ABSTRACT
This chapter describes the types of the histiocytic lesions, including benign lesions and malignant histiocytosis. It also describes the histopathology and differential diagnosis of some of the benign lesions, such as juvenile xanthogranuloma, xanthoma, verruciform xanthoma, multicentric reticulohistiocytosis and other tumor-like depositions. The chapter explains the histopathology and differential diagnosis of the langerhans cell histiocytosis. A case of hyperlipidemic xanthomas of the nail folds of two toes was described that clinically mimicked Koenen tumors of tuberous sclerosis. Xanthomas may be arranged in a coral bead-like fashion at the free margin of the proximal nail fold similar to multicentric reticulohistiocytosis. Typical lesions of the nail organ are small firm nodules at the margin of the proximal nail fold causing the so-called coral bead sign. Lesions in the matrix cause nail dystrophy whereas those in the nail bed are seen as hemorrhages or subungual pustules.
