missed AAA

AAA

As William Osler said, “There is no disease more conducive to clinical humility than aneurysm of the aorta.” Ruptured AAA classically presents as abdominal pain radiating to the back, shock and a pulsatile abdominal mass. But like all “classic” presentations this occurs in a minority of cases and there is a high misdiagnosis or delayed diagnosis rate for those who don’t confirm to this presentation.

 

The misdiagnosis of AAA as renal colic is longstanding: Symptomatic Abdominal Aortic Aneurysm Misdiagnosed as Neprhoureterolithiassis. Ann Vasc Surg 1988;2(2):145-149. In this review of 134 symptomatic AAA patients from the late 1970s and early 1980s, 24 had an initial diagnosis of nephrolithiasis. Ten of these patients had the correct diagnosis made within five hours and half survived surgery; 14 patients had a delay greater than five hours and all died. AAA can also be assigned other abdominal diagnoses: Misdiagnosis of ruptured abdominal aortic aneurysm. J Vasc Surg 1992 July;16(1): 17-22. Symptoms: 70% abdo pain, 50% back pain. Signs: 57% shock, 26% pulsatile mass. Misdiagnoses: renal colic, diverticulitis, GI bleed

 

Twenty-five years later misdiagnosis remains a challenge:

  1. Ruptured abdominal aortic aneurysm: a 7-year retrospective observational study in an emergency department of Hong Kong. Hong Kong J of Emerg Med 2010; 17(2): 118-125. Patients had the following symptoms: 73% abdo pain, 46% syncope, 27% back pain, 19% dizzy, 12% vomiting, 8% groin pain. Only 19% had the “classic triad” of hypotension, abdo pain and abdo mass. The diagnosis was made in the ED in 69% of cases, and misdiagnoses included abdo pain NOS, renal colic, appendicitis, syncope, bowel obstruction and aortic dissection.
  2. Misdiagnosis of ruptured abdominal aortic aneurysm: a systematic review and meta-analysis. J Endovasc Ther 2014 Aug;21(4):568-75. Pooling 1109 patients from nine studies there was a misdiagnosis rate of 42% overall, down to 32% in studies after 1990. The most common misdiagnoses were renal colic and MI. As is often the case, relying on “classic” symptoms probably contributed to misdiagnosis, as abdominal pain was present in 61%, shock in 46% and pulsatile mass in 45%.
  3. Diagnosis of ruptured abdominal aortic aneurysm: a multicentre cohort study. Eur J Emerg Med 2015 May 5. In this observational study of 85 consecutive cases, of which 26% were initially misdiagnosed. Contributing factors were that 17% had subacute presentations with symptoms up to three weeks before presentation; 8% had atypical pain and 12% had no pain; a minority of patients had syncope (37%), tachycardia (19%) and hypotension (37%).
  4. The Canadian Medical Protective Association analyzed 27 cases over a 10 year period:
    • age 58-93, average 70
    • risk factors: 69% cardiovascular, 66% obesity, 62% smoking
    • symptoms: 66% sudden severe radiating pain (back-abdo, back-groin, back-leg), 50% flank/back pain, 40% abdo pain, 30% vomiting, 15% syncope
    • misdiagnoses: 30% renal colic, 26% mechanical back pain, 18% diverticulitis/gastro, 11% constipation
    • outcome: 63% discharged, 44% bounceback, 78% death, 15% major disability

 

Like all emergencies, time makes a difference, and waiting for hypotension to make the diagnosis increases mortality rate. Like SAH, the patients we can help the most are those who are the easiest to miss because they at the beginning of their emergency, without advanced signs: headache without altered mental status in the case of SAH, or abdo/back/flank pain without hypotension in the case of AAA. Emergency abdominal aortic aneurysm presenting without haemodynamic shock is associated with misdiagnosis and delay in appropriate clinical management. Emerg Med J 2009;May;26(5):334-9. In this review of 98 patients, stable patients had twice the rate of misdiagnosis (60% vs 26%), taking two hours longer to make the diagnosis (144min vs 12 min) and doubling their time to the OR (90min vs 48min). As a consequence, 19 of the the 59 initially stable patients decompensated before surgery, which doubled their mortality (74% vs 39%).

 

This highlights the importance of Point of Care Ultrasound for the rapid diagnosis of AAA in stable patients. POCUS has the potential to be very accurate: Systematic Review: Emergency Department Bedside Ultrasonography for Diagnosing Suspected Abdominal Aortic Aneurysm. Acad Emerg Med 2013;20:128-138. This review of seven papers found a sensitivity of 98% and specificity of 95%, giving a LR+ >10 and LRi < 0.025. Like all aspects of ultrasound, this depends on the experience of the provider: Successful sonographic visualization of the abdominal aorta differs significantly among a diverse group of credentialized emergency department providers. Emerg Med J 2011 June;28(6):472-6.

 

In summary, AAA is a lethal disease with ongoing challenges of missed or delayed diagnosis, which can benefit from both cognitive strategies of considering the diagnosis and technical strategies of using point of care ultrasound

  1. consider AAA in all elderly patients with abdo/back/flank/groin pain, syncope or vomiting, and look at their aorta at the bedside
  2. before the diagnostic delay of sending patients for CT to r/o appy/diverticulitis/renal colic/bowel obstruction, look at their aorta at the bedside
  3. use an integrated approach to diagnosis considering all systems. Most missed/delayed AAA are not because they present with cardiovascular symptoms (like shock) and are misdiagnosed as another cardiovascular disease, but because they present with other symptoms that are reduced to other systems: flank pain reduced to the renal system, abdo pain/vomiting reduced to the GI system,  back pain reduced to joints/bones. But if we use an integrated approach
  • flank pain: consider B (eg pneumonia), C (eg PE, AAA) and D (eg nerve root compression) before F (eg renal colic)
  • abdo pain: consider B, C (eg MI, dissection, AAA), E (eg DKA) and F (eg torsion) before G (eg appy)
  • back pain: consider B (eg lung ca), C (eg dissection, AAA), D (eg spinal cord compression), F (eg pyelo), G (eg chole), before J(eg sciatica)

 

 

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