General Information

• Intracortical osteosarcoma is an extremely rare type of osteosarcoma that arises within and is usually confined to the cortex of the bone.
• It is a high grade osteosarcoma that is confined to the cortex of a long bone
• Intracortical osteosarcoma is very rare and only a handful of cases have been reported.
• It is often initially misdiagnosed as an osteoid osteoma, bone abscess, non ossifying fibroma, osteoblastoma or adamantinoma until it is biopsied or removed

Clinical Presentation

Signs/Symptoms:

• Pain, swelling, tenderness, <1 year

Sex Predilection:

• Possible slight male predilection

Age:

• 10-30 years

Sites:

• Diaphysis of femur or tibia are the most common sites

Radiographic Presentation

Plain Radiographs:

• Intracortical lytic lesion with surrounding sclerosis
• The junction of the lesion with the normal bone is usually irregular but sharply demarcated
• Size of lesion is usually between 1 cm to 5 cm
• Lesion may demonstrate ossification or mineralization within it
• No intramedullary or soft tissue involvement
• Minimal or no periosteal reaction or periosteal reaction may appear benign
• CT may show cortical permeation

Gross Pathology

• Intracortical, well defined tumor with very thick expanded cortex
• Irregular borders
• Thick and expanded cortex
• Tumor is grey/tan/yellow and gritty from mineralized osteoid or bone production

Microscopic Pathology

• Highly osteoblastic & sclerotic similar to a conventional osteosarcoma
• Neoplastic cells when become entrapped in osteoid may appear to normalize and have less nuclear pleomorphism and atypia
• Residual cortical bone will be entrapped by malignant cells producing osteoid (evidence of malignancy)
• There may be very small chondrosarcomatous and fibrosarcomatous foci
• Cartilage production is minimal (as opposed to a periosteal osteosarcoma)

• Malignant spindle cell tumor producing osteoid
• Malignant cells have large nuclei, minimal cytoplasm, nuclear pleomorphism, mitoses
• They appear crowded and haphazard
• The osteoid is layed down in lace-like manner in between malignant cells

Differential Diagnosis

• Osteoid Osteoma
• Brodie's Abscess
• Osteoblastoma
• Nonossifying fibroma
• Eosinophillic Granuloma
• Osteofibrous Dysplasia
• Adamantinoma

Treatment

• En bloc Resection/Limb Sparing Surgery whenever feasible
• Patients treated by curettage and intralesional procedures have experienced local recurrences according to the literature
• Efficacy of chemotherapy is uncertain given the small number of cases

Prognosis

• Metastases to the lungs along with unusual sites of metastases have been reported
• Exact statistics are unavailable given the small number of patients who have been reported to develop this disease.