A 10-year-old mixed medium size breed dog was presented with a 4 months of gradually enlarging swelling in the left zygomatic area of the head. Clinical examination revealed a facial deformation, due to the localization of the mass and mild dyspnea. Neurological examination didn't reveal any specific dysfunctions. The skin over the mass was tense and no ulcerations were observed. Radiographic examination of the head was performed and revealed the presence of a homogeneous radiodense bony swelling attached to the skull and involved a large area, from the left zygomatic arch to the left nasal cavity (Fig. 1).
The pathognomonic findings of a lytic geographic lesion with expansion and chondroid matrix seen on radiographic were diagnostic for a tumor. Prior to surgery, 3-view thoracic radiographs were performed to assess whether metastatic disease was present but the results were within normal limits. Initial diagnostic tests included a complete blood cell count, serum biochemical profile, prothrombin time (PT) and partially thromboplastin time (PTT).
All results were within reference limits similar to the values on urinalysis on voided urine. The dog was sedated by 5 microgm/Kg bodyweight (BW) of Medetomidine (Domitor 0,2 ml EV) and 0,1 mg/Kg BW of Butorphanol (Dolorex 0,4 ml EV) premedication. The induction was achieved using propofol at 4 mg/Kg BW (17 ml EV) followed by isoflurane for maintenance. The surgery was performed using a lateral access, on the left side of dog's face. After a careful isolation of anatomic structures and the exposure of the tumor, the mass was removed. Grossly the mass consisted of multiple, variably sized, grayish-white to yellow nodules which occasionally contained whitish, hard areas on cut surface interpreted to be mineral.
The resected mass was fixed in 10% neutral buffered 10% formalin and submitted to the Dipartimento di Scienze Biopatologiche e Igiene delle Produzioni Animali e Alimentari, Universita degli Studi di Perugia, Italy.
Histologically, the tumor was characterized by the presence of multiple lobules of irregularly shaped and sized islands and nests containing well differentiated osteoid and cartilage separated by diffuse anastomosed fibrovascular septa (Fig. 2).
In some areas there were broad poorly differentiated areas of mesenchymal tissue which blended into the lobules and islands of cartilagineous, osseous or osteocartilagineous tissue. Within the islands there were also diffuse areas of ossification and mineralization. The mitotic index of neoplastic cells was always low grade in all the examined samples. According to the characteristics and histological appearance of the tumor a diagnosis of MTB was made.
A radiation therapy was declined by the owner and after 3 months a recurrence was not observed and the dog did not present clinical signs.