Page 574 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

552 PART IV Specific Malignancies in the Small Animal Patient

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• Fig. 25.14 Lateral radiograph of a multiple cartilaginous exostosis lesion of the dorsal spinous process
in a dog.

There is one report of an MLO of the vertebra that did not have Benign Tumors of Bone
radiographic abnormalities. 375 Histologically, these tumors are
composed of multiple lobules, each centered on a core of carti- Osteomas
laginous or bony matrix that is surrounded by a thin layer of spin- Osteomas are benign tumors of bone. 377 Radiographically, these
dle cells. A histologic grading system has been described. 162,371 are well circumscribed, dense bony projections that are usually not
In one report of 39 dogs with MLOs, the median age was 8 painful on palpation. Histologically, they are composed of tissue
years, the median weight was 29 kg, and there was no breed nearly indistinguishable from reactive bone. The diagnosis is made
or sex predilection. 373 Local tumor recurrence was reported in after considering the history and physical examination as well as
47% of dogs after a median time of 797 days. 373 Metastasis the radiographic and histologic findings. The most important dif-
was reported in 56% of dogs; however, time to metastasis was ferential diagnosis is MLO when the lesion occurs on the skull.
prolonged with a median of 542 days. The MST was 800 days. Treatment for osteoma is simple surgical excision and this is usu-
Local tumor recurrence and metastasis after treatment were pre- ally curative.
dicted by histologic grade and the ability to obtain histologically
complete resection. 373 Local tumor excision with histologically Multiple Cartilaginous Exostosis
complete surgical margins appears to offer a good opportunity Multiple cartilaginous exostosis (MCE) is a developmental condi-
for long-term tumor control, especially for low-grade lesions. tion of growing dogs. There is evidence that the etiology of this
When metastatic lesions are identified by thoracic radiography, condition may have a heritable component. 354,378 The actual inci-
dogs may remain asymptomatic for their lung disease for 1 year dence of MCE is difficult to determine because affected dogs may
or more. The role of chemotherapy and RT in the management show no clinical signs and the diagnosis is often incidental. Endo-
of MLO is not well defined. chondral ossification is responsible for formation of these lesions
with new bone being formed from a cartilage cap analogous to a
Metastatic Tumors of Bone physis. Lesions are located on bones that form from endochondral
ossification, and lesions stop growing at skeletal maturity. Malig-
Almost any malignant tumor can metastasize to bone via the nant transformation of MCE lesions has been reported, but gener-
hematogenous route. The lumbar vertebrae, femur, humerus, ally they remain as unchanged, mature, bony projections from the
rib, and pelvis are common sites for metastasis, possibly surface of the bone from which they arose. 353
because these are predilection sites for bone metastasis from Dogs typically present because of a nonpainful or moderately
urinogenital malignancies such as prostate, bladder, urethral, painful palpable mass on the surface of a bone or bones. The
and mammary cancer. 376 Metastatic lesions in long bones pain and lameness is thought to be due to mechanical interfer-
frequently affect the diaphysis, likely because of the proxim- ence of the mass with overlying soft tissue structures. In the case
ity to a nutrient foramen. Nuclear scintigraphy is a sensitive of MCE of vertebral bodies, animals can present with clinical
technique to detect bone metastasis. A whole-body bone scan signs associated with spinal cord impingement. Radiographi-
or PET/CT imaging is recommended when metastatic bone cally, there is a bony mass on the surface of the affected bone
cancer is suspected because it is common for multiple sites of that has a benign appearance and a fine trabecular pattern in
metastasis to be present, even if the patient is symptomatic for the body of the mass (Fig. 25.14). To obtain a histologic diag-
only one bone. nosis, biopsy material must be collected so that sections include