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03-08-2009 - Cystoscopic removal of a urolith from a pet guinea pig

Cystoscopic removal of a urolith from a pet guinea pig

R. Pizzi, BVSc, MSc, DZooMed, FRES, MACVSc, MRCVS1

1 Zoological Medicine, 79A Garvock Hill, Dunfermline, Fife KY12 7UT

Correspondence: E-mail for correspondence:

THE guinea pig (Cavia porcelles) is a domesticated monogastric herbivorous hystricomorph rodent originating from South America. Believed to have been domesticated as early as 5000 BC in the Andean region of South America, they were used as a food item, predominately during ceremonial meals (Morales 1995). No longer extant in the wild, several related species occur in the grass plains of the region (Nowak 1999). First described in the West by Konrad Gesner in 1554 (Gmelig-Nijboer 1977), traders brought guinea pigs to Europe in the 16th century, where they became a popular exotic pet among the upper classes and royalty, including Queen Elizabeth I (Morales 1995).

Figure 1
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FIG 1 : Marked haematuria evident on catheterisation of the guinea pig's urinary papilla

Figure 2
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FIG 2 : Lateral radiography showing a radio-opaque urolith in a female guinea pig

Figure 3
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FIG 3 : Urolith following removal. Note the very uneven surface

A pet female guinea pig aged two years and seven months and weighing 1·058 kg was referred for recurrent haematuria over the previous two months. The guinea pig demonstrated pain on caudal abdominal palpation, and a small thickened bladder was discovered. Previous treatment with two 10-day courses of 5 mg/kg oral enrofloxacin (Baytril 2·5 per cent oral solution; Bayer) twice daily resulted in clinical improvement, but haematuria recurred after treatment.

Urine collected by catheterisation revealed marked haematuria (Fig 1), degenerate neutrophils and a small amount of calcium oxalate crystals, and was submitted for microbiological culture. Serum urea and creatinine levels were normal. Anaesthesia was induced with 4 per cent isoflurane (Isoba; Schering-Plough Animal Health) in an induction chamber after premedication with 0·1 mg/kg subcutaneous atropine (Atropine Sulphate; Hameln Pharmaceuticals). Anaesthesia was maintained with 2 per cent isoflurane using a face mask (Longley 2008), with analgesia provided by 0·6 mg/kg subcutaneous meloxicam (Metacam; Boehringer Ingelheim). A radiodense urolith was seen on lateral and dorsoventral abdominal radiographs (Fig 2).

A rigid endoscope 2·7 mm in diameter, 180 mm length and 30° forward oblique, with a 14·5 Fr (4·83 mm) operating sheath (Karl-Storz), was gently passed into the urinary papilla and directed into the bladder. The bladder was flushed with sterile 0·9 per cent saline via the operating sheath. The bladder wall appeared thickened, with a hyperaemic mucosa, ecchymosis and free haemorrhage. The urolith, which had an uneven surface (Fig 3), was grasped on the second attempt with 5 Fr (1·66 mm) forceps via the operating sheath. The operating sheath was removed with the forceps. The entire cystoscopy and removal of the urolith took just under six minutes, according to the video cystoscopy recording. The procedure was quicker and less invasive than surgical removal via cystotomy.

On recovery the guinea pig was given 30 mg/kg oral trimethoprim-sulphonamide (Septrin Paediatric Suspension, GlaxoSmithKline) twice daily for two weeks (Morrisey and Carpenter 2004, Carpenter 2005) and 0·6 mg/kg oral meloxicam (Metacam; Boehringer Ingelheim) twice daily for five days. There was no microbial growth from the urine culture. The guinea pig remained free from any clinical abnormalities six months after the procedure.

Quesenberry and others (2004) reported guinea pigs as hardy animals with few disease problems. As a prey animal they may conceal clinical signs of disease (Riggs 2008), or show non-specific signs (Flecknell 2002). Urolithiasis may not result in clinical signs notable to owners, unless they are associated with cystitis or cause urinary obstruction (Flecknell 2002, O'Rourke 2004).

There is conflicting information in the literature on urolithiasis in guinea pigs. While Riggs (2008) and O'Rourke (2004) have reported urinary tract calculi occurring commonly in pet guinea pigs, Flecknell (2002) instead reported uroliths as being relatively uncommon. O'Rourke (2004) and Flecknell (2002) state that uroliths most commonly consist of calcium oxalate, while Riggs (2008) found uroliths to be predominately calcium carbonate. Both are radioopaque. While the underlying causes are not completely understood, Riggs (2008) believed a genetic predisposition and an association with high calcium diets was likely. Other authors have thought cystitis, which is common in older females, to be an important predisposing factor (Peng and others 1987, Percy and Barthold 2001, Flecknell 2002). Okewole and others (1991) have also described a number of laboratory guinea pigs that developed calcium oxalate urolithiasis during an outbreak of systemic and urinary tract infection with Streptococcus pyogenes. In the author's experience, urolithiasis is common in older guinea pigs of both genders and is commonly associated with urinary tract infections.

Most texts recommend removal of uroliths by cystotomy (Flecknell 2002, O'Rourke 2004, Riggs 2008) and while cytoscopy of pet guinea pigs has been described (Lennox 2005), this is, to the author's knowledge, the first report of cystoscopic removal of a urolith performed in a pet guinea pig. Although the use of potassium citrate to prevent the formation of uroliths has been reported (O'Rourke 2004), no efficacy has been proven, and as guinea pigs cannot remove an acid load, urinary acidifiers are not indicated (Harkness and Wagner 1989).

The separate urinary papilla present in guinea pigs (Breazile and Brown 1976, Quesenberry and others 2004, Lennox 2005) made introduction of the cystoscope into the bladder simpler in this case than in dogs and cats (McCarthy 2005, Hotston Moore and England 2008).

This procedure is a rapid and less invasive alternative to surgical cystotomy in some female guinea pigs with urolithiasis.


The author thanks Elizabeth Grant and Kirsty Moir for their assistance with this case, and Adam Tjolle and Ken Davison for support of the endoscopy service.


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