Figure 10. Histology characteristics of LCH, JXG and RDD.

A. Although Langerhans cell histiocytosis (LCH), histiocytoses of the xanthogranuloma family (including Erdheim Chester Disease (ECD) and juvenile xanthogranuloma (JXG),), and Rosai Dorfman Disease (RDD) have certain classic morphologies and defining phenotypes, our understanding of histiocytic lesions continues to evolve and may be best conceptualized along a spectrum, sometimes with morphology and phenotypes overlapping in certain instances and often with similar mutation profiles. In fact, ECD and JXG share similar morphological cell types under the microscope, including xanthomatous cells with variable admixture of Touton giant cells, vacuolated cells, spindled cells, oncocytic cells, and epithelioid cells. B. H&E images for LCH, xanthogranuloma family, and RDD (original magnification at 400x). C Immunostaining specific for BRAF-V600E (known as BRAF-VE1, brown) Although the mutant specific immunohistochemistry for BRAF-VE1 is more commonly expressed in LCH and ECD, with strong granular cytoplasmic staining of the histiocytes, rare examples in pediatric JXG family (limited to the central nervous system of children) and isolated case reports of RDD have been identified to also harbour the mutation and express the mutant protein, which reacts to the immunostaining. Original magnification at 1000x for LCH, 400x for CNS-JXG, and 1000x for RDD. Photos made with assistance of Mr Chris Woods Cincinnati Children’s Department of Pathology.