Urinary tract stone disease. Classic studies

Etiopathogenesis of canine struvite urolithiasis

Urine must be oversaturated with magnesium ammonium phosphate for struvite uroliths to form. Oversaturation of urine with magnesium ammonium phosphate may be associated with several factors, including urinary tract infections with urease-producing microbes, alkaline urine, diet, and genetic predisposition. Of the urease-producing microbes, staphylococci are most struvitogenic in dogs. The precise mechanisms resulting in formation of sterile struvite uroliths in dogs have not been determined.

Usefulness of abdominal flat plate radiographs in patients with suspected ureteral calculi

A total of 120 plain abdominal radiographs (PARs) from intravenous pyelograms (IVPs) were presented without patient history in a random manner to a staff radiologist and staff emergency physician (EP). Scout films were used as the PAR to minimize calculus movement. Each reader examined each film for the presence of ureteral calculi. The readers localized all calculi and rated the likelihood of their presence. Fifty-one PARs from IVPs demonstrated ureteral calculus disease; 40 of these films demonstrated 41 radiopaque calculi, while 11 films demonstrated obstruction without radiopaque calculi. These readings were then matched to the known IVP results. Together the readers were correct on 50% of the predictions (radiologist, 51%; EP, 48%). The EP and the radiologist had similarly correct percentages on PARs from positive IVPs (33% and 36%, respectively) and on PARs from negative IVPs (60% and 64%). True-positive (33% and 25%), true-negative (76% and 71%), false-positive (27% and 35%), and false-negative (36% and 55%) rates were constructed for the radiologist and EP, respectively. Our study demonstrates that PARs are unreliable and do not appear to add useful information in the evaluation of suspected ureteral colic.

Bacteriology and composition of infected stones

One hundred forty-two stones from 106 male and 36 female patients were investigated bacteriologically and chemically. Twenty (14%) of these stones were infected; 65 per cent were associated with infected urine. In 45 per cent of these infected stones an identical bacteria species was isolated from urine and stone of the same patient. Most of the infected stones were of the oxalate type (II), followed by uric acid/urate (5) and calcium phosphate (4) types. Only one stone grew a definite urea-splitting organism.