Osteochondromas
From Felipedia
Osteochondromas, both the solitary and multiple forms, are a rare cancer of cats. Solitary osteochondromas are rare and are found in mature cats, arising only on the axial skeleton. Multiple osteochondromas, known also as osteochondromatosis or multiple cartilaginous exostoses, are more common in the cat. Unlike the disease in dogs, horses, and humans, the disease in the cat arises in mature, young adult animals ranging in age from 1.3 years to 8 years. The tumor arises in the perichondnum of flat bones, rather than from long bones. The masses, which appear after skeletal maturity, become larger and increase in number with increasing age of the cat. The enlarging masses produce functional impairment that varies with the sites involved. Gross and histologic examination shows the lesions to be covered by a cap of cartilage and bone; the underlying mass comprises bony trabeculae.
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Etiology
Virus particles have been identified ultrastructurally from feline osteochondromas and are morphologically identical to feline leukemia virus. Other viruses suggested are feline fibrosarcoma virus or another member of the feline retrovirus family [223].
Clinical signs
Osteochondromatosis is frequently a subclinical condition diagnosed as an incidental radiographic finding. However, neurological signs occasionally occur in animals associated with spinal cord compression secondary to vertebral osteochondromas in any region of the spinal column, but most commonly cervical and/or thoracic areas. Signs observed will depend on the location of the masses (e.g., cervical syndrome, cervicothoracic syndrome, and thoracolumbar syndrome). There may be variable signs of pain on palpation of the thoracic or cervical spine. Onset of neurological signs typically occurs prior to 1 year of age, although osteochondromatosis may be first diagnosed in older dogs (see also, malignant transformation, below). Osteochondromatosis may involve other tissues such as synovial joints, and tracheal rings.
Diagnosis
Diagnosis may be made using survey radiography but evidence of cord compression will require myelography and/or imaging. Radiographically, osteochondromas usually appear as large, smoothly contoured cystic bony masses, with irregular or well-delineated borders, sometimes with mottled patterns of radiolucency and radiodensity. Fusion of vertebrae at articular facets in the presence of normal intervertebral disks, may be observed. Microscopic examination of a biopsy specimen, which includes the cartilage cap and bony stalk covered by a membrane continuous with the periosteum, will confirm the diagnosis. During active growth, the cartilage resembles a physis with typical endochondral ossification present. The cartilage cap may be incomplete or absent in mature lesions. Osteochondromas may also be characterized using special imaging techniques, such as CT.
Treatment
Surgical excision (including removal of the perichondrial membrane on the surface of the cartilage cap), spinal cord decompression, and perhaps vertebral stabilization, are necessary in animals with clinical evidence of spinal cord attenuation. While post-operative vertebral fracture has been reported, there are several reports of successful surgical outcomes. Surgical removal may be easier when osteochondromas are less well developed, at which time they are softer and poorly vascular, since within a few months, the cancellous bone becomes harder and much more vascular. Recurrences may occur. Prognosis is guarded, especially in young animals with osteochondromas involving multiple vertebral sites where subclinical masses may assume importance as they grow until the skeleton matures. Early surgical removal may eliminate development of clinical complications.
Osteochondromatosis typically first appear in the skeletons of mature cats (e.g., from 2 to 4 years of age), growth of the bony mass is progressive, and the lesions show microscopic transformation from hyperplasia to characteristics of virus-induced parosteal sarcomas. Any bone can be affected in cats, including the flat bones of the skull. Most common sites, in decreasing frequency, are rib cage, scapulae, vertebrae, skull and pelvis [223]. Osteochondromatosis in cats has no breed or sex predisposition or hereditary pattern. Prognosis is grave for any affected cat. Some tumors undergo transformation into osteosarcoma and chondrosarcoma and no cat has lived longer than a year after onset of clinical signs.
References
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