History
A 4-year-old intact male alpaca presented to the Louis Bates Acheson Veterinary Teaching Hospital at Oregon State University for evaluation of a mass of the right maxilla. About 10 days prior to admission, the owners noticed that the alpaca had difficulties eating grain. No nasal discharge, oral discharge, halitosis, or any sign of lethargy or emaciation was noticed. The alpaca was not receiving any medications and was on a diet consisting of orchard grass hay and pelleted feed.
On presentation, the alpaca was bright, alert, and responsive, with vital signs within normal limits (rectal temperature, 37.1 °C; heart rate, 64 beats/min; respiratory rate, 28 breaths/min; mucous membranes, pink and moist; capillary refill time, < 2 seconds). There was no nasal discharge, oral discharge, halitosis, or any evidence of drooling. There was a 3 X 5-cm firm enlargement on the right maxilla rostroventral to the right eye. Palpation of the mass did not seem to elicit pain. The skin over the mass was devoid of lesions, movable (ie, did not seem to be infiltrated by the mass), and not warmer than the opposite side of the face. The intraoral exam revealed that the mass extended into the mouth, had a multinodular surface, and was covered by mucosa (ie, no evidence of bleeding, ulceration, or discharge was noted). The third and fourth right maxillary premolars were displaced rostrally and loose.
Analysis of blood samples collected from the left jugular vein revealed a PCV of 30%, total solids of 6.2 g/dL, ionized calcium of 4.87 mg/dL (normal range, 3.8 to 4.7 mg/dL), serum amyloid < 20 µg/mL, WBCs of 7,290/µL (normal range, 8,000 to 21,400/µL), and neutrophil count of 3,937/µL (normal range, 4,711 to 14,686/µL). The alpaca was anesthetized, and the head was evaluated with CT (Figure 1).
Diagnostic Imaging Findings and Interpretation
At the level of the right maxillary premolars and first and second molars, there was a large, multilobulated, expansile, primarily soft tissue–attenuating lytic mass expanding medially into the hard palate. The mass was heterogeneously contrast enhancing and had a moderate amount of amorphous mineral stippling. The mass expanded dorsally, causing narrowing of the right caudal nasal passage, and dorsally displaced the right infraorbital canal. Medially, the mass caused severe lysis of the hard palate. Laterally, the mass expanded toward the buccal vestibule, forming a drop-like expansion that had not invaded the buccal mucosa. Most of the right maxillary first molar was absent. The right maxillary third and fourth premolars were rostrally displaced, and part of the fourth premolar tooth root and surrounding alveolar bone was absent. The right maxillary second and third molars were caudally angled. A compartment of the right middle conchal sinus was filled with liquid (Figure 2).
The CT images were suggestive that the mass was likely neoplasia. Odontogenic tumor was the first differential diagnosis suggested, although other neoplasms were also considered, including primary bone neoplasms. The abnormalities of the teeth, including the absence of the right maxillary first molar, and the rhinosinusitis were considered secondary to the neoplastic process.
Treatment and Outcome
Two days after admission, the alpaca was subjected to general anesthesia once again. The loose teeth (third and fourth right maxillary premolars) were extracted. A large fragment of the lateral expansion of the mass (2 X 1.5 cm) was excised with bone-cutting forceps. Histopathologic examination of the sample revealed that the mass was an inductive odontogenic tumor characterized as an odontoameloblastoma. In other species, treatment for this type of lesion usually entails debulking combined with chemotherapy or radiotherapy. Due to the size and location of the lesion and its expansive nature, debulking was not a viable option. Chemotherapy and brachytherapy were not considered an option due to livestock animal drug regulations and the potential of New World camelids to enter the food chain. Therefore, external beam radiation therapy administered as multiple sessions under general anesthesia and prolonged hospitalization was recommended. The owners declined this treatment mostly untested in camelids due to its high cost and the uncertainty regarding the final outcome. The alpaca did well while hospitalized and was discharged with the following recommendations: (1) continuous monitoring for comfort, appetite, ability to eat, and body condition; (2) return the alpaca to reproductive function while in good condition; and (3) periodic rechecks by the referring veterinarian to assess the need for any palliative care and, when the alpaca’s quality of life was compromised, to perform humane euthanasia. Six months after discharge, the alpaca was still doing well and no further growth of the mass had been observed externally.
Comments
Odontogenic tumors are classified according to their interaction with the epithelial and mesenchymal cells of the dental tissues. This classification is based on their inductive behavior.1 Inductive odontogenic tumors encourage differentiation of the odontogenic mesenchymal cells leading to formation of dental tissues including pulp, dentin, and enamel. The most differentiated of these entities induce formation of whole teeth or small tooth-like structures known as “denticles.” In the present case, the inductive characteristics of the tumor noted on the microscopic examination ruled out noninductive odontogenic tumors like ameloblastoma or peripheral odontogenic fibroma. The scant and ill-defined nature of the inductive component excluded more differentiated odontogenic tumors including ameloblastic fibroma or ameloblastic odontoma. Therefore, the mass was characterized as an odontoameloblastoma.
Odontoameloblastomas have been described in multiple species, including horses, dogs, nonhuman primates, cervids, camelids,2 and humans.3 These neoplasms usually present as an aggressive multiloculated mass, invading the surrounding tissues, leading to bone lysis and teeth displacement.2–5
In the present case, CT provided essential information to guide the diagnosis toward an odontogenic tumor. The heterogeneous, multilobulated, and locally infiltrative appearance was consistent with a neoplasm. Although final diagnosis required histopathology, the location of the mass and disruption of the surrounding bone and teeth, visible in the form of bone osteolysis, were consistent with an odontogenic tumor.
The CT images also played an essential role in the consideration of therapeutic options. Whenever possible, the treatment for this type of tumors is complete mass excision. However, the CT images revealed that complete mass removal was unviable due to the size, location, and extension of the mass. The lesion had already invaded and compromised a large area of hard palate, maxillary bone, gingiva, and sinuses.
Since the mass was deemed unresectable, the treatment of choice for this animal that could potentially enter the human food chain was external beam radiation therapy, which has been used successfully for advanced ameloblastomas in humans.3 However, an attempt to treat a large maxillary ameloblastoma in an alpaca with this approach was not successful.4 Radiation therapy is expensive and can damage surrounding tissues and produce significant side effects.4 Furthermore, in the best-case scenario, radiation-induced regression of such a large tumor would likely result in significant deformation of the right maxilla that could affect the alpaca’s ability to eat. Considering the high cost of external beam radiation therapy, the guarded prognosis for a full recovery, and the fact that the alpaca was still able to eat normally, the owner’s choice of palliative care was not unreasonable.
Acknowledgments
The authors would like to acknowledge Dr. Christopher Cebra, DACVIM, for his wise advice.
Disclosures
The authors have nothing to disclose. No AI-assisted technologies were used in the generation of this manuscript.
Funding
The authors have nothing to disclose.
References
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