A three-year-old guinea pig was referred to the RVC Exotics and Small Mammals Service with an eight-week history of vocalising when urinating, progressing to haematuria and dysuria.

A few weeks before referral, an ultrasound of her bladder was performed, revealing a focal area of bladder wall thickening and the presence of sediment within the bladder lumen. Clinical signs resolved after a 10-day course of meloxicam and enrofloxacin but there was a subsequent recurrence of haematuria and treatment was repeated.  

First referral to the RVC   

On presentation the patient appeared tense on caudal abdomen palpation and vocalised when the bladder was palpated. A 5mm subcutaneous soft swelling was palpated at the ventral midline of the caudal abdomen, in the region of the umbilicus.

A blood sample was taken from the cranial vena cava for complete blood count and biochemistry. There were no significant findings. Abdominal radiographs showed no evidence of urolithiasis, and ultrasound examination of the urinary tract was within normal limits. Cystocentesis was not possible as the bladder was empty, but a free catch sample obtained later revealed a specific gravity of 1.010 and a moderate presence of blood on dipstick. Microscopy showed no evidence of active infection. She was discharged with ongoing meloxicam.

Clinical signs were controlled by the referring vet over the next three months, with various courses of treatment, including meloxicam and enrofloxacin, trimethoprim sulfamethoxazole, intermittent pentosan polysulfate sodium, gabapentin and an N-acetyl-D-glucosamine and hyaluronic acid supplement.

Return to the RVC  

The patient had an acute neurological episode four months after the first referral, with lethargy, an abnormal head position and possible seizure noted by the owner. She recovered within 24 hours. Treatment was started with fenbendazole for 28 days, due to the possibility of Encephalitozoon cuniculi infection. CT of the skull and the whole body was performed for further investigation.

The urinary bladder was uniformly soft tissue attenuating, and the wall could not be delineated from the lumen. Two irregular calculi were identified in the lumen, measuring approximately 1 × 1 and 5.7 × 3.8 mm. These were located about 0.4 cm from the outer surface of the dependent wall, suggesting marked thickening of the bladder wall.

A separate, irregular mineral-dense, poorly defined structure was identified adjacent to the apex of the urinary bladder. This structure was surrounded by a soft tissue dense linear band connecting the apex of the urinary bladder to the ventral abdominal wall.

These findings were most consistent with cystitis, cystolithiasis and persistent urachal remnant and/or vesicourachal diverticulum. No cause for the neurological episode was identified.

The patient was taken to surgery a few days later. Following premedication with methadone and midazolam, anaesthesia was induced with isoflurane in oxygen. Lateral and dorsoventral abdominal radiographs revealed a small area of radiopaque material within the ventral bladder, but no defined uroliths.

Lidocaine and bupivacaine were used to perform an incisional block, and subcutaneous Hartmann’s with hyaluronidase was administered as intravenous access was unsuccessful. A ventral midline coeliotomy was performed. Multiple adhesions were found between the bladder and abdominal wall.

A thickened tubular structure was found extending from the bladder towards the umbilicus, consistent with a persistent urachus. This was dissected from other tissues, excised with a small portion of bladder wall and submitted for histological evaluation.

A 1 × 1 cm partially mineralised haematoma was found within the bladder lumen, consistent in size and position with the structure seen on the radiographs. The histology samples were consistent with a persistent urachal remnant.

The patient made a good recovery from the procedure and was discharged three days later with oral meloxicam and gabapentin, and a 10-day course of trimethoprim sulfamethoxazole. She was weaned off pain medications in the weeks following surgery. No relapse of clinical signs was noted at nine months after surgery.