6-year-old male neutered mixed breed canine

• There is a 6.9 x 5.6 x 2.8 cm (LWH) homogeneously soft tissue attenuating mass arising from the rostral maxilla. It is minimally contrast-enhancing along the periphery and centrally non-contrast enhancing (37 HU pre-contrast, 43 HU post-contrast). It causes lysis of the rostral maxillary bones, incisive bone, and palatine bones and causes widening of the alveolar spaces of the maxillary incisors and canines. Lysis of the palatine bone extends to the level of the 3rd maxillary premolars. It partially invades into the rostral nasal cavity, left more severe than right, to the level of the 2nd premolars.
• The mandibular lymph nodes are moderately enlarged and rounded.
• The right thyroid gland lobe contains a 1.4 cm soft tissue attenuating and heterogeneously contrast-enhancing nodule.
• The walls of the external ear canals are partially mineralized.

•  Rostral maxillary neoplasia such as squamous cell carcinoma, fibrosarcoma, or myxosarcoma is prioritized. Malignant melanoma cannot be excluded, though it is less likely given the poor contrast enhancement.
• Metastatic or reactive mandibular lymphadenopathy.
• Right thyroid adenoma or adenocarcinoma.
• Bilateral chronic otitis externa

Histopathology of the maxillary mass was consistent with a biologically high-grade, histologically low-grade fibrosarcoma (high – low FSA).

Histopathology of the maxillary mass was consistent with a biologically high-grade, histologically low-grade fibrosarcoma (high – low FSA). This distinctive form of canine orofacial fibrosarcoma was first described in 1994 by Ciekot et al. Golden retrievers are overrepresented¹. This tumor contains highly differentiated fibroblastic cells that sometimes can be misclassified as granulation tissue. However, clinically this subset of orifical FSA is very aggressive and is reflected in its CT appearance. According to a retrospective analysis of 70 high-low FSA canine patients, the typical CT appearance of high-low FSA is described as a soft tissue mass with peripheral contrast enhancement, permeative osteolysis of adjacent bones, and soft tissue mineralization³.

A study² stated the median survival time of patients with surgically resected orofacial FSA was 743 days. The high– low subset of FSA does not carry a worse prognosis than general oral FSA. However, the same study also found that golden retrievers tend to have a higher rate of local recurrence. The author concluded that this discrepancy could be due to the limitation that high – low FSA are not always accurately diagnosed. Golden retrievers with a high local recurrence could have been misclassified as low-grade FSA.

Case resolution/follow-up.

The owner elected palliative therapy and did not pursue surgery or radiation therapy. Unfortunately, a few days after Tucker was diagnosed, he was euthanized after developing seizures and epistaxis.

1. Ciekot, P. A., Powers, B. E., Withrow, S. J., Straw, R. C., Ogilvie, G. K., & LaRue, S. M. (1994). Histologically low-grade, yet biologically high-grade, fibrosarcomas of the mandible and maxilla in dogs: 25 cases (1982-1991). Journal of the American Veterinary Medical Association, 204(4), 610–615.

2. Frazier, S. A., Johns, S. M., Ortega, J., Zwingenberger, A. L., Kent, M. S., Hammond, G. M., Rodriguez, C. O., Steffey, M. A.,; Skorupski, K. A. (2012). Outcome in dogs with surgically resected oral fibrosarcoma (1997-2008). Veterinary and Comparative Oncology, 10(1), 33–43.

3. Paul, H., Kessler, M. (N.A.) Canine “high grade –low grade” orofacial fibrosarcomas –a retrospective analysis of 70 cases.