I've Had A History Of Kidney Stones And Last Week

I've had a history of kidney stones and last week the very familiar pain struck again. I hoped I would simply pass it as usual, but 8 days later I went in to see a doctor and was sent for a renal ultrasound. Results came back as a 1cm shadow in the left lower lobe. I am scheduling a CT scan with contrast to be certain its a kidney stone (which would be too large to pass, I'm guessing), but is there any other likely cause? No blood in urine, white blood cell count normal, BUN levels elevated, but the ultrasound is apparently not conclusive. I thought this particularly exquisite pain was pretty singularly associated with kidney stones...