A 74-year-old man is brought to the emergency department due to acute-onset lower abdominal and back pain that was followed by an episode of syncope 2 hours ago. The pain is sharp and constant. He has had no changes in bowel or bladder function. Other medical conditions include hypertension and hyperlipidemia. The patient has a 50-pack-year history of smoking cigarettes. Temperature is 36.9 C (98.4 F), blood pressure is 90/60 mm Hg, pulse is 108/min and regular, and respirations are 18/min. BMI is 34 kg/m². The patient is diaphoretic and appears pale. Heart and lung sounds are normal. Abdominal examination reveals moderate tenderness to deep palpation in the lower abdomen; there is no guarding or rebound tenderness. Bowel sounds are normal. Which of the following is the most likely diagnosis?

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11ec160b_38b3_0469_9249_7b2b85b5e067_MD0001_00 Ruptured abdominal aortic aneurysm (AAA) is a surgical emergency involving full-thickness compromise of the aortic wall with extravasation of blood into surrounding tissues and spaces. The acute onset of severe abdominal and back pain is the most common presenting symptom. In general, anterior rupture into the peritoneal cavity is quickly accompanied by syncope, hypotension, and shock, whereas posterior rupture into the retroperitoneum may be temporarily contained, resulting in delayed onset of hemodynamic instability. Other signs suggesting AAA rupture include abdominal distension, a pulsatile abdominal mass, and umbilical or flank hematoma (indicators of retroperitoneal hemorrhage). Early detection of AAA can be difficult because patients frequently have few symptoms until the AAA either ruptures or markedly expands. Therefore, ruptured AAA should be suspected in patients with consistent symptoms and known risk factors, which include advanced age (>60), smoking, male sex, and a history of atherosclerosis or connective tissue disease. CT imaging can confirm the diagnosis, but hemodynamically unstable patients with suspected ruptured AAA should go straight to emergent surgical repair. (Choice A) Acute mesenteric ischemia has similar risk factors to AAA. Patients typically describe severe abdominal pain but have few findings on physical examination (eg, minimal tenderness) and hypotension and syncope are not usually seen. (Choice B) Colonic perforation can be due to diverticulitis, malignancy, or complications from colonoscopy. Patients can develop hypotension due to sepsis, but signs of infection (eg, fever) and peritonitis (eg, rebound, guarding) are also expected. (Choice C) Renal colic is characterized by episodic (eg, every 30 min) flank or groin pain due to capsular stretch from nephrolithiasis-associated obstruction. Hypotension and syncope are not typical features. (Choice E) Vertebral compression fractures can cause acute back pain exacerbated by minimal movement (eg, coughing, bending). Although the pain can occasionally refer to the abdomen, it is most commonly at the midline over the spinous processes. There should not be associated hypotension. Educational objective: Ruptured abdominal aortic aneurysm is a surgical emergency that usually presents with the acute onset of severe abdominal and back pain in patients with appropriate risk factors (eg, advanced age, smoking, atherosclerosis). Accompanying syncope, hypotension, and shock may occur quickly (intraperitoneal rupture) or may be delayed (retroperitoneal rupture). __________ References: Abdominal aortic aneurysm. (http://www.ncbi.nlm.nih.gov/pubmed/25884861) Ruptured abdominal aortic aneurysm: the state of play. (http://www.ncbi.nlm.nih.gov/pubmed/23181137)

A 74-Year-Old Man Is Brought to the Emergency Department Due