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→Introduction
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|backcolour =C1F0F6
Also known as: '''''Urethral Calculi — Urinary Calculi'''''
|linkpage =Urinary System - Pathology
|linktext =Urinary System
==Introduction==
[[File:Struvite crystals dog with scale 1.JPG|200px|right|thumb|Struvite crystals (sourced from Wikipedia.org)]]
|pagetype =Pathology
[[File:Calcium oxalate crystals in urine.jpg|200px|right|thumb|Calcium oxalate (sourced from Wikipedia.org)]]
Urolithiasis is the main cause of obstruction in the lower urinary tract. Although it occurs in both males and females, urolithiasis is '''more common in mammalian males''' due to their long, narrow urethra.
Common sites of obstruction in the different species include:
:''cats'' - the terminal urethra
:''dogs'' - base of the os penis
:''bulls'' - the proximal end of the sigmoid flexure or the ischial arch
:''rams'' - vermiform appendage
:''birds'' - cloaca
The most common location for urolith formation is the '''bladder lumen''' although they may also occur in the renal pelvis, ureters or urethra.
Consequences include '''obstruction, ulceration, cystitis, urethritis, nephritis, [[Hydronephrosis|hydronephrosis]] and rupture of the bladder or urethra'''.
Predisposing factors include bacterial infection, alterations in pH of the urine, heredity, sex, species and decreased water intake.
In '''birds''', the condition arises during breeding or following egg incubation. Some birds sit very tight on their eggs and fail to void their cloacal contents regularly. Urates can precipitate in the cloaca and lead to the formation of a urolith.
'''Definitions:'''
:'''Urolithiasis''' - the presence of calculi, or uroliths, in the urinary passages.
:'''Urolith''' (calculus, stone) - polycrystalline concretion of precipitated urinary solutes, urinary proteins and proteinaceous debris.
===Types of Uroliths===
'''Struvite'''
:most common urolith in small animals commonly associated with '''infection''' by urease producing organisms such as [[:Category:Staphylococcus species|''Staphylococcus'']] or ''[[Proteus]]''
:more common in females due to increased susceptibility to urinary tract infections
:formation enhanced by the presence of alkaline urine
:struvite uroliths may contain calcium and become '''radiodense''' on radiographs
'''Calcium oxalate'''
:form due to supersaturation of urine with calcium
:often have spine-like projections
:markedly '''radiodense''' on radiographs
'''Urate'''
:'''Dalmations''' predisposed, urolith of birds
:urolith associated with hepatic disease, especially [[Portosystemic Shunt|'''portosystemic shunts''']]
:'''radiolucent''' on radiographs
'''Cystine'''
:occurs with cystinuria
:'''radiodense''' on radiographs, but may occasionally be radiolucent
'''Calcium carbonate'''
:occurs in horses
:'''radiodense''' on radiographs
'''Silica'''
:occurs in pastured ruminants, development may be related to diet
:'''radiodense''' on radiographs
==Clinical Signs==
Clinical signs are due to the macroscopic uroliths in the lower urinary tract which interfere with the flow of urine or irritate the mucosal lining. This leads to signs such as: '''dysuria, stranguria and haematuria'''.
'''Nephroliths''' are often asymptomatic unless [[pyelonephritis]] develops or the stone passes into the ureter.
'''Ureteroliths''' may present as pain which is difficult to detect, or signs of vomiting, lethargy, especially if there is distension of the renal capsule and developing [[hydronephrosis]]. Clinical signs may not be apparent unless both ureters are affected, there is contralateral chronic kidney disease, or a renal infection develops.
'''Urethral obstruction''' may occur suddenly or may develop over days or weeks. There will be dysuria and stranguria, and complete obstruction leads to: depression, anorexia, vomiting, dehydration, coma and death.
'''Birds''' may present weakened, straining frequently and passing only small volumes of faeces and uric acid.
==Diagnosis==
'''Abdominal palpation''' is helpful in finding bladder stones. Rectal palpation may help identify urethral calculi.
However, multiple uroliths can be present throughout the urinary tract, and '''radiographic examination''' is always indicated.
Radiodense calculi >3mm in diameter can usually be seen, but '''contrast radiography and ultrasonography''' may be necessary to identify radiolucent calculi.
'''Contrast studies''' include: excretory urogram for nephroliths and ureteroliths, double contrast radiography for bladder stones, retrograde urethrogram for urethroliths.
'''Urinalysis''', including examination of urine, '''urine culture and sensitivity''' and crystal identification on microscopic examination, is also indicated.
Urethral obstruction is diagnosed by palpating a distended, hard and painful bladder.
Once removed, stones can be sent for quantitative assessment.
==Treatment==
'''Nephroliths and ureteroliths''': if only one side is affected, '''benign neglect''' can be used if the other kidney is functional. If hydronephrosis has occurred, '''ureteronephrectomy''' should be performed on the affected side.
'''Surgical removal''' of the stone may be possible, and '''dietary dissolution''' can be considered if the ureter is not obstructed.
'''Bladder stones''' can be '''dissolved medically''', or stones removed by '''voiding urohydropropulsion''' or '''cystotomy'''.
'''Urethral stones''' should be flushed back into the '''bladder''' and removed by cystotomy, or a '''urethrostomy''' can be performed in refractory or recurrent cases.
'''Medical management''' can be attempted if there is no obstruction, and the stone is amenable to dissolution (struvite, cystine or urate). Options include: diet or drug therapy, increasing water intake, changing uring pH.
'''Treatment of a urethral obstruction''' is an emergency and the animal should be stabilised prior to sedation and manipulation, due to the hyperkalaemia which predisposes to cardiac arrhythmias.
'''In birds''', cloacal urolithiasis is treated by breaking up the urolith with a pair of forceps and removing it piecemeal. Antibiotics should be administered for 3-5 days after due to the local trauma which can be caused by the removal.
{{Learning
|flashcards = [[Feline Medicine Q&A 21]]<br>[[Avian Medicine Q&A 18]]
}}
}}
{{Chapter}}
{{Mansonchapter
|chapterlink = http://www.mansonpublishing.co.uk/book-images/9781840761283_sample.pdf
|chaptername = Struvite stones
|book = A Colour Handbook - Urinary Stones in Small Animal Medicine
|author = Albrecht Hesse, Reto Neiger
|isbn = 9781840761283
}}
==References==
Kahn, C. (2005) '''Merck veterinary manual''' ''Merck and co''
Forbes, N. '''Self-assessment colour review: avian medicine''' ''Manson Publishing''
Syme, H. (2009) '''Urogenital system: urolithiasis''' ''RVC student notes''
{{review}}
{{OpenPages}}
[[Category:Urological Diseases - Dog]]
[[Category:Urological Diseases - Cat]]
[[Category:Urological Diseases - Horse]]
[[Category:Urological Diseases - Cattle]]
[[Category:Urological Diseases - Sheep]]
[[Category:Expert Review]]
[[Category:Lower Urinary Tract - Pathology]]
[[Category:Urological Diseases - Birds]]