Which condition presents with unilateral lower-extremity swelling and is typically evaluated with D-dimer, venous duplex ultrasound as first-line imaging, and venography as the gold standard imaging test?

• A. Pulmonary embolism
• B. Venous thrombosis
• C. Lymphedema
• D. Arterial occlusion

Answer: (B)

Deep vein thrombosis presents with unilateral leg swelling, and its evaluation follows a stepwise diagnostic approach using D-dimer and imaging. D-dimer is a sensitive screening test that helps rule out DVT in patients with low to moderate pretest probability; a negative result makes DVT unlikely. If suspicion remains or D-dimer is positive, the next test is compression venous duplex ultrasonography, which is the first-line imaging because it directly visualizes intraluminal thrombus in the deep veins of the leg and has high accuracy. Venography, while historically the gold standard, is invasive and reserved for cases where ultrasound results are nondiagnostic or conflicting, but it confirms thrombus presence when needed. Other conditions like pulmonary embolism are related but present differently (not unilateral leg swelling), lymphedema typically involves non-pitting, chronic swelling not driven by thrombosis, and arterial occlusion causes acute pain with pallor and pulselessness rather than the swelling pattern seen with DVT.