A 27-year-old woman with a history of nephrolithiasis presented for a renal ultrasound prior to lithotripsy. A cystic structure in the upper pole of the right kidney contained highly echogenic material.
A 27-year-old woman with history of nephrolithiasis presented for a renal ultrasound prior to lithotripsy.
Sagittal and transverse supine views (Figure 1A and 1B) of the right kidney demonstrate a cystic structure in the upper pole. This structure contained highly echogenic material that layered dependently and presented a sharp horizontal interface with the anechoic fluid content of the cyst. The echogenic material caused posterior shadowing. The rest of the kidney and the visualized liver appeared normal. Another transverse set of images of the same kidney showed layering and shifting of hyperechoic material in a cystic structure in the supine (Figure 2A), left lateral decubitus (Figure 2B), and right-side (Figure 2C) positions.
Milk of calcium layering in a calyceal diverticulum, milk of calcium layering in a renal cyst, renal calculus.
Milk of calcium layering in a calyceal diverticulum.
Milk of calcium in a calyceal diverticulum or renal cyst can pose a diagnostic dilemma. Milk of calcium is a fine colloidal suspension of precipitated calcium salts (carbonate, phosphate, and oxalate) and may be radiopaque or radiolucent. If radiopaque, it may closely mimic renal calculus. It is important to distinguish milk of calcium from other entities, specifically renal calculus, to avoid unnecessary intervention. Milk of calcium is usually asymptomatic and of little clinical significance. In this case, lithotripsy was canceled.
Although no definitive factors or pathogenetic mechanisms are known, milk of calcium is known to occur in urinary tract locations where there is suboptimal drainage from a cavity such as a calyceal diverticulum. Factors thought to contribute to the development of milk of calcium include stasis, urinary tract infection, and long-term physical immobility as a result, for example, of spinal cord injury or chronic debilitating illness.
Gravity-dependent sonography is a sensitive and specific method of diagnosis. According to a 1992 study by Yeh et al, the main ultrasound features include highly echogenic material layering in the dependent part of a cystic-appearing mass, a sharp horizontal-level, mobile material that changes positions as patient moves, echogenic substance associated with reverberation (not seen in this case), and usually no shadowing unless milk of calcium is present in larger amounts. CT scan and plain radiographs in supine and standing positions (the latter not always feasible) can also show the layering of hyperdense calcium salts, thereby leading to the diagnosis.
Case submitted by Oksana H. Baltarowich, M.D., an associate professor of radiology at Thomas Jefferson University, and Chaitali Shah, M.D., a radiology resident at New York Presbyterian Hospital of Columbia University. This case provided courtesy of Sono-World (www.sono-world.com).
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