What is the best imaging approach for a patient presenting with a forearm mass?

Imaging for Forearm Mass

Start with plain radiographs of the forearm as the initial imaging study, followed by ultrasound for superficial masses or MRI without and with contrast for deep or indeterminate masses. 1, 2

Initial Imaging: Plain Radiographs

Radiographs are the mandatory first-line imaging modality for any forearm mass, regardless of clinical suspicion. 1

• Radiographs demonstrate positive findings in 62% of soft tissue masses, including calcification (27%), bone involvement (22%), and intrinsic fat (11%). 1, 3
• They can be diagnostic for specific entities such as phleboliths within hemangiomas, osteocartilaginous masses of synovial chondromatosis, or the peripheral ossification pattern of myositis ossificans. 1
• Radiographs identify mineralization patterns that guide subsequent imaging decisions and may reveal unsuspected skeletal abnormalities presenting as soft tissue masses. 1, 4

Second-Line Imaging: Superficial vs. Deep Masses

For Superficial/Palpable Masses

Ultrasound is the preferred next imaging study for superficial forearm masses. 1, 4

• Ultrasound demonstrates 94.1% sensitivity and 99.7% specificity for superficial soft tissue masses, with highest accuracy for lipomas, followed by vascular malformations, epidermoid cysts, and nerve sheath tumors. 1
• It effectively differentiates solid from cystic lesions, confirms fluid content in suspected ganglion cysts, and demonstrates the relationship between masses and adjacent neurovascular structures. 1
• Critical caveat: When ultrasound or clinical features are atypical, proceed immediately to MRI rather than delaying diagnosis. 1

For Deep or Indeterminate Masses

MRI without and with IV contrast is the definitive imaging study for deep forearm masses or when ultrasound findings are inconclusive. 4, 5

• Contrast-enhanced MRI provides superior soft tissue characterization, better visualization of tumor margins and extent, and identifies areas of viable tumor crucial for biopsy planning. 5
• MRI can distinguish benign from malignant lesions in approximately 50% of cases using imaging and clinical information combined. 5
• The American College of Radiology explicitly states that literature does not support MRI as the initial examination, but it becomes essential after radiographs when dealing with deep, complex, or suspicious masses. 1

Role of CT Imaging

CT is not typically ordered for initial evaluation but serves as a useful adjunct for specific indications. 1

• CT is particularly valuable for characterizing mineralization patterns in areas with complex anatomy, distinguishing ossification from calcification, and identifying the zonal pattern of myositis ossificans. 1
• CT with multiplanar capability optimally depicts the interface between soft tissue masses and adjacent bone cortex for assessing cortical remodeling or invasion. 1

Critical Clinical Pitfalls

Physical examination alone correctly identifies only 85% of soft tissue tumors, making imaging mandatory even when clinical suspicion is low. 1, 4

Never proceed directly to biopsy without appropriate imaging, as this leads to sampling error, tissue plane contamination, and inadequate surgical planning. 5

Radiographs have significant limitations for small, deep-seated, or non-mineralized masses, particularly in the deep soft tissues of the forearm where complex anatomy obscures findings. 1

Algorithmic Approach

1. Always obtain radiographs first (AP and lateral views minimum). 1, 2
2. If the mass is superficial/palpable and radiographs are non-diagnostic: Order ultrasound. 1, 4
3. If the mass is deep, ultrasound is inconclusive, or features are atypical: Order MRI without and with IV contrast. 4, 5
4. If mineralization characterization is needed or MRI is contraindicated: Consider CT without contrast. 1
5. If imaging demonstrates concerning features (size >5 cm, deep location, heterogeneous enhancement, aggressive characteristics): Refer to a specialized sarcoma center before biopsy. 5

PET/CT has no role in initial evaluation of forearm masses. 1