The Rarity in the Rarity: Presentation of Two Rare and Unusual Cases of Nodular Fasciitis and Proliferative Fasciitis.

Nodular fasciitis (NF) and proliferative fasciitis (PF) are benign, reactive mesenchymal neoplasms that can mimic malignancies due to their rapid growth and histological characteristics. NF typically affects the subcutaneous tissue, occasionally involving muscles and fascia, predominantly in young adults, and appears frequently in the upper extremities, trunk, and head/neck. PF, a pseudosarcomatous lesion, primarily occurs in the subcutaneous tissue of adults aged 40-70 years and is uncommon in younger populations. This article presents two pediatric cases of NF and PF in unusual locations: a six-year-old girl with a vulvar NF and a 10-year-old girl with a gluteal PF. Both cases demonstrated rapid growth and distinct histological features, confirmed by immunohistochemical analyses and fluorescence in situ hybridization (FISH). These cases underscore the importance of accurate histological recognition to avoid misdiagnosis and ensure appropriate treatment, highlighting the rarity of such occurrences in children and the need for awareness among clinicians and pathologists.