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Abdomen » Kidneys/Ureters
Milk of calcium in a renal diverticulum
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Presentation A 27 year old woman with history of nephrolithiasis in the past presents for a renal ultrasound.
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.
Caption: Transverse view of the right kidney
Description: The cystic structure containing the highly echogenic material is noted again.
Caption: Sagittal view with patient semi-prone
Description: This image demonstrates that the echogenic material layers in the most dependent portion.
Caption: Sagittal view with the patient in oblique position
Description: Change in position of the patient again demonstrates a change in the position of the echogenic material.
Caption: Transverse image with the patient supine again
Description: The echogenic material has returned to the original location where it was first seen and again demonstrates a sharp horizontal level.
Caption: Delayed contrast CT scan of the abdomen
Description: This image shows the highly attenuating material forming a horizontal level in dependent position.
Differential Diagnosis Milk of calcium layering in a calyceal diverticulum, milk of calcium layering in a renal cyst, renal calculus
Final Diagnosis Milk of calcium in renal diverticulum
Discussion 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.

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  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]

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 include:
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

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.
Case 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. 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.
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