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Imaging in Eosinophilic Granuloma of the Skeleton

Practice Essentials

Eosinophilic granuloma (EG) is a rare, benign tumorlike disorder characterized by clonal proliferation of antigen-presenting mononuclear cells of dendritic origin known as Langerhans cells. It is the most common variant of Langerhans-cell histiocytosis (LCH). Any organ or system of the human body can be affected, but 80% of cases are skeletal and account for less than 1% of all bone tumors.
  Children between 1 and 15 years of age make up more than 50% of cases of LCH, with peak incidence in children younger than 3 years.
  

Eosinophilic granuloma is characterized by single or multiple skeletal lesions, but solitary lesions are more common than multiple lones. When multiple lesions occur, the new osseous lesions appear within 1-2 years, and the condition is still classified as eosinophilic granuloma. Any bone can be involved; the more common sites include the skull, mandible, spine, ribs, and long bones (see the images below).
Pathologic fractures may ensue.
 

The other two variants of LCH, Letterer-Siwe disease and Hand-Schuller-Christian disease, are multisystem syndromes, with the manifestations ranging from isolated bone lesions to multisystem disease.

Chest radiograph in a 30-year-old woman who presen

Chest radiograph in a 30-year-old woman who presented with shortness of breath and a palpable swelling over the right parietal region. The radiograph shows an interstitial lung pattern with a honeycomb appearance in the upper zones (see the next image).

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Lateral skull radiograph in a 30-year-old woman wi

Lateral skull radiograph in a 30-year-old woman with shortness of breath and a palpable swelling over the right parietal region shows 2 purely lytic lesions in the frontoparietal region of the skull. The larger parietal lesion has beveled edges, suggestive of an eosinophilic granuloma. Biopsy results confirmed the diagnosis of eosinophilic granuloma.

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Transaxial nonenhanced computed tomography scans o

Transaxial nonenhanced computed tomography scans of the skull in a 28-year-old woman who presented with a palpable swelling over the calvarium. Scanogram of the patient’s skull shows a geographic lytic lesion within the parieto-occipital region. Transaxial scan through the vertex, examined in a bone window, shows an expanding lytic lesion within the diploic space (see the next image).

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Transaxial nonenhanced computed tomography scans t

Transaxial nonenhanced computed tomography scans through the vertex in a 28-year-old woman with a palpable swelling over the calvarium, examined in a brain window. Images show destruction of both the outer and inner tables of skull; however, no brain involvement is noted.

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Because patients with EG may present with multiple bone lesions at a single site (single-system multifocal bone), differentiation must be made from other variants of LCH with bone lesions affecting other organ systems (multisystem, including bone).
 Radiologists need to be aware that additional eosinophilic granuloma of bone, occurring as long as 4 years after initial diagnosis, should be interpreted as a localized form of LCH. This differentiation is important, because decreased mortality has been found in high-risk multisystem LCH patients who had bone involvement, suggesting that those with bone LCH may have more indolent disease.

Lung involvement occurs in 20% of patients with eosinophilic granuloma and in an older group (age, 20-40 yr), with a strong association with smoking. Diffuse pulmonary infiltrates may be a manifestation of a covert osseous disease. In 50-75% of patients, the disease is monostotic. Skull involvement is seen in 50% of patients.
Rarely, the growing epiphysis is involved with eosinophilic granuloma; in most such cases, transphyseal extension can be demonstrated, both by the radiologic findings and by the histopathologic results.

Eosinophilic granuloma may masquerade as an aggressive periodontitis
; therefore, eosinophilic granuloma should be considered when an expanding lytic jaw lesion is encountered.

Preferred examination

A skeletal survey, skull series (or low-dose whole bone CT), and chest radiograph (AP and lateral) are the first radiographic examinations to be done. CT of specific areas of the skeleton are indicated when mastoid, orbital, scapular, vertebral, or pelvic lesions are found by plain radiographs. MRI may detect additional osseous or extraosseous lesions. A skeletal scintigram (bone scan) alone does not suffice.

A wide variety of bone lesions may mimic eosinophilic granuloma; these include infections, traumatic lesions, and neoplasms. A false-negative diagnosis of eosinophilic granuloma is exceptional when plain radiographic findings are used, although difficulty may be encountered with lesions in areas with more complex anatomy, such as the posterior elements of the vertebral bodies. In these cases, conventional tomography or CT scanning may be useful. With radionuclide scanning, the false-negative rate is 30%.

Differential diagnosis

The differential diagnosis of eosinophilic granuloma includes aneurysmal bone cyst, bone infarct and bone metastases, thoracic eosinophilic granuloma, and fibrous dysplasia, as well as acute pyogenic, chronic, and variant osteosarcoma.

When the skull is involved, the following conditions should be considered: venous lake; meningocele, encephalocele, and cranium bifidum; arachnoid granulation; parietal foramen; epidermoid cyst; hemangioma; cholesteatoma; fibrous dysplasia; metastasis; surgical defect; and osteomyelitis.

The presence of vertebra plana should prompt consideration of causes such as fracture, hemangioma, osteomyelitis, metastasis, lymphoma, leukemia, plasmacytoma, chordoma, aneurysmal bone cyst, and Ewing sarcoma. Although eosinophilic granuloma is the most common cause of vertebra plana, it is distinguished by isolated spinal disease, the lack of constitutional symptoms, and minimal laboratory abnormalities. Cervical spine eosinophilic granuloma more often manifests with osteolytic lesions, rather than vertebra plana.

When the long bones are affected, Ewing sarcoma, chronic osteomyelitis, Brodie abscess, and chondroblastoma should be considered.

Other interstitial lung diseases should be taken into consideration with pulmonary involvement.

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