Types of Renal Calculi

Calculus	Radiopacity on radiographs	Comment
Mixed calcium oxalate/phostphate	Radiopaque
Calcium oxalate	Radiopaque	Often have spiculated or dotted shape (toy jack or mulberry) Easily broken down by extra-corporeal shockwave lithotripsy (EWSL) Causes include inflammatory bowel disease, vitamin C overdose, and renal failure. Increased incidence in patients with short small bowels (e.g., after Roux-en-Y gastric bypass) and a preserved colon.
Calcium phosphate	Radiopaque	Seen with dehydration, calcium supplements Least responsive to EWSL
Magnesium ammonium phosphate (Struvite)	Radiopaque	Typically due to infection by urea-splitting bacteria such as Proteus, Klebsiella, and Pseudomonas Despite common infectious cause, large percentage have an underlying metabolic disorder. Can get large and branching May have a laminated appearance due to presence of calcium phosphate EWSL not feasible due to large size Preferred extraction is via percutaneous nephrostomy
Cystine	Semi-opaque/faint	Homogeneous, low density Least fragile renal cacluli: Smooth stones least responsive to ESWL. Rough stones more responsive.
Uric Acid	Lucent	Small smooth stones Radiolucent on radiographs but opaque on CT Can also be seen with small-bowel disease or resection
Xanthine	Lucent
Matrix	Lucent	Caused by inspissation of mucoproteins in patients with a chronic Proteus infection Can have soft tissue attenuation
Indinavir	Lucent	Caused by inspissation of indinavir May not be visible even on CT

References

• Bambach CP, Robertson WG, Peacock M, Hill GL. Effect of intestinal surgery on the risk of urinary stone formation. Gut. 1981 Apr;22(4):257-63.
• Chu G, Rosenfield AT, Anderson K, Scout L, Smith RC. Sensitivity and value of digital CT scout radiography for detecting ureteral stones in patients with ureterolithiasis diagnosed on unenhanced CT. AJR Am J Roentgenol. 1999 Aug;173(2):417-23.
• Duffey BG, Pedro RN, Makhlouf A, Kriedberg C, Stessman M, Hinck B, Ikramuddin S, Kellogg T, Slusarek B, Monga M. Roux-en-Y gastric bypass is associated with early increased risk factors for development of calcium oxalate nephrolithiasis. J Am Coll Surg. 2008 Jun;206(3):1145-53.
• Zagoria RJ and Tung GA. The Renal Sinus, Pelvocalyceal System, and Ureter. in Genitourinary Radiology: The Requisites. 1997