M72: Fibroblastic disorders

M72.4: Pseudosarcomatous fibromatosis

Pseudosarcomatous fibromatosis, also known as nodular fasciitis, is a rare, benign (non-cancerous) condition that affects the connective tissues under the skin and around muscles, nerves, and blood vessels. It includes the fast but benign growth of fibrous tissue, causing firm lumps or nodules. These nodules can appear anywhere in the body but are most commonly found in the upper extremities including the arms and shoulders. Symptoms may include swelling, pain, or tenderness in the affected areas. Despite the rapid initial growth, the nodules typically stop growing and may even shrink on their own. While the condition mimics certain types of cancer in its rapid growth and invasion into surrounding tissues, it is not a form of cancer nor does it increase the risk of developing cancer. The exact cause of pseudosarcomatous fibromatosis remains unknown to science.