What could be causing a pulsating mass and an urge to defecate in an older adult with a history of hypertension and possibly smoking, who has different blood pressure readings in both arms?

Abdominal Aortic Aneurysm with Impending Rupture

This clinical presentation—a pulsating abdominal mass with urge to defecate and a significant blood pressure difference between arms—is a medical emergency requiring immediate evaluation for abdominal aortic aneurysm (AAA) with possible rupture or aortic dissection extending into the abdomen. 1

Critical Clinical Findings

The combination of symptoms points to a vascular catastrophe:

• Pulsating abdominal mass: This is the hallmark physical finding of an AAA, representing the aneurysmal aorta transmitting pulsations through the abdominal wall 1

• Urge to defecate: This occurs when an expanding or leaking AAA compresses adjacent structures, particularly the rectum and sigmoid colon, creating a sensation of rectal pressure or urgency 1

• Blood pressure difference between arms: A difference >20 mmHg systolic or >10 mmHg diastolic between arms mandates urgent investigation for vascular abnormalities, including aortic dissection or subclavian artery involvement 1, 2. In the context of a pulsating abdominal mass, this finding raises concern for Type B aortic dissection extending into the abdominal aorta 1

Immediate Diagnostic Approach

Confirm Blood Pressure Findings

• Measure blood pressure in both arms simultaneously or sequentially with proper technique—both arms at heart level, appropriately sized cuffs, after 5 minutes of rest 2, 3
• A confirmed difference ≥20 mmHg systolic strongly suggests subclavian artery stenosis, aortic coarctation, or aortic dissection 1, 2, 4

Physical Examination Priorities

• Palpate for abdominal aortic pulsation: A pulsatile mass in the midline abdomen, particularly if >3 cm in diameter, indicates AAA 1
• Auscultate for abdominal bruits: May indicate renovascular disease or turbulent flow through an aneurysm 1
• Check femoral pulses bilaterally: Diminished or delayed femoral pulses compared to radial pulses suggest aortic coarctation or aortic dissection involving the descending aorta 1
• Assess for signs of shock: Hypotension, tachycardia, pallor, or diaphoresis indicate possible rupture requiring immediate surgical intervention 1

Red Flag Symptoms Requiring Emergency Evaluation

If any of the following are present, this constitutes a hypertensive emergency or vascular catastrophe requiring immediate ED transfer 1, 4:

• Acute chest or back pain (especially between shoulder blades)
• Syncope or near-syncope
• Acute neurological symptoms
• Hypotension or shock
• Signs of limb ischemia

Urgent Imaging

Do not delay imaging if AAA with possible rupture is suspected:

• CT angiography of chest, abdomen, and pelvis: This is the gold standard for diagnosing AAA, detecting rupture or leak, and identifying aortic dissection 1, 2
• Bedside ultrasound: Can rapidly confirm AAA presence and approximate size if CT is not immediately available, though it cannot reliably detect rupture 1

Most Likely Diagnoses

Primary Concern: Abdominal Aortic Aneurysm

• The pulsating mass with rectal pressure symptoms is classic for AAA, particularly if the patient has hypertension and smoking history (both major risk factors) 1
• AAAs >5.5 cm have high rupture risk and require urgent surgical evaluation 1

Secondary Concern: Aortic Dissection

• The inter-arm blood pressure difference raises concern for Type B dissection extending into the abdominal aorta 1, 2
• Approximately 20% of patients with acute aortic dissection present with hypotension or shock, which carries high mortality 1
• Up to one-third of dissection patients present without chest pain, making diagnosis challenging 1

Alternative: Subclavian Artery Stenosis with Coincidental AAA

• A difference ≥15-20 mmHg between arms most commonly indicates subclavian artery stenosis, which may coexist with AAA in patients with diffuse atherosclerotic disease 2, 4

Immediate Management

If Hemodynamically Stable

• Transfer to emergency department for urgent vascular surgery consultation 4
• Obtain CT angiography immediately 1, 2
• Control blood pressure cautiously—avoid excessive reduction that could compromise organ perfusion, but prevent further aneurysm expansion 1, 5
• Use the arm with the higher blood pressure reading for all subsequent measurements to avoid underestimating true blood pressure 2, 4, 3

If Hemodynamically Unstable

• Activate emergency medical services immediately
• This represents a ruptured AAA or complicated aortic dissection requiring emergency surgical intervention 1
• Mortality for ruptured AAA approaches 80-90% without immediate surgery 1

Common Pitfalls to Avoid

• Do not dismiss the pulsating mass as normal aortic pulsation in thin patients—any palpable pulsatile mass warrants imaging 1
• Do not attribute the inter-arm blood pressure difference to measurement error without confirmation—differences ≥20 mmHg require vascular evaluation even if asymptomatic 2, 4
• Do not aggressively lower blood pressure in suspected aortic dissection without surgical consultation—excessive reduction can worsen organ malperfusion 1, 5
• Do not delay imaging for "observation" if AAA is suspected—the combination of symptoms suggests impending rupture 1