Diagnosis: Langerhans cell histiocytosis X (eosinophilic granuloma)

Discussion: LCH (Langerhans cell histiocytosis X) may manifest as a solitary lesion or as multiple lesions and occurs most often during childhood with a peak incidence between the ages of 5 and 10 years. The most commonly affected sites are the skull, the ribs, the pelvis, the spine, and the long bone. Clinical manifestations include local pain, tenderness, and swelling or a soft tissue mass adjacent to the site of the skeletal lesion. Fever, an elevated sedimentation rate, and leukocytosis may also be present. If a vertebra is affected, the patient may present with neurologic symptoms resulting from a collapse of the vertebral body. Imaging feature of the lesion may vary according the its location, such as a beveled lytic lesion in the skull or a “vertebra plana” in the spine. In the long bone, LCH presents as aradiolucent destructive lesion, commonly associated with a lamellated periosteal reaction, mimicking that of round cell malignant tumor, such as lymphoma or Ewing sarcoma. The lesion may have well-defined or poorly defined margins, with or without sclerotic borders. Computed Tomography (CT) effectively demonstrates periosteal reaction, beveled edges, and reactive sclerosis of the lesion. The MRI appearance varies and appears to correlate with the radiographic appearance. The MRI findings of early stage of LCH are nonspecific and may simulate an aggressive lesion, such as osteomyelitis or Ewing sarcoma, and benign tumors, such as osteoid osteoma or chondroblastoma. Usually, LCH shows marked enhancement and the recent study reported that most common MRI appearance of LCH is that of a focal lesion, surrounded by an extensive, ill-defined signal from bone marrow and by soft tissue reaction with low signal intensity on T1-weighted images and high signal intensity on T2-weighted images, considered to represent bone marrow edema and soft tissue edema or the flare phenomenon.

References: A. Greenspan et al. Differential diagnosis in orthopaedic oncolongy, second edition. 2007 by LIPPINCOTT WILLIAMS & WILKINS.