What is the diagnosis and treatment for significant swelling and a palpable lump in the thenar web space with swelling extending up the forearm?

Urgent Evaluation for Deep Vein Thrombosis and Soft Tissue Infection

Obtain urgent duplex ultrasound of the upper extremity immediately to exclude deep vein thrombosis (UEDVT), which can lead to pulmonary embolism, and obtain plain radiographs to evaluate for soft tissue infection, gas, foreign body, or underlying bone pathology. 1, 2

Initial Diagnostic Approach

Immediate Imaging Studies

• Plain radiographs in two planes are the mandatory first investigation for any suspected musculoskeletal pathology with swelling and a palpable mass 2
• Radiographs can identify soft tissue swelling, gas formation (suggesting infection with gas-producing organisms), foreign bodies, fractures, bone destruction, or tumors 2, 3
• Duplex ultrasound of the upper extremity must be performed urgently because unilateral hand and forearm swelling indicates an obstructive process at the level of the brachiocephalic, subclavian, or axillary veins 1
• Ultrasound has >80% sensitivity and specificity for UEDVT and allows assessment of vein compressibility, blood flow patterns, and central venous obstruction 1

Critical Red Flags Requiring Immediate Action

• Unilateral swelling always indicates obstruction requiring urgent evaluation, unlike bilateral swelling which suggests systemic causes 1, 4
• Persistent non-mechanical pain lasting more than a few weeks, especially night pain, requires immediate investigation for possible bone sarcoma 2
• Swelling with erythema, warmth, and fever suggests soft tissue infection or septic arthritis requiring urgent evaluation 2

Differential Diagnosis Priority

Most Critical: Deep Vein Thrombosis

• UEDVT accounts for up to 10% of all DVTs and can cause pulmonary embolism 1
• Risk factors include indwelling venous devices, cancer, recent surgery, hypercoagulability, and trauma 4
• If UEDVT is confirmed on ultrasound, initiate therapeutic anticoagulation immediately following standard DVT treatment protocols 1

Soft Tissue Infection

• If radiographs show soft tissue swelling, gas, or foreign bodies, proceed to MRI or CT for detailed evaluation of soft tissue compartments to differentiate cellulitis, myositis, abscess, or necrotizing fasciitis 2
• Image-guided aspiration with culture is essential when imaging cannot distinguish infected from noninfected fluid collections 2
• Aspiration allows identification of the infectious organism, which directly affects treatment 2

Bone or Soft Tissue Tumor

• Any patient under 40 years with a palpable mass and persistent pain should be referred urgently to a bone sarcoma center before biopsy 2
• Radiographic features requiring referral include bone destruction, new bone formation, periosteal swelling, or soft tissue mass 2
• Poorly performed biopsies can compromise treatment, so all biopsies must be performed at specialized centers 2

Other Considerations

• Traumatic subcutaneous emphysema can occur from puncture injuries to the first web space, causing impressive swelling but is clinically benign in otherwise healthy patients 3
• Lymphangioma presents as a soft tissue mass with episodic pain, swelling, induration, erythema, and fever, responding to elevation, analgesics, and antibiotics 5
• Scar sarcoidosis can develop in pre-existing scars, mimicking a rapidly growing soft tissue tumor, requiring biopsy for diagnosis 6

Advanced Imaging Algorithm

When to Proceed to MRI

• MRI of the entire compartment with adjacent joints is indicated when malignancy cannot be excluded on radiographs 2
• MRI is the best modality for local staging of extremity tumors and evaluating soft tissue infections 2
• MRI should be obtained before referral to a sarcoma center if there is minimal delay 2

When to Use CT

• CT is appropriate for visualizing calcification, periosteal bone formation, cortical destruction, or when diagnostic problems exist 2
• CT helps differentiate cellulitis, myositis, tenosynovitis, and abscess formation 2

Management Based on Findings

If UEDVT Confirmed

• Start therapeutic anticoagulation immediately 1
• Investigate lower extremities if no local cause identified, as correlation between upper and lower extremity DVT exists 1
• Reassess within 48-72 hours to evaluate response 1

If Infection Suspected

• Obtain image-guided aspiration for culture 2
• Start broad-spectrum antibiotics after cultures obtained 3
• Splint the affected area 3

If Tumor Suspected

• Refer to bone sarcoma center before biopsy 2
• All biopsies must be performed by the surgeon who will perform definitive resection or by a radiologist member of the specialized team 2
• Core-needle biopsies under imaging control are appropriate alternatives to open biopsy 2

Common Pitfalls to Avoid

• Do not dismiss unilateral swelling as benign—it always indicates obstruction requiring urgent evaluation 1
• Do not perform biopsy before referral to a sarcoma center if tumor is suspected, as this can compromise treatment 2
• Do not assume recent trauma excludes malignant tumor—this must not prevent appropriate diagnostic procedures 2
• Recognize that catheter-associated UEDVT may be asymptomatic, manifesting only as catheter dysfunction 1

Follow-Up Protocol

• Reassess within 48-72 hours to evaluate response to initial management and ensure no progression 1
• Schedule formal evaluation at 6 weeks if edema persists to detect delayed complications or underlying pathology 1
• If swelling persists beyond 2 weeks without clear diagnosis, perform venography or CT venography to evaluate central veins 1