Diagnostic Approach for Painful Forearm Lump

Initial Imaging and Diagnosis

Plain radiographs of the forearm are the first-line imaging study to exclude fracture, particularly if there was any trauma, even minor, as recommended by the American College of Radiology 1
The American College of Radiology suggests that radiographs can identify occult fractures, avulsion injuries, and joint effusions that may present as soft tissue swelling 1
The British Sarcoma Group guidelines recommend urgent direct access ultrasound for unexplained lumps that are increasing in size, to assess for soft tissue sarcoma 4

Occult fracture with soft tissue injury may present as soft tissue swelling before bruising becomes visible, according to the American College of Radiology 1
Soft tissue sarcoma, although rare, warrants evaluation, particularly if the lump is deep-seated, larger than expected, or without clear trauma, as suggested by the British Journal of Cancer 4
The British Journal of Cancer recommends referral to a sarcoma specialist within 2 weeks if ultrasound findings are uncertain and clinical concern persists 4

CT without contrast is the next appropriate study if fracture is suspected but radiographs are normal, as recommended by the American College of Radiology 1
MRI without contrast is highly sensitive for detecting soft tissue pathology, including muscle tears, hematomas, and bone marrow edema, according to the American College of Radiology 1
MRI provides superior soft tissue detail compared to other modalities, as suggested by the American College of Radiology 1

Fever, spreading erythema, or systemic symptoms warrant evaluation for osteomyelitis or septic arthritis, as recommended by the American College of Radiology 5
Rapid progression with warmth and redness suggests an infectious process, according to the American College of Radiology 5
A lump that continues to increase in size over days, is deep-seated, or is larger than 5 cm, requires urgent referral, as suggested by the British Journal of Cancer 4