Indications and Results of Exploratory Laparotomy in the Horse

Introduction

The first use of laparoscopy in exploration of the equine abdomen was probably associated with visual assessment of the female reproductive tract [1]. In 1986, Fischer published a case series of five horses where laparoscopic examination proved useful as a diagnostic tool [2]. During the next decade, the emphasis was clearly directed toward the management of conditions of the genital systems of the male and female. The laparoscopic anatomy of both standing and recumbent horses has been detailed [3,4].

Patient Preparation

Exploratory laparoscopy can be performed in the standing or recumbent horse. In either case, horses are fasted for 36 to 48 hours to reduce gastrointestinal fill and facilitate the exploration. For standing procedures, the paralumbar fossae are clipped and prepared for aseptic surgery. The entire ventral abdomen should be clipped and prepared in horses undergoing the procedure in dorsal recumbency.

Laparoscopic Anatomy of the Standing Horse

The author prefers to insufflate the abdomen before inserting the laparoscope. A 1 cm stab incision is made in the left paralumbar fossa, midway between the 18th rib and the tuber coxae immediately ventral to the dorsal crus of the internal abdominal oblique muscle. The stab incision is carried through the external fascia of the external abdominal oblique muscle and a 12 Fr chest trocar (Medicut Argyle Trocar Catheter; Sherwood Medical, St. Louis, MO) is inserted into the abdomen. Upon entering the abdomen, there is an audible in-rush of air as the negative pressure within the abdomen is lost. The insufflation tubing is connected and the abdomen is inflated with CO2 to a pressure of 15 - 20 mmHg. The insufflation catheter is removed and the laparoscope cannula with its sharp obturator are inserted into the abdomen. The obturator is replaced with the laparoscope. The caudal abdomen can be adequately viewed with a standard 33 cm long laparoscope. Viewing of the cranial abdomen is enhanced by using a laparoscope that is at least 50 cm long.

Exploration of the left side of the abdomen begins with the laparoscope directed caudally. Structures observed may include the urinary bladder (Fig. 1), the vaginal ring in males, the ovary and left uterine horn in females, the descending colon and mesocolon (Fig. 2) and parts of the large colon and possibly the jejunum. As the laparoscope is directed cranially, the area of the left kidney appears and the nephrosplenic ligament (Fig. 3) and the base of the spleen can be seen. As the laparoscope is advanced cranially over the nephrosplenic ligament, the stomach and the left side of the diaphragm come into view (Fig. 4). Other structures that can be seen include the left lateral lobe of the liver and the gastrophrenic ligament. Upon completion of exploration of the left side, the cannula is left in place while the procedure is repeated from the right side.

Figure 1. Standing laparoscopy, viewing caudally on left side. B: urinary bladder; arrow: left lateral ligament of the bladder.

Figure 2. Standing laparoscopy, viewing from the left side. Arrows: spleen; SC: descending colon; m: mesocolon.

Figure 3. Standing laparoscopy, viewing from the left side. RSL: renosplenic ligament; arrows: spleen.

Figure 4. Standing laparoscopy, viewing cranially on left side. L: left lobe of liver; S: stomach; arrow: gastrophrenic ligament.

The anatomy of the caudal abdomen on the right side is similar to the left side. As the laparoscope is directed cranially, the cecal base and the descending duodenum are consistently observed (Fig. 5). Further forward, the right lobe of the liver is consistently visible (Fig. 6). Other structures that can be seen include: the hepatoduodenal ligament, the hepatorenal ligament, the caudal vena cava, the portal vein, the caudate lobe of the liver and the epiploic foramen.

Figure 5. Standing laparoscopy, viewing from the right side. D: duodenum; C: cecum, m: mesocolon.

Figure 6. Standing laparoscopy, viewing cranially from the right side. D: duodenum; L: right lobe of liver; C: caudate lobe of liver; Arrow: triangular ligament.

Laparoscopic Anatomy of the Recumbent Horse

A 1 cm stab incision is made at the umbilicus. A teat cannula is introduced into the abdomen and intra-abdominal positioning is confirmed using a hang drop technique. The abdomen is insufflated with CO2 to a pressure not exceeding 25 mm Hg. The teat cannula is removed and the laparoscope is inserted through the same incision. Viewing of structures in the cranial and caudal abdomen is facilitated by tilting the horse. Cranially, the liver and the apex of the spleen can be consistently seen. Caudally, the urinary bladder and internal inguinal areas are readily visible. Parts of the large colon, small intestine and cecum can be seen; however, comprehensive assessment of these structures is not possible at this time.

Indications and Results of Exploratory Laparoscopy

Exploratory laparoscopy can be used as a primary diagnostic technique; however, the technique is often used to further define an already detected disease process. Horses with chronic weight loss and horses with chronic colic episodes may be excellent candidates for this minimally invasive technique. Conditions that have been detected laparoscopically include: abscesses [2], ischemic necrosis of the descending colon [5], subcapsular splenic hematoma [6], gastric squamous cell carcinoma [2], and a variety of other conditions [7]. While the technology to safely perform intracorporeal biopsy of hollow organs is not currently available, laparoscopic assisted biopsy of the jejunum and small colon can readily be performed.