Case reveal


  • Centered on the rostral aspect of the mandible, more severely affecting the left side, there is a large, expansile, lytic, multilobular mass with a short zone of transition completely obliterating the mandible. Surrounding this mass, the soft tissues are moderately thickened.
  • The roots of the mandibular incisors (301-303 and 401) are variably foreshortened and blunted, as well as mildly displaced.
  • The remainder of the osseous structures in the field of view are within normal limits.


  • Large, aggressive, monostotic rostral mandibular mass with lysis of the adjacent incisor roots (301-303 and 401). Differentials for this include ameloblastoma, carcinoma or less likely ossifying fibroma.


Rostral mandibulectomy with wide margins (intra-op radiograph).
  • Histopathology: Poorly differentiated carcinoma of the mandible (confirmed with cytokeratin staining). NOTE: The mass had some histopathologic features of squamous cell carcinoma.

A little bit more…

  • Not uncommon for horses to present for evaluation of mandibular swelling. Neoplasia as an etiology is rare (Bass et al.).
  • Mandibular neoplasms are primarily of dental (odontogenic), bone (osteogenic), or soft tissue origin (Bass et al.).
  • Tumors are often advanced time of diagnosis due to delayed recognition (Bass et al.).
  • Reported clinical signs include weight loss, dysphagia, bleeding from the oral cavity and halitosis (Bass et al.).
  • Radiography is standard imaging modality; however, CT may be preferred for better characterization of the lesion/surgical planning (Bass et al.).
  • Imaging features of mandibular aggressive osseous lesions overlap between different tumor types:
  • Deep incisional biopsies are preferred to avoid sampling solely surrounding inflammatory tissues (Derham et al).
  • Durham et al. describe the use of CT sentinel mapping to guide surgical planning and screen of metastasis.
  • Rostral mandibulectomy is a reported successful treatment option with few complications, and mostly requiring regular dental care (Derham et al.).


  • Morgan, Rhiannon E., et al. “Equine odontogenic tumors: clinical presentation, CT findings, and outcome in 11 horses.” Veterinary radiology & ultrasound 60.5 (2019): 502-512.
  • Bass, Kathryn, et al. “Equine mandibular fibrosarcoma in two horses: clinical, diagnostic, and therapeutic considerations.” Journal of equine veterinary science 48 (2017): 31-38.
  • De Cock, H. E. V., P. Labelle, and K. G. Magdesian. “Ameloblastic carcinoma in a horse.” Journal of comparative pathology 128.2-3 (2003): 210-215.
  • Surgical treatment of a mandibular ameloblastic carcinoma with metastases to the mandibular lymph nodes in a pony.
  • Monteiro, S., K. Lemberger, and M. Gangl. “Mandibular squamous cell carcinoma in a young horse.” Equine Veterinary Education 21.8 (2009): 406-410.
  • Strohmayer, Carina, Andrea Klang, and Sibylle Kneissl. “Computed tomographic and histopathological characteristics of 13 equine and 10 feline oral and sinonasal squamous cell carcinomas.” Frontiers in Veterinary Science 7 (2020): 591437.
  • Van Thielen, Bert, et al. “MRI and CT features of an equine juvenile mandibular ossifying fibroma.” Journal of equine veterinary science 33.8 (2013): 658-662.