Diagnostic Approach to Hardened Large Area Tissue Swelling on Posterior Upper Arm

Immediate Diagnostic Approach

The American College of Radiology recommends beginning with plain radiographs of the affected area as the first-line imaging study, followed by MRI with and without IV contrast if soft tissue infection is suspected, rating plain radiographs as "usually appropriate" (9/9) for initial study 1
For soft-tissue or juxta-articular swelling with suspected infection, MRI with and without IV contrast is rated as "usually appropriate" (9/9) following radiographs, providing superior delineation of fluid collections and areas of necrosis 1

Unilateral upper extremity swelling indicates potential obstruction at the brachiocephalic, subclavian, or axillary vein level, requiring urgent evaluation, with upper extremity DVT accounting for up to 10% of all DVTs and potentially leading to pulmonary embolism 2
Perform urgent duplex ultrasound if DVT is suspected, which has sensitivity and specificity above 80% for upper extremity DVT 2, 3

Hardened swelling suggests possible abscess formation or necrotizing infection, requiring urgent evaluation, with MRI with contrast superior to CT for identifying fluid collections and necrotic tissue in suspected soft tissue infections 1
If MRI is contraindicated, CT with IV contrast (rating 6/9) is an acceptable alternative for suspected soft tissue infections 1

For nonsuperficial or deep masses, radiographs remain the initial study despite limitations for nonmineralized lesions, with CT particularly useful when radiographs are unrewarding, especially for detecting mineralization patterns 4

Obtain plain radiographs of the posterior upper arm to assess for bone involvement, periosteal reaction, soft tissue gas, or calcification patterns, with MRI without and with IV contrast providing best soft tissue detail and identifying abscesses if radiographs are negative or equivocal 1, 4
For suspected DVT, order duplex ultrasound urgently, and for suspected mass, consider MRI or CT depending on clinical context 2, 3, 4

Consider drainage if abscess is identified on imaging, with control of inflammation important to prevent fibrosis and contractures 1

Initiate therapeutic anticoagulation immediately following standard DVT treatment protocols, and investigate for underlying causes including prior central venous catheters or pacemakers 2

Reassess within 48-72 hours to evaluate response to initial management and ensure no progression, and schedule formal evaluation at 6 weeks if swelling persists to detect delayed complications or underlying pathology 2, 3
Persistent swelling beyond 2 weeks warrants investigation for central venous stenosis or other obstructive processes 2