19-year old Quarter Horse mare

Signalment: 19 year old, Quarter Horse Mare

History: Patient presented with dysphagia of one-month duration, bilateral swelling of the neck, increased respiratory sounds and nasal discharge

Physical Examination: Upon presentation the patient was quiet, alert, and responsive with a body condition of 5/9. Patient exhibited bilateral mucopurulent discharge and excessive salivation. There was bilateral swelling of the cranial cervical region, which was worse on left.

Radiographic Imaging Findings:

There is marked irregularity, moth-eaten lysis, and patchy sclerosis of the angle of the left mandible, as well as the caudal aspect of the left mandibular ramus. Similar findings, as well as an ill-defined oblique fracture, are present within one of the stylohyoid bones (presumed left). There is also moderate, ill-defined soft tissue swelling within the retropharyngeal area, and surrounding the upper esophageal sphincter on the lateral projections.

Radiographic Imaging Conclusions:

Lysis of the left mandible and stylohyoid bone, with a pathologic stylohyoid bone fracture and extensive retropharyngeal soft tissue swelling . Differentials include a neoplastic or a regional infectious process.

Given the severe soft tissue swelling and lysis seen radiographically, CT was elected for further anatomic detail.

CT Imaging Findings:

There is severe, ill-defined swelling of the submandibular and retropharyngeal region, which is worst on the left.

Moderate to severe multifocal regions of lysis are present along the base and left side of the skull, involving the basisphenoid bone, left mandible, left side of the hyoid apparatus, left paracondylar process of the occiput and left tympanic bulla. Pathologic fractures of the left stylohyoid bone and left paracondylar process are present. C1 is also involved, with multiple regions of lysis and a pathologic fracture of the right wing.

There is a mild amount of gravitationally dependent, fluid attenuating material accumulated within the left dorsal conchal sinus.

Incidental findings include mild, irregularly marginated osseous proliferation surrounding the right temporohyoid joint (temporohyoid osteoarthropathy) and small, ovoid, bilaterally symmetrical, mineral attenuating foci within the lateral ventricles (consistent with small cholesterinic granulomas). There is mild right lateral ventriculomegaly.

CT Imaging Conclusions:

Severe retropharyngeal soft tissue swelling, with associated marked polyostotic lysis.

Computed tomography revealed more extensive lysis than what was suspected radiographically, with involvement of various bones of the skull, hyoid apparatus, and first cervical vertebral body. Neoplasia was considered most likely due to the severity and extensive nature of these findings.

Case Outcome:

Surgical exploration was performed at the request of the owner which confirmed extensive osseous destruction of the left mandible and fracture of the first cervical vertebral body. After contacting the owner humane euthanasia was elected.

Post Mortem Diagnosis:

Histopathology revealed a carcinoma of connective tissue with metastasis to lungs, kidneys, and lymph nodes.

Case Discussion:

Malignant neoplasia of the equine head often results in nonspecific signs such as facial swelling and nasal discharge as seen in this patient (1,3.)

Squamous cell carcinoma is the second most frequently reported neoplasm in the horse with the most commonly reported sites including genitalia, ocular/periocular tissue, and the stomach. Less commonly reported sites include oral, pharyngeal and nasal cavities (1,4,5,6,7.) In cases of squamous cell carcinoma, local tissue infiltration is a common finding, with incidence of lymph node metastasis varying between 10-25% (1,2,3,4,5.) However; the metastatic spread to distant body sites seen in this patient is uncommonly reported (1,2,3,4,5.) In a series of 4 equids with pharyngeal SCC, the reported radiographic abnormalities were limited to soft tissue changes. No apparent bone lysis was appreciated radiographically in this group of horses but was confirmed in a single patient following computed tomography (5.) A case study of SCC invading the temporomandibular joint documented multifocal regions of lysis of the skull, hyoid apparatus and mandible on CT, similar to the findings in this case (8.)

References:

1. Schuh J.C.L. Squamous Cell Carcinoma of the Oral, Pharyngeal and Nasal Mucosa in the Horse. Vet. Pathology, Volume 23,1986, Pages 205-207
2. Hendrix D., Equine Ocular Squamous Cell Carcinoma. Clinical Techniques in Equine Practice, Volume 4, Issue 1, 2005, Pages 87-94
3. Faustina M., Diba R., Ahmadi M., Gutstein B., Esmaeli B. Ophthalmology. Volume 111, Issue 10, 2004, Pages 1930-1932
4. Jones DL. Squamous cell carcinoma of the larynx and pharynx in horses. Cornell Veterinarian; Issue 84, 1994, Pages 15–24.
5. Etienne A., Evrard L., Bolen G., Esman M., Grulke S., Busoni V. Imaging findings in horses with pharyngeal squamous cell carcinoma, Diagnostic Imaging Section, Large Animal Surgical Section, Faculty of Veterinary Medicine, University of Liège, Belgium, 2012
6. Knottenbelt, D.C. and Kelly, D.F. (2010) Oral and dental tumors. Equine Dentistry, 3rd Edition, Eds: J. Easley, P.M. Dixon and J. Schumacher, Elsevier, 2010, Pages 149‐181.
7. Valentine, B.A. Neoplasia. In: Equine Geriatric Medicine and Surgery, Ed: J. Bertone, Elsevier, 2006, Pages 147‐167
8. Perrier M, Schwarz T, Gonzalez O, Brounts S. Squamous cell carcinoma invading the right temporomandibular joint in a Belgian mare. Can Vet J. 2010;51(8):885–887.