History
A 12-month-old 98-kg (215-lb) Hampshire Down ram was evaluated at the Oklahoma State University Veterinary Teaching Hospital because of a 3-month history of progressively increasing, clear nasal discharge and a 1-week history of left-sided facial swelling and increased respiratory noise. A long-acting injectable eprinomectin product had been administered to the ram 2 months before the initial examination. One year earlier, another sheep in the flock showed similar clinical signs and was culled; however, the underlying cause of the condition was not determined.
On examination, the ram had a firm swelling over the dorsolateral aspect of the left side of its face, mild respiratory distress with inspiratory stridor, and copious clear nasal discharge that exuded from both nares and pooled on the ground. Airflow from the left nostril was less than that detected from the right. The ram was tachypneic (52 breaths/min; reference range, 16 to 24 breaths/min) but in good body condition (body condition score of 3 on a scale of 1 to 5). Differential diagnoses considered for upper airway obstruction with facial distortion included nasal parasites, sinusitis, neoplasia, granuloma formation, foreign body, and trauma. Radiography of the skull was performed (Figure 1).
Dorsoventral (A) and left lateral (B) radiographic views of the skull of a 12-month-old 98-kg (215-lb) Hampshire Down ram with a 3-month history of progressively increasing, clear nasal discharge and a 1-week history of left-sided facial swelling and increased respiratory noise.
Citation: Journal of the American Veterinary Medical Association 253, 12; 10.2460/javma.253.12.1541
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Diagnostic Imaging Interpretation and Findings
Radiographic examination of the skull revealed a rounded, amorphous soft tissue mass in the left ethmoid labyrinth that caused right-sided deviation of the nasal septum. (Figure 2). Enlargement and left-sided lateral displacement of the maxillary sinus and a fluid opacity in the frontal sinus were evident. On the basis of these radiographic findings, differential diagnoses included nasal adenoma, adenocarcinoma, granuloma, or cyst.
Same radiographic images as in Figure 1. Notice the soft tissue mass in the ethmoid labyrinth (arrows; A and B), enlargement and left-sided lateral displacement of the maxillary sinus (asterisks; A), and fluid opacity in the frontal sinus (double asterisk; B).
Citation: Journal of the American Veterinary Medical Association 253, 12; 10.2460/javma.253.12.1541
With the ram anesthetized and in dorsal recumbency, CTa was performed. Contiguous images with a 1.3-mm transverse slice thickness and a pitch of 0.75 were obtained of the head and neck from the level of the nasal planum to C3 before and after IV administration of 180 mL of iohexolb (350 mg of iodine/mL) contrast medium and were reformatted into sagittal and dorsal planes (Figure 3). A large, lobular, contrast-enhancing, soft tissue–attenuating mass was evident in the left nasal cavity. The mass extended through the nasal septum into the right nasal passage and from the first premolar tooth through the ethmoid labyrinth to the cribriform plate, completely obstructing the choana. Evidence of lysis was identified in the left and right nasal turbinates, nasal bone, frontal bone, orbit, vomer, and cribriform plate. Both the frontal and maxillary sinuses were fluid filled, and there was notable expansion of the left maxillary sinus. These findings were consistent with an aggressive, predominantly left-sided nasal mass with extension through the cribriform plate and secondary sinusitis, rhinitis, and nasopharyngeal obstruction. The differential diagnoses for this ram were narrowed down to nasal adenocarcinoma, adenoma, or granuloma.
Transverse (A and C) and reconstructed sagittal (B) CT images of the same ram as in Figure 1 after administration of contrast medium. A large, lobular, contrast-enhancing, soft tissue–attenuating mass (white arrows; A and B) is evident in the left nasal cavity. The mass extends caudally through the cribriform plate (black arrows; C). The right (asterisk; A and B) and left (double asterisk; A) maxillary sinuses appear fuid-filled, with the left notably expanded.
Citation: Journal of the American Veterinary Medical Association 253, 12; 10.2460/javma.253.12.1541
Treatment and Outcome
The ram was given a grave prognosis because of the extensive bony destruction and evidence of extension through the cribriform plate. Surgical resection was considered infeasible, and surgical debulking was not recommended owing to the high risk of hemorrhage, invasiveness of the procedure, and long duration of recovery. Tracheostomy was offered as a temporary treatment to extend the life of the ram, such as for breeding or semen collection; however, the owner elected euthanasia. A necropsy was performed, and results from histologic evaluation of the nasal mass were consistent with the diagnosis of nasal adenocarcinoma. In light of these findings combined with the farm's history, enzootic nasal adenocarcinoma was presumed. Molecular diagnostic procedures to definitively confirm the diagnosis were not pursued by the owner.
Comments
Common causes of obstructive nasal masses in sheep include granulomas, nasal bot infestations, nasal adenomas, and enzootic nasal adenocarcinomas. Inciting causes of nasal granulomas include plant pollens and fungi, with recurrent and chronic exposure leading to type IV hypersensitivity reaction and granuloma formation. Nasal bot infestation with Oestrus ovis was considered unlikely in this ram because it had recently received eprinomectin, a macrocyclic lactone effective against nasal bots.
Enzootic nasal adenocarcinoma of sheep is caused by the contagious oncogenic b-retrovirus, ovine nasal adenocarcinoma virus.1 Such tumors originate in secretory epithelial cells of the nasal turbinates and may exhibit locally invasive behavior.2 Young adult sheep are often affected and exhibit signs that may include facial asymmetry, profuse nasal discharge, decreased nasal airflow, and dyspnea.3 There is no reported curative treatment for ovine enzootic nasal adenocarcinoma. Rhinotomy for surgical debulking of these tumors is described and can result in intermediate-term survival in valuable breeding animals.4,5 However, isolation or culling is often recommended because affected animals can spread the disease in their flocks.6 For this reason, the ram of the present report was culled, and the owner was instructed to monitor for similar clinical signs in sheep that had been in contact with the ram.
Radiography and CT provided useful diagnostic and prognostic information. The invasiveness and bony destruction detected in this ram were suggestive of a neoplastic process, rather than a granulomatous lesion. Contrast enhancement enabled assessment of tissue vascular perfusion and revealed areas of necrosis in the mass. This finding was suggestive of a tumor that outgrew its blood supply, rather than a slow-growing granuloma. Computed tomography allowed improved visualization of the extent of osseous destruction of the skull, including extension through the cribriform plate, a feature that could not have been determined radiographically in this ram. Erosion through the cribriform plate into the calvarium carries a grave prognosis because it could likely result in neurologic deficits necessitating euthanasia. In the ram of the present report, detailed evaluation of the cribriform plate with CT helped guide the decision not to pursue surgical treatment.
Although immunohistochemical or reverse transcription PCR analysis is necessary to make a definitive diagnosis of enzootic nasal adenocarcinoma,7 histologic evaluation, as was performed on the mass from the ram of the present report, can be used to help differentiate neoplasia (eg, adenomas, adenocarcinoma, and adenopapilloma) from granulomas. The combination of a histologic diagnosis of nasal adenocarcinoma, findings from physical examination and diagnostic imaging, and history of another sheep with similar signs having been culled from the flock strongly supported a diagnosis of enzootic nasal adenocarcinoma in this ram.
Footnotes
LightSpeed 4-slice helical CT scanner, GE Healthcare, Waukesha, Wis.
Omnipaque 350 mg/mL, GE Healthcare, Princeton, NJ.
References
1. Walsh SR, Linnerth-Petrik NM, Yu DL, et al. Experimental transmission of enzootic nasal adenocarcinoma in sheep. Vet Res 2013;44:66.
2. McKinnon AO, Thorsen J, Hayes MA, et al. Enzootic nasal adenocarcinoma of sheep in Canada. Can Vet J 1982;23:88–94.
3. Svara T, Gombac M, Vrecl M, et al. Enzootic nasal adenocarcinoma of sheep in Slovenia. J Vet Med A Physiol Pathol Clin Med 2006;53:26–29.
4. Trent AM, Smart ME, Fretz PB. Surgical management of nasal adenocarcinoma in sheep. J Am Vet Med Assoc 1988;193:227–229.
5. Rings DM, Rojko J. Naturally occurring nasal obstructions in 11 sheep. Cornell Vet 1985;75:269–276.
6. Leroux C, Mornex JF. Retroviral infections in sheep and the associated diseases. Small Rumin Res 2008;76:68–76.
7. Walsh SR, Stinson KJ, Menzies PI, et al. Development of an antemortem diagnostic test for enzootic nasal tumor virus and detection of neutralizing antibodies in host serum. J Gen Virol 2014;95:1843–1854.
