ULTRASONOGRAPHY: A Skill For Nephrologists

Since its introduction in the early 1960s, ultrasonography has become an essential part of the workup and management of patients with kidney disease owing to its safety, low cost, and the ease of visualizing the kidneys, bladder, and blood vessels. Given ultrasonography’s simplicity and utility, it is curious it is not routinely performed by many nephrologists, considering that ultrasonography has become a standard procedure for many other specialists and subspecialists. This article discusses why modern nephrologists should acquire skills in ultrasonography and incorporate it into their practice. With the availability of portable, low-cost scanners and training specifically for nephrologists, incorporating ultrasonography into a practice is not a difficult undertaking.

Ultrasonography is ideally suited for imaging the kidneys and bladder, and is indicated in many situations including renal failure, hematuria, severe hypertension, pain, recurrent or refractory infection, and nephrolithiasis. Both organs are easily visualized and exhibit a limited spectrum of anatomic variation and pathologic changes. The renal cortex, medulla, and collecting system have different acoustic properties, and pathological changes are usually easily discernible and correlate well with histological findings (1).

Sonography is particularly useful in the evaluation of chronic renal failure. The finding of a small kidney or thin cortex through ultrasonography indicates irreversible damage, thereby avoiding further unnecessary workup and biopsy (2,3). Obstructive uropathy (Figure 1) and polycystic disease (as causes of renal failure) can be diagnosed or excluded with certainty, and other disorders such as nephritis, amyloidosis, and chronic pyelonephritis can be implicated. Although useful in the evaluation of acute renal failure as well, sonography is not indicated in all cases. When the clinical picture points strongly to acute tubular necrosis or volume depletion, and urinary obstruction is very unlikely, sonography adds little to the diagnostic workup (4).

Figure 1.

Sonogram of a kidney obstructed by a ureteral stone, showing dilated calyces.

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Ultrasonography is indicated for acute failure in most solitary and transplanted kidneys, in which urinary obstruction is a common and unpredictable cause of renal failure (5). Sonography also plays a key role in vascular access, including placement of hemodialysis catheters, preoperative vein mapping, and evaluation of arteriovenous grafts and fistulas.

The addition of ultrasonography to a nephrology practice offers significant advantages to both the patient and the nephrologist. The most important advantage is better integration of diagnostic evaluation and patient care. Because the nephrologist is aware of the clinical situation, the ultrasound examination can be appropriately focused. Furthermore, sonographic findings often require clinical correlation, which is best provided by the nephrologist. Sonography allows the nephrologist to take a systematic approach to the patient with either acute or chronic renal failure. A rapid increase in serum creatinine with minimal or no calyceal dilatation effectively rules out urinary obstruction as a cause of acute renal failure. Hydronephrosis in the absence of bladder distension indicates ureteral obstruction. Swelling of the renal cortex in conjunction with a history of an inciting event or the presence of granular casts in the urine indicates acute tubular necrosis, while enlarged, echogenic kidneys in conjunction with hematuria are indicative of nephritis.

In a patient with nephrotic syndrome and acute renal failure, swollen, echogenic kidneys may instead indicate renal vein thrombosis, particularly if there is new onset hematuria or the renal vein is prominent with luminal echoes. Unilateral cortical atrophy with hypertension and unremarkable urinary sediment should raise suspicion for renovascular disease. Sonography can usually identify the cause of poor fistula maturation. The continual feedback from clinical correlation allows nephrologists to develop expert interpretive skills.

Another readily apparent benefit is improved patient care. Ultrasonography can be performed within minutes of evaluating a patient with acute renal failure, expediting the diagnosis and therapy of urinary obstruction. Studies can be performed at the bedside or in the outpatient clinic or office, avoiding scheduling appointments with and patient travel to the radiology department. Kidney biopsy can be performed entirely by the nephrologist, avoiding delays associated with scheduling and transportation and resulting in expedited diagnosis and treatment. Urinary retention can be excluded noninvasively, eliminating the discomfort of catheterization. Additionally, the same ultrasound equipment (with a different transducer) can be used to guide insertion of central venous catheters for hemodialysis and to evaluate dysfunctional arteriovenous grafts and fistulas.

Another benefit of ultrasonography in kidney care is increased physician efficiency. This is most apparent with renal biopsies, which can be performed at nephrologists’ convenience without additional arrangements. 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 visit. Because sonography is critical in the initial evaluation of most patients, using it in the outpatient setting substantially streamlines the evaluation of patients. Ultrasound guidance also substantially shortens the time required for insertion of central venous catheters.

Another advantage that should not be overlooked is the benefit to the practice of nephrology in general. This procedure can expand the domain and increase the diagnostic and procedural capabilities of nephrologists. As evidenced by the interest shown by residents and fellows, ultrasonography can also improve the attractiveness of a career in nephrology.

The growing number of nephrologists who have incorporated ultrasonography into their practices attests to the technique’s feasibility. Cost is not an obstacle. The equipment is not expensive and cost can be recovered with as few as two outpatient studies per week. Other concerns include training and credentialing. Our experience in the renal division at Emory University demonstrates that nephrology trainees can become competent sonographers with appropriate training, yet few programs offer such training. This remains a major and puzzling obstacle. For nephrologists seeking training in ultrasonography, the renal division at Emory University offers comprehensive CME-accredited training in the form of a weekend comprehensive course offered several times a year, and a weeklong mini-fellowship that can be scheduled throughout the year. A textbook (1) and other teaching materials are also available. Information can be obtained at the following website (www.medicine.emory.edu/divisions/renal/ultrasound).

The American Society of Diagnostic and Interventional Nephrology (ASDIN) has established training standards for sonography limited to kidneys and bladder as well as a certification program based on these standards. These are available at www.ASDIN.org.

In summary, ultrasonography is an integral part of nephrology that is clearly a feasible procedure for nephrologists. Equipment is not expensive, and training and certification are available. Incorporation of sonography into the practice of nephrology is satisfying for both the patient and the physician and improves patient care. The major obstacle continues to be the lack of exposure to sonography in training programs.

Notes

[1] Elvira O. Gosmanova, MD, is assistant professor of medicine and W. Charles O’Neill, MD, is professor of medicine in the renal division at Emory University School of Medicine in Atlanta.

References

1.

O’Neill WC. Atlas of renal ultrasonography. Philadelphia: Sanders; 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, Weinberg EP, Rubens DJ, 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.