Nephrosplenic space ablation in horses

Laparoscopic nephrosplenic space (NSS) ablation is an effective and safe treatment for preventing recurrence of nephrosplenic entrapment (NSE). NSE occurs in larger barrel horses of any age such as warmbloods, drafts, and thoroughbreds, with geldings more commonly affected than mares.

With NSE, the large colon becomes gas distended and migrates dorsally between the body wall and the spleen, subsequently becoming entrapped in a trough between the head of the spleen and the nephrosplenic ligament (the NSS). The diagnosis is made on rectal examination when the colon is palpable in the NSS or when the distended large colon is palpated extending into the NSS. Findings on an abdominal ultrasound that support the diagnosis include colonic gas shadowing at the dorsal extent of the spleen, which obscures the kidney, and ventral displacement of the spleen, often beyond midline to the right.¹ Medical management of NSE includes fasting, laxatives, administration of phenylephrine to decrease splenic size, and moderate exercise. Although used in the management of NSE, phenylephrine can result in dose-related cardiovascular adverse effects in addition to age-associated idiosyncratic hemorrhage.¹

Figure 1a: Ultrasound image obtained over the left flank demonstrating normal proximity of the kidney and spleen. Transverse probe orientation with dorsal to the left and ventral to the right.

Figure 1b: Abnormal ultrasound image obtained over the left flank in a horse with a nephrosplenic entrapment. Dorsal to the spleen, shadowing due to a gas-filled viscus (colon) is observed. Transverse probe orientation with dorsal to the left and ventral to the right.

Alternative medical intervention includes rolling the horse with abdominal ballottement under general anesthesia. The reported success of rolling is variable (50%-93%).¹ If medical care is ineffective in resolving the patient’s NSE, surgical treatment via exploratory celiotomy or flank laparotomy are recommended. A small proportion of patients with NSE will have a concurrent gastrointestinal lesion that will be best managed with exploratory celiotomy. Recently reported short-term survival for patients undergoing exploratory celiotomy for NSE is 94%¹; concurrent gastrointestinal lesions and an increase in postoperative packed cell volume are associated with nonsurvival in patients treated for NSE.² A recurrence rate of 3.2% to 21% has been reported for NSE.¹ Therefore, following 1 or 2 documented episodes of NSE or following 1 documented NSE episode and a history of colic signs, preventive surgery is usually recommended.³ Potential surgical options include colopexy, colon resection, and NSS ablation.

NSS ablation is a reliable method of preventing NSE. It is a standing procedure, performed without the need for anesthesia, and has a low rate of complication with a good cosmetic outcome. Fasting prior to the surgery increases intra-abdominal working space and improves ease of the procedure. Horses are sedated, and local anesthetic is administered to the left flank. A laparoscope portal and 2 instrument portals are generally used. One large instrument portal (2-3 cm in diameter) facilitates movement of a large needle or introduction of mesh into the abdomen. Although insufflation is performed for portal placement, the intra-abdominal and ambient pressures equilibrate when the larger cannula is placed. NSS ablation can be performed with suture or with tacked mesh spanning the cranial to caudal extent of the space, effectively making the nephrosplenic ligament and head of the spleen adjacent. Locking suture, particularly barbed polydioxanone, is often preferred to simplify the start and end of the suture line as well as to maintain tension on the closure. A small amount of blood accumulates in the NSS from the passage of the needle through the tissue and will contribute to the formation of a strong adhesion between the spleen and nephrosplenic ligament. Surgical time for NSS ablation is approximately 1 to 2 hours.^4-6 Horses are slowly and incrementally reintroduced to their full ration of roughage postoperatively to minimize their risk of colic. Recovery from laparoscopic closure of the NSS takes approximately 4 weeks, during which time a mature adhesion will form between the spleen and nephrosplenic ligament or surrounding the mesh implant.⁷

Figure 2a: Laparoscopic view of the nephrosplenic space from the left flank. The nephrosplenic ligament is observed as a vertical sheet of connective tissue on the right of the image, adjacent to the head of the spleen (center). The stomach and liver are noted in the distance in the cranial abdomen.

Figure 2b: Laparoscopic view of a nephrosplenic space ablation with suture in progress (cranial extent closed).

In recent literature, the barbed suture technique was faster and less expensive and had fewer complications than the mesh prosthesis.⁶ Uncommonly, suture can dehisce, resulting in failure of the NSS ablation.⁶ Compared with mesh placement, suture closure results in less foreign material exposed within the abdomen and is less likely to result in adhesion formation to viscera or mesentery.^4,6

Although aberrant adhesion formation can result in recurrent colic, NSS ablation by either technique results in a very favorable outcome, with uncommon recurrence of NSE. Findings from several studies have identified that NSS closure significantly decreases the rate of colic in horses treated with NSS ablation, although they might experience colic again because of an unrelated cause.^2,3,8,9 Cosmetic outcome associated with the procedure is good and does not appear to be a substantial source of owner concern.^2,10 Owner satisfaction with NSS ablation relies on the understanding that it will decrease the risk of NSE recurrence only; the patient can still experience colic as a result of other causes.^2,8

In conclusion, NSS ablation is a short procedure that can be performed standing with sedation and local anesthesia. The complication rate associated with the surgery is low, particularly with the use of barbed suture, and the cosmetic outcome is acceptable. Following management of NSE, closure of the NSS significantly decreases the patient’s risk of recurrent NSE.

Rebecca C. McOnie, DVM, DACVS-LA, is an ACVS board–certified large animal veterinary surgeon and fellow candidate in minimally invasive soft tissue surgery at Cornell University in Ithaca, New York. She attends to horses and a variety of farm animal species, working with students and resident trainees in her role as clinical instructor. McOnie enjoys sports and exploring the outdoors.

References

1. Baker WT, Frederick J, Giguere S, Lynch TM, Lehmkuhl HD, Slone DE. Reevaluation of the effect of phenylephrine on resolution of nephrosplenic entrapment by the rolling procedure in 87 horses. Vet Surg. 2011;40(7):825-829. doi:10.1111/j.1532-950x.2011.00879.x
2. Nelson BB, Ruple-Czerniak AA, Hendrickson DA, Hackett ES. Laparoscopic closure of the nephrosplenic space in horses with nephrosplenic colonic entrapment: factors associated with survival and colic recurrence. Vet Surg. 2016;45(S1):O60-O69. doi:10.1111/vsu.12549
3. Arévalo Rodríguez JM, Grulke S, Salciccia A, de La Rebière de Pouyade G. Nephrosplenic space closure significantly decreases recurrent colic in horses: a retrospective analysis. Vet Rec. 2019;185(21):657. doi:10.1136/vr.105458
4. Epstein KL, Parente EJ. Laparoscopic obliteration of the nephrosplenic space using polypropylene mesh in five horses. Vet Surg. 2006;35(5):431-437. doi:10.1111/j.1532-950x.2006.00171.x
5. Gandini M, Nannarone S, Giusto G, et al. Laparoscopic nephrosplenic space ablation with barbed suture in eight horses. J Am Vet Med Assoc. 2017;250(4):431-436. doi:10.2460/javma.250.4.431
6. Gialletti R, Nannarone S, Gandini M, et al. Comparison of mesh and barbed suture for laparoscopic nephrosplenic space ablation in horses. Animals (Basel). 2021;11(4):1096. doi:10.3390/ani11041096
7. Marië n T, Adriaenssen A, Hoeck FV, Segers L. Laparoscopic closure of the renosplenic space in standing horses. Vet Surg. 2001;30(6):559-563. doi:10.1053/jvet.2001.28436
8. Burke MJ, Parente EJ. Prosthetic mesh for obliteration of the nephrosplenic space in horses: 26 clinical cases. Vet Surg. 2016;45(2):201-207. doi:10.1111/vsu.12434
9. Röcken M, Schubert C, Mosel G, Litzke LF. Indications, surgical technique, and long-term experience with laparoscopic closure of the nephrosplenic space in standing horses. Vet Surg. 2005;34(6):637-641. doi:10.1111/j.1532-950x.2005.00098.x
10. Farstvedt E, Hendrickson D. Laparoscopic closure of the nephrosplenic space for prevention of recurrent nephrosplenic entrapment of the ascending colon. Vet Surg. 2005;34(6):642-645.
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