Multilobular tumour of bone in an animal

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The Multilobular tumour of bone (MTB), although uncommon, is the most common tumour of the canine skull.

MTB usually presents as a firm, circumscribed and generally slow growing bone tumour in older dogs from medium or large breeds. Its biological behaviour may range from benign to malignant, as it has the potential to invade, metastasise and recur. Histologically, it is characterised by the dominant presence of multiple osteoid- or cartilage- containing lobules that are separated by fibrous septae. MTB should be differentiated from other bone tumours. Although most frequently found in dogs, MTB has been reported in humans, cats, a horse and a ferret. The clinical signs depend on the tumour location. Depending on its location and stage in the clinical course, surgical resection may result in long-term remission.

In dogs it is uncommon and primarily represents a disease of middle-aged to older animals, occurring most often in medium or large breeds and rarely in giant breeds. This tumor often recurs locally after surgical excision, and it has been found to metastatize the lungs. The tumor is usually present as a firm immovable mass on the surface of skull bones. Direct extension into adjacent structures is common. Depending of the location, the tumor can manifest in various clinical signs in the affected dogs; which include difficulty in mastication, obstruction of sinuses, neurological signs, exophthalmia and disfiguration of the face and head due to the protruding tumor mass.

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.

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).

Although these tumors often appear well circumscribed clinically, radiographically, and histologically, surgical management can be a challenge due to the fact that the tumors arise very commonly from the skull bones. Obtaining microscopically tumor-free margins can be difficult.  CT is critical in determining extent of disease and for surgical planning.

The role of chemotherapy and radiation therapy for higher grade multilobular tumors of bone is not well defined.  Local tumor excision appears to result in long-term control for lower grade tumors.  We do recommend adjunct radiation therapy for incompletely excised higher grade tumors to potentially slow the rate of reoccurrence.  For incompletely excised lower-grade tumors, reoccurrence can take months to years.  For inoperable tumors, radiation therapy can provide palliation. 

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Regards,

Stella

Editorial Team

Journal of Orthopedic Oncology