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E1478. More Than Just Bones: A Multimodality Multi-Organ Radiologic Review of Langerhans Cell Histiocytosis
Authors
  1. Pwint Khine; Penn State Health Milton S. Hershey Medical Center
  2. Tao Ouyang; Penn State Health Milton S. Hershey Medical Center
  3. Asef Khwaja; The Children's Hospital of Philadelphia, Perelman School of Medicine at University of Pennsylvania
  4. Nancy Chauvin; Penn State Health Milton S. Hershey Medical Center
Background
Langerhans Cell Histiocytosis (LCH) is one of a group of disorders caused by overproduction of bone marrow-derived antigen-presenting cells of dendritic cell line, also known as Langerhans Cells. Patients with LCH present with varied clinical manifestations. LCH has various radiologic appearances and osseous lesion may sometimes appear aggressive. Familiarity with characteristic imaging findings enables the radiologist to facilitate a correct and timely diagnosis.

Educational Goals / Teaching Points
Describe clinical presentations and pathophysiology of LCH. Present multiorgan imaging findings of LCH using a multimodality approach. Illustrate imaging findings for mimics, highlighting specific characteristics unique to LCH. Review management of LCH and treatment approaches.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
LCH is a rare disease with a reported incidence of 4.6 cases per 1 million in children under the age of 15 years with a male-to-female ratio of 1.2:1. LCH is composed of three clinical forms based on the number of lesions and systems involved. The most common form is the unifocal form, which is limited to a single bone or a few bones and may involve the lung. The multifocal unisystem form involves multiple bones as well as the reticuloendothelial system. This form is often accompanied by diabetes insipidus when the pituitary gland is involved. The least common and most fatal form is the multifocal multisystem form, which is characterized by disseminated involvement of the reticuloendothelial system, anemia, and thrombocytopenia. Bone lesions are the most common radiographic finding of LCH and occur in 80% of affected individuals with a predilection of flat bones, especially the skull followed by mandible, rib, pelvis, and spine. The classic imaging findings include vertebra plana, skull lesions with beveled edge, and the “floating tooth” sign. Long bone lesions demonstrate endosteal scalloping and may often appear aggressive, mimicking a malignancy or infection. In 15% of cases, LCH affects the lungs, liver, or hematopoietic system. Visceral findings include hepatosplenomegaly with focal solid or cyst like liver lesions and hepatic dysfunctions. LCH may involve lymph nodes and the neck is the most common site for lymphadenopathy. Lung involvement more commonly occurs in adults and often characterized by centrilobular micronodules in the middle and upper lung zones. These nodules can undergo cystic degeneration as the disease progresses. A confluence of pulmonary cysts may result in bullous formation. The central nervous system (CNS) is involved in 16% of cases and the most common clinical CNS manifestation is diabetes insipidus from infiltration of the posterior pituitary gland and thickening of the pituitary stalk.

Conclusion
Patients with LCH can present with a wide spectrum of clinical manifestations and radiologic findings. Familiarity and knowledge of this disease as well as specific imaging findings are crucial for the radiologist to make a correct and timely diagnosis.