A Fibrous Hamartoma of Infancy with Overlying Hypertrichosis

Jeong, Ki Heon; Shin, Min Kyung; Lee, Mu Hyoung

Abstract

Fibrous hamartoma of infancy (FHI) is a rare benign lesion occurring in the first 2 years of life, particularly in males. Most lesions present as a painless subcutaneous mass. Although the lesion is not distinctive clinically, it has a characteristic microscopic appearance. The lesion histologically consists of three different tissue elements: disorderly collagenous fibrous tissue, myxoid mesenchymal tissue and islands of mature adipocytes. A few cases have overlying skin changes, including alteration in pigmentation, eccrine gland hyperplasia, and increased hair. A 6-month-old male infant had a 6x4 cm sized asymptomatic mass on the right lower back. Multiple coarse hairs were present on the surface. Histopathologic findings showed the typical features of FHI, that is well defined intersecting fibrous trabeculae, small immature cells within loosely textured areas, and mature adipose areas in the lower dermis and subcutaneous layer. Immunohistochemically, vimentin was present in both the trabecular and loosely textured areas, but desmin was not present in any of the components. We report a case of FHI on the right lower back with overlying hypertrichosis in a 6-month-old male patient.