Clinical considerations of intestinal entrapment through the gastrosplenic ligament in the horse

The gastrosplenic ligament (GSL) is rarely involved in intestinal accidents and consequently is infrequently mentioned in the equine veterinary literature. The vast majority of reports of the GSL involve small intestinal incarceration through a rent (Yovich et al. 1985; Mariën and Steenhaut 1998; Jenei et al. 2007; Hunt et al. 2013) with few reports describing incarceration of other gastrointestinal structures including the small colon (Rhoads and Parks 1999) and large colon (Trostle and Markel 1993; Torre 2000). Although there is documentation of strangulation of the jejunum alone, jejunum and ileum, or ileum alone through rents in the GSL, Jenei et al. (2007) reported that GSL entrapment accounted for only 1.5% of all horses undergoing exploratory celiotomy and only 4.6% of horses with primary small intestinal lesions.

The anatomy of the GSL has been described in detail in the recent case report by Hunt et al. (2013) in which the authors provided in-depth description and images of the GSL in situ. Briefly, the GSL is a broad, thin band of omentum located between the hilus of the spleen and left greater curvature of the stomach. It is continuous with the greater omentum ventrally and the gastrophrenic and nephrosplenic ligament dorsally. The ligament is considerably thicker at its dorsal attachment and becomes progressively thinner ventrally as it joins the greater omentum. The blood supply to the GSL is from the left and right gastroepiploic arteries. The gastroepiploic artery is a continuation of the splenic artery where it exits the tip of the spleen and enters the greater omentum. The splenic artery is a branch of the coeliac artery, which exits the cranial abdominal aorta. Intestines are normally located axial and caudal to the GSL. The role of the GSL in the horse remains largely unknown but Hunt et al. (2013) suggest that it may act as a suspensory apparatus of the stomach and spleen helping to maintain their normal anatomical position in the abdomen.

Horses with gastrointestinal entrapment through the GSL can present with mild to severe colic signs depending on the duration and severity of incarceration. All reports of small intestinal incarceration through the GSL have been in mature horses (Yovich et al. 1985; Mariën and Steenhaut 1998; Jenei et al. 2007; Hunt et al. 2013). The largest case series of GSL entrapment by Jenei et al. (2007) included 16 horses and reported a median age of 15.5 years (range 8–23 years), although Torre (2000) did report a case of incarceration of the ascending colon in an 8-month-old Thoroughbred colt. A predilection for geldings has been suggested, although an anatomical explanation has not been determined (Tennant 1975; Jenei et al. 2007). On presentation, most horses are moderately tachycardic, haemoconcentrated with an elevated packed cell volume and variable serum total protein depending on the degree of vascular compromise and intestinal oedema (Yovich et al. 1985; Rhoads and Parks 1999; Jenei et al. 2007; Hunt et al. 2013). Intestinal hypomotility is common and although small intestinal incarceration is the most common form of GSL entrapment, net reflux on presentation is not common. Jenei et al. (2007) suggested that this may be due to the distal small intestine becoming entrapped most frequently, recent gastric decompression, dehydration and/or a short duration of entrapment prior to presentation. Small intestinal distension may be palpated on rectal examination but this does not appear to be a consistent finding. Transabdominal ultrasonography is a useful diagnostic tool for confirming small intestinal dilation (Beccati et al. 2011) in equine colic. Small intestinal dilation noted in the left cranioventral abdomen lateral to the spleen may be positively correlated with GSL entrapment as suggested by Hunt et al. (2013); however, this has yet to be confirmed by a prospective study. The vast majority of horses with GSL entrapment have increased free peritoneal fluid that is serosanguineous in nature with elevated nucleated cell counts (3.2–39.0 x10⁹ cells/l) and total protein (26–42 g/l) concentrations consistent with strangulating gastrointestinal lesions (Yovich et al. 1985; Rhoads and Parks 1999; Jenei et al. 2007; Hunt et al. 2013). Although not reported in cases of GSL entrapment, it is likely that peritoneal fluid would also have elevated lactate levels as noted in other strangulating lesions (Latson et al. 2005; Yamout et al. 2011).

All reported cases of small intestinal GSL entrapment have involved variable lengths of devitalised intestine necessitating surgical intervention with resection and anastomosis. Incarceration occurs in a caudal to cranial direction in all reported cases (Yovich et al. 1985; Mariën and Steenhaut 1998; Jenei et al. 2007; Hunt et al. 2013). Most case reports of GSL entrapment suggest that manual traction on the entrapped bowel is sufficient to reduce the incarceration (Yovich et al. 1985); however, some reports have described manual dilation of the rent (Mariën and Steenhaut 1998). The GSL has little blood supply therefore, haemorrhage following manual dilation or partial transection does not appear to be a major concern. In the case report by Hunt et al. (2013), traction and manual dilation were unsuccessful requiring partial transection of the GSL to the ventral free border. The LigaSure vessel sealing system (LigaSure-8)¹ was used to limit bleeding during transection by Hunt et al. (2013). Alternatively, ligatures could be placed in the accessible portion of the ventral GSL during transection.

Recurrence of GSL entrapment has not been reported; however, Vachon and Fischer (1995) have described reincarceration of small intestine through the epiploic foramen. Rents in the ligament are most commonly not repaired following reduction of the incarceration. Repair of GSL is usually not possible during exploratory celiotomy due to poor accessibility. Additionally, the tissue tends to be friable and unable to hold sutures. Partial transection of the GSL to the nearest free border can be performed and may prevent re-entrapment. Transection of the GSL does not appear to cause long-term complications; however, Hunt et al. (2013) propose that loss of anatomical support could result in lateral displacement or torsion across the long axis of the spleen or that small intestine could be displaced lateral to the spleen. Standing laparoscopic evaluation and repair of the dorsal GSL may be possible; however, based on the current literature, repair does not seem to be indicated as no long-term complications have been reported when tears are left open. Moreover, most GSL tears occur in the ventral aspect of the ligament, which is not accessible with standing laparoscopy.

Rents in the GSL may be associated with trauma or increased intra-abdominal pressure due to pregnancy, dystocia, strenuous exercise and/or severe gastrointestinal distention (Trostle and Markel 1993). Congenital defects in the GSL may also occur. The horse described by Hunt et al. (2013) had a traumatic event several days prior to presentation; however, direct association with the GSL entrapment could not be determined. Yovich et al. (1985) reported that histopathological examination of the torn ligament in 1/5 horses showed fibrin and haemorrhage consistent with a recent tear, while 2/5 horses had haemorrhage without gross fibrosis.

Hunt et al. (2013) propose that transabdominal ultrasonography may aid in preoperative diagnosis of GSL entrapment and that this information could be used to vary surgical technique to allow better access to the GSL. Although small intestinal dilation noted in the left cranioventral abdomen lateral to the spleen may be suggestive of GSL entrapment, a confirmed preoperative diagnosis does not appear necessary as these horses all present with signs of a strangulating small intestinal lesion for which surgical intervention is always indicated. Additionally, a standard ventral midline celiotomy provides good access to the entire gastrointestinal tract and a confirmed diagnosis of GSL entrapment would probably not change the abdominal approach.

Overall, horses appear to have a good long-term prognosis following surgical correction of GSL entrapment. Jenei et al. (2007) reported a long-term success rate of 78% following resection and anastomosis of devitalised small intestine. Some of the rents were enlarged to allow reduction but partial transection was not performed in any horse. None of the GSL rents were repaired and no long-term complications associated with this defect were reported.

Author's declaration of interests

No conflicts of interest have been declared.

Manufacturer's address

¹ Tyco Health Care UK Ltd, Hampshire, UK.