Langerhans cell histiocytosis (LCH) is a clonal proliferative disorder of Langerhans cells, representing the most common tumor-like bone lesion in childhood. Solitary bone involvement (eosinophilic granuloma) is the most frequent form; the skull, femur, pelvis, and vertebra are predilection sites. Radiologically, geographic lytic lesion, 'beveled edge' skull defect, and 'vertebra plana' are characteristic findings.
Age Range
1-15
Peak Age
5
Gender
Male predominant
Prevalence
Uncommon
Langerhans cell histiocytosis develops from clonal proliferation of Langerhans cells of the dendritic cell lineage, driven by oncogenic signaling pathways such as the BRAF V600E mutation. The proliferating Langerhans cells accumulate in bone marrow and activate osteoclasts, leading to aggressive bone resorption that produces geographic lytic lesions. In the skull, differential resorption rates of the inner and outer tables create the 'beveled edge' appearance; this radiological finding results from faster destruction of the inner table. Extensive involvement of the vertebral body leads to complete loss of vertebral height (vertebra plana), while reactive granulomatous tissue can form a 'button sequestrum' — a central island of residual viable bone. On MRI, T2 hyperintense signal reflects high cellular density and perifocal edema, while contrast enhancement demonstrates the vascularity of granulomatous tissue.
Asymmetric beveled-edge lytic defect in the skull created by greater resorption of the inner table compared to the outer table. This finding is pathognomonic for LCH and is the most important radiological criterion distinguishing it from other lytic skull lesions (epidermoid, myeloma, metastasis).
Asymmetric destruction of inner and outer skull tables creating a beveled-edge lytic defect. The inner table is resorbed to a greater diameter than the outer table, with the 'bevel' clearly visible on cross-sectional imaging. Sclerotic margin is typically absent or minimal.
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A beveled-edge lytic defect is noted in the skull with the inner table destroyed to a greater extent than the outer table; this finding is pathognomonic for Langerhans cell histiocytosis.
Sharply marginated, 'punched-out' geographic lytic lesion in long bones (femur, humerus) or flat bones (pelvis, skull). Demonstrates Lodwick type IA-IB pattern. Cortical thinning or perforation may accompany; periosteal reaction can be solid or lamellar type, with sunburst pattern rarely seen in aggressive cases.
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A sharply marginated geographic lytic lesion (Lodwick type IB) is identified in the femoral diaphysis, accompanied by cortical thinning and solid periosteal reaction.
A round or oval dense bone fragment (sequestrum) remaining in the center of a lytic lesion. Particularly typical in skull lesions, surrounded by granulomatous tissue. On CT, the high-density central island creates a striking contrast with the surrounding lytic area.
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A high-density bone island (button sequestrum) is noted in the center of the calvarial lytic lesion, consistent with Langerhans cell histiocytosis.
On T1-weighted images, the lesion demonstrates hypointense signal with loss of normal bone marrow fat signal. Lesion margins are generally sharp, though a transition zone may form due to perifocal bone marrow edema. The T1 signal intensity of the lesion is isointense or slightly hypointense to muscle.
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On T1-weighted series, the lesion demonstrates hypointense signal with loss of normal marrow fat signal, consistent with marrow infiltration.
On T2-weighted images, the lesion shows heterogeneous hyperintense signal. High cellularity of granulomatous tissue and areas of necrosis create the heterogeneity. Surrounding bone marrow edema manifests as high T2 signal and may make the lesion appear larger than its true size.
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On T2-weighted series, the lesion demonstrates heterogeneous hyperintense signal with prominent surrounding bone marrow edema.
On STIR sequence, fat suppression makes perifocal bone marrow edema and accompanying soft tissue component prominently visible. Edema typically extends beyond the true lesion margins, creating an aggressive appearance. Soft tissue extension — particularly in the aggressive phase of eosinophilic granuloma — forms a periosteal/subperiosteal component through cortical perforation.
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On STIR sequence, prominent bone marrow edema surrounding the lesion and a soft tissue component arising from cortical perforation are demonstrated.
On post-gadolinium T1-weighted series, the lesion demonstrates intense heterogeneous enhancement. Rich vascularity of granulomatous tissue leads to intense enhancement, while central necrotic areas do not enhance. The periosteal/subperiosteal soft tissue component also enhances. In vertebra plana cases, the collapsed vertebra may show diffuse enhancement.
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On post-contrast series, the lesion demonstrates intense heterogeneous enhancement with central non-enhancing necrotic areas.
On diffusion-weighted imaging (DWI), restricted diffusion is observed in the cellular component of the lesion (high DWI signal, low ADC value). This finding reflects the high cellular density of granulomatous tissue. Necrotic areas show facilitated diffusion and appear bright on ADC maps. ADC values are typically in the range of 0.8-1.2 × 10⁻³ mm²/s.
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On diffusion-weighted series, restricted diffusion is noted in the solid component of the lesion (ADC: ~1.0 × 10⁻³ mm²/s), indicating high cellularity.
Symmetric complete collapse and flattening of the vertebral body (vertebra plana). Disc spaces are preserved — this is important in differential diagnosis from malignant compression fractures. Posterior elements are typically spared. During the healing phase, vertebral height may partially recover through reossification.
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Complete vertebra plana is identified in the thoracic vertebra with preserved disc spaces; this finding is highly suggestive of Langerhans cell histiocytosis in childhood.
Active LCH lesions demonstrate increased FDG uptake (SUVmax typically 3-15). PET-CT is important for whole-body screening in multisystem disease and treatment response assessment. Inactive/healing lesions show decreased or normalized FDG uptake. Extra-osseous involvement (lung, liver, lymph node) can also be assessed with PET-CT.
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On PET-CT, increased FDG uptake is noted in the lesion (SUVmax: X), consistent with active Langerhans cell histiocytosis.
Criteria
Single bone involvement, typically 5-15 years, most common in skull/femur/pelvis, diagnosis and treatment via surgical biopsy or curettage
Distinct Features
Best prognosis form. Isolated lytic lesion, variable periosteal reaction. Spontaneous regression possible. Can radiologically mimic aggressive bone tumor.
Criteria
Multiple bone involvement, no organ involvement, typically age 1-5, staging with PET-CT required
Distinct Features
Multiple lytic lesions simultaneously present in different bones. Each lesion may be at different stages (active/healing). Vertebra plana more common in polyostotic form. Metastatic neuroblastoma and leukemia should be considered in differential.
Criteria
Classic triad: diabetes insipidus + exophthalmos + lytic skull lesions. Age 2-10, chronic course, hypothalamic/pituitary involvement
Distinct Features
Pituitary stalk thickening and enhancement on MRI is pathognomonic. Temporal bone mastoid involvement can be confused with otitis media. 'Geographic map skull' — multiple coalescent lytic lesions create a map-like appearance.
Criteria
<2 years, multiple organ involvement (bone + liver + spleen + lung + skin + bone marrow), aggressive clinical course, poor prognosis
Distinct Features
Lung involvement shows diffuse cystic changes and pneumothorax. Liver involvement demonstrates sclerosing cholangitis pattern. Widespread skin rash (seborrheic dermatitis-like). Requires chemotherapy, mortality 20-50%. Radiological findings are diffuse and aggressive.
Distinguishing Feature
Ewing sarcoma shows more aggressive periosteal reaction ('onion skin', sunburst), larger soft tissue mass, and presents at younger age (10-20 years). LCH demonstrates less soft tissue component and more sharply marginated lytic lesion.
Distinguishing Feature
Osteomyelitis presents clinically with fever and leukocytosis. On MRI, osteomyelitis shows the 'penumbra sign' (hyperintense rim around abscess on post-contrast T1) while LCH does not show this finding. Sequestrum in osteomyelitis is dead bone, while the button sequestrum in LCH is viable bone.
Distinguishing Feature
Multiple myeloma occurs in adult age group (>40 years) and produces multiple 'punched-out' lytic lesions. Myeloma does not show beveled edge or button sequestrum in the skull. Serum protein electrophoresis shows M-band in myeloma, which is absent in LCH.
Distinguishing Feature
Metastases generally occur in the presence of known primary malignancy and have irregular margins. The sharp geographic margin and beveled edge of LCH are not seen in metastases. In childhood, bone metastasis originates from neuroblastoma and can be distinguished by paravertebral soft tissue mass.
Distinguishing Feature
Simple bone cyst is typically a fluid-filled, sharply marginated metaphyseal lesion in the proximal humerus or femur. On MRI, it shows homogeneous T2 hyperintense (fluid) signal, while LCH demonstrates heterogeneous T2 signal and solid enhancement. The cyst wall is thin and smooth, lacking the granulomatous solid tissue seen in LCH.
Urgency
semi-urgentManagement
Monostotik eozinofilik granülom: küretaj/biyopsi veya intralezyonel kortikosteroid enjeksiyonu. Poliostotik veya multisistemik: kemoterapi (vinblastin + prednizon). Vertebra plana: konservatif izlem (reossifikasyon potansiyeli).Biopsy
NeededFollow-up
Monostotik: 6-12 aylık radyolojik takip. Poliostotik/multisistemik: 3-6 aylık PET-BT ile tedavi yanıtı değerlendirmesi.LCH diagnosis requires histopathological confirmation (CD1a+/CD207+ Langerhans cells, Birbeck granules). BRAF V600E mutation analysis is important for prognostic and treatment planning. Monostotic form generally has good prognosis, while multisystem form (Letterer-Siwe) requires aggressive chemotherapy. Development of diabetes insipidus indicates hypothalamic involvement and requires endocrinological evaluation.
Single bone involvement (eosinophilic granuloma) has the best prognosis and may regress spontaneously or be treated with curettage. Multisystem involvement (Hand-Schuller-Christian, Letterer-Siwe) may require chemotherapy. Vertebra plana is treated with bracing. Biopsy is needed for diagnosis (CD1a and S100 positive Langerhans cells).