Ultrasound Case of the Month: A Silent Killer

The Case:

A 72 year old male with no PMH presents to the emergency department (ED) for vague abdominal discomfort and fullness. The patient is hemodynamically stable on arrival and received a point of care ultrasound (POCUS) for evaluation of his abdominal pain. FAST performed was negative for free fluid, however, the renal ultrasound showed unilateral mild hydronephrosis on the right side. POCUS was then performed to evaluate the aorta, and a large abdominal aortic aneurysm (AAA) was seen, measuring 14cm at its largest diameter.

Introduction:

When performing a POCUS it is important to remember the differential diagnosis for hydronephrosis is broad, and not limited to renal colic. The ureter can be obstructed either internally from a stone, or externally from surrounding structures.  When renal colic is on your differential, and you find hydronephrosis, be sure to also consider alternative diagnosis such as a AAA. In older patients, consider performing a AAA evaluation in all patients with suspected renal colic, and/or hydronephrosis. 

In this case, the patient had compression of the ureter from the large AAA resulting in hydronephrosis, but if the aorta had not been evaluated, we may have missed the more dangerous diagnosis. In addition, please remember that a patient may have leaking or rupture from the AAA which is located retroperitoneally and may not be seen on POCUS.

A ruptured abdominal aortic aneurysm (AAA) is a vascular catastrophe responsible for 1-3% of deaths in men from the age 65-85 in developed countries. Rupture from an AAA is the 10th leading cause of death in males over 50, the mortality rate of a ruptured AAA approaches 90% and the incidence of AAA continues to increase. Therefore, it is essential for the EM physician to diagnose a AAA in a timely manner. (1) The minority of patients with a ruptured AAA (<25%) will present with the classic triad of hypotension, back pain and a pulsatile abdominal mass.  This results in a delay in diagnosis, or misdiagnosis. Patients may present with referred pain to the scrotum, buttocks, thighs, shoulders, and/or chest and can be misdiagnosed as having renal colic, diverticulitis or MSK pain.

Indications:

The current indications by ACEP for obtaining POCUS to detect AAA include:

Presence of syncope, shock, hypotension, abdominal pain, abdominal mass, flank pain or back pain- especially in patients >50 years old.(3) Currently, the U.S. Preventive Service Task Force recommends that men from the age of 65-75 years who have ever smoked be screened for an AAA sonography.(4)

Utility of bedside ultrasound for AAA in the ED?

While CTA is considered the surveillance study of choice(5),  research suggests that the sensitivity of point of care bedside ultrasound approaches 99% for abdominal aortic aneurysm (AAA). With such a excellent sensitivity and a high prevalence of AAA in specific patient populations (10-15% in men who smoke >65), providers should consider performing this scan at the bedside for an expedited diagnosis.(6)

Performing the scan:

• The probe of choice is the 3.5 MHz curvilinear probe

• Start just caudal to xyphoid process

• Measure the aorta proximally, mid and distally in the transverse plane with the probe marker to the patient’s right (should be <3cm from outer to outer wall)

• Measure the iliac arteries after the bifurcation in transverse (should be <1.5cm)

• Evaluate the aorta distally in the longitudinal view with the probe marker to patient’s head as most aneurysms will be located infrarenally

• Identify vertebral body as relevant landmark

• Aorta is anterior to vertebral body

• IVC is anterior & right (patient’s right) of vertebral body

Vertebral body: horseshoe shaped with hyperechoic anterior & posterior shadowing

Tips and Tricks

• Aorta and IVC can be confused in longitudinal view:

  • Aorta is rounder, less compressible, & has brighter thicker walls

• Bowel gas & body habitus can make imaging difficult:

  • Apply steady pressure to move gas

  • Jiggle the probe to move bowel aside

  • Flex patients hips & knees to relax abdominal muscles

  • Lower probe frequency to improve sound wave penetration

Conclusion

POCUS scanning for AAA enables timely diagnosis of a condition with high mortality which is frequently misdiagnosed, or suffers a delay in diagnosis. AAA POCUS has high sensitivity and specificity that can be easily learned and performed in ED. In a patient with hydronephrosis, consider also AAA evaluation, even if renal colic is high on your differential diagnosis.

Faculty Reviewer: Dr. Kristin Dwyer

References:

1. Sakalihasan N, Limet R, Defawe OD. Abdominal Aortic Aneurysm. Lancet 2005;365:15577-89.

2. Fink HA, Lederle FA, Roth CS, Bowels CA, Nelson DB, Haa MA. The Accuracy of physical examination to detect abdominal aortic aneurysm. Arch Intern Med.2000;160(6):833-6.

3. American College of Emergency Physicians. Policy Statement. 2001: Emergency Ultrasound Guidelines.

4. U.S. Preventive Services Task Force. Screening for abdominal aortic aneurysm: recommendation statement. Ann Inter med. 2005;142(3):198-202.

5. Cantisani V, Ricci P, Grazhdani H, et al. Prospective comparative analysis of colour-doppler ultrasound, contrast-enhanced ultrasound, computed tomography and magnetic resonance in detection endoleak after endovascular abdominal aortic aneurysm repair. Eur J Vasc Endovasc Surg. 2011;41:(2)186-92.

6. Rubano, Elizabeth, Ninfa Mehta, William Caputo, Lorenzo Paladino, and Richard Sinert. Systematic Review: Emergency Department Bedside Ultrasonography for Diagnostic suspected Abdominal Aortic Aneurysm. Acad Emerg Med Academic Emergency Medicine 20.2 (2013): 128-38.