Multilobular Osteochondrosarcoma

Multilobular osteochondrosarcoma (MLO) is a tumor of dogs that has been called many names, including multilobular tumor of bone and chondroma rodens. The tumor has been reported in dogs, cats, ferrets and horses. Locations typically seen are skull based with the cranium, mandible, maxilla, orbit and zygomatic arch. They have also been observed in the pelvis, rib and os penis.

MLOs are malignant bone tumors that are attributable to abnormal cellular activity arising from the periosteum of bones formed by intramembranous ossification with the cells of origin periosteal cells of the common chondrocranium and viscerocranium, both of which share a common embryonic origin. They may metastasize to the lungs and this ability to disseminate has been linked to tumor grade. When observed, pulmonary metastases are typically slow growing and the average time to death following their detection is more than a year on average. Thus, MLOs are one of the few tumors for which surgical excision of a primary tumor with known pulmonary involvement may still be recommended, particularly if then primary tumor is negatively impacting the quality of life of the patient (e.g. a tumor of the mandibular ramus that is made opening of the mouth difficult) and the lung metastases are in early stages.

Diagnostic imaging consists of three view thoracic radiographs and CT for evaluation of primary tumor extent and better evaluation of the lungs for early metastasis. 3D reconstructions of skull-based lesions can be very helpful for operative planning. Primary lesions often have a classic „popcorn ball“ appearance and low-grade tumors typically have a very well defined peripheral border. High-grade tumors may be less well defined and more invasive into the surrounding tissues.

Surgery consists of excision of the primary tumor along with a margin of the surrounding bone. With low-grade tumors this margin can be somewhat narrow (e.g. 1 cm); however, wider margins are recommended with high-grade tumors. Cranial lesions cause compression of underlying brain but the nervous tissue is not typically invaded. Resectability, is often dictated by size, location and the degree of venous sinus involvement.  [...]