Long-term assessment of nephrosplenic space closure in horses

Abstract

Long-term assessment of nephrosplenic space (NSS) closure and comparisons with ultrasonography and rectal palpation are lacking. The objective was to evaluate NSS closure in 12 research horses 5 y following laparoscopic ablation, using a novel adhesion scoring system, and to assess whether rectal examination and ultrasonographic findings could predict adhesion adequacy. The NSS was examined via rectal palpation and ultrasonography prior to surgery, and at 30 d and 5 y after surgery. Ultrasonographic measurements of the distances between the renal fascia and spleen were recorded. The NSS adhesions were scored laparoscopically at 5 y and compared with ultrasound and rectal findings. Logistic regression was used for statistical analysis (P < 0.05). Three of 11 horses had adhesions considered inadequate for preventing colon entrapment. The remaining horses had strong adhesions in greater than 50% of the NSS. Ultrasonographic measurements of the caudal NSS decreased significantly over time (P < 0.05) but these changes were not predictive of adhesion adequacy. Surgery time, number of suture bites, or bleeding did not predict an adequate adhesion. Overall, laparoscopic NSS closure resulted in adequate adhesions in 8 out of 11 horses, persisting for at least 5 y. Rectal palpation was a reliable method for assessing NSS closure, whereas ultrasonography showed limited utility due to bowel interference and lack of predictive value. These findings support the long-term effectiveness of NSS closure and may help increase client confidence and adherence to this preventative surgical intervention.

Introduction

Nephrosplenic entrapment (NSE) accounts for 3 to 6% of equine colic cases referred to veterinary hospitals (1). Although short-term survival following medical or surgical management is high (91.5%) (2), recurrence remains a significant concern, with reported rates ranging from 7.5 to 23% (1,3).

To prevent recurrence of NSE, laparoscopic closure of the nephrosplenic space (NSS) has become the preferred treatment. Studies have demonstrated a decreased incidence of NSE colic for up to 7 y following NSS ablation (1,4). Since its initial description, the laparoscopic technique for NSS closure has undergone several modifications, including changes to portal placement closure methods and to sedation protocols (5–8).

Although previous studies evaluating NSS closure techniques have documented the presence of adhesions via repeat laparoscopy or post-mortem examination, none has quantified adhesion characteristics using a standardized scoring system, such as those used in human surgery (9). Furthermore, the long-term presence of adhesions remains unclear; prospective studies have not reported adhesion status beyond 12 mo after surgery (7).

It is also unknown whether intra-operative factors, such as bleeding, influence the adequacy and duration of the adhesions formed. A case report describing NSE recurrence 6.5 y after NSS closure attributed the recurrence to incomplete adhesion formation, highlighting the importance of long-term evaluation when assessing new surgical techniques and discussing prognosis with owners.

Although laparoscopy remains the gold standard for assessing NSS closure in research settings, its use in clinical follow-up is limited by cost and owner consent. Rectal palpation is commonly recommended prior to resuming exercise after surgery (1), but in the large breeds predisposed to NSE, the NSS is often inaccessible by palpation. Although ultrasonography has been proposed as a non-invasive and inexpensive alternative (7), its diagnostic accuracy compared to laparoscopy has not been validated.

To address these gaps in the long-term assessment of the NSS, 4 objectives were established:

1. to develop a comprehensive adhesion-scoring system to standardize laparoscopic evaluation of NSS closure;

2. to assess adhesion status 5 y after laparoscopic NSS closure;

3. to determine whether intra-operative variables influence adhesion formation; and

4. to evaluate whether adhesion status is consistent with ultrasonographic assessment and rectal examination findings.

Based on clinical data showing a low recurrence rate of NSE following NSS closure, it was hypothesized that i) mature, firm adhesions would cover the NSS 5 y postoperatively; ii) variations in intra-operative occurrences would not affect adhesion formation; and iii) ultrasonography could be used to quantitatively assess NSS closure.

Materials and methods

Horses

Twelve mature, healthy mares from a research herd, including 10 Standardbreds and 2 draft horse crossbreeds, were used. The age of the horses at the time of follow-up laparoscopy ranged from 8 to 23 y. The study was approved by the Institutional Animal Care Committee.

Surgical procedures

NSS closure

The 12 research horses used in this study and the laparoscopic surgery to close the NSS have been described previously (8). In brief, the procedure was carried out with the horses standing under sedation. A 240-cm, size-1 polyglyconate suture with a 48-mm 1/2-circle taper needle was used to suture the perirenal fascia to the dorsomedial capsule of the spleen using a simple continuous suture pattern in a cranial-to-caudal direction, with the caudal knot approximately 3 cm from the caudal-most aspect of the ligament.

Data collected from a review of laparoscopy video included closure time (measured from the first cranial bite to completion of the caudal knot), the number of suture bites, and bleeding severity. Bleeding was classified as none, minimal (present but not impairing visualization), or moderate (requiring temporary interruption of the procedure to address bleeding). The intra-operative variables were later analyzed to determine whether they predicted the adequacy of adhesion formation.

Laparoscopy for adhesion scoring

A standing left flank exploratory laparoscopy under sedation was conducted to evaluate adhesion formation 5 y after NSS closure. Horses were fed a pelleted feed only for 48 h, followed by a 24-hour fast period before surgery. A single dose of flunixin meglumine (distributed by Zoetis Canada, Kirkland, Quebec, manufactured by Norbrook Laboratories Newry, Northern Ireland), 1.1 mg/kg body weight (BW) IV, was administered 30 min before surgery. The left flank was prepared using aseptic technique and local anesthetic was injected at 2 portal sites: 1 in the paralumbar fossa, midway between the caudal aspect of the 18th rib and the cranial aspect of the mid-tuber coxae, and the other in the 17th intercostal space at the level of the ventral aspect of the tuber coxae.

A 12-mm-diameter cannula with a conical-blunt obturator (VersaStep Plus dilator and cannula; Coviden/Medtronic, Neustadt, Germany) was inserted to allow introduction of a long, 10-mm-diameter, 30-degree laparoscope, as previously described (8) for portal 1. Portal 2 was used for insertion of a cherry dissector (Ethicon, Raritan, New Jersey, USA) to retract (Figure 1 A) and bluntly dissect adhesions and laparoscopic scissors for sharp dissection (Figure 1 B).

Figure 1.

Caudal-to-cranial laparoscopic view of the nephrosplenic space (NSS). A — View of the cranial NSS in Horse 8, which had inadequate closure, showing the nephrosplenic ligament under tension due to retraction of spleen by cherry dissector and spleen scars from previously placed sutures, as shown by arrow, with no adhesions present. B — Assessment of strength and vascularization of adhesion with sharp dissection by laparoscopic scissors. Arrowhead shows adhesion. C — View of the NSS in Horse 1, which showed strong adhesions in 76 to 100% of the cranial third only and was therefore considered an inadequate closure. Adhesions shown by arrowhead. D — Adequate closure with strong adhesions along all thirds of the NSS in Horse 4, as shown by arrowheads. E — Caudal-to-cranial view of adequate closure of the NSS in Horse 3. (Ei) Adhesion located in the cranial third of NSS between asterisks (*), scored as strong adhesion with 75 to 100% closure. (Eii) Cherry dissector positioned in the middle third of NSS to assess adhesion strength score. The caudal third of the NSS, as shown between the asterisks, scored as no adhesions, with 0 to 25% closure.

Note: This figure does not show the entirety of the middle and caudal third.

S — Spleen; R — Renal fascia; ST — Stomach; D — Diaphragmatic musculature; CD — Cherry dissector instrument; LS — Laparoscopic scissors; N — Nephrosplenic ligament.

Adhesion score

An adhesion-scoring system was adapted from a human peritoneal adhesion index (9). One Board-certified surgeon and one surgical resident scored the adhesions intra-operatively by consensus agreement. The NSS was divided into cranial, middle, and caudal thirds, and each segment was assessed for both adhesion extent and strength (Table I). If adhesions were present, a small (< 5 mm) dissection was made in a representative portion of each third, using the instruments previously described. A 2-step process was used to determine whether adhesion formation was adequate. First, the total adhesion extent score across the cranial, middle, and caudal thirds of the NSS had to exceed 6. This was to ensure that adhesions were present in more than half of the space. However, because a range was used in the scoring system and a score > 6 could still reflect limited coverage (e.g., scores of 2, 2, and 3), a visual assessment was also carried out intra-operatively to confirm that adhesions covered more than 50% of the NSS.

Table I.

Adhesion-scoring system and classification criteria for long-term evaluation of nephrosplenic space (NSS) closure in horses.

Adhesion extent score	Coverage description	Adhesion strength score	Strength description
1	0 to 25%	0	No adhesions
2	26 to 50%	1	Filmy; removable by blunt dissection
3	51 to 75%	2	Strong; requires sharp dissection
4	76 to 100%	3	Very strong and vascularized; requires sharp dissection

NSS — Nephrosplenic space.

This scoring system was used to assess adhesion extent and strength across the cranial, middle, and caudal thirds of the NSS.

If these criteria were met, the total strength score was then evaluated. A strength score of 4 or more was required, indicating strong or very strong adhesions in at least 2 regions. This approach ensured that in order to be classified as “adequate,” the adhesion had to both cover more than 50% of the space and have a strength score of 4 or more. Any adhesion not meeting both of these standards was classified as “inadequate.”

Post-mortem examination for adhesion assessment

Any horse euthanized for health reasons unrelated to the study prior to the laparoscopy for adhesion scoring, underwent post-mortem examination and the adhesions were scored using the same system previously described.

Rectal palpation

Rectal palpation was carried out by an experienced Board-certified surgeon, blinded to the ultrasonographic examination done on the same day, at both 30 d and 5 y after surgery, to determine if palpable adhesions were obliterating the palpable aspect of the NSS. Laparoscopy was carried out the same day following rectal palpation at 5-year follow-up.

Ultrasonography

Transabdominal ultrasonography was conducted to measure the distance between the dorsal aspect of the spleen and the left kidney. Although NSS measurements were taken at the cranial and caudal poles of the left kidney, they do not necessarily correspond to the cranial and caudal thirds of the NSS. Therefore, measurements are reported based on kidney landmarks rather than presumed NSS regions.

Examinations were conducted immediately before surgery to closure of the NSS, at 30 d, and immediately before surgery to laparoscopic assessment of adhesions at 5 y. Imaging was carried out by 1 of 4 ACVR Board-certified radiologists using either a GE Logic 500 or Logic E ultrasound system with 8C or 4C convex probe (frequency of 2 to 6 Mhz), or a Philips Lumify C5-2 probe connected to an Android tablet (Samsung Galaxy A8, SM-X200), over the time period of the project.

Hair was clipped for the preoperative and 5-year examinations, but not for the 30-day follow-up. Alcohol and/or acoustic coupling gel was used to ensure appropriate probe contact. The left paralumbar fossa was scanned in a cranial-to-caudal direction to visualize the spleen and left kidney. Using a transverse image with the dorsal side oriented to the left, the distance between the dorsal aspect of the spleen and the cranial and caudal poles of the left kidney was measured (Figures 2 and 3). During each examination, the presence of bowel obscuring the NSS was recorded, as this occasionally prevented acquisition of cranial or caudal measurements. Any other abnormalities within the NSS region were also documented.

Figure 2.

Transabdominal ultrasonographic image of the left paralumbar fossa of Horse 5 showing measurement of the distance between the dorsal aspect of the spleen and the cranial pole of the left kidney in transverse section at 5-year follow-up. Left side of the image corresponds to the dorsal aspect.

K — Kidney; S — Spleen; Cr pole — Cranial pole.

Figure 3.

Transabdominal ultrasonographic image of the left paralumbar fossa of Horse 1 showing measurement of the distance between the dorsal aspect of the spleen and the caudal pole of the left kidney in transverse section at 5-year follow-up. Left side of the image corresponds to the dorsal aspect.

K — Kidney; S — Spleen; Cd pole — Caudal pole.

Post-mortem examination following study completion

Horses that were euthanized after the completion of the study due to health issues unrelated to the study, underwent post-mortem examination.

Statistical analysis

Descriptive statistics

Descriptive statistics were used to summarize laparoscopic time (mean, standard deviation, minimum, and maximum), number of suture bites (median, minimum, and maximum), and changes in cranial and caudal ultrasonographic measurements from day 0 to 30 d and at the 5-year follow-up.

Prediction of adhesion adequacy from intra-operative variables and rectal palpation

To determine whether rectal palpation findings, bleeding severity, number of suture bites, or laparoscopic closure time predicted successful adhesion (adequate versus inadequate), an exact univariate logistic regression model was constructed for each parameter.

Ultrasonographic measurements over time

To determine if there was a quantitative difference in the size of the space pre- and postoperatively at 30 d and at the 5-year follow-up, individual measures of cranial and caudal spaces were analyzed with a repeated measure of analysis of variance (ANOVA). Residual data were tested for normality using the Shapiro-Wilk, Anderson-Darling, and Cramér-von Mises tests, along with examination of residual plots. Data were log-transformed to meet the assumptions of normality.

Prediction of adhesion adequacy from ultrasonographic changes

To determine the association of ultrasonography with adhesion adequacy (adequate versus inadequate), the difference in ultrasonographic measurements between time 0 and 5 y, when the laparoscopy was carried out, was assessed with logistic regression to see if the magnitude of change was associated with an adequate adhesion. A significant level of P < 0.05 was used for all statistical tests.

Results

Intra-operative variables

Video recordings were available for 10 of the 12 horses that underwent laparoscopic closure of the NSS. The mean surgical closure time was 54 min (SD = 17; range: 41 to 101 min). The number of suture bites was only available from 9 video recordings and ranged from 6 to 9, with a median of 8 bites. Bleeding severity was classified as moderate in 5 horses (requiring temporary interruption of the procedure), minimal in 3 horses (present but did not impair visualization), and absent in 2 horses.

There was no significant predictive effect of any intra-operative variable on adhesion adequacy, including NSS closure time, number of suture bites, and bleeding severity.

Adhesion scoring

One horse was lost to follow-up. One horse (Horse 2) was euthanized prior to laparoscopy and adhesions were scored at post-mortem examination 14 mo after NSS closure. Ten out of the 12 horses were available for the 5-year follow-up laparoscopic evaluation of adhesion status. Representative laparoscopic images illustrating both adequate and inadequate adhesion formation are shown in Figure 1, with horse numbers corresponding to detailed individual horse data presented in Table II.

Table II.

Individual horse data including ultrasonographic measurement difference, rectal palpation findings, and adhesion scores following nephrosplenic space closure.

Horse no.	US measurement difference with day 0 (cm)				Rectal palpation		Adhesion extent 5 y				Adhesion strength 5 y				Final classification 5 y
	30 d		5 y
	Cr	Cd	Cr	Cd	30 d	5 y	Cr	Mid	Cd	Score	Cr	Mid	Cd	Score
1	N/A	N/A	N/A	N/A	Space closed	Space not felt	4	1	1	6	2	0	0	2	Inadequate
2	N/A	N/A	N/A	N/A	Space closed	Deceased	3	3	4	10	2	2	2	6	Adequate
3	–0.2	–0.3	0.1	0.2	Space closed	Space closed	4	2	1	7	2	3	0	5	Adequate
4	N/A	3.5	N/A	2.9	Space closed	Space closed	4	4	3	11	3	3	2	8	Adequate
5	–0.1	0.5	0.1	0.5	Space closed	Space not felt	4	4	4	12	2	2	2	6	Adequate
6	–0.8	0	0	0.9	Space closed	Space not felt	4	4	2	10	2	2	2	6	Adequate
7	0.1	N/A	0	N/A	Space not felt	Space open	1	1	1	3	3	2	2	7	Inadequate
8	0.4	3.4	–0.7	4	Space closed	Space open	1	1	1	3	0	2	2	4	Inadequate
9	0	0.7	–0.1	N/A	Space closed	Space closed	4	4	1	9	3	2	2	7	Adequate
10	0	1.3	0	0.5	Space closed	Space closed	4	4	2	10	2	3	3	8	Adequate
11	0	1.4	–0.9	2	Space closed	Space closed	3	3	2	8	1	2	2	5	Adequate

Cr — Cranial; Cd — Caudal; Mid — Middle; N/A — Not applicable due to a measurement not being obtained due to either horse being deceased or presence of bowel obscuring measurement; NSS — Nephrosplenic space; US — Ultrasonographic; 30 d — 30 d postoperatively; 5 y — 5 y postoperatively. Note: Positive values in ultrasonographic measurement differences represent a reduction in the NSS measured over time. Negative values represent an increase in the space.

Inadequate adhesion formation

Three of the 11 evaluated horses had adhesions obliterating less than 50% of the NSS and were determined to have inadequate closure (Table II). Horses 7 and 8 had minimal adhesion coverage across all thirds (Figure 1 A), whereas Horse 1 had strong adhesions in the cranial third only, with no coverage in the middle or caudal thirds (Figure 1 C). This same horse also had a large caudal NSS ultrasonographic measurement (3.04 cm; Figure 3).

Adequate adhesion formation

The remaining 8 horses were determined as having adequate adhesion formation (Table II). In 7 of these, adhesions were scored as strong or very strong. Five out of 8 horses had adhesions covering 76 to 100% of at least two-thirds of the NSS (e.g., Horse 4 in Figure 1 D). The caudal NSS third was the least consistently covered, with 6 of the 8 horses showing reduced adhesion extent in this region (Figures 1 Ei and 1 Eii).

Rectal palpation

Rectal examination of the NSS was done in all 12 horses at 30 d after surgery. Closure of the space was confirmed in 11 horses; in 1 horse (Horse 7), the space could not be reached for palpation. At the 5-year follow-up, rectal examination was done in 10 horses. In 7 of these, the NSS could be reached for assessment. Among these 7 horses, adhesions were palpated in 5; in the remaining 2 (Horses 7 and 8), the space was open, with no palpable adhesions. There were no false positives or false negatives. Results for each horse are shown in Table II.

When these findings were compared with the laparoscopic adhesion (adequate versus inadequate), rectal palpation at 5 y was determined to be a significant predictor of adhesion adequacy (OR = 10.86; P = 0.047).

Ultrasonography

Ultrasonographic evaluation of the NSS was limited in some horses due to the presence of bowel that obscured the imaging window, resulting in variable sample sizes for each time point and measurement location (Figure 4). The presence of bowel (likely small colon or large intestine) was an incidental finding with no associated colic signs.

Figure 4.

Transabdominal ultrasonographic image of the left paralumbar fossa of Horse 9 showing bowel interference at the site of nephrosplenic space (NSS) measurement at 5-year follow-up. The left kidney (K) is partially obscured and reverberation artifact from intraluminal gas is visible. Left side of the image corresponds to the dorsal aspect.

K — Kidney; S — Spleen.

In 2 horses, the NSS could not be visualized either preoperatively or at 30 d postoperatively. In an additional 2 horses, only one aspect (cranial or caudal) of the space could be visualized preoperatively. At the 5-year follow-up, 2 horses were missing and in 1 horse (Horse 9), the caudal aspect could not be visualized due to bowel interference. Differences in ultrasonographic measurements at 30 d and 5 y compared to Day 0 are shown in Table II.

Repeated measures of ANOVA revealed a significant decrease in caudal NSS measurements over time. Specifically, caudal measurements were significantly reduced from baseline to 30 d (P = 0.017) and from baseline to 5 y (P = 0.003). No significant difference was observed between 30 d and 5 y. In contrast, cranial measurements did not show significant changes over time. See Table III for the mean measurements over time.

Table III.

Mean and 95% confidence interval (CI) of cranial and caudal ultrasonographic measurements of the distance between spleen and left kidney at 0 d and 30 d preoperatively and at 5 y postoperatively.

Time	Cranial	Caudal
0 d	0.45 cm; 95% CI: 0.30 to 0.69	1.80 cm; 95% CI: 1.10 to 3.00
30 d	0.48 cm; 95% CI: 0.32 to 0.72	0.85 cm*; 95% CI: 0.52 to 1.38 (P = 0.017)
5 y	0.59 cm; 95% CI: 0.40 to 0.88	0.63 cm*; 95% CI: 0.38 to 1.06 (P = 0.003)

^*Denotes significant difference with Day 0.

Logistic regression analysis showed that changes in ultrasonographic measurements were not predictive of adhesion adequacy. For both cranial and caudal measurements, the odds ratios for predicting adequate adhesions were not significant at 5 y.

Post-mortem examination for adhesion assessment

Following completion of the study, 3 horses were euthanized for health reasons unrelated to the study and underwent post-mortem examination. The strength and extent of adhesions observed were comparable to laparoscopic findings.

Incidental finding

At the 5-year follow-up, Horse 1 had a 6.9 × 8.2 cm renal cyst on the lateral aspect of the left kidney, which was visualized only by ultrasonography; no changes were observed laparoscopically. This horse showed no clinical signs of renal disease and serum biochemistry results were within normal limits.

Due to absence of the video recording from the original NSS closure, intra-operative data could not be collected for this case, although no complications were reported during the first surgery. The horse was euthanized for health reasons unrelated to the study. Post-mortem examination confirmed the presence of the cyst, which was located caudally and not directly adjacent to the adhesion site.

Discussion

Our findings support the hypothesis that, in most of the cases, mature firm adhesions remained over the NSS for a minimum of 5 y after surgery. To systematically evaluate these adhesions, we developed and applied a standardized adhesion-scoring system. No predictive relationship was determined between the adhesion score and intra-operative NSS closure variables. The hypothesis that ultrasonography would be useful to quantitatively assess closure of the NSS following laparoscopic ablation was rejected, as this imaging modality did not allow reliable assessment of the NSS. However, the overall findings are valuable for clinical practice, as clients are often concerned about whether the surgical repair offers a permanent solution.

In this study, 8 of 11 horses had adhesions deemed adequate, either by laparoscopy and/or necropsy findings, which represents the longest reported follow-up period for assessing the presence of adhesions. We estimated that closure of at least 50 to 75% of the NSS with strong or very strong adhesions was necessary to be considered adequate. However, the literature does not yet clarify whether partial closure would be sufficient to prevent recurrence of entrapment.

Based on descriptions of the colon entering the NSS from the cranial aspect (10), we speculate that adhesions in the cranial third might be more important than more caudal adhesions. This theory is supported by other studies that showed that incomplete caudal closure was still successful in preventing recurrence of entrapment (4). In our study, 1 horse had adhesions only on the cranial third, yet this was judged inadequate due to the limited overall coverage and potential for re-entrapment in a clinical case (see Figure 1 Ei).

The detail of adhesions in the present study could only be reported by developing and using a scoring system. Our study is the first to apply a detailed scoring system to assess the NSS closure. Previous studies have relied on broad visual categories that describe only the extent of the closure, such as “partial” versus “complete.” Such broad categories lack comprehensive details about strength of adhesion. Similarly, other equine studies describing adhesions have not used standardized scoring (11), which highlights a gap in existing methodologies.

In human surgery, pathologic adhesions have recently been scored using an index system (9). This methodology was proven valuable and was adapted to our purpose. Despite using a final designate of “adequate” or “inadequate” in the statistical analysis, the scoring system was useful in defining this designate by allowing the combination of the variables of strength and extent to determine a decision on adhesion adequacy.

Although the current scoring system provides a structured and clinically intuitive classification scheme for evaluating adhesion formation in the NSS, the thresholds used to define adequacy — specifically, a total extent score > 6 and a total strength score of ≥ 4 — are based on reasoned extrapolation from the scoring scale, as well as clinical judgment. Future research incorporating outcome-based data could help validate or refine cutoffs, whether obtained as a continuous or categorical variable.

For example, statistical modeling or receiver operating characteristic (ROC) curve analysis could be used to determine whether alternative thresholds or scoring combinations more accurately predict clinically relevant outcomes, such as prevention of colon entrapment or recurrence of nephrosplenic entrapment (NSE). This would allow for evidence-based refinement of the scoring criteria, while preserving the system’s utility for standardized assessment.

Post-mortem examinations conducted in 3 horses after the study period provided confirmation of laparoscopic findings. The extent and quality of adhesions observed at necropsy were consistent with laparoscopic scores, suggesting that the same scoring system can be applied in both circumstances. Limitations of the scoring system we used include the use of a categorical rather than continuous scale, which may reduce accuracy.

We attempted to use a measurement instrument during the first follow-up laparoscopies, but measurements were unreliable due to inconsistent portal angles and conformational variation among horses. Future studies could benefit from blinded observers or the use of imaging software to improve scoring accuracy. Establishing inter-observer reliability would also strengthen the validity of the system.

We did not determine any association between adhesion adequacy and intra-operative variables. Inadequate suture size or spacing has been proposed as a cause of failure (12). Although the closure technique and suture material used in our study population were consistent, we did not measure the precise height or spacing of suture bites. We speculate that the reduced presence of adhesions in the caudal third may be due to decreased stability in that region, potentially influenced by interference from bowel, lack of splenic support by the gastrosplenic ligament, or technical challenges in placing bites and knots at the caudal aspect of the NSS.

Although these factors have been discussed or implied in prior literature as potential contributors to variable closure outcomes (4,13), none has been definitively proven. Our small sample size limits the ability to draw firm conclusions about intra-operative variables. In addition, the use of research horses may not fully represent the clinical population due to differences in conformation, although recent evidence suggests this may not be a significant limitation (14). More importantly, horses with recently active disease may exhibit greater inflammation or surface trauma, which could influence adhesion formation and outcomes.

The hypothesis that ultrasonography would be useful to quantitatively assess closure of the NSS following laparoscopic ablation was rejected for 2 reasons. First, although other authors (7) have proposed ultrasonography as a non-invasive alternative to rectal palpation, this imaging modality did not reliably allow assessment of the NSS due to frequent bowel interference, which limited visualization and resulted in a complete ultrasonographic dataset being available for only 7 horses in this study. This limitation is consistent with our clinical experience, in which preoperative imaging of the NSS is often unsuccessful due to incidental bowel presence and gas artefact.

The second factor leading to a rejection of the hypothesis is that changes in ultrasonographic measurements over time were not statistically associated with adhesion adequacy. Although, interestingly, a significant decrease in caudal NSS measurements was observed, this was not associated with adhesion scores, which was likely due to a limited dataset. Further studies with a larger number of horses are warranted to investigate this association. The finding that the ultrasonographic measurements of the cranial aspect of the NSS did not concurrently decrease over time with the caudal aspect may also be due to a limited number of horses in the study.

Further studies should also investigate intra- and inter-observer variability of ultrasonographic NSS measurements, as well as technical factors that likely contributed to measurement inconsistency. Although all examinations were supervised by the surgical team in order to standardize technique, the use of different upgraded ultrasound equipment may have affected image quality and measurement accuracy.

Moreover, despite all radiologists being Board-certified, inter-operator variability is a well-recognized source of disagreement in ultrasonographic assessment (15). Although this was not formally quantified in our study, future research should aim to standardize imaging protocols and equipment and incorporate inter- and intra-observer reliability assessments and include a larger sample size to better characterize and control these factors.

The significant predictive value of rectal palpation for adhesion scores reinforces its continued use in assessing adhesion adequacy following NSS closure, provided the NSS is accessible via palpation. However, this diagnostic method may be limited in larger breeds commonly affected by NSE, such as Warmbloods, which differ in size from the Standardbreds and draft horse crosses used in this study.

An incidental but noteworthy finding was the identification of a cystic structure in the left kidney of 1 horse during long-term ultrasonographic follow-up. Although renal cysts have not been previously reported as a complication of NSS closure, this structure was not present before surgery. Given the rarity of renal cysts in horses, its emergence raised concerns about a potential association with the surgery. Necropsy findings confirmed that the cyst was not located near the adhesion site. Nevertheless, because the laparoscopic recording of this particular case was unavailable for retrospective review, the possibility that a deep, penetrating needle bite contributed to cyst formation cannot be entirely excluded.

The study acknowledges several limitations, including the use of research horses, which may not fully represent the broader equine population susceptible to NSE colic. Despite these constraints, our research contributes to a more systematic approach to classifying induced peritoneal adhesions, which enables more consistent comparisons across different studies.

In conclusion, our results indicate that rectal palpation remains a more reliable method than transabdominal ultrasonography for assessing the adequacy of NSS closure.

Importantly, our study demonstrates not only the technical success of the surgical procedure, but also its long-term durability, with mature, firm adhesions persisting for at least 5 y after surgery. This evidence may help reassure clients about the stability of the repair and could encourage more owners to consider surgical intervention for their horses.