Abstract:

Objective: To analyze the clinic-pathological features, immunohistochemical phenotype and differential diagnosis of a child with fibroblastic connective tissue nevus（FCTN）. Methods: A 2-year-old girl developed bright red sclerotic plaque on her right thigh with clear boundary and irregular shape. Biopsy was performed on the lesion, and the pathological tissues were stained with HE and immunohistochemistry. The immunohistochemical phenotypes for differential diagnosis were analyzed along with literature review. Results: Histologically, the lesion was composed of bundles of bland spindle cells of fibroblastic/myofibroblastic lineage irregularly branching within the reticular dermis and along fibrous septa in the subcutis, without affecting the adnexal structures. The dermal adipocytes were entrapped by tumor cells, and elastic fibers were fragmented and decreased. Immunohistochemically, cells of FCTN were positive for CD34, and weak positive for SMA（smooth muscle actin） locally, while negative for S100, des, and low index of Ki-67(1%). Among the 45 cases reported, it was found that the patients generally had an early onset age (median 10 years old), and FCTN occured mostly in children’s trunk, head and neck, with painless spots or nodules as primary presentations. The clinic-pathological features and immunohistochemical phenotype of the patient described hereby were consistent with cases previously reported. Conclusions: FCTN is a rare variant of nevus of connective tissue, which could differentiate into myofibroblast and mechanocyte cells. Immunohistochemically, CD34 is usually positive and SMA is weakly positive in spindle cells. The FCTN should be differentiated with soft tissue tumor, such as dermatofibrosarcoma protuberans,congenital infantile fibrosarcoma and rhabdomyosarcoma.

Key words: Spindle cell proliferation in children, Connective tissue nevus, Immunohistochemistry