An elderly gentleman presents with severe lower abdominal to groin pain resolved with morphine with the ambulance crew. On abdominal examination you think you can feel a central pulsatile/expansile mass. You wonder what to do.

Overview:

Abdominal aortic aneurysm (AAA) is the most common true aneurysm. A true aneurysm is a full thickness focal dilatation of an artery to >50% its original diameter. 95% of the human population will have an aorta <3.0cm in thickness(1) so if a patient is found to have an aorta >3.0cm in diameter then we can consider it to be aneurysmal.

Risk factors for AAA include:

● Older age

● Male gender

● Cigarette smoking

● Caucasian race

● Atherosclerosis

● Hypertension

● Family history of AAA

● Other large artery aneurysms (eg, iliac, femoral, popliteal)

Only 20-30% of patients presenting with a ruptured AAA have a known history of AAA(2,3). 50% of patients with AAA present with the classic triad of severe abdominal pain, hypotension and and a pulsatile mass on abdominal palpation(4). Abdominal palpation can reliably identify a patient with a AAA >5.5cm. Whilst palpation identifies <50% of patients with asymptomatic AAA(5) it will identify up to 62% of patients with ruptured AAA so it is important to look out for(6). In a study of 200 patients, the overall sensitivity of abdominal palpation for detecting AAA was 68% and the specificity was 75%(7). The likelihood of successful palpation of a AAA is proportional to the diameter of the AAA and inversely proportional to the patient's diameter. Palpation of a AAA has never been known to provoke rupture despite what urban legends regarding OSCEs you may have heard!(6).

In all patients presenting with abdominal pain and haematological instability with a known AAA rupture must be considered and ruled out with imaging. For patients not known to have a AAA but where rupture is suspected imaging is once again essential. POCUS (Point of Care Ultrasound) can be used but is dependent on the skill of the practitioner and can be degraded by patient habitus or bowel gas however it is a useful rule out tool. CT can confirm rupture as well as guide management or identity other pathology but doesn't carries risks of radiation and isn't appropriate for severely unwell patients.

Learning Points:

The majority of patients presenting to ED with ruptured AAA don't have previous history of AAA
Not all patients with ruptured AAA will have the classic triad of pain, low blood pressure and pulsatile mass
The sensitivity and specificity of palpation of a ruptured AAA is high and so ruptured AAA must be considered in all patients with abdominal pain and known AAA or in patients not known to have AAA but presenting with pain and a pulsatile mass

References:

(1) Johnston KW, Rutherford RB, Tilson MD, Shah DM, Hollier L, Stanley JC, Suggested standards for reporting on arterial aneurysms. Subcommittee on Reporting Standards for Arterial Aneurysms, Ad Hoc Committee on Reporting Standards, Society for Vascular Surgery and North American Chapter, International Society for Cardiovascular Surgery, J Vasc Surg. 1991;13(3):452.

(2) Akkersdijk GJ, van Bockel JH, Ruptured abdominal aortic aneurysm: initial misdiagnosis and the effect on treatment, Eur J Surg. 1998;164(1):29.

(3) Gloviczki P, Pairolero PC, Mucha P Jr, Farnell MB, Hallett JW Jr, Ilstrup DM, Toomey BJ, Weaver AL, Bower TC, Bourchier RG , Ruptured abdominal aortic aneurysms: repair should not be denied, J Vasc Surg. 1992;15(5):851.

(4) Rinckenbach S, Albertini JN, Thaveau F, Steinmetz E, Camin A, Ohanessian L, Monassier F, Clément C, Brenot R, Camelot G, ChakféN, Kretz JG , Prehospital treatment of infrarenal ruptured abdominal aortic aneurysms: a multicentric analysis, Ann Vasc Surg. 2010;24(3):308.

(5) Lederle FA, Johnson GR, Wilson SE, Littooy FN, Krupski WC, Bandyk D, Acher CW, Chute EP, Hye RJ, Gordon IL, Freischlag J, Averbook AW, Makaroun MS, Yield of repeated screening for abdominal aortic aneurysm after a 4-year interval. Aneurysm Detection and Management Veterans Affairs Cooperative Study Investigators, Arch Intern Med. 2000;160(8):1117.

(6) Azhar B, Patel SR, Holt PJ, Hinchliffe RJ, Thompson MM, Karthikesalingam A, Misdiagnosis of ruptured abdominal aortic aneurysm: systematic review and meta-analysis, J Endovasc Ther. 2014;21(4):568.

(7) Fink HA, Lederle FA, Roth CS, Bowles CA, Nelson DB, Haas MA, The accuracy of physical examination to detect abdominal aortic aneurysm, Arch Intern Med. 2000;160(6):833.