[A hard subcutaneous swelling: not always as malignant as it seems]

Area of Science:

• Pathology
• Oncology
• Dermatology

Background:

• Nodular fasciitis is a rare, benign soft tissue tumor.
• Typically affects young adults on the arms or trunk.

Observation:

• A 24-year-old woman presented with a rapidly growing, painless subcutaneous forearm swelling.
• Initial ultrasound suggested malignancy, but the swelling resolved spontaneously.
• Subsequent ultrasound showed an inflammatory lesion, confirmed as nodular fasciitis by biopsy.

Findings:

• Histopathology revealed a spindle cell lesion with erythrocyte extravasation, characteristic of nodular fasciitis.
• The lesion resolved completely within three months without intervention.
• Ultrasound findings evolved from suspicious for malignancy to inflammatory.

Implications:

• Nodular fasciitis should be considered in the differential diagnosis of rapidly growing subcutaneous masses in young adults.
• Distinguishing nodular fasciitis from malignancy solely on ultrasound is challenging.
• Biopsy is essential for definitive diagnosis and appropriate management.