The paramesonephric (Müllerian) ducts are crucial embryological structures that give rise to the oviducts, uterus, uterine tubes, and cranial vagina in mammals (8). Abnormal development of these ducts can result in congenital anomalies, such as the absence or segmental aplasia of the uterus (21). Segmental uterine aplasia is characterized by the absence or underdevelopment of specific portions of the uterine horn, leading to the isolation of cranial segments from the distal segments and the uterine body (17). Despite these malformations, the ovaries are often normal despite the presence of congenital urogenital abnormalities, because they develop from a distinct cell population at the gonadal ridge and respond to a different set of signals (11).

Renal agenesis, defined as the congenital absence of one or both kidneys, frequently coexists with abnormalities of the reproductive tract owing to their shared embryological origin in the intermediate mesoderm. During fetal development, the differentiation of the Wolffian and Müllerian ducts orchestrates the formation of the kidneys and reproductive structures (4). Disruptions in this process can result in concurrent anomalies in both systems. In humans, nearly half of all females with Müllerian duct anomalies also exhibit congenital renal abnormalities, with unilateral renal agenesis being the most common (16). Similarly, segmental uterine aplasia has been documented in felines, particularly in conjunction with ipsilateral renal agenesis (2,3,6).

One well-known human syndrome related to these anomalies is the Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome, which is characterized by hypoplasia or agenesis of the uterus and upper vagina, often accompanied by renal defects (9). Since MRKH also occurs in males, the term genital-renal-ear-skeletal (GRES) syndrome may be more appropriate for both sexes. In males, disruptions in Wolffian duct development due to renal agenesis can result in anomalies such as vas deferens agenesis, seminal vesicle hypoplasia, or cryptorchidism. Moreover, the phenotypic manifestations of MRKH overlap with those of various other syndromes or associations, requiring precise differentiation and a clear understanding. Despite these structural anomalies, the precise mechanisms underlying the relationship between Müllerian duct anomalies and renal agenesis remain unclear.

The clinical implications of renal agenesis extend beyond the structural malformations. The absence of a kidney often leads to compensatory hypertrophy of the contralateral kidney, which increases the long-term risk of renal disease (1). In surgical contexts, such as elective ovariohysterectomy (OHE), preexisting renal dysfunction or intraoperative factors such as anesthesia-induced hypoperfusion, may significantly increase the risk of postoperative acute kidney injury (AKI) (23). Although extensive literature exists on renal anomalies in humans, reports addressing their impact on perioperative outcomes in veterinary species remain limited.

This case report describes the case of an 8-month-old cat presenting with segmental uterine aplasia and ipsilateral renal agenesis that developed postoperative AKI following elective OHE. By highlighting this case, we aimed to highlight the importance of thorough pre-operative screening for congenital anomalies in cats. Awareness of these conditions can help veterinary practitioners mitigate perioperative risks and improve surgical outcomes. Additionally, this report highlights on the broader significance of congenital urogenital anomalies and their potential implications on renal and reproductive health in veterinary patients.

On April 11, 2024, an eight-month-old, 3 kg, intact female mixed breed cat was presented to a local animal hospital for elective ovariohysterectomy (OHE). The cat had a history of dermatophytosis, feline upper respiratory tract infection (FURI), and feline uveitis. No signs of urinary or reproductive issues were observed prior to presentation. Physical examinations revealed no abnormalities. Preanesthetic blood tests were also normal.

For the OHE procedure, the patient was premedicated with midazolam (0.2 mg/kg, intravenously, Midacom^®, Myungmoon Pharm., Seoul, Korea) and tramadol Hydrochloride (2 mg/kg, intravenously, Maritrol^®, Jeil Pharm., Daegu, Korea) prior to induction with alfaxalone (2 mg/kg, intravenously, Alfaxan^®, Jurox Pty Ltd., Rutherford, New South Wales, Australia). General anesthesia was maintained with isoflurane (Ifran^®, Hana Pharm., Seoul, Korea). A midline incision was made caudal to the umbilicus. The right ovarian horn was identified using a spay hook and a normal structure connected to the uterine body. However, the identification of bifurcation in the uterine body is difficult, and the right uterine horn could not be located. The surgeon attempted to locate the right uterine horn with the spay hook but was unsuccessful. The midline incision was then extended cranially to for an exploratory laparotomy. The left kidney was found to be absent. The round ligament and ligamentous structures attached to the left ovary were normally developed (Fig. 1A, B). Despite left-sided uterine aplasia, the left ovary had a normal structure, and the left ovarian vascular pedicle, fimbria, and fallopian tubes were also well-developed (Fig. 1B). Both ovarian vascular pedicles were ligated and both ovaries were removed (Fig. 1C). Histological examinations were not performed, leaving the functional status of the ovaries undetermined.

Figure 1. Surgical findings during ovariohysterectomy (OHE). (A) Intraoperative photograph showing the aplastic left uterine horn (indicated by the black arrow), and the aplastic segment is visible as a thinner, underdeveloped structure compared to a normal uterine horn, reflecting the congenital anomaly of uterine horn aplasia. (B) The normal ovary (indicated by the white arrow) is adjacent to the aplastic left uterine horn. The ovarian vascular pedicle, fimbria, and fallopian tubes appear well-developed despite the absence of a normal left uterine horn, indicating isolated segmental uterine aplasia without affecting ovarian morphology. (C) Post-surgical comparison of the excised right and left uterine horns. The right uterine horn and ovary (indicated by the black arrowhead) are normal in structure and size. In contrast, the aplastic left uterine horn with the normal ovary (indicated by the white arrowhead) shows a significant disparity, illustrating the severity of the congenital anomaly.

Right lateral abdominal radiography performed immediately after surgery (post-operative day [POD] 0) revealed only one kidney. On the ventrodorsal view, the presence of oval-shaped, enlarged (Length = 5.5 cm; Normal range = 3.0-4.3 cm, Kidney-to-L2 ratio = 3.4; Normal range = 2.4-3.0) (10) right kidney was detected in the absence of a left kidney (Fig. 2). On POD 1, the cat had acute lethargy and anorexia, and the blood screening test revealed a decrease in red blood cell (RBC), hemoglobin (HGB), and hematocrit (HCT) and an increase in monocyte (MONO), neutrophil (NEU), blood urea nitrogen (BUN), creatinine (CREA), phosphorus (PHOS), BUN/creatinine ratio, and symmetric dimethylarginine (SDMA) (Table 1). Post-operative AKI was diagnosed based on the enlarged right kidney, inflammatory leukogram, hyperphosphatemia, and severe azotemia, as evidenced by elevated CREA and BUN/CREA ratios and elevated SDMA levels, which are all indicative of impaired kidney function (15). Nonregenerative anemia was suspected based on decreased RBC, HGB, and HCT levels, likely resulting from intraoperative bleeding or post-operative AKI (15). For intravenous fluid therapy, the cat received 500 mL of 0.9% normal saline supplemented with taurine and vitamins at a rate of 3 mL/kg/h. To prevent postoperative infections, the patient was administered intravenous injections of Cefotaxime (40 mg/kg, intravenously, Cefotaxime Sodium^® Inj., Kyungbo Pharm., Asan, Korea) and Marbofloxacin (2 mg/kg, intravenously, Marbocyl^® FD 1%, Vetoquinol, Goyang, Korea).

Figure 2. Abdominal radiographs on postoperative day (POD) 0. In ventrodorsal view (A) and right lateral view (B), the absence of the left kidney is evident, as it is not visualized in the typical anatomical location (at the level of L1-3). The right kidney (indicated by the white arrow) appears enlarged (Length = 5.5 cm, Kidney-to-L2 ratio = 3.4). Despite its enlargement, the right kidney maintained an anatomically normal appearance.

Table 1 . Abnormal blood test results related to non-regenerative anemia and acute kidney injury (AKI).

Parameters	Value					Reference
	Pre-operative		Post-operative
	Day 1		Day 1	Day 4	Day 12
RBC (×106/μL)	10.42		5.98*	6.73	6.78	6.54-12.2
HGB (g/dL)	14.7		7.6*	9.4*	9.1*	9.8-16.2
HCT (%)	41.8		22.7*	26.0*	25.9*	30.3-52.3
MONO (×103/μL)	0.3		0.8*	0.93*	0.33	0.05-0.67
NEU (×103/μL)	3.27		11.86*	14.42*	4.75	1.48-10.29
BUN (mg/dL)	29.6		76.9*	50.1*	10*	17.6-32.8
CREA (mg/dL)	1.17		2.16*	1.47	0.9	0.8-1.6
PHOS (mg/dL)	-		10.2*	7.4	7.3	3.1-7.5
BUN/CREA ratio	25.3		35.61*	34.08*	11	4-27
SDMA (μg/dL)	-		32*	20*	9	0-14

The specific values of blood test parameters that were outside the normal limits in the postoperative monitoring. Decreases in RBC, HGB, and HCT levels from pre-operative values to postoperative day (POD) 1 indicated anemia. These parameters were partially recovered on POD 4 and 12 but remained below normal limits. Abnormal increases in renal parameters (BUN, CREA, P, SDMA) on postoperative day (POD) 1 indicated AKI. The renal parameters gradually improved on POD 4 and 12. An inflammatory leukogram was suspected due to eleveted levels of MONO and NEU. On POD 12, both parameters returned to within the reference range..

RBC, red blood cell; HGB, hamoglobin; HCT, hamatocrit; BUN, blood urea nitrogen; CREA, creatinine; PHOS, phosphorus; SDMA, symmetric dimethylarginine..

*Abnormal values..

On POD 4, although abdominal radiography revealed that the enlargement of the right kidney was more severe (Length = 6.5 cm, Kidney-to-L2 ratio = 3.9), the renal function parameters in the blood tests improved and approached normal ranges (Fig. 3C, Table 1). Additionally, overhydration was suspected because of pleural effusion and pulmonary infiltration observed on thoracic radiography (Fig. 3A), and the cat subsequently received intravenous fluid therapy at a slower rate. On POD 12, cardiac radiography revealed no pleural effusion or pulmonary infiltration (Fig. 3B). Abdominal radiography showed a reduction in the size of the right kidney (Length = 5.6 cm, Kidney-to-L2 ratio = 3.5). Blood tests revealed that most renal function parameters (CREA, PHOS, BUN/CREA ratio, and SDMA) and inflammatory leukogram parameters (MONO and NEU) returned to normal levels, indicating significant recovery of kidney function (Fig. 3D, Table 1). At subsequent checkups after discharge, the cat was reported to be in good condition without any symptoms of renal abnormalities.

Figure 3. Thoracic and abdominal radiographs of the cat on postoperative day (POD) 4 and 12. (A, C) On POD 4, the thoracic radiograph shows pleural effusion and pulmonary infiltration, and the abdominal radiograph reveals an enlarged right kidney (indicated by the white arrow, Length = 6.5 cm, Kidney-to-L2 ratio = 3.9). (B, D) On POD 12, the thoracic radiograph shows resolution of pleural effusion and pulmonary infiltration, and the abdominal radiograph reveals a reduction in the right kidney size (Length = 5.6 cm, Kidney-to-L2 ratio = 3.5). It indicates successful management of fluid overload and significant recovery of renal function.

The present case of an eight-month-old female mixed-breed cat undergoing elective OHE highlights that renal agenesis with segmental uterine aplasia may increase the risk of postoperative AKI in cats. In humans, these congenital abnormalities can be diagnosed before or after puberty via gynecological examination. In cats, OHE is usually performed at a relatively young age and urogenital abnormalities may not be observed during pre-operative assessment. Renal agenesis is rare in cats or dogs and thus not frequently diagnosed before OHE surgery. Based on this, veterinarians may unknowingly approach the OHE procedure of patients with congenital renal abnormalities as general procedure, causing unexpected kidney damage. In most cats, these abnormalities, which may cause complications such as infections or organ dysfunction, are incidentally detected during exploratory laparotomy or OHE (22). In the present case, pre-operative blood tests showed no abnormalities. However, the absence of the left kidney and a malformed uterine horn was discovered during OHE, which complicated the surgical procedure and led to postoperative AKI.

The development of AKI in this cat could be attributed to several factors, including the presence of unilateral renal agenesis and the impact of anaesthesia and surgery (5,18). Intra-abdominal pressure increases the risk of postoperative AKI by causing venous congestion, increasing intrarenal pressure, and reducing kidney perfusion, thereby impairing glomerular and tubular functions. Anesthesia may reduce blood pressure and renal perfusion, leading to an increased risk of postoperative AKI (5). Patients with unilateral renal agenesis can live normal and healthy lives, as renal function is generally normal (18). However, this case showed that kidney abnormalities, such as unilateral renal agenesis, can lead to AKI more easily compared to cases where both kidneys are present.

Although segmental uterine aplasia and renal agenesis have been reported as congenital urogenital diseases in cats, their associated risk of postoperative AKI has not been extensively reported (2,3,6). In this case, the diagnosis of AKI was based on a combination of elevated renal function indicators in the serum and radiographic evidence of renal enlargement. BUN, creatinine, phosphorus, and SDMA are excreted through the kidneys into the urine, and their levels can increase with a reduction in glomerular filtration rate (GFR), making them important indicators of renal function (13). Although renal enlargement can result from various factors such as infection, neoplasms, and metabolic disorders, it can also occur in cases of renal dysfunction such as AKI (14). In this case, renal enlargement observed during the postoperative monitoring of the patient was likely due to fluid retention caused by decreased renal function and postoperative inflammatory reactions.

To prevent and manage the risk of postoperative AKI in patients with renal agenesis, it is essential to establish effective strategies both intra- and postoperatively. During surgery, it is crucial to avoid excessive fluid overload, implement individualized, goal-directed fluid therapy, and using vasopressors early, if needed, to maintain hemodynamic stability and minimize renal complications (7,19,20). Postoperatively, intensive blood pressure monitoring and timely interventions with intravenous fluids and vasopressive medications are necessary to prevent AKI (12,19). In this case, immediate postoperative intervention included intravenous fluid therapy with taurine and vitamins to enhance renal perfusion, correct dehydration, and provide antioxidant support. Despite the initial severity of renal impairment, the gradual improvement in renal function parameters and the reduction in kidney size on POD 12 indicated significant recovery, highlighting the effectiveness of the therapeutic interventions.

This case report highlights the critical need for pre-operative awareness and screening for congenital renal anomalies in felines. Through pre-operative imaging and thorough physical examinations, identifying conditions such as segmental uterine aplasia and renal agenesis pre-operatively can significantly influence surgical and postoperative management strategies, ultimately improving the health and recovery of affected animals. This case demonstrates the complex interplay between congenital anomalies and surgical outcomes, emphasizing the importance of comprehensive veterinary care. In congenital renal abnormalities, the potential for postoperative complications, such as AKI, necessitates vigilant postoperative monitoring and prompt therapeutic interventions to ensure favorable outcomes.

This study was supported by Korea Institute of Planning and Evaluation for Technology in Food, Agriculture, and Forestry (IPET) through the Agriculture and Food Convergence Technologies Program for Research Manpower Development (RS-2024-00398561), and the Gyeongsang National University Fund for Professors on Sabbatical Leave, 2022.

The authors have no conflicting interests.