| Discussion: |
Eosinophilic granuloma .
This is a tumor like condition belonging to a group of disorders known as reticuloendothelioses. This spectrum of diseases includes eosinophilic granuloma (condition with bone lesions only) ; Hand-Schuller-Christian disease or xanthomatosis (characterized by the triad of bone lesions, diabetes insipidus and exophthalmos); and Letterer-Siwe disease or nonlipid reticulosis (when disseminated disease is marked by wasting, lymphadenopathy , hepatosplenomegaly and anemia).
Eosinophilic granuloma may manifest as a solitary lesion or as multiple lesions. It occurs most often during childhood with a peak incidence between the ages of 5 and 10 years. It is slightly more common in males. The most commonly affected sites are the skull, the ribs, the pelvis, the spine and the long bones. Epiphyseal lesions are relatively rare. Clinical manifestations include local pain, tenderness, swelling or a soft tissue mass adjacent to the site of the skeletal lesion.
Plain radiographs remain the most effective modality for the diagnosis of eosinophilic granuloma. In the mandible, radiolucent lesions secondary to destruction of the alveolar bone are characteristic. In the skull, a beveled lytic lesion is typical. In the center of the lytic lesion there is sometimes a small sclerotic focus referred to as a button sequestrum. In the spine, so-called vertebra plana is the usual manifestation and results from a collapsed vertebral body. In the long bones, eosinophilic granuloma presents as a radiolucent destructive lesion commonly associated with a laminated periosteal reaction. This appearance may mimic that of a round cell malignant tumor, such as lymphoma or Ewing sarcoma. A distinct and characteristic feature of many lesions is pointing or beveling of the edges.
The distribution of lesion may be determined by radionucleotide bone scan, which can aid in the detection of silent lesions and in differentiating Langerhans cell granuloma from Ewing sarcoma, which rarely has multiple foci. This study has its limitations, however, because approximately 35 percent of these lesions show normal uptake of tracer.
CT may be helpful if plain film radiography inadequately defines the extent of the process, particularly in cases of spine and pelvic involvement. This modality effectively demonstrates periosteal reaction, doubled edges and reactive sclerosis.
The differential diagnosis depends on the site and extent of bony involvement, the phase of the disease, and the age of the patient.
In a solitary lesion in long or flat bones, the main considerations are Ewing sarcoma and osteomyelitis. Both lesions may exhibit moth-eaten or permeative types of bone destruction and laminated, onionskin periosteal reaction. If a solitary lesion of eosinophilic granuloma in a long tubular bone does not develop a periosteal reaction, the differential diagnosis of simple bone cyst must be considered.
The differential diagnosis of a solitary skull lesion in a child or young adult should include osteomyelitis, hemangioma and fibrous dysplasia. In an elderly patient, the considerations are the lytic phase of Paget's disease, myeloma and a metastasis. The beveled edge or double contoured appearance of the lesion is always highly suggestive of eosinophilic granuloma.