Intracortical osteosarcoma

Intracortical osteosarcoma is the rarest variety of osteosarcoma and represents less than 1% of all osteosarcoma cases.

Epidemiology

Like other subtypes of osteosarcoma, it also typically presents in adolescents and young adults (mean age 19 years). It has a slight male predominance.

Pathology

Intracortical osteosarcoma is a low-grade tumor of cortical bones and typically does not extend into the medullary canal and surrounding soft tissue until the late stages of the disease. Histologically, it is characterized as a sclerosing variant of the osteosarcoma and contains osteoid matrix with few fibroblastic foci and a mild degree of cellular atypia.

Location

The tibial diaphysis is the most common site of this tumor.

Radiographic features

Plain radiograph

It typically presents as an oval intracortical geographic osteolytic lesion in the diaphysis with surrounding sclerosis and usually measures about 4 cm in length. Multiple calcific foci can be seen within the lytic region, suggesting osteoid matrix.

CT

CT reveals an osteolytic lesion with surrounding sclerosis and, rarely, calcific specks in its matrix.

MRI

It was believed that an intracortical osteosarcoma is confined to the cortex of the bone and does not show intramedullary or superficial involvement but, in fact, it may invade the medullary canal as well as the surrounding soft tissue.

T1: hypointense
T2: intermediate to high signal intensity
STIR: to facilitate detection of perilesional edema and intramedullary tumor extension
T1 C+: peripheral enhancement

Treatment and prognosis

Although reported cases have shown slow progression and a low-grade histological appearance, recurrence and distant metastases have been reported. The ideal treatment is surgical resection with an adequate margin; adjuvant chemotherapy can be considered. Following surgical resection and adjuvant chemotherapy, the overall prognosis is good.

Differential diagnosis

Differential considerations on plain radiograph include: