[Langerhans cell histiocytosis in children: clinicopathological and ultrastructural analyses of 345 cases]

Objective: To investigate the clinicopathological and ultrastructural characteristics of Langerhans cell histiocytosis (LCH) in children. Methods: A total of 345 cases of LCH from the Department of Pathology, Beijing Children Hospital from January 2012 to March 2016 were investigated by hematoxylin-eosin stain, EnVision immunohistochemistry and transmission electron microscopy. Results: The rate of primary clinical diagnosis of LCH in children was 46.0%(210/457). Among 345 patients of LCH, 213 were male and 132 were female, the male to female ratio was 1.6∶1.0, and the median age was 21 months (range from 2 days after birth to 13.3 years). There were total 597 lesions, including bony lesions (258, 43.2%), skin lesions (206, 34.5%) , followed by lymph node (16, 2.7%), lung (28, 4.7%), liver (25, 4.2%) and head-neck (50, 8.4%). Single organ system LCH (SS-LCH) was seen in 295 cases (85.5%) and 50 cases (14.5%) presented with multiple organ system involvement LCH (MS-LCH). There was no significant difference in age and gender between SS-LCH and MS-LCH groups. Regarding sites, more lesions were seen in bone and skin in SS-LCH group, in contrast lymph node, lung, liver and head-neck involvements were often seen in MS-LCH group. Immunohistochemically, the expression of CD1a and Langerin was seen in 99.7% (341/342) and 98.8% (338/342) of the cases respectively. The diagnostic rates by light and transmission electron microscopy were 98.8% (341/345) and 97.4% (112/115) respectively (P>0.05). Conclusions: LCH of children occurs predominantly in SS-LCH pattern, frequently involving bone, skin, lymph node, lung and liver and other sites with unique histopathological, immunophenotypical and ultrastructural features. Accurate diagnosis relies on the morphology, immunophenotype and ultrastructural features. Further refinement of specimen processing may improve the accuracy of pathological diagnosis.