6. Osteogenic Tumours

Question 1

Types of osteogenic tumours

Answer 1

1. Osteoblastoma
2. Osteoid osteoma
3. Osteosarcoma

Question 2

Epidemiology of osteoblastoma

Answer 2

1. 10-30 years of age (mean age = 20), 2/3 male

2. 25% as common as osteoid osteoma

Question 3

Morphology of osteoblastoma

Answer 3

Grossly:

1. Affected sites
   - Spine, sacrum or major bones of lower extremity, typically at metaphysis

Histologically:

1. Anastomosing bony trabeculae rimmed by osteoblasts with a relatively small size, well-defined margins & benign cytologic features
2. Loose & vascular intratrabecular spaces
3. May have bizarre tumour cells
4. No spindle cells / infiltration into adjacent soft tissues

Question 4

Clinical findings of osteoblastoma

Answer 4

1. X-ray findings:
   - Well-delineated radiolucent / radiopaque lesions (often large, up to 10cm)
   - May appear malignant due to cortical expansion & destruction
   - Nidus (actual tumour encircled by reactive bone formation, appears as a small round radiolucency) may be identifiable
2. Treatment
   - Curettage followed by bone grafting
3. Prognosis
   - 20% recur
   - Poorer prognosis if it occurs within central neuraxis
   - Malignant change due to osteogenic sarcoma rare

Question 5

Definition of osteoid osteoma

Answer 5

Mini version of osteoblastoma (<2cm in greatest dimension)

Question 6

Epidemiology & associations with osteoid osteoma

Answer 6

75% under age 25, 2/3 male

Question 7

Morphology of osteoid osteoma

Answer 7

Grossly:
Affected sites:
- 50% of cases involve femur or tibia
- Cortex or metaphysis

Histologically:
Similar to osteoblastoma

Question 8

Clinical features of osteoid osteoma

Answer 8

1. X-ray findings
   - Nidus within bone lesion
2. Presentation
   - Intense localized pain, particularly nocturnal pain (caused by excess of prostaglandin E2 or nerve fibre stimulation)

Question 9

Epidemiology & associations with osteosarcoma

Answer 9

1. 60% male
2. Bimodal age distribution (10-25 & 40+ with other disease)
   - Older patients often associated with Paget’s disease, post-radiation exposure, chemotherapy in childhood or some other pre-existing bone disease

Question 10

Morphology of osteosarcoma

Answer 10

Grossly:

1. Affected sites
   - Typically found in metaphysis of long bones (distal femur, proximal tibia, proximal humerus)
   - Occasionally found in diaphysis
2. Fleshy, grey-white, solid hemorrhagic or necrotic tumour that typically arises within the medullary cavity & extends to the cortex

Histologically:

1. High grade spindle cell tumour that produces osteoid matrix unconnected by cartilage
2. Neoplastic osteoid appearance: eosinophilic, homogenous glassly, irregular contours, surrounding atypical tumour cells, lacelike pattern of neoplastic bone
3. Histological variants
   - Osteoblastic osteosarcoma
   - Fibroblastic osteosarcoma (pure spindle cell growth with minimal matrix)
   - Chondroblastic osteosarcoma (malignant appearing cartilage with peripheral spindling & osteoid production)
   - Low-grade osteosarcoma (uncommon variant with low-grade dysplasia that may be confused with benign conditions; better prognosis than usual high-grade variants)

Question 11

Clinical features of osteosarcoma

Answer 11

X-ray findings:

1. Large destructive, lytic or sclerotic mass with permeative margins
2. Sunburst pattern due to reactive bone formation
3. Codman’s triangle (when tumour elevates periosteum, with the space between the elevated periosteum & underlying bone becoming filled with neoplastic & non-neoplastic bone)

Prognosis

1. 5-year survival rate has dramatically improved over the last 20 years
   - Previously at about 20%
   - With current preoperative chemotherapy, has approached 70%
2. Metastasis common (main sites are the lungs, other bones, heart)