Ultrasound Case of the Month
Case: Submitted by Dr. Alyssa Mierjeski
87 year old female presented to the ED with the chief complaint of anemia found on routine lab testing. The patient had a known history of an infrarenal abdominal aortic aneurysm but denied any flank, abdominal or chest pain. She did, however, endorse some fatigue and urinary complaints.
What's the diagnosis?
Discussion:
This ultrasound shows an AAA with intra-luminal hematoma extending into the iliac vessels, as well as mild hydronephrosis. The hydronephrosis is represented by the anechoic enhancement of the renal pelvis (the black region in the collecting system of the kidney).
The aorta images were acquired with the curvilinear probe placed transversely in the epigastrium (probe marker to the patient right), perpendicular to the skin, with the patient supine. ACEP recommends 5 measurements: proximal aorta, mid aorta, distal aorta, bifurcation of the iliacs (just above the level of the umbilicus) and a longitudinal view of the aorta infrarenally. Normally, you would expect the abdominal aorta to measure less than 3 cm in diameter (measuring from the outer wall to the outer wall to include any clot in the lumen).
The renal images were obtained with the curvilinear probe in the mid-axillary line at the level of the xiphoid process on the left and right. These images are similar to those you may acquire of the RUQ and LUQ in a FAST exam.
However, in this patient with a known AAA, the aorta is measuring larger than 3 cm in diameter. Hydronephrosis can be seen in conjunction with an AAA due to compression of the ureters from the enlarging aorta (confirmed on CT). Hydronephrosis can be unilateral or bilateral depending on the size of the abdominal aneurysm and whether one or both ureters are obstructed.
Ultrasound is an excellent modality for diagnosing an AAA as it is very fast, cost effective and accurate. However, a ruptured AAA is not always seen on ultrasound due to their tendency to bleed into the retroperitoneum. Ultrasound can also be good for evaluation of hydronephrosis, however it maybe difficult to determine the degree of hydronephrosis due to some subjectivity. In an elderly patient with flank pain, an US of the kidneys and the aorta are both reasonable. While a patient may present with symptoms consistent with renal colic, if they are older, the diagnosis of AAA with RP bleed must be considered.
Faculty Reviewer: Dr. Kristin Dwyer