Korean Journal of
Veterinary Service

In veterinary medicine, ovariohysterectomy (OVH) is considered a simple and safe procedure; however, there are several risks and complications (Pollari et al., 1996). Common complications include hemorrhage and accidental ligation or trauma to the ureter (Adin, 2011). Hemorrhage is the most common intraoperative complication in OVH, and to prevent this, proper vessel ligation techniques are required (Bohling, 2020). Accidental ligation or injury to the ureter can occur during ligation of the ovary or uterine stump, potentially leading to hydronephrosis (Howe, 2006). To prevent ureteral injury, the anatomical location of the ureter and its proximity to the surgical site must be recognized (Adin, 2011). Hydronephrosis is caused by partial or complete obstruction of the upper urinary tract, leading to progressive dilation of the renal pelvis and ultimately causing compression and atrophy of the renal parenchyma (Şahal et al., 2005). It is important to confirm whether the obstruction is unilateral or bilateral to determine the cause and prognosis of hydronephrosis, and to identify the path from the ureter to the bladder to find the source of the obstruction (Wajczyk et al., 2020). This study reports a rare case of iatrogenic unilateral hydronephrosis caused by a ligation surgical clip used in the process of controlling hemorrhage. It highlights the importance of delicate surgical techniques and postoperative imaging to prevent ureteral injury and subsequent hydronephrosis during OVH surgery.

A 7-year-old spayed female poodle (weighing 3.1 kg) was presented with abdominal distension. The dog had undergone spaying surgery at a local animal hospital approximately two years ago. The owner reported that the abdominal distension had been present since that time. On physical examination, the dog was active, with an enlarged abdomen, but no abdominal pain was noted. Initial diagnostic tests included a complete blood count (CBC), serum biochemistry panel, electrolyte tests, and coagulation tests (PT, APTT), all of which were within normal limits (Table 1). The bacterial culture of the urine obtained via cystocentesis was negative.

Table 1 . Complete blood count (CBC), electrolyte levels, serum chemistry, and coagulation test results at the initial visit.

Blood analysis	Name	Result	Reference range
CBC	White blood cell count (K/μL) Neutrophils (K/μL) Lymphocytes (K/μL) Monocytes (K/μL) Eosinophils (K/μL) Basophils (K/μL) Red blood cell count (M/μL) Hemoglobin (G/D) MCV (fL) MCHC (g/dL)	11.39 9.00 1.50 0.56 0.30 0.03 8.26 19.5 66.1 35.7	5∼16.7 2.9∼11.64 1∼5 0.16∼1.12 0.06∼1.29 0∼0.1 5.6∼8.8 13.1∼20.5 61∼73.5 32∼37.9
Electrolytes	Platelets (K/μL) Na (mEq/L) K (mEq/L) Cl (mEq/L)	311 150 4.6 112	148∼484 144∼160 3.5∼5.8 109∼122
Serum chemistry	Glucose (mg/dL) Total protein (G/D) Albumin (G/D) Globulin (G/D) AST (U/L) ALT (U/L) GGT (U/L) ALP (U/L) Total bilirubin (mg/dL) BUN (mg/dL) Creatinine (mg/dL) Phosphorus (MG) Amylase (U/L)	96 6.4 3.2 3.2 43 99 1 99 0.7 21 1.1 2.9 651	74∼143 5.2∼8.2 2.3∼4 2.5∼4.5 0∼50 10∼130 0∼11 23∼212 0∼0.9 7∼27 0.5∼1.8 2.5∼6.8 500∼1,500
Coagulation test	PT (sec) APTT (sec)	81 14	60∼93 11∼14

MCV, mean ccorpuscular volume; MCHC, mean corpuscular hemoglobin concentration; ALP, alkaline phosphatase; ALT, alanine aminotransferase; AST, aspartate aminotransferase; BUN, blood urea nitrogen; GGT, gamma-glutamyl transferase; PT, prothrombin time; APTT, activated partial thromboplastin time..

On thoracic and abdominal radiographs, six radiopaque metallic objects, presumed to be ligation surgical clips, were observed (Fig. 1), and the left kidney was significantly enlarged compared to the right, displacing the intestines. The size of the right kidney was within normal limits. Abdominal ultrasound revealed left kidney enlargement, renal cortical atrophy, renal pelvis dilation, and proximal left ureteral dilation, confirming hydronephrosis and hydroureter (Fig. 2). The remaining ultrasound findings were clinically normal.

Figure 1. Abdominal radiographs images of lateral (A) and ventrodorsal (B) recumbency view. A round mass (edges marked by arrows) is observed in the mid-to-left caudal abdomen. Six metallic surgical ligation clips are visible.

Figure 2. Ultrasonographic images of the left kidney and left proximal ureter. (A) Dorsal view of the left kidney showing severe hydronephrosis with marked enlargement, and the renal parenchyma is almost completely lost. (B) Dilation of the left proximal ureter (arrow) is observed.

A computed tomography (CT) urography was performed to further assess anatomical abnormalities and evaluate kidney function. The dog was positioned in sternal recumbency, and an iodine-based contrast agent (2.5 mL/kg, Omnipaque; GE Healthcare, Princeton, NJ) was administered intravenously before imaging. On the CT scan, the left kidney was severely enlarged (5.3×4.7×7.3 cm), and loss of renal parenchyma with severe hydronephrosis was observed (Fig. 3). The proximal left ureter (12 mm) was dilated, and the distal ureter was not visualized, with no contrast enhancement seen. The CT scan also revealed metallic surgical clips, but due to metal artifacts, image quality was compromised. No abnormalities were found in the right kidney, ureter, or bladder. Based on these findings, surgical treatment for hydronephrosis was recommended, including the removal of the surgical clip and exploratory laparotomy to clarify the diagnosis and address the left kidney’s hydronephrosis.

Figure 3. Images of computed tomography urography taken preoperatively. Coronal (A), saggital (B), and transverse (C) section of CT scan demonstrating the enlarged left kidney (asterisk) and surgical ligation clips (arrow).

One week later, surgery was performed. The dog was sedated with butorphanol (0.2 mg/kg, IV) (Butophan Inj., 1 mg/mL, Myung Moon, Korea) and midazolam (0.2 mg/kg, IV) (Midazolam Inj, 1 mg/mL, Bukwang Pharm, Korea), induced with propofol (5 mg/kg, IV) (Anepol Inj., 10 mg/mL, Hana Pharm, Korea), and maintained on isoflurane with oxygen. Cefazolin (22 mg/kg, IV) (cefazoline Inj., 1 g, Chongkundang, Korea) was administered at the time of induction. Upon exploration of the abdomen, palpation of the left kidney revealed no renal parenchyma, and a fluctuant, encapsulated left kidney. While exposing the kidney for removal, surgical clips adhered to surrounding fatty tissue below the kidney was identified. Since almost no renal parenchyma remained on imaging, and severe enlargement of the left kidney was causing displacement of adjacent organs, a left nephrectomy was performed (Fig. 4A). The renal blood vessels and ureter were ligated, and the kidney was excised. A metallic surgical clip firmly adhered to the surrounding tissue was also removed (Fig. 4B). The right kidney and bladder appeared normal on gross inspection. No free fluid was observed in the abdominal cavity. The abdomen was flushed and routinely sutured, and the dog recovered uneventfully from anesthesia.

Figure 4. Operative and postoperative images of the removed hydronephrotic kidney. (A) The cystic kidney is observed. (B) Close-up image of the surgical ligation clip (arrow). (C) The excised kidney and the dilated proximal ureter (arrow). (D) Ligation clip presumed to have obstructed the proximal ureter (arrow).

On gross examination, the excised kidney showed severe atrophy of both the renal cortex and medulla. The kidney was generally enlarged, and on sagittal sectioning, only a thin renal capsule was observed. A surgical clip, typically used for vascular ligation, was found, along with another clip, suspected to have ligated the ureter, was identified (Fig. 4C, 4D). It is presumed that these clips were used to control hemorrhage during the OVH performed two years prior. The kidney tissue was submitted for histopathological examination.

The dog was hospitalized for two days postoperatively and received fluid therapy. For the subsequent seven days, the dog was prescribed tramadol (5 mg/kg, q 12 h, p.o.) (Tridol Retard Tab., 100 mg, Yuhan, Korea) and cephalexin (25 mg/kg, q 12 h, p.o.) (Falexin Cap., Dong Wha Pharm, Korea). On postoperative day 12, the skin sutures were removed, and the dog’s vital signs were normal with no abnormalities detected in its overall physical condition. Serum biochemical analysis revealed a creatinine level of 0.6 mg/dL (reference range: 0.5∼1.8) and a blood urea nitrogen (BUN) level of 16 mg/dL (reference range: 7∼27). Histopathological examination showed glomerular loss in the cortical area and separation of the cortex and medulla due to edema. Hydronephrosis was confirmed, with no signs of neoplasia or inflammation.

On postoperative day 120, no abnormalities were noted in the CBC or serum biochemical tests. One year after the surgery, the dog continued to maintain excellent health. BUN and creatinine levels remained within normal limits, as they had been preoperatively.

Ovariohysterectomy (OVH) is considered a relatively simple procedure frequently performed in small animal clinical practice (Bencharif et al., 2010; Adin, 2011). Considering the high frequency of this procedure, it is unsurprising that a wide spectrum of complications has been reported. These include hemorrhage, wound healing disorders, ovarian remnant syndrome, stump pyometra, ureteral injury, gossypiboma, and urinary incontinence (Adin, 2011; Bohling, 2020). Among these, hemorrhage is one of the most commonly encountered intraoperative complications during OVH, often occurring due to rupture of the ovarian pedicle or improper ligation of the ovarian pedicle vessels (Berzon, 1979). Several retrospective studies suggest that hemorrhage during OVH rarely leads to severe morbidity or mortality (Burrow et al., 2005; Shaver et al., 2019). Nonetheless, when intraoperative hemorrhage occurs, identifying and ligating the bleeding vessels should always be ensured, as this complication can be life-threatening and is one of the potential causes of mortality following OVH in dogs (Pearson, 1973; Bohling, 2020). Internal bleeding from inadequately ligated vessels and the resulting hypovolemic shock can be fatal (Pearson, 1973). Proper management of intraoperative hemorrhage involves identifying and correcting the source of bleeding. Additional incisions and the use of self-retaining retractors to ensure adequate visualization may be necessary to resolve the bleeding quickly and definitively, thus minimizing the risk of unintended complications, such as ureteral injury (Bohling, 2020). In the presented case, the dog underwent an OVH two years ago, during which unexpected hemorrhage appears to have occurred around the left ovarian pedicle. Given that ligation clips were observed exclusively around the left renal region, it is presumed that hemorrhage occurred near the left ovarian pedicle, and multiple surgical ligation clips were used to control it.

Direct ureteral obstruction typically occurs when the ureter is inadvertently included in a surgical ligature (Adin, 2011). The proximal ureter is more often involved due to its close anatomical relationship with the uterine body (Mehl and Kyles, 2003). This situation is similar in humans, where most ureteral injuries occur during gynecological surgeries (Elliott and McAninch, 2006). Such complications can also be prevented through careful identification of the uterine horns, uterine stump, and cervix before ligation (Howe, 2006). Despite this anatomical proximity to the urogenital tract, reports of ureteral injuries associated with OVH in dogs are limited (Adin, 2011). It is likely that this complication occurs more frequently and goes undetected, as unilateral ureteral obstruction in previously healthy animals does not typically result in azotemia (Adin, 2011). Additionally, the true incidence of ureteral injury related to OVH remains unclear, as many studies evaluating spay-related complications do not include routine abdominal imaging (Cavrenne and Mai, 2009; Mathews, 2017). In this case, it is suspected that a surgical clip used during the OVH two years prior caused an iatrogenic obstruction, leading to complete ureteral occlusion. This unilateral upper urinary tract obstruction, although causing one kidney to become non-functional, did not result in azotemia or clinical symptoms, as the contralateral kidney remained functional.

Treatment for ureteral obstruction depends on renal function and whether the obstruction is unilateral or bilateral (Mesquita et al., 2015). Unilateral lesions, if classified as end-stage hydronephrosis and the contralateral kidney is functional, can be treated with nephrectomy (Mesquita et al., 2015; Griffin et al., 2021). If preserving renal function is critical for survival, ureteral surgery may be necessary (Mesquita et al., 2015). In this case, given the absence of clinical symptoms, lack of azotemia on biochemical analysis, and the severely diminished function of the remaining kidney, nephrectomy was indicated. Histopathological findings were consistent with severe kidney atrophy along with hydronephrosis.

The main limitation of the case we reported is the uncertainty regarding the extent to which the nephrectomy contributed to the patient’s overall clinical symptoms. According to the owner, aside from abdominal distention following the OVH, there were no other significant clinical signs. Preoperative physical examination and hematological evaluations revealed no abnormalities. However, there is a risk that the hydronephrotic kidney could become infected or progress to more severe conditions such as pyonephrosis (Szatmari et al., 2001). Therefore, if the contralateral kidney is functional and the hydronephrosis is at an end stage, a preemptive nephrectomy may be indicated to prevent such severe complications.

Hemorrhage and ureteral injury are major complications during ovariohysterectomy. To prevent these, proper surgical field visualization, thorough knowledge of anatomical structures, and delicate tissue handling techniques are required. Additionally, routine abdominal imaging tests are recommended postoperatively. In cases of unilateral hydronephrosis, if the contralateral ureter and kidney are functionally normal, the prognosis after nephrectomy is generally favorable. To the best of the authors’ knowledge, this is the first reported case in which a ligation clip used during a neutering procedure led to unilateral hydronephrosis, which was subsequently surgically resected.

No potential conflict of interest relevant to this article was reported.