Problem:

Diagnostic imaging studies from three different patients with the same condition are shown, including T1-weighted transaxial and T2-weighted coronal images from an MR examination of a foot lesion. What is the most likely diagnosis?

Discussion:

This relatively common malignant tumor of bone has a varied histological pattern. The tumor cells are arranged in broad sheets. Some cells have a larger, lightly stained, finely granular nucleus with pale, ill-defined cytoplasm, whereas others possess small, darker staining nuclear chromatin feltwork with a rim of moderately well delineated cytoplasm; cells may be located about vessels in a perithelial arrangement. A large-cell variety also has been described. The origin of Ewing's sarcoma is unknown; it may be derived from mesenchymal cells of the bone marrow of immature reticulum cells or from vascular or myelogenic elements.

Ewing's sarcoma usually is identified in patients in their first, second, or third decades of life, and the ratio of affected men to affected women is approximately 3:2. Symptoms of localized pain and swelling may be combined with fever, weight loss, anemia, and leukocytosis, simulating the clinical findings of an infection. Any skeletal site can be involved, although the most frequent sites of involvement are the long tubular bones (the femur, tibia,1 humerus, and fibula), the pelvic girdle, the vertebrae, the ribs, and the scapula. Ewing's tumor found in the craniofacial region or the small bones of the hand and foot2 is less typical. It is found more frequently in patients who are over the age of 18 years.

In the tubular bones, Ewing's sarcoma predilects the diaphyseal or diametaphyseal region. It is characterized by a long permeative osteolytic lesion with poorly defined margins, cortical disruption, and a periosteal reaction.3 The periostitis frequently is described as being of the "onion peel" or "hair-on-end" type. Pathologic fractures are identified in 5 to 10% of cases. Saucerization and excavation of the cortex also are noted in some tumors and this feature may be the most prominent radio-graphic finding. In some of these cases, an eccentric or cortical location of the tumor may be apparent on pathological examination. In the flat bones, permeative destruction also is typical. In this location, the amount of new bone formation may be striking. In the vertebral column, the sacrum, lumbar spine, thoracic spice, and cervical spine may be involved, in order of descending frequency. Osteolysis and vertebral collapse predominate. Occasionally, uniform sclerosis of a vertebral body may be seen. Tumor extension into the posterior elements also can be evident. Paravertebral masses, loss of height of intervertebral disc spaces, and spread to contiguous vertebral bodies are additional radio-graphic features of spinal involvement.

Skeletal and extraskeletal metastasis due to Ewing's sarcoma is frequent. Osseous changes in these cases may simulate those in leukemias, lymphomas, or metastatic neuroblastomas.

References

1. Resnick D: Bone and Joint Imaging. 2nd edition. Philadelphia, WB Saunders, 1996.

This series of diagnostic challenges is prepared by David J. Sartoris, MD,

Professor, Department of Radiology, University of California School of Medicine,

San Diego, CA.