The MRI Findings of Collagenous Fibroma (Desmoplastic Fibroblastoma) Arising in the Supraspinatus Muscle: A Case Report

Collagenous fibroma (desmoplastic fibroblastoma) is a rare benign fibrous soft tissue tumor. This lesion commonly presents with painless, non-tender, mobile and slowly growing mass in subcutaneous tissue or skeletal muscle at various anatomic location. On magnetic resonance image (MRI), the mass shows area of low signal intensity on both T1- and T2-weighted pulse sequences. This low signal intensity presents areas of low cellularity in a background of abundant collagen. We describe the unique case of collagenous fibroma in the shoulder joint presenting with 4-years history of long-standing pain, which is unusual clinical manifestation of this benign soft tissue tumor without previous trauma history.