Location of bone tumors

Location

Most expansile, lucent lesions are located in the medullary space of the bone. However, we can further define the location of the lesion by noting its relationship to the physis. Many lesions tend to occur in a "favorite" part of the bone. The favored locations are listed in the figure below.

figure after Madewell, et al 1981

Epiphysis

Very few lesions tend to arise in the epiphysis. Chondroblastoma is one of the very few tumors that arise here before the physis closes. Osteomyelitis can also arise in the epiphysis.

Several entities can spread across the physis. Osteomyelitis is a classic example of this. Although the dogma for years has been that malignancies such as osteosarcoma and Ewing's tumor rarely cross the physis, more recent experience with MRI has shown this to be untrue. With very sensitive pulse sequences such as STIR (short-tau inversion recovery), subtle extension across the physeal plate may be seen not uncommonly.

After the plate closes, the physis ceases to be an anatomic barrier to disease, and a variety of lesions can be seen involving the epiphyseal area, such as giant cell tumor, enchondroma or aneurysmal bone cyst. Helpful tips in steering the differential diagnosis among these entities include the facts that most enchondromas will exhibit chondroid matrix, most giant cell tumors will abut an articular margin, and most aneurysmal bone cysts appear, well, "aneurysmal" or expansile. It was once thought that aggressive tumors, such as Ewing's tumor and osteosarcoma tended to "respect" the physeal plate and only rarely cross it. However, more recent studies (Panuel, Norton) of the behavior of such tumors with sensitive MR pulse sequences show that osteosarcomas may cross the plate into the epiphysis in 70 - 80 % of cases and Ewing's tumor in about 20 %.

Metaphysis

This is the fastest growing area of a bone, and also the most likely area for a primary neoplasm to arise. This is especially true in the distal femur and proximal tibia, which are the fastest growing metaphyseal areas in the skeleton. The metaphysis also has the best blood supply of the bone, so entities such as infection or metastasis will commonly be seen in this area as well. In general, most of the entities in FOGMACHINES (with the exception of chondroblastoma) will be most commonly seen in the metaphyseal area of a given bone.

Diaphysis

Most of the entities in FOGMACHINES can also appear in the diaphysis, although with less frequency. Notable exceptions are: chondroblastoma, which almost always occurs in an epiphysis or epiphyseal equivalent (most apophyses, the patella and the calcaneus); giant cell tumor, which almost always occurs in an apophysis or in the bone adjacent to a join space; osteoblastoma, which usually occurs in the posterior elements of the spine; and aneurysmal bone cyst, which is usually metaphyseal in location.