A 65-year-old male patient was referred to our institute for the treatment of his left ureteral and renal calculi (Figure 1A–B). After two months, he was admitted to our department for treating his left ureteral and renal calculi with ureteroscopic lithotripsy using a holmium yattrium aluminum garnet (Ho: YAG) laser. After inserting ureteral access sheath, we firstly made stone fragment and retracted them in the ureter using rigid ureteroscope (URS) with Ho: YAG laser lithotripsy. There after, we observed the renal collecting system using flexible URS. In the view of flexible URS findings, renal stones were formed like mushrooms (Figure 2). Because of large stone volumes, we made stone fragments and retracted them in the second session of URS one month after initial treatment.

In general, ureteral and renal stones were usually formed as a round ball, except for the large renal staghorn calculi. Our institute is a large referral stone disease center in Japan, more than 400 shockwave lithotripsy (SWL), 300 URS and 80 percutaneous nephrolithotomy (PCNL) were performed per year. However, it is our first time to see these ridiculously formed renal stones like mushrooms. A total of nine stones were successfully removed and chemical composition showed calcium oxalate monohydrate.

It was the first report of strange formed renal stone. For gallbladder stone, stone formation was sometimes a clue for suspecting the chemical composition. [1] [2] In the previous report of ureteral stones, stone surface formation might be a clue to be easily broken or not for SWL in cystine stone. [3] However, the correlation between renal stone formation and chemical stone composition was not widely accepted. Further reports about stone formation will be needed.

We herein report the first case of unfamiliar formation of renal stone.

1. Drury DR, McMaster PD, Rous P. OBSERVATIONS ON SOME CAUSES OF GALL STONE FORMATION : III. THE RELATION OF THE REACTION OF THE BILE TO EXPERIMENTAL CHOLELITHIASIS. J Exp Med 1924;39(3):403–23.   [CrossRef]   [Pubmed]    
2. Sandstad O, Osnes T, Skar V, Urdal P, Osnes M. Structure and composition of common bile duct stones in relation to duodenal diverticula, gastric resection, cholecystectomy and infection. Digestion 2000;61(3):181–8.   [CrossRef]   [Pubmed]    
3. Kim SC, Hatt EK, Lingeman JE, Nadler RB, McAteer JA, Williams JC Jr. Cystine: helical computerized tomography characterization of rough and smooth calculi in vitro. J Urol 2005;174(4 Pt 1):1468–70.   [CrossRef]   [Pubmed]