X-Ray Findings of Langerhans Cell Histiocytosis in Children
The characteristic X-ray appearance of LCH in children shows well-defined osteolytic "punched-out" lesions, most commonly affecting the skull (60% of cases), with distinctive features including beveled edges in skull lesions, vertebra plana in the spine, and aggressive-appearing central destructive lesions in long bones. 1
Skeletal Distribution
Bone involvement occurs in approximately 60% of pediatric LCH cases, with specific predilection sites: 1
- Skull (most common): Calvarium and temporal bones show lytic lesions with characteristic beveled or scalloped edges, creating a "geographic" pattern 2, 3
- Long bones: Femur (38%), tibia (32%), humerus (15%), and radius (12%) are most frequently affected 4
- Spine: Vertebral body collapse producing the pathognomonic "vertebra plana" appearance 2, 5, 3
- Other sites: Pelvis, mandible (producing "floating tooth" sign), and ribs 2, 3
Classic Radiographic Features
Skull Lesions
Plain radiographs demonstrate distinctive patterns that help differentiate LCH from other pathologies: 2, 3
- Lytic lesions developing in the diploic space with well-defined margins 2
- Beveled edges creating asymmetric destruction of inner and outer tables 2, 3
- "Button sequestrum" - a characteristic finding where a central bone fragment appears within the lytic defect 2, 3
- Scalloped or confluent (geographic) edges distinguishing it from more aggressive malignancies 2
Long Bone Lesions
The radiographic appearance in long bones differs from skull involvement: 2, 4
- Ovoid or round radiolucent lesions with central destructive pattern 4
- Aggressive periosteal reaction that can mimic malignancy or osteomyelitis 2, 4, 5
- Endosteal scalloping creating a "budding appearance" 5
- Swelling of surrounding soft tissues visible on plain films 4
Spine Lesions
Vertebral involvement has a pathognomonic appearance: 2, 5, 3
- Vertebra plana - complete or near-complete collapse of vertebral body height 2, 5, 3
- This finding in a child should immediately raise suspicion for LCH 1, 5
Critical Diagnostic Considerations
Important pitfalls to recognize when interpreting pediatric bone lesions:
- Cortical thickening may be present, distinguishing LCH from vitamin D or calcium deficiency rickets where bone resorption features predominate 1
- Absence of bone resorption features helps differentiate from metabolic bone disease 1
- Aggressive appearance can mimic Ewing sarcoma or osteomyelitis, requiring careful correlation with clinical presentation 1, 5
- Plain radiographs in two planes should always be the first investigation before any biopsy is considered 6
When X-Ray Findings Are Insufficient
Plain radiography limitations require advanced imaging in specific scenarios: 2, 4
- Normal X-rays with persistent symptoms warrant MRI evaluation 6
- Bone marrow involvement and soft tissue extension are better assessed with MRI 2, 4
- Polyostotic disease detection benefits from bone scintigraphy or PET-CT for complete staging 2
- Detailed anatomic assessment of skull base or spine lesions requires CT 2
Distinguishing Features from Other Conditions
Key radiographic differences help narrow the differential diagnosis:
- Unlike osteomyelitis: LCH shows sharply demarcated margins on imaging and lacks the diffuse periosteal reaction typical of infection 1
- Unlike Ewing sarcoma: LCH demonstrates sharply demarcated margins rather than permeative bone destruction, though soft-tissue mass and cortical breach can occur in both 1
- Unlike aneurysmal bone cyst: While LCH can have secondary ABC-like changes with fluid-fluid levels, the primary lytic lesion pattern differs 7