Nodular fasciitis

Nodular fasciitis
Other names	Nodular pseudosarcomatous fasciitis, subcutaneous pseudosarcomatous fibromatosis
Micrograph of nodular fasciitis showing the haphazard arrangement of cells (tissue culture-like pattern). H&E stain.
Specialty	Rheumatology
Types	Cranial fasciitis, intravascular fasciitis

Nodular fasciitis (NF) is a benign, soft tissue tumor composed of myofibroblasts that typically occurs in subcutaneous tissue, fascia, and/or muscles.^[1][2][3][4] The literature sometimes titles rare NF variants according to their tissue locations. The most frequently used and important of these are cranial fasciitis^[5] and intravascular fasciitis.^[6] In 2020, the World Health Organization classified nodular fasciitis as in the category of benign fibroblastic/myofibroblastic tumors.^[7] NF is the most common of the benign fibroblastic proliferative tumors of soft tissue.^[4]

Nodular fasciitis is a rapidly growing, usually self-limiting neoplasm that occurs primarily but not exclusively in adults. Due to its rapid growth, NF is often misdiagnosed as a malignant tumor, usually a sarcoma.^[8] Indeed, NF was originally termed subcutaneous pseudosarcomatous fibromatosis when first described in 1955 by Konwaler et al.^[9] The correct diagnosis of a tumor as NF is pivotal to prevent its overtreatment as a more aggressive or malignant growth.^[8]

While nodular fasciitis may be precipitated by localized injuries, recent studies indicate that NFs are true neoplasms (i.e. abnormal proliferations of cells without any precipitating event). Up to 92% of NF cases have a specific type of fusion gene in their tumor cells which may be responsible for disrupting the regulation of cell growth and death.