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Urolithiasis
4 URINARYSYSTEM
Thrusfietd MV, et at. Acquired urinary incontinence in bitches: its incidence and retationship to neutering practices.J SmattAnim Pract 1998;39:559-566. Voss ED, et at. Use of a temporary indwetLing ureteraL stent catheter in a mare with a traumatic ureterat tear. J Am Vet Med Assoc 1999;214:1523-1526. Weisse C, et at. Traumatic rupture of the ureter: 10 cases. J Am Anim Hosp Assoc 2002;38:188-192. White RAS, Herrtage ME. BLadder retroflexion in the dog. J SmaLLAnita Pract 1986:27:735-746. WiLson DG, MacWiLtiams PS. An evaluation of the cLinicaLpathologic findings in experimentaLLy induced urinary bladder rupture in pre-ruminant calves. Can J Vet Res 1998:62:140-143. Woodcock S, McCreath CE ProLapse of the urinary bladder of the bovine. Vet Rec 1994:134:660.
CIRCULATORY DISTURBANCES Hemorrhages are the most important and most common indicator of circulatory disturbances. In the ureters and urethra, they are associated with obstructive calculi, and ureteral hemorrhage is part of acute ascending infections. Urethral hematomas following pelvic trauma may predispose to urinary bladder rupture. In the bladder, hemorrhages are typically located in the propria mucosa and may occur in any septicemia. Small hemorrhages with the shape of tiny hematomas are common and considered diagnostically significant in classical swine fever, African swine fever, porcine salmoneHosis, and equine purpura hemorrhagica. Larger hemorrhages are present in bracken fern poisoning of cattle. Hemorrhage occurs with acute cystitis and neoplastic diseases, and hemorrhage with hematoma formation is seen following rupture of the bladder.
Bibliography BettinetLi L, Nuss K. Post-traumatic urethral obstruction with bladder rupture in a calf. Tierarztt Prax 1990;18:237-238. LLoyd KC, et at. ULceration in the proximal portion of the urethra as a cause of hematuria in horses: four cases (1978-1985).J Am Vet Med Assoc 1989:194: 1324-1326.
UROLITHIASIS Urolithiasis is the presence of calculi (uroliths or stones) in the urinary passages. Calculi are grossly visible aggregations of precipitated urinary solutes, urinary proteins, and proteinaceous debris; minerals predominate in calculi, whereas matrix usually predominates in urethral plugs. Calculi typically have a central nidus, surrounded by concentric laminae ("stone"), an outer shell, and su~ce crystals. Many calculi are hard spheres or ovoids with a small amount of organic matrix impregnated with inorganic salts. Urethral plugs are masses of sandy sludge with a much higher organic component whose form is largely determined by the shape of the cavity they fill. Even densely mineralized calculi of the same type may have quite a different appearance depending on whether they are located in renal pelvis or urinary bladder. Many calculi contain significant quantities of"contaminants" such as calcium oxalates in "silica" calculi; a few are relatively pure. The diseases caused by uroliths are among the most important urinary tract problems of domesticated animals. Several factors are important in predisposing to calculus formation and several are important in
Ur0tithiasis
precipitating disease. These are not the same for all conditions. Obviously, calculogenic material must occur in urine in quantities sufficient to be precipitated. Sometimes this concentration is achieved because a substance is metabolized in an unusual way, as is uric acid in Dalmatian dogs; or it may be processed abnormally by the kidney, as is cystine in cystine stone-formers; or abnormally high levels of a substance in the diet, such as silicic acid in native pastures, may produce potentially dangerous urinary levels. Regardless of the type of calculus, certain factors are more or less important; these are urinary pH, in terms of its optimum for solute precipitation, and reduced water intake, in relation to the degree of urine concentration. Other predisposing conditions include infection (see section on Struvite calculi, below), obstruction, structural abnormalities, foreign bodies, and drug-induced changes in urine composition, e.g., by sulfonamides.A foreign body, such as a suture, grass awn, catheter, or needle, can act as a nidus for urolith formation. Deficiency of vitamin A is frequently suggested as a factor predisposing to urolithiasis, but the evidence is equivocal; it may contribute in exceptional circumstances by producing metaplastic changes in the urinary epithelium. Urine is often supersaturated with respect to the components of stone-forming salts, and this supersaturation is the essential precursor to initiation of urolith formation (nucleation). Supersaturation may be in the unstable region where spontaneous precipitation occurs (homogeneous nucleation, the precipitation-crystallization theory of urolith initiation), or in the metastable range where precipitation occurs by epitaxy or heterogeneous nucleation (one type of crystal grows on the surface of another type). Although formerly it was thought that urinary proteins such as uromucoid, which make up 5-20% or more of some calculi, were pre-eminent initiators of crystal formation in the metastable range (the matrix-nucleation theory of urolith initiation), it is now believed that in many cases either co-precipitation of proteins and minerals occurs or that proteins are adsorbed on to formed crystals. It is possible that crystals of one salt, for which urine is supersaturated in the unstable range, cause epitactic induction of crystals of another salt, for which supersaturation is metastable. Crystals are much more common in urine than are calculi. Even though equine urine, for example, is normally supersaturated with calcium carbonate and crystalluria is normal, horses experience a low prevalence of calculi. The factors that promote crystal growth and crystal aggregation or, more importantly, prevent them in some animals, are poorly understood. Experimentally, high levels of urinary inorganic pyrophosphate and magnesium are important inhibitors of calcium phosphate and calcium oxalate crystallization, and pyrophosphate also inhibits aggregation of calcium phosphate crystals. Certain urinary macromolecules, probably glycosaminoglycans, are also strong inhibitors of crystal aggregation in experimental systems. Deficiency of inhibitors of crystallization may be important in calcium oxalate and calcium phosphate calculogenesis (crystallization-inhibition theory of urolith initiation). It is not known why calculi stay in the renal pelvis and urinary bladder until they are large enough to cause disease. The important types of urinary calculi are given below according to species (Table 4.5). Although one mineral may predominate in a urolith, many uroliths are of mixed composition. Overlap in the gross appearance of uroliths usually precludes specific gross diagnosis of mineral type. The division indicated in Table 4.5 is arbitrary. Obviously, silica calculi are only important where ruminants are pastured, and clover stones are only important where subterranean
Thrusfietd MV, et at. Acquired urinary incontinence in bitches: its incidence and retationship to neutering practices.J SmattAnim Pract 1998;39:559-566. Voss ED, et at. Use of a temporary indwetLing ureteraL stent catheter in a mare with a traumatic ureterat tear. J Am Vet Med Assoc 1999;214:1523-1526. Weisse C, et at. Traumatic rupture of the ureter: 10 cases. J Am Anim Hosp Assoc 2002;38:188-192. White RAS, Herrtage ME. BLadder retroflexion in the dog. J SmaLLAnita Pract 1986:27:735-746. WiLson DG, MacWiLtiams PS. An evaluation of the cLinicaLpathologic findings in experimentaLLy induced urinary bladder rupture in pre-ruminant calves. Can J Vet Res 1998:62:140-143. Woodcock S, McCreath CE ProLapse of the urinary bladder of the bovine. Vet Rec 1994:134:660.
CIRCULATORY DISTURBANCES Hemorrhages are the most important and most common indicator of circulatory disturbances. In the ureters and urethra, they are associated with obstructive calculi, and ureteral hemorrhage is part of acute ascending infections. Urethral hematomas following pelvic trauma may predispose to urinary bladder rupture. In the bladder, hemorrhages are typically located in the propria mucosa and may occur in any septicemia. Small hemorrhages with the shape of tiny hematomas are common and considered diagnostically significant in classical swine fever, African swine fever, porcine salmoneHosis, and equine purpura hemorrhagica. Larger hemorrhages are present in bracken fern poisoning of cattle. Hemorrhage occurs with acute cystitis and neoplastic diseases, and hemorrhage with hematoma formation is seen following rupture of the bladder.
Bibliography BettinetLi L, Nuss K. Post-traumatic urethral obstruction with bladder rupture in a calf. Tierarztt Prax 1990;18:237-238. LLoyd KC, et at. ULceration in the proximal portion of the urethra as a cause of hematuria in horses: four cases (1978-1985).J Am Vet Med Assoc 1989:194: 1324-1326.
UROLITHIASIS Urolithiasis is the presence of calculi (uroliths or stones) in the urinary passages. Calculi are grossly visible aggregations of precipitated urinary solutes, urinary proteins, and proteinaceous debris; minerals predominate in calculi, whereas matrix usually predominates in urethral plugs. Calculi typically have a central nidus, surrounded by concentric laminae ("stone"), an outer shell, and su~ce crystals. Many calculi are hard spheres or ovoids with a small amount of organic matrix impregnated with inorganic salts. Urethral plugs are masses of sandy sludge with a much higher organic component whose form is largely determined by the shape of the cavity they fill. Even densely mineralized calculi of the same type may have quite a different appearance depending on whether they are located in renal pelvis or urinary bladder. Many calculi contain significant quantities of"contaminants" such as calcium oxalates in "silica" calculi; a few are relatively pure. The diseases caused by uroliths are among the most important urinary tract problems of domesticated animals. Several factors are important in predisposing to calculus formation and several are important in
Ur0tithiasis
precipitating disease. These are not the same for all conditions. Obviously, calculogenic material must occur in urine in quantities sufficient to be precipitated. Sometimes this concentration is achieved because a substance is metabolized in an unusual way, as is uric acid in Dalmatian dogs; or it may be processed abnormally by the kidney, as is cystine in cystine stone-formers; or abnormally high levels of a substance in the diet, such as silicic acid in native pastures, may produce potentially dangerous urinary levels. Regardless of the type of calculus, certain factors are more or less important; these are urinary pH, in terms of its optimum for solute precipitation, and reduced water intake, in relation to the degree of urine concentration. Other predisposing conditions include infection (see section on Struvite calculi, below), obstruction, structural abnormalities, foreign bodies, and drug-induced changes in urine composition, e.g., by sulfonamides.A foreign body, such as a suture, grass awn, catheter, or needle, can act as a nidus for urolith formation. Deficiency of vitamin A is frequently suggested as a factor predisposing to urolithiasis, but the evidence is equivocal; it may contribute in exceptional circumstances by producing metaplastic changes in the urinary epithelium. Urine is often supersaturated with respect to the components of stone-forming salts, and this supersaturation is the essential precursor to initiation of urolith formation (nucleation). Supersaturation may be in the unstable region where spontaneous precipitation occurs (homogeneous nucleation, the precipitation-crystallization theory of urolith initiation), or in the metastable range where precipitation occurs by epitaxy or heterogeneous nucleation (one type of crystal grows on the surface of another type). Although formerly it was thought that urinary proteins such as uromucoid, which make up 5-20% or more of some calculi, were pre-eminent initiators of crystal formation in the metastable range (the matrix-nucleation theory of urolith initiation), it is now believed that in many cases either co-precipitation of proteins and minerals occurs or that proteins are adsorbed on to formed crystals. It is possible that crystals of one salt, for which urine is supersaturated in the unstable range, cause epitactic induction of crystals of another salt, for which supersaturation is metastable. Crystals are much more common in urine than are calculi. Even though equine urine, for example, is normally supersaturated with calcium carbonate and crystalluria is normal, horses experience a low prevalence of calculi. The factors that promote crystal growth and crystal aggregation or, more importantly, prevent them in some animals, are poorly understood. Experimentally, high levels of urinary inorganic pyrophosphate and magnesium are important inhibitors of calcium phosphate and calcium oxalate crystallization, and pyrophosphate also inhibits aggregation of calcium phosphate crystals. Certain urinary macromolecules, probably glycosaminoglycans, are also strong inhibitors of crystal aggregation in experimental systems. Deficiency of inhibitors of crystallization may be important in calcium oxalate and calcium phosphate calculogenesis (crystallization-inhibition theory of urolith initiation). It is not known why calculi stay in the renal pelvis and urinary bladder until they are large enough to cause disease. The important types of urinary calculi are given below according to species (Table 4.5). Although one mineral may predominate in a urolith, many uroliths are of mixed composition. Overlap in the gross appearance of uroliths usually precludes specific gross diagnosis of mineral type. The division indicated in Table 4.5 is arbitrary. Obviously, silica calculi are only important where ruminants are pastured, and clover stones are only important where subterranean