Staghorn blood clot.

A 61-year-old man with autosomal dominant polycystic kidney disease suffered from alternating anuria and polyuria resulting from cyst bleeding with clot formation in renal pelvis, a finding which could not be detected by ultrasonography. Subsequent magnetic resonance imaging revealed the right renal pelvis and major calyces were filled with staghorn-shaped blood clots in both coronal sections of T1-weighted image (Picture A) and axial section of T2weighted image (Picture B). The left collecting system was also obstructed (Picture C). Alternating anuria and polyuria is an uncommon but classical manifestation of urinary tract obstruction, and it is usually caused by fluctuating accumulation and release of urine behind the obstructing lesion (1). The term “staghorn blood clot” as first described by Ronchi et al (2), refers to a blood clot filling the collecting system and it results in obstructive uropathy.