40 yo M presents to ED complaining of L flank pain w/ hematuria x 1 day. He denies prior history of UTI or nephrolithiasis. CT a/p kidney stone protocol is obtained and shown below. What's the diagnosis? (scroll down for answer) 

Answer: L renal mass, concerning for renal cell carcinoma (no nephrolithiasis) 

• Differential diagnosis for flank pain/renal colic:
• ureterolithiasis, aortic dissection, AAA, pyelonephritis, renal cell carcinoma, renal infarct, ureteral stricture, ureteral tumor, biliary colic, divericulitis, ectopic pregnancy, ovarian cyst, ovarian torsion, shingles
• Obtain imaging for patients suspecting FIRST-time stone (American Urology Association recommendation)
• Renal cell carcinoma:
• more common in men
• increased incidence likely due to increased utilization of abdominal imaging
• typically asymptomatic until advanced stage
• classic triad- hematuria, flank pain, palpable mass
• MRI kidney is superior to CT for diagnosis 

References:

Manthey DE, Nicks BA. Urologic Stone Disease. In: Tintinalli JE, Ma O, Yealy DM, Meckler GD, Stapczynski J, Cline DM, Thomas SH. eds. Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 9e New York, NY: McGraw-Hill.

Motzer RJ, Bander NH, Nanus DM. Renal-cell carcinoma. N Engl J Med. Sep 19;335(12):865-75.