A 45-year-old tall, thin, male has acute onset of chest pain radiating into the back. In the emergency room his right radial pulse is bounding but his femoral pluses are absent. The most likely diagnosis is? SELECT ONE.
First, acute chest pain radiating to the back is a classic sign of aortic dissection. But wait, there's also the issue with the pulses. Bounding radial and absent femoral pulses... Oh, right! That's a sign of aortic dissection involving the aortic arch or descending aorta. The dissection could block the blood flow to the lower extremities, leading to absent femoral pulses. Alternatively, maybe it's a thoracic aortic aneurysm with dissection. But another possibility is aortic coarctation, but that's usually present from birth and might not explain the acute chest pain. Then there's pulmonary embolism, but that doesn't typically cause pulse discrepancies. Let me think again. The key here is the pulse difference. In aortic dissection, the dissection can cause occlusion of branches, leading to different pulses in different areas. The right radial being bounding could be because the dissection is in the left side, allowing the right to still get good flow. Meanwhile, the femoral pulses being absent suggests that the dissection is blocking the iliac arteries. Alternatively, if it's a Stanford Type A dissection (involving the ascending aorta), it might present with different signs, but the femoral pulses being absent would be more typical of a Type B. Also, the patient is tall and thin, which is a risk factor for Marfan syndrome, which is a known cause of aortic dissection. So putting it all together, the most likely diagnosis is aortic dissection. The other options like thoracic aortic aneurysm might not explain the pulse differences as well. Coarctation of the aorta is usually congenital and might not present with acute chest pain. So the answer should be aortic dissection.
**Core Concept**
This scenario tests recognition of **aortic dissection**, a life-threatening condition involving tearing of the aortic intima. Key signs include **acute chest/back pain**, **pulse discrepancies**, and **hypotension**. The **Stanford classification** categorizes dissections as Type A (involving ascending aorta) or Type B (confined to descending aorta).
**Why the Correct Answer is Right**
Aortic dissection causes **tearing of the aortic wall**, allowing blood to enter the media and form a false lumen. **Radiating chest/back pain** and **pulse/pressure asymmetry** (e.g., bounding radial vs. absent femoral pulses) occur when dissection occludes arterial branches. In this case, **Type B dissection** is likely, as femoral pulse absence suggests distal aortic or iliac artery involvement. Risk factors include **hypertension**, **Marfan syndrome**, and **tall stature** (as seen here).
**Why Each Wrong Option is Incorrect**
**Option A:** *Thoracic aortic aneurysm* lacks acute pain and pulse discrepancies; it typically presents with mass effect (e.g., dysphagia) or incidental imaging findings.
**Option B:** *Coarctation