Pearls & Pitfalls for Renal Ultrasound
1. Be Thorough: Image the entire organ by sweeping and fanning through the kidneys in two different planes. Don’t just go for one static shot through the middle and don’t stop scanning just because you visualize an abnormality. Always complete the entire scan so you don’t put yourself, and the patient, at risk for missing peripherally located pathology. If you have a difficult time imaging the left kidney, have the patient hold their breath to bring the kidney more caudally. Use the spleen and liver as your acoustic windows and don’t be afraid to reposition the patient to achieve better images. Any abnormal findings should be confirmed with comprehensive imaging via radiology, but this can often be done as an outpatient.
2. Look for Hydro: Hydronephrosis is seen as a black or anechoic area in the center of the kidney and represents downstream obstruction.
3. Compare Sides: Because most people have two kidneys, any questionable findings on one side may benefit from a comparison view of the other kidney.
4. Don’t Forget the Aorta: An aortic aneurysm often mimics renal colic, so always take a look at the aorta, even if your suspicion is low. It’s essential to practice looking at normal anatomy and even more essential to pick up an aneurysm before it ruptures.
5. Recognize Your Limitations: Remember that bedside ultrasound is meant to answer a specific, focused set of questions. It is not the same as a comprehensive, formal scan. You do not necessarily have to visualize the culprit stone if you see hydronephrosis. Likewise, it’s not always necessary to evaluate for ureteral jets within the bladder. Use the data and information you acquire from your beside scan to help guide management and treatment, but recognize that your scan is limited.
6. Take Responsibility for Your Findings: Document and archive all bedside ultrasound images and findings. If you find something incidental on your bedside scan, you are responsible for informing and educating the patient about the finding and advising or arranging appropriate follow-up.
7. Image in Urosepsis: Don’t miss renal obstruction in the setting of urosepsis as relieving the obstruction is a critical part of treatment. These patients may have little to no pain if they are elderly and/or the obstruction has become chronic. Be especially suspicious for obstruction if the patient does not have any other risk factor for UTI.
8. Practice Makes Perfect: With bedside ultrasound, there is no substitute for experience. The more ultrasounds you do, the better you will be able to differentiate abnormal from normal, even when you may not be sure exactly what the abnormality is. An image library of normal and abnormal ultrasounds helps immensely, and we can help. Just go to the ultrasound section on www.epmonthly.com.
Brady Pregerson manages a free online EM Ultrasound Image Library and is the editor of the Emergency Medicine Pocketbook series. For more information visit ERPocketBooks.com
Teresa Wu is the EM Ultrasound Director and Co-Director for Simulation Based Training for the Maricopa Emergency Medicine Program in Phoenix, Arizona.
A tip sheet from www.EMResource.org
Type: CaOxylate: 67%, TriplePhos: 12%, CaPhos: 8%, Cystine: 3%, Uric acid (radiolucent): 2%
Tests: UA: RBC:80-90%. KUB: 40-60% (1cm from spine). US: 65-95% (less if <6h). IVP: 87%
CT: 96%/98% (may miss uric acid, often due to Crixivan, but should detect hydronephrosis)
Passage: If < 2mm, 90% will pass w/in 4 days (up to 2wk).
Greater than 4mm, needs urology f/u.
8mm: Less than 10% pass.
Rx: Most pass w/in 2 weeks, lithotripsy (proximal stones <1cm), surgery, cystoscopy, (blocker
New: Nifedipine or Flowmax 0.4mg PO qd may lead to earlier passage. Steroids may help too.
Infection: Beware: fever, +UA, pH>7, staghorn stone, chronic obstruction (voided urine not sensitive)
Admit: Intractable pain or vomiting, hypercalcemia, solitary kidney,
Renal failure, high-grade obstruction, renal transplant, sepsis
Consider Admission: RI, stone>5mm, ruptured calyx, UTI (pH>7, >10 WBC/hpf on UA), urine extravasation
Risks: Dehydration, family history, Crohn’s, hypercalcemia, hyperthyroid, RTA, obesity (uric acid)
Meds: Crixivan (radiolucent stone), triamterene, sulfa…(See A to Z Pocket Pharmacopoeia for more)
DDx: PE, AAA (age>50), thrombosis/embolus (contrast CT to dx), diverticulitis, appy, pyelo
Papillary necrosis (NSAID, sickle cell), renal infarct, gynecologic conditions, CA