Fibrous Hamartoma of Infancy : Differential
Differential Diagnosis: When the classic triphasic morphology is present, the diagnosis of fibrous hamartoma of infancy (FHI) is straightforward. However, in two-thirds of cases, one component dominates over others (usually fibroblastic or adipose tissue) and could make the diagnosis challenging. When adipose tissue is prominent, the differential includes: Lipofibromatosis: It usually involves distal extremities and lacks the organoid pattern of FHI. It consists of an admixture of mature fat, lipoblast-like cells, and short fascicles of bland fibroblastic cells infiltrating the subcutis and skeletal muscles.Lipofibromatosis-like Neural Tumor: Resembles lipofibromatosis but shows greater degree of cytologic atypia and nuclear hyperchromasia, positivity for S100 protein, and NTRK1 gene rearrangements.Lipoblastoma: Well-circumscribed tumor with a lobular growth pattern, lipoblasts, myxoid foci with capillary network, and rearrangements of PLAG1 gene. The image shows scattered lymphocytes and plasma cells in fibroblastic areas of FHI. The differential diagnosis continues in the next image.