large incisional or complete excisional biopsy, preferably with a regional tooth, is required for definitive diagnosis.⁴

Preferred treatment of odontogenic tumors is complete excision by partial maxillectomy or mandibulectomy.⁴ Although narrow partial maxillectomies are tolerated by cats, many maxillary tumors cannot be fully excised because of their significant nasal and periocular involvement.⁵ Favorable prognostic indicators of these tumors are rostral location, small diameter, and histologically complete resection.⁴ Radiation or chemotherapeutic adjunctive therapies have been proposed for odontogenic tumors with greater metastatic potential, although evidence to their benefit is limited.^4,5 Prognosis of CA with complete surgical excision is usually excellent.⁴

While complete excision of odontogenic cysts is curative, usually so is surgical curettage of unerupted teeth and the epithelial lining paired with bone grafting.⁴ Cancellous bone graft application within the cavernous lesion will promote osseous healing and help prevent local recurrence.⁴

This case presents the complicated differentiation between primary odontogenic cysts and cystic odontogenic tumors. The young age of the cat, previous nondiagnostic histology, and relatively mild clinical signs were primary factors in leading toward a presumptive diagnosis of an odontogenic cyst. Factors including bone lysis and expansion, asymmetric facial swelling, and worsening clinical signs led to suspicion of a tumor, but the differential of odontogenic cyst remained to be considered. Odontogenic tumor became highly suspected with the key radiographic finding of multilocular expansion of maxillary bone outside of regional cortical plates. Final diagnosis of ameloblastoma required histologic photomicrographs. Characteristics of this lesion that ultimately classified it as CA included: clinically apparent facial swelling, multilocular cysts of the affected maxilla, historical tooth resorption and displacement, and conventional histologic findings of large epithelial islands with central stellate reticulum without induced papillary mesenchyme.^1,2 This case exceptionally highlights the importance of careful consideration of clinical, radiographic, and histologic data when reaching a definitive diagnosis for rare and inconspicuous diseases such as conventional ameloblastoma.¹

Disclosures

The authors have nothing to disclose. No AI-assisted technologies were used in the generation of this manuscript.

Funding

There was no funding associated with this case and its presentation.