What is the most likely cause of a patient's right upper extremity pain, numbness, decreased sensation, and decreased grip strength after a previous brachial artery (artery in the arm) injury?

Compressive Pseudoaneurysm

The most likely cause of this patient's findings is a compressive pseudoaneurysm of the brachial artery causing delayed median nerve compression. 1

Clinical Reasoning

Why Pseudoaneurysm is Most Likely

The clinical presentation strongly suggests a delayed vascular complication from the previous brachial artery injury:

• Timing: Symptoms developing weeks after penetrating trauma to the brachial artery is classic for pseudoaneurysm formation 2
• Nerve distribution: Decreased sensation in digits 1-4 with preserved grip strength indicates median nerve compression rather than complete nerve transection 1
• Preserved pulses: Symmetric radial pulses exclude acute arterial occlusion or compartment syndrome 1, 3
• Progressive symptoms: The one-week duration suggests an expanding mass lesion compressing adjacent neural structures 1

Pathophysiology of This Complication

Following brachial artery injury, pseudoaneurysms can develop when:

• The arterial wall is incompletely repaired or develops delayed breakdown 2
• Blood accumulates in surrounding tissue, contained only by fibrous tissue rather than intact arterial wall 2
• The expanding pseudoaneurysm progressively compresses the median nerve, which runs immediately adjacent to the brachial artery 1
• Thrombosis within the pseudoaneurysm can occur while maintaining distal perfusion through collaterals, explaining preserved pulses 1

Why Other Diagnoses Are Excluded

Compartment Syndrome - Excluded

• Timing incompatible: Compartment syndrome develops within hours of injury or reperfusion, not weeks later 2
• Pulses preserved: Compartment syndrome typically presents with diminished or absent pulses 2
• No acute ischemia: Absence of the "5 P's" (pain, pallor, pulselessness, paresthesias, paralysis) rules out acute compartment syndrome 2

Erb Palsy - Excluded

• Wrong nerve distribution: Erb palsy affects the upper brachial plexus (C5-C6), causing shoulder and elbow weakness, not hand numbness 2
• Mechanism incompatible: Erb palsy results from traction injuries to the brachial plexus, not penetrating trauma to the brachial artery 2

Thoracic Outlet Syndrome - Excluded

• Wrong anatomic location: TOS involves compression at the thoracic outlet (costoclavicular or interscalene spaces), not the mid-arm 2
• No positional symptoms: TOS symptoms are typically provoked by arm positioning or overhead activities 2
• Unilateral presentation: The patient has isolated right arm symptoms following documented right brachial artery injury 2

Diagnostic Approach

Immediate Imaging Required

Duplex ultrasound is the initial diagnostic test of choice:

• Can identify pseudoaneurysm with characteristic "to-and-fro" flow pattern 2
• Evaluates relationship between pseudoaneurysm and adjacent median nerve 1
• Non-invasive and rapidly available 3

Important caveat: Ultrasound may miss completely thrombosed pseudoaneurysms, as occurred in the case reported by 1. If clinical suspicion remains high despite negative ultrasound, proceed to MRI or CTA 1

Critical Physical Examination Findings

• Tinel sign over the mass suggests nerve compression 1
• Thenar muscle weakness indicates median nerve motor involvement 1
• Sensory loss in median nerve distribution (thumb, index, middle, and radial half of ring finger) 1
• Palpable mass in the antecubital fossa or distal arm 1, 4

Management Algorithm

Surgical Intervention Required

Urgent surgical exploration and repair is indicated because:

• Progressive neurological symptoms indicate ongoing nerve compression 1
• Delayed treatment results in permanent neurological sequelae 1, 5
• Pseudoaneurysm requires resection to prevent rupture or thromboembolism 2

Surgical Technique

The procedure should include:

• Microsurgical neurolysis of the compressed median nerve 1
• Pseudoaneurysm resection with vascular reconstruction 1, 4
• Interposition grafting using reversed saphenous vein if primary repair not possible 2, 4
• Consider postoperative anticoagulation (heparin transitioning to oral anticoagulant) for graft patency 4

Critical Pitfalls to Avoid

• Do not delay surgery waiting for "conservative management" - progressive nerve compression requires urgent decompression 1
• Do not rely solely on ultrasound if clinical suspicion is high; thrombosed pseudoaneurysms may appear as solid masses 1
• Do not assume normal pulses exclude vascular pathology - collateral circulation can maintain distal perfusion despite proximal pseudoaneurysm 1, 3
• Operate within 4-6 months maximum of symptom onset to optimize neurological recovery 1