ABNORMAL CALCIFICATIONS IN THE URINARY-TRACT

A wide variety of calcifications may develop in the urinary tract. Cal culi, the most common form of urinary tract calcification, are usually radiopaque due to their calcium content, whereas cystine stones tend to be less opaque. In cortical nephrocalcinosis, calcification may be spotty or may appear as a thin rim outlining the cortex. Intracystic c alcification is usually thin and peripheral and is often described as having an ''eggshell'' appearance. In renal masses, pure central calci fication usually indicates malignancy, although malignancy may also be present with pure peripheral calcification. An incomplete ring of cal cification seen over the central portion of the kidney should suggest the presence of an abnormal vascular structure. A sloughed papilla may lead to calcification that is usually triangular or ring-shaped or ha s a broken rim pattern. Ureteral calculi usually have a uniform radiop acity, whereas phleboliths are often less opaque centrally. Like renal calculi, bladder calculi usually contain a calcium component; they ma y be laminated, faceted, spiculated, or seedlike in appearance. Uracha l carcinoma is commonly associated with tumor calcification, which typ ically occurs at the dome of the bladder. Schistosomiasis of the bladd er may produce mural calcification with a typical thin arcuate pattern and may be associated with calcification in other portions of the uri nary tract. Although urinary tract calcifications may be difficult to characterize specifically, they can be classified according to locatio n, appearance, and relation to various pathologic conditions.