Bones IV

Question 1

What is exostosis?

Answer 1

• benign bony growth projecting outward from the outer surface of a bone
• by convention, an exostosis is a nodular growth

Question 2

What is an osteophyte?

Answer 2

• another term for exostosis
• however, the term osteophyte is, by convention, used to describe a small bony outgrowth at the periphery of a joint, usually in association w/ degenerative joint disease

Question 3

What is a enthesophyte?

Answer 3

• a small exostosis at the site of attachment of a ligament, tendon, or joint capsule (an enthesis)

Question 4

What is a enostosis?

Answer 4

a benign bony growth w/in the medullary cavity of a bone

Question 5

What is hyperostosis?

Answer 5

• by convention, is used to indicate that the dimension of a bone has increased (that a bone is thickened along 1 or more periosteal surfaces)
• use of the term hyperostosis implies a more-than-less uniform thickening of bone along a periosteal surface rather than nodular growths, which are referred to as exostoses

Question 6

What are the different types of proliferative lesions in bone?

Answer 6

1. hypertrophic osteopathy (HO)
2. osteochondromas & multiple cartilaginous exostoses (MCE)
3. craniomandibular osteopathy
4. calvarial hyperostotic syndrome
5. deforming cervical spondylosis

Question 7

What is hypertrophic osteopathy?

Answer 7

• aka hypertrophic pulmonary osteopathy or hypertrophic osteoarthropathy (but NOT metaphyseal osteopathy, aka hypertrophic ostodystrophy)
• it is most commonly recognized in dogs but DOES OCCUR IN OTHER MAMMALS
• the disease involves progressive periosteal new bone formation along the bones of the distal limbs
• the lesions of the bone are associated w/ a concurrent disease, usually an intrathoracic neoplasm (therefore hypertrophic osteopathy may be a paraneoplastic syndrome) or inflammation
• the lesions of the bone will usually regress if the concurrent disease is treated successfully

Question 8

What are osteochondromas or multiple cartilaginous exostoses?

Answer 8

• have been described in people, Eq, Ca, & possibly Fe
• it is an inherited disease in people, Eq, & probably Ca
• lesions consist of masses of trabecular bone w/ a cartilaginous cap projecting from the metaphyseal areas of endochondral bones
• the trabecular bone of each mass is continuous w/ that of the bone of origin
• the masses appear early in life, increase in size through endochondral ossification of the cartilaginous cap, & stop growing at skeletal maturity

Question 9

What is craniomandibular osteopathy?

Answer 9

• aka “lion jaw”
• a heritable disease of West Highland White, Scottish, & Cairn terriers
• other breeds of Ca have been affected, but rarely
• the pathogenesis is unknown
• lesions consist of periosteal new bone production (exostoses of hyperostosis) of the mandible, tympanic bullae, & other bones of the head

Question 10

what is calvarial hyperostotic syndrome?

Answer 10

• is a condition that is most often described in young bullmastiff dogs
• the lesions involve progressive, asymmetric cortical thickening of the bones of the skull cap (frontal, parietal, temporal, & occipital bones)
• the cause is not known

Question 11

what is deforming cervical spondylosis?

Answer 11

• a condition most recognized in ADULT Fe caused by prolonged exposure to excess vitamin A
• the exposure is most often due to feeding an unconventional diet, usually beef liver
• as the name of the condition suggests, the lesions involve the formation of extensive & confluent exostoses over the dorsal & lateral aspects of the cervical vertebrae, often leading to ankyloses (ankylosing spondylosis)
• sometimes, in more severe cases, the occipital bone, cranial thoracic vertebrae, sternum, & proximal forelimbs can be affected
• if the intervertebral foramina are reduced in size, which is common, there can be compression & degeneration of the associated nerves

Question 12

What are the 3 types of benign primary neoplasms?

Answer 12

1. osteoma
2. chondroma
3. ossifying fibroma

Question 13

describe neoplastic diseases of bone (the organ):

Answer 13

• may be primary or secondary
• primary neoplasms of bone arise most often from bone (the tissue) - about 85% - & less often from cartilage - ~ 15%
• other primary neoplasms of bone occur rarely & may arise from fibrous tissue, blood vessels, adipose, etc.
• primary neoplasms may be benign or malignant

Question 14

What are osteomas?

Answer 14

• uncommon, benign neoplasms that grow slowly but progressively by intramembranous ossification
• they usually arise from bones of the head
• they are composed of well-differentiated trabecular bone

Question 15

What is a chondroma?

Answer 15

• uncommon, slow growing, benign neoplasms of hyaline cartilage that usually arise from bones of the head

Question 16

What is an ossifying fibroma?

Answer 16

• uncommon & occur as large masses on the mandible or maxilla of Eq & Bo
• they are composed of well-differentiated fibrous tissue that contains scattered spicules of woven bone
• w/ time, a greater proportion of the mass becomes ossified, & it resembles an osteoma

Question 17

What are the 8 types of malignant primary neoplasms?

Answer 17

1. osteosarcoma
2. chondrosarcoma
3. fibrosarcoma
4. hemangiosarcoma
5. giant cell tumour of bone
6. multilobular tumour of bone
7. maxillary fibrosarcoma
8. bone surface neoplasms

Question 18

What are osteosarcomas?

Answer 18

• relatively common, usually rapidly growing, malignant tumours in which the neoplastic cells form osteoid or bone
• besides the production of osteoid or bone, growth of osteosarcomas usually cause the destruction (lysis) of preexisting bone
• osteosarcomas are characterized by aggressive local invasion & early metastasis, but not the invasion of joint spaces
• osteosarcomas arise most commonly in the long bones of limbs

Question 19

what is a chondrosarcoma?

Answer 19

• not common, grow slowly, cause local destruction of bone, but metastasize late
• defining feature of chondrosarcomas is that the malignant cells produce cartilaginous ECM, but NEVER osteoid or bone

Question 20

What is a fibrosarcoma?

Answer 20

• malignant tumors composed of fibroblasts & the CT they produce
• fibrosarcomas arising in bones can result in the destruction of bone

Question 21

What is a hemangiosarcoma?

Answer 21

• malignant neoplasms of vascular endothelium that, in this context, arises from w/in a bone

Question 22

What is a giant cell tumor of bone?

Answer 22

• refers to a malignant neoplasm of bone marrow stromal cells
• there are many osteoclasts in the lesion, but they are not the neoplastic cells
• these neoplasms used to be called osteoclastomas (but the osteoclasts are not neoplastic)

Question 23

What is a multilobular tumor of bone or canine multilobular osteochondrosarcoma?

Answer 23

• uncommon, slow-growing, but often malignant neoplasm of the skull bones of the Ca (& Fe & Eq)
• this tumor tends to be locally invasive & this feature typically leads to the euthanasia of affected dogs
• metastasis has been described but is not common

Question 24

What is a maxillary fibrosarcoma?

Answer 24

• occur only in dogs
• they are intriguing neoplasms b/c they have a benign, if not innocuous, histologic appearance but are malignant; mostly invasive, sometimes metastatic
• these so-called histologically low grade fibrosarcomas can also arise in other bones of the head

Question 25

What is a bone surface neoplasm?

Answer 25

• neoplasms that arise from the periosteum
• all are malignant, but slower growing & less aggressive than corresponding neoplasms originating from w/in a bone
• tumor types include periosteal osteosarcoma, periosteal chondrosarcoma, periosteal fibrosarcoma, & parosteal osteosarcoma
• periosteal sarcomas invade the underlying cortex while parosteal sarcomas, typically, do not (or do so much later in the disease)

Question 26

Stats of osteosarcomas?

Answer 26

• > 8,000 new cases/yr in US
• appendicular skeleton of mature, large & giant breed dogs (~75%)
• front limbs twice as often as hind limbs (“away from the elbow”)
• axial skeleton of small breed dogs
• similar prognosis
• many subtypes: osteoblastic, chondroblastic, fibroblastic, etc.
• < 15% have “detectable” metastasis at diagnosis; 90% die of metastatic disease w/in 1 year

Question 27

What are secondary neoplasms of bone?

Answer 27

• malignant neoplasms that usually spread via circulation & begin to grow w/in bones (metastasize to bones)
• bones appear to be involved as sites of metastatic neoplasia b/c of the vascular nature of bone marrow
• metastatic neoplasms in bone can be associated w/ pain, lysis of bone, pathologic fracture, & new bone formation
• why some neoplasms metastatic to bone result in more bone lysis than bone formation, while other neoplasms metastatic to bone result in the reverse effects (more bone formation than bone lysis) is not known
• carcinomas are reported to metastasize to bone more frequently than sarcomas

Question 28

What is a myeloma?

Answer 28

• a primary bone marrow neoplasm
• can also affect bone
• the most common type of bone marrow neoplasm to affect bone is so-called multiple myeloma or plasma cell myeloma

Question 29

What are bone cysts & cyst-like lesions?

Answer 29

• rare, discrete cavities w/in a bone that may distort the cortex
• the cavity is usually filled w/ fluid or soft tissue
• by definition, a cyst is a closed cavity or sac lined by an epithelium
• the term bone cyst, therefore, is not always accurate as there is no epithelial lining
• so, some authorities use the term ‘cyst-like lesion’ to refer to these lesions
• the presence of a bone cyst may reduce the strength of the bone & may cause lameness

Question 30

What is fibrous dysplasia?

Answer 30

• refers to an uncommon lesion found in young animals & probably represents a developmental defect
• it consists of an expanding mass of fibro-osseous tissue that results in the distortion & weakening of the cortex of the affected bone