Characterising benign fibrous soft-tissue tumours in adults: why is it so difficult and what do we need to know?

Fibrous, myofibroblastic, and fibrohistiocytic soft-tissue tumours are amongst the most common benign soft-tissue lesions encountered in clinical practice. They demonstrate varied biological behaviour and imaging characteristics. Benign fibroblastic lesions, such as nodular fasciitis, are small, have a self-limited course, and rarely recur after excision, whereas deep fibromatosis and plexiform fibrohistiocytic tumours tend to exhibit more aggressive features and often have high recurrence rates. MRI with its superior tissue contrast, multiplanar imaging capability, and lack of ionising radiation is regarded as the preferred method of tumour evaluation, tissue characterisation, and assessment of treatment response. Histopathological features are depicted at MRI, reflecting the amount and distribution of the cellular and fibrous matrix. Cellular tumours tend to show higher T2 signal intensity and post-contrast enhancement as compared to tumours with greater collagenous content, which appear dark and show less enhancement. Awareness of MR characteristics, pathological behaviour, and common sites of occurrence of fibrous soft-tissue tumours will help radiologists to determine the appropriate differential diagnosis and guide patient management.