What is the role of ultrasonography in the diagnosis of nephrolithiasis?

Updated: Jun 21, 2018
  • Author: Chirag N Dave, MD; Chief Editor: Bradley Fields Schwartz, DO, FACS  more...
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Answer

Renal ultrasonography by itself is frequently adequate to determine the presence of a renal stone. The study is mainly used alone in pregnancy [26] or in combination with plain abdominal radiography to determine hydronephrosis or ureteral dilation associated with an abnormal radiographic density believed to be a urinary tract calculus. A stone easily identified with renal ultrasonography but not visible on the plain radiograph may be a uric acid or cystine stone, which is potentially dissolvable with urinary alkalinization therapy.

For some stones, ultrasonography works quite well; however, it has been found to be less accurate than IVP or CT in diagnosis of ureteral stones, especially those in the distal ureter. Diagnostic criteria include direct visualization of the stone, hydroureter more than 6 mm in diameter, and perirenal urinoma suggesting calyceal rupture. [27]

In addition, ultrasonography is not reliable for small stones (ie, those smaller than 5 mm) and does not help in the evaluation of kidney function.

A urine-filled bladder provides an excellent acoustic window for ultrasound imaging; sonograms occasionally may demonstrate a stone at the ureterovesical junction that is not definitive on helical CT or IVP.

Ultrasonography requires no intravenous (IV) contrast and can easily detect any significant hydronephrosis, although this must be differentiated from ureteropelvic junction (UPJ) obstruction or an extrarenal pelvis. A large extrarenal pelvis or UPJ obstruction can easily be misread for hydronephrosis if ultrasonography alone is used.

Middleton et al reported perhaps the most successful use of ultrasonography for renal colic: a 91% stone detection rate. Most authors report rates of approximately 30%. The unusually high success rate achieved by Middleton et al is partly explained by the fact that a radiologist specializing in ultrasonography performed the studies, which typically required at least 15-20 minutes to complete. The success of diagnostic ultrasonography is very dependent on operator skill and experience, which is probably demonstrated by the unique setting of this study. [28]

Renal ultrasonography works best in the setting of relatively large stones within the renal pelvis or kidney and sometimes at the UPJ. Whether the stones are radiolucent or radio-opaque does not matter because an ultrasound image is based strictly on density, not on calcium content. Ultrasonography is a good way to monitor known stones after medical or surgical therapy if the stones are large enough to be detected by this modality and are in a suitable position.

Ultrasonography can also be used to check the abdomen for a possible abdominal aortic aneurysm (AAA) or cholelithiasis, which can sometimes be mistaken for acute renal colic. It is also useful in differentiating filling defects observed on contrast studies because stones are much more echogenic than tumors, clots, or tissue. It is the initial imaging modality of choice for pregnant patients with acute renal colic because it avoids all potentially hazardous ionizing radiation.

Ultrasonography relies on indirect visualization clues to identify stones. Differentiating an extrarenal pelvis from an obstructed one is sometimes difficult when using ultrasonography alone. Intermittent obstruction or mild hydronephrosis can be easily missed with ultrasonography, and, with the few exceptions mentioned above, it generally does not provide much information about most other disease processes capable of causing acute flank pain.


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