Skeletal involvement in Langerhans cell histiocytosis
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Langerhans cell histiocytosis (LCH) represents a disorder characterised by an abnormal accumulation of histiocytes in miscellaneous tissues. The bone is commonly affected, especially the flat bones, the spine and the long bones. Some lesions in children such as a “vertebra plana” or a solitary lytic lesion of the skull may be suggestive for LCH, whereas others can be confused with a malignant tumour or osteomyelitis. This pictorial essay presents the main usual and unusual skeletal manifestations observed in LCH.
• Osseous involvement in children with LCH is very similar to that seen in multiple myeloma.
• A solitary lytic lesion of the cranial vault is a typical radiographic finding of LCH.
• A vertebra plana appearance in the spine is another typical radiographic finding.
• Extensive signal intensity changes within bone marrow on MRI are a helpful sign for the diagnosis.
• In long bones, endosteal scalloping may be responsible for a “budding appearance”.
KeywordsLangerhans cell histiocytosis Children Diagnostic imaging Radiography Tomography Spiral computed Magnetic resonance imaging
Langerhans cell histiocytosis (LCH) represents a spectrum of rare disorders characterised by idiopathic infiltration and accumulation of abnormal histiocytes (i.e. the Langerhans cells) within various tissues (bone marrow, skin, central nervous system, lung, liver, spleen, lymph nodes) causing focal or systemic effects . LCH predominates in children and its annual incidence is estimated at 4.6 per million in children under 14 years of age .
LCH was formerly known as “histiocytosis X”, a term that grouped three major syndromes, which are now considered as clinical variants of the same disease: the eosinophilic granuloma (unifocal LCH with a solitary bone lesion), the Hand-Schüller-Christian disease (multifocal LCH with the classic triad of skull lesions, exophtalmos, and diabetes insipidus) and the Letterer-Siwe disease (fulminant LCH with multiple organ involvement) . The aetiology of LCH remains unknown, and it is still uncertain whether LCH is a neoplastic disorder, suggested by the monoclonality in lesions, or a reactive disorder resulting from a dysregulation of the immune system [4, 5].
Clinical presentations of LCH vary widely, from an asymptomatic solitary bone lesion to a multisystem life-threatening affliction [1, 6, 7]. Any organ or system of the human body can be involved, but the skeleton, the skin and the central nervous system are more commonly affected [1, 6, 7]. Biopsy taken from the most easily accessible lesion (usually a skin or a soft tissue biopsy) is necessary to confirm the diagnosis. Histopathological examination shows tissue infiltration by abnormal Langerhans cells as well as normal inflammatory cells (T cells, eosinophils, macrophages and multinucleated giant cells) . Diagnosis is confirmed by the morphologic identification of the Langerhans cells and positive immunohistochemical staining with CD1a and/or CD207. The identification of Birbeck granules on electron microscopy, which are cytoplasmic tennis-racket-shaped organelles characteristic of Langerhans cells, is nowadays rarely performed . A bone biopsy is often not needed for the diagnosis of LCH, but it may be required in some cases. When the risk of such a biopsy outweighs the need for a definitive diagnosis (as this may be the case in some children with isolated upper cervical vertebral involvement), careful monitoring by clinical examination and appropriate imaging for at least the next 6 months is necessary in order to exclude a malignancy and to reassess the need for biopsy .
Once the diagnosis has been ascertained, the treatment depends on the extent and severity of LCH. Extent of the disease makes the distinction between single system disease and multisystem disease. Severity of the disease takes into account the involvement or not of risk organs (i.e. the haematological system, the spleen and the liver) and the presence or not of central nervous system risk lesions (i.e. skull bone lesions with the exception of the vault) . Therefore, different therapeutic approaches may be applied; they include conservative management, local therapy (curettage, excision, intralesional corticosteroid injection, low-dose radiation therapy) and systemic therapy (chemotherapy, corticosteroids, stem cell transplantation) [4, 7].
Imaging techniques in assessment of skeletal involvement
Imaging features of skeletal involvement
Mandible and maxilla
Pelvis and spine
LCH is a rare disorder, mostly affecting children. Osseous involvement in children with LCH is very similar to that seen in adults with multiple myeloma (i.e. predominance of destructive lesions in axial skeleton). It is best assessed with conventional or digital skeletal surveys. Radiographic features are variable, from a suggestive appearance to a more aggressive one, which may mimic Ewing’s sarcoma or osteomyelitis. Radiography may be complemented by CT and/or MRI to delineate the extent of osseous destruction or the extent of bone marrow and soft tissue involvement respectively. MR findings are non-specific, but extensive bone marrow changes and/or a “budding appearance” of bone lesions may be suggestive of the diagnosis. Biopsy is necessary to obtain diagnosis confirmation.
Conflicts of interest
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