Ultrasound
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Dx: Renal Cyst

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Your sonogram shows not hydronephrosis, but instead a renal cyst. And it’s not even a simple cyst, but rather an infected cyst that has internal echoes causing a hypoechoic (dark gray), rather than an anechoic (black) center on its lower half. To the neophyte sonographer, a cyst might be mistaken for hydronephrosis caused by a kidney stone. Cysts, however, can be distinguished by both their shape and location; they tend to be both more peripheral and more circular. This patient actually had other cysts and an abnormal renal parenchyma, which made the boundaries of kidney somewhat difficult to identify. She later underwent a comprehensive ultrasound in the radiology department, which diagnosed polycystic kidney disease complicated by an infected cyst. She was continued on antibiotics during her 3 day hospitalization and on day 2 had a CT-guided drainage of the infected cyst. Though you did your best to avoid radiation exposure in the ED, your colleagues upstairs did not continue in the same spirit. Her CT with contrast is shown, in addition to an image from her comprehensive ultrasound.

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You are glad you decided to take your evaluation one step further than you normally do for what at first appeared to be routine pyelonephritis. Remember, when things don’t seem to fit, it’s wise to look further and consider a broader differential. In this case the rule, “If red cells exceed white cells in the urine for a patient who clinically has pyelonephritis, look for another cause” was the one that started the search that eventually led to a diagnosis of polycystic kidney disease which explained both the patient’s elevated creatinine and her hematuria. Had this diagnosis been missed, antibiotic therapy alone would have likely been ineffective. Definitive management required drainage of the infected cyst.

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However, when things do fit together well, you don’t always need advanced imaging to care for patients with headache, chest pain, flank pain or abdominal pain. Renal colic is a perfect example of where we can cut down the use of unnecessary CT scanning. CT adds significant radiation exposure, not to mention cost as well as delays for other patients. When you are worried about more serious causes of flank pain, such as a AAA, image liberally, but since for the most part, kidney stones can be treated expectantly and most stones will pass on their own, it makes little sense to CT most young, healthy, afebrile patients with flank pain and blood in their urine, especially if they’ve had a kidney stone in the past. If you are uncomfortable with no imaging, at least consider ultrasound, as it is radiation free.

Minimizing radiation exposure is an important part of patient care. Though more testing tends to be in our best interest as providers, it is often not in our patients’ best interest. We all took an oath in medical school that included a phrase promising to put our patient’s well-being before our own. Let’s make good on that oath. For more information on radiation stewardship and radiation doses from various tests, visit the Image Gently campaign at www.pedrad.org and also the Radiation Stewardship page on www.erpocketbooks.com

Continue to next page for Pearls and Pitfalls for Renal Ultrasonography

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