Renal Ultrasonography for Nephrologists: Unmet Expectations

Over the past four decades, ultrasonography has become an indispensable tool because of its safety, availability, and low cost. Accordingly, many specialties have incorporated ultrasonography into their core training programs for visualization of relevant organs and guidance of procedures (e.g., echocardiograms in cardiovascular medicine, pelvic ultrasounds in gynecology and obstetrics, thyroid ultrasounds in endocrinology, abdominal ultrasounds in trauma and emergency medicine).

In nephrology, ultrasonography is ideally suited for visualizing the kidneys, bladder, and blood vessels and is essential for the diagnosis and treatment of patients with kidney diseases. However, formal training in ultrasonography is rarely included in nephrology training programs. This article discusses the reasons why modern nephrologists should acquire this skill and how they can incorporate it into their daily practice.

Owing to their acoustic properties, the kidneys and urinary bladder are easily visualized by ultrasonography and present a limited spectrum of anatomic variations and pathologic conditions. The renal cortex, medulla, and collecting system are usually easily discernible, and pathologic changes correlate well with histologic findings (1). Sonography is indicated in the evaluation and diagnosis of renal failure (acute and chronic), hematuria, severe hypertension, pain, refractory urinary tract infections, and nephrolithiasis and in the screening for hereditary cystic diseases. It is particularly useful in the evaluation of chronic renal failure, where the findings of small kidneys or cortical thinning usually indicate irreversible damage, thereby avoiding further unnecessary evaluation and biopsy (2, 3).

Obstructive uropathy and polycystic kidney disease (as causes of renal failure) can be easily diagnosed or excluded, and other disorders such as nephritis, amyloidosis, and chronic pyelonephritis can be suspected. The utility of sonography is more limited in the evaluation of acute renal failure in native kidneys, when clinical and urinary sediment features strongly point toward acute tubular necrosis, volume depletion, and urinary obstruction (4). However, ultrasonography remains indicated for acute renal failure in known solitary kidneys and transplanted kidneys, where urinary obstruction is a common and unpredictable cause of renal failure (5). Sonography also plays a central role in percutaneous renal biopsy, insertion of hemodialysis catheters, preoperative vein mapping, and evaluation of arteriovenous grafts and fistulas.

Nephrologists can effectively improve patient care by incorporating sonography into their practice, thereby increasing patient convenience, expediting patient care, and providing improved scanning and interpretation (6). By performing ultrasonography during evaluation of patients in the office, nephrologists can make a prompt diagnostic assessment and take therapeutic steps that ultimately improve patient care and satisfaction by avoiding unnecessary waiting time, multiple trips to different locations, or additional testing and hospital admissions. As a simple example, urinary retention can be excluded noninvasively, eliminating the discomfort of catheterization.

Incorporating ultrasonography into nephrology practices streamlines the evaluation of the patient and increases the physician’s efficiency. In the outpatient setting, delays associated with scheduling ultrasonography and obtaining results can be avoided because the sonogram can be performed and interpreted during the patient’s visit.

Ultrasonography also enhances the ability of nephrologists to perform important procedures on our patients. It is indispensable for guiding central venous catheter insertion, substantially shortening the required time and significantly reducing the risks of complication. Sonography is the imaging modality of choice for performing percutaneous renal biopsies because of its low cost and lack of radiation. It also enables biopsies to be performed by nephrologists at the bedside, enhancing patient and physician convenience. Most renal biopsies are performed under computed tomographic guidance despite the increased cost and radiation exposure and the lack of data showing any advantage over ultrasound guidance (7). An additional advantage of ultrasound in this setting is that a patient whose condition is otherwise stable can be safely discharged after observation without an overnight hospital stay if a postbiopsy ultrasound is normal (8).

Knowledge of patients’ personal and family histories, clinical presentation, and complementary test results enables nephrologists to appropriately focus the imaging study and also correlate ultrasound and clinical findings on a real-time basis. Visualization of dilated calyces with or without bladder distension may point toward radically different pathologic processes such as prostatic enlargement or ureteral obstruction. Absence of calyceal dilatation almost invariably rules out obstruction as a cause of acute renal failure. The finding of enlarged renal cortex may be consistent with acute tubular necrosis (in the presence of urinary granular casts) or nephritis (in the presence of proteinuria and hematuria).

Renal enlargement with increased cortical echogenicity may evoke renal vein thrombosis if new-onset hematuria and flank pain are present and should direct the imaging study toward visualization of the renal veins. The same sonographic findings may also point toward amyloidosis in the presence of other cardiac or hematologic features. Major renal asymmetry with unilateral cortical atrophy in the context of severe hypertension and bland urinary sediment strongly suggests the possibility of renovascular disease. Ultrasonography can usually identify the basis for dysfunctional or poorly maturing arteriovenous fistulae.

Finally, renal ultrasonography is an enjoyable and relatively easy skill to acquire, and the incorporation of new diagnostic and procedural modalities can improve the attractiveness of a career in nephrology. The relatively low cost of the equipment, which can be recovered with as few as two outpatient studies per week, and the availability of good-quality portable scanners should make this modality practical for any nephrology practice.

Unfortunately, very few nephrology programs offer comprehensive training in ultrasonography. The Renal Division at Emory University was the first program to provide such training, with all fellows receiving training since 1994. Since 1997, Emory has offered continuing medical education—accredited training for other nephrologists that includes a weekend didactic course held four times a year, followed by an individual week-long minifellowship that includes performance and interpretation of scans and completion of a computerized, interactive teaching file. Information on training can be obtained at http://www.medicine.emory.edu/renal/ultrasound.

Over the past 14 years, more than 1200 nephrologists have attended the didactic courses, and over 350 of them have completed minifellowships. In addition, more than 100 nephrology fellows have been fully trained. Despite the increasing interest, the number of nephrologists who have received training at our institution is still less than 7 percent of all board-certified nephrologists practicing in the United States (9). This training satisfies the didactic requirements for certification by the American Society of Diagnostic and Interventional Nephrology. Additional requirements for certification are a requisite number of ultrasound studies and submission of sample studies of different pathologic conditions. Further information on certification can be obtained at http://www.ASDIN.org.

If ultrasonography is to become an established tool for nephrologists, it must be incorporated into their training. A recent survey of renal fellowship programs (10) revealed that only 8 percent included diagnostic ultrasonography and only 42 percent included ultrasound guidance for kidney biopsies without the help of a radiologist. These numbers were slightly higher for transplanted kidneys (diagnostic: 11 percent; biopsy guidance: 51 percent).

In summary, ultrasonography is an integral part of nephrology that is clearly a feasible procedure for nephrologists, enhancing patient care and both patient and physician satisfaction. The equipment is affordable, and certification is available, but training opportunities remain limited to a very few centers that cannot accommodate the training of all nephrologists. The major obstacle remains the absence of exposure to sonography in training programs. This obstacle can primarily be surmounted by increasing the number of trained faculty members and ultimately incorporating ultrasonography training into nephrology training programs.

Notes

[1] Frederic Rahbari-Oskoui, MD, is an assistant professor of medicine and William Charles O’Neill, MD, is a professor of medicine and physiology in the renal division at Emory University School of Medicine in Atlanta.

References

1.O’Neill WC. Atlas of Renal Ultrasonography. Philadelphia, W.B. Saunders, 2000.

2.O’Neill WC. Sonographic evaluation of renal failure. Am J Kidney Dis 2000; 35:1021–1038.

3.Buturović-Ponikvar J, Visnar-Perovic A. Ultrasonography in chronic renal failure. Eur J Radiol 2003; 46:115–122.

4.Gottlieb RH, et al. Renal sonography: can it be used more selectively in the setting of an elevated serum creatinine level? Am J Kidney Dis 1997; 29:362–367.

5.O’Neill WC, Baumgarten DA. Ultrasonography in renal transplantation. Am J Kidney Dis 2002; 39:663–678.

6.O’Neill WC. Renal ultrasonography: a procedure for nephrologists. Am J Kidney Dis 1997; 30:579–585.

7.Nass K, O’Neill WC. Bedside renal biopsy: ultrasound guidance by the nephrologist. Am J Kidney Dis 1999; 34:955–959.

8.Maya ID, Allon M. Percutaneous renal biopsy: outpatient observation without hospitalization is safe. Semin Dial 2009; 22:458–461.

9.American Board of Internal Medicine (ABIM) certificate statistics 2010. http://www.abim.org/pdf/data-candidates-certified/all-candidates.pdf.

10.Berns JS, O’Neill WC. Performance of procedures by nephrologists and nephrology fellows at U.S. nephrology training programs. Clin J Am Soc Nephrol 2008; 3:941–947.


February 2012 (Vol. 4, Number 2)