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Retroperitoneum » Kidneys, Ureters
Milk of calcium – Role of Ultrasound
Author(s): Chaitali Shah, FRCR
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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 closely mimics 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.

Pathogenesis

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, for example a pyelocalyceal diverticulum.

Factors thought to contribute to the development of milk of calcium include-
1. Stasis
2. Urinary tract infection
3. Gravity and
4. Long term physical immobility [for example patients with spinal cord injury or chronic debilitating illnesses]


Ultrasound Imaging

Gravity dependent sonography is a sensitive and specific method of diagnosis. According to a study by Yeh, et al the main ultrasound features that are seen are:
1. Highly echogenic material layering in the dependent part of a cystic appearing mass;
2. A sharp horizontal level is visualized;
3. Mobile material that changes positions with changes in position of the patient;
4. The echogenic substance is associated with reverberation echoes;
5. Usually no shadowing, but if large amount of milk of calcium is present then shadowing might be present.


Caption : Sagittal view of the right kidney.

Description : A cystic structure is seen in the upper pole of the right kidney. It contains highly echogenic material that shows posterior shadowing. The rest of the kidney and the visualized liver appear normal.

Please click here to view the source of this image.

Other modalities

CT scan and plain radiographs in supine and standing positions [the latter not always feasible] can also show the layering of calcium salts, thereby leading to the diagnosis.

References

1. Melekos MD, et al. Milk of calcium cysts masquerading as renal calculi. Eur J Radiol. 1998 Aug; 28(1):62-6.
2. Yeh HC, et al. Milk of calcium in renal cysts: new sonographic features. J Ultrasound Med. 1992 May; 11(5):195-203.
3. Patriquin H, et al. Urinary milk of calcium in children and adults: use of gravity-dependent sonography. AJR Am J Roentgenol. 1985 Feb; 144(2):407-13.


4. Langer W, et al. Atypical findings in a patient with a renal milk-of-calcium cyst. Urology. 1996 Jul; 48(1):135-8.
5. Gayer G, et al. Clin Radiol. 1998 May; 53(5):369-71.
6. V Rathaus, et al. Pyelocalyceal diverticulum: the imaging spectrum with emphasis on the ultrasound features. British Journal of Radiology 74 (2001), 595-601.
7. Garcia-Cuerpo E et al. New location of milk-of-calcium. Urology 1985; 25: 425–427.
8. Vaidyanathan S, Parry R, et al. Spinal Cord. 2000 May; 38(5):325-6.