Langerhans Cell Histiocytosis

Langerhans cell histiocytosis (LCH) is a disease of children and young adults that can affect any organ. It leads to a variable infiltration of the organ by cells belonging to the mononuclear phagocytic system. Bone is most often involved (60–80% of cases). Bone involvement in LCH predominates in the axial skeleton, but spinal involvement is rare. It may be unique or more rarely multifocal. In decreasing order of frequency, the thoracic, lumbar, and cervical spines are affected. Involvement of the sacrum is exceptional. On conventional radiography and CT scan, LCH causes nonspecific osteolysis of the vertebral body, which may or may not extend to the posterior arch. The intervertebral disks are preserved. Variable degree of vertebral compression is sometimes associated, sometimes resulting in a vertebra plana, which is highly suggestive—although nonspecific—for the LCH in children. MRI is very useful to evaluate tumor extension to the paravertebral soft tissues and especially the epidural and/or foraminal extension, which is generally limited. The final diagnosis is based on histopathological examination of the biopsy specimen from the most accessible site, either osseous or not. Distant staging is based on skeletal radiographs, even if they lack sensitivity. Whole-body MRI (distant staging) and PET-PET/CT (for follow-up and response to treatment) provide useful information but do not necessarily alter treatment management. Since treatment depends largely on the location of the lesions and the potential functional consequences, it varies from watchful waiting to systemic chemotherapy. If the bone involvement is isolated, the prognosis is generally good. It is more reserved in case of multisystemic involvement, especially if the child is very young.