572 EQUINE VETERINARY EDUCATION / AE / november 2008

Clinical Commentary Gastrointestinal tract diverticula: What, when and why? L. L. SOUTHWOOD University of Pennsylvania, School of Veterinary Medicine, Department of Clinical Studies, New Bolton Center, 382 West Street Rd, Kennett Square, Pennsylvania 19348, USA.

Congenital gastrointestinal disease is rare in the horse. importance of the short jejunum is unknown; however, this Congenital gastrointestinal abnormalities include malrotation, author has seen this in at least one documented case. duplication, stenosis or atresia, and diverticulum (Ciftci et al. Meckel’s diverticulum (Table 1) is the most common 1998). The most common type of congenital abnormalities in congenital gastrointestinal tract diverticulum in horses and horses are Meckel’s diverticulum and mesodiverticular bands man (Freeman 2006; McKay 2007). In horses, a Meckel’s (Table 1). Diverticula, however, can be congenital or acquired diverticulum forms a blind extension from the antimesenteric and can occur along almost any part of the gastrointestinal side of the aboral jejunum or ileum usually 40–120 cm from tract between the oesophagus and colon (Simstein 1986). the ileocecal junction (Freeman 2006). The diverticulum is Congenital diverticula, apart from Meckel’s diverticulum, usually 5–10 cm in diameter and 10–15 cm long but can be are rare in both man and horses, and in man are usually longer (Freeman 2006). A band of fibrous tissue asymptomatic (Ciftci et al. 1998). As Robert et al. (2008) point (vitelloumbilical band) will occasionally persist between the out, while congenital malformations involving the mesenteric diverticulum and the umbilicus and can lead to jejunal and attachments, mesocolon and other malformations of the ileal volvulus (Freeman 2006). colon have been described, there are no other cases in the A mesodiverticular band (Table 1) is usually found in the literature of congenital gastrointestinal diverticula in horses. In same region as a Meckel’s diverticulum and in the horse it human patients, recent cases of gastric (Ciftci et al. 1998), extends from one side of the mesentery, most commonly the caecal (Griffiths et al. 2003), small intestine (van Twisk 1984), left, to the antimesenteric side of the small intestine to form a and sigmoid colon (Jeppesen and Willerth 2002) diverticula triangular space. Intestine can become strangulated in the have been reported. Congenital cardiac and urogenital mesenteric rent that forms in the space and a mesodiverticular diverticula are reported considerably more frequently than band can also be associated with a small intestinal volvulus gastrointestinal diverticula in the human literature. It was (Freeman 2006). Mesodiverticular bands are often incidental interesting that the case described by Robert et al. (2008) had findings at surgery or necropsy in horses. multiple congenital diverticula because in human patients, Acquired diverticula are also an uncommon cause of colic congenital diverticula are usually solitary whereas acquired in the horse; however, they are relatively common in human diverticula are often multiple (Assenza et al. 2007). The clinical patients. Colonic diverticula and diverticular disease

TABLE 1: Definitions of clinical conditions associated with diverticula

Term Definition

Diverticulum A circumscribed pouch or sac occurring normally (true diverticulum) or created by herniation of the lining mucous membrane through a defect in the muscular coat of a tubular organ (pseudodiverticulum). Diverticula The pleural of diverticulum. True diverticulum A diverticulum that comprises all layers of the intestinal wall. Pseudodiverticulum A diverticulum that involves herniation of the submucosa and mucosa through a defect in the smooth muscle layer. Pulsion diverticulum A diverticulum formed by pressure from within a hollow organ, often causing herniation of the mucous membrane through the muscular layer (pseudodiverticulum). Traction diverticulum A diverticulum formed by the pulling force of contracting bands of adhesion (true diverticulum). Meckel’s diverticulum A Meckel’s diverticulum occurs in the aboral jejunum or ileum and is a remnant of structures within the fetal digestive tract (omphalomesenteric [vitelline] duct that provided communication between the yolk sac and embryonic gut) that were not fully reabsorbed before birth. Mesodiverticular band A remnant of a vitelline artery appearing as a fold of mesentery stretching from the cranial mesenteric artery to the antimesenteric side of the distal jejunum or ileum. The pouch that it forms with the normal mesentery may entrap a loop of intestine and cause an obstruction that is often strangulating. EQUINE VETERINARY EDUCATION / AE / november 2008 573

(Tappenden and Shrestha 2007) are probably the most diverticula are associated with several other diseases, one of commonly recognised acquired diverticula in man. which is a peripheral neuropathy thought to occur secondarily Cricopharyngeal or pharyngoesophageal diverticula that occur to abnormal bacterial proliferation, malabsorption and vitamin proximal to the upper oesophageal sphincter (Zenker’s B deficiency (Assenza et al. 2007). diverticulum) are the most common diverticula in the upper Colonic diverticula have a similar aetiology to jejunal gastrointestinal tract (Ferreira et al. 2008). Other acquired diverticula and are considered “a disease of the 20th century” diverticula have been reported in human patients including and a “disease of Western civilization” (Tappenden and oesophageal (Varghese et al. 2007) and jejunal (Assenza et al. Shrestha 2007). A low fibre diet, altered collagen structure 2007). Acquired jejunal diverticula are often associated with with increasing age, and motility disorders are thought to be concurrent colonic, duodenal, oesophageal, gastric and cystic the likely aetiology with subsequent increases in intraluminal diverticula (Assenza et al. 2007). In horses, acquired pressure leading to mucosal herniation (Tappenden and oesophageal diverticula (Stick 2006) have been described with Shrestha 2007). A clinical syndrome such as this has not been a relatively frequent occurrence compared to other acquired seen in the horse. diverticula. Traction oesophageal diverticula in horses occur at the site of a post surgical (e.g. oesophagostomy) or post traumatic Aetiology and pathogenesis wound of the oesophagus that healed by secondary intention. Pulsion diverticula occur as a result of external trauma to the Congenital diverticula are an anomaly similar to other cervical area that ruptures the muscle layers with subsequent intestinal duplications (Assenza et al. 2007). Colonic herniation of the mucosa through the muscular defect (Stick duplications have been classified as simple cysts, diverticula, or 2006). tubular colonic duplications (McPherson et al. 1969). Human colonic diverticula, for example, occur on the mesenteric side Clinical signs and diagnosis of the bowel and share a common blood supply and muscle layers with the normal colon (Ravitch 1953; Holcomb et al. Most human patients with diverticula are asymptomatic. The 1989; Brown and Azizkhan 1999; Sisil Kumara et al. 2001). diagnosis is most often made incidentally. Patients may have Proposed causes include median septum formation, failure of vague and chronic or acute symptoms. Chronic symptoms regression of embryonic diverticulum, partial twinning and include weight loss, failure to thrive in children and errors of epithelial canalisation (Ravitch 1953; Holcomb et al. intermittent mild to moderate abdominal pain. Acute 1989; Brown and Azizkhan 1999; Sisil Kumara et al. 2001). symptoms are associated with obstruction (acute or chronic Meckel’s diverticulum forms as a failure of embryological impaction, enterolith formation, volvulus, intussusception or structures to regress (Table 1). functional obstruction), haemorrhage (ulceration, Acquired diverticula probably occur as a consequence of inflammation, trauma, irritation or congenital arteriovenous abnormal intestinal motility with a secondary increase in malformation) or perforation (acute necrotising inflammation, intraluminal pressure and out pouching of the mucosal and blunt trauma, foreign body impaction) (Assenza et al. 2007). submucosal layers through a defect in the smooth muscle In human patients, diverticula are usually diagnosed with (Table 2). Acquired diverticula occur at mesenteric sites where contrast radiography or computerised tomography, the vessels perforate the intestinal wall. In human patients, endoscopy, or at laparotomy. small intestinal diverticula occur most commonly in the oral The incidence of subclinical diverticula in the equine jejunum and aboral ileum where the vessels are of the greatest population is unknown because horses do not routinely diameter (Assenza et al. 2007). Hypermotility or irregular undergo abdominal radiography or computerised tomography motility is likely to increase intraluminal pressure and cause the as in human patients. However, in one study, a Meckel’s mucosa to protrude through the weak areas in the smooth diverticulum was found at necropsy in 5 horses and was muscle (i.e. where the vessels penetrate) (Assenza et al. 2007). responsible for death in all 5 cases (Sprinkle et al. 1984) In human patients, obesity, venous stasis, and constipation suggesting that they are likely to become clinically important. lead to an increase in intraluminal pressure and diverticula Meckel’s diverticula can become impacted and grow to an formation (Assenza et al. 2007). An alternate enormous size, become necrotic and perforate, or be aetiopathogenesis is that there is a visceral myopathy associated with a small intestinal volvulus (Freeman 2006). associated with smooth muscle functional and structural Therefore, horses with diverticula are likely to present with abnormality (Krishnamurthy et al. 1983). Interestingly, jejunal typical signs of colic that may be acute or chronic and intermittent. Weight loss and inappetence may also be a TABLE 2: Congenital vs. acquired diverticula feature. These clinical signs would lead the attending Congenital Acquired veterinarian to recommend an abdominal exploratory laparotomy at which time the diagnosis should be made. In True diverticulum Pseudodiverticulum equine patients, the diagnosis is usually made at laparotomy or Solitary Multiple (66%) Antemesenteric location Mesenteric location necropsy. Oesophageal pulsion diverticula, on the other hand, Clinical signs at young age Clinical signs usually in 50–70-year- are usually associated with a swelling in the cervical region of in human patients old human patients the neck and dysphagia and traction diverticulum are usually 574 EQUINE VETERINARY EDUCATION / AE / november 2008

subclinical (Stick 2006). Pulsion diverticula can become quite expense to the client associated with their resection and large and cause oesophageal obstruction or can perforate. A because the intestinal strangulation that can be associated diagnosis is made with contrast radiography or endoscopy. with them may be fatal, particularly if a second abdominal exploration is not an option. The importance of a thorough Surgical treatment abdominal exploration in each case, particularly if an unusual lesion is identified, can not be over emphasised. In human patients, complete resection of an acquired diverticulum and adjacent involved intestine is recommended References (Holcomb et al. 1989; Brown and Azizkhan 1999; Sisil Kumara et al. 2001; Jeppesen and Willerth 2002; Assenza et al. 2007). Assenza, M., Ricci, G., Antoniozzi, A., Clementi, I., Simonelli, L. and While successful cases have been reported, diverticulectomy Modini, C. (2007) Perforated jejuneal diverticulosis. Case report and review of literature. Ann. Ital. Chir. 78, 247-250. (i.e. resection of the diverticulum only) is contraindicated Brown, R.I. and Azizkhan, R.G. (1999) Gastrointestinal bleeding in because of the high incidence of intestinal surgical site infants and children. Semin. Pediatr. Surg. 8, 202-209. dehiscence and subsequent septic peritonitis (Assenza et al. Ciftci, A.O., Tanyel, F.C. and Hiçsönmez, A. (1998) Gastric 2007). Introflexion of the diverticulum is also contraindicated diverticulum: An uncommon cause of abdominal pain in a 12 year because of the high risk for intestinal ulceration, old. J. Pediatr. Surg. 33, 529-531. haemorrhage, and mechanical obstruction. Therefore, the Ferreira, L.E.V.V.C., Simmons, D.T. and Baron, T.H. (2008) Zenker’s entire segment of affected intestine should be resected. diverticula: pathophysiology, clinical presentation, and flexible Colonic diverticula are often managed medically; however, endoscopic management. Dis. Esophagus. 21, 1-8. when symptoms are severe a colectomy is performed Freeman, D.E. (2006) Small intestine. In: Equine Surgery, Eds: J.A. Auer (Tappenden and Shrestha 2007). and J.A. Stick, W.B. Saunders Co., Philadelphia. pp 401-436. Conversely, diverticulectomy of congenital diverticula have Griffiths, E.A., Bergin, F.G., Henry, J.A. and Mudawi, A.M. (2003) been reported. A gastric diverticulum was successfully treated Acute inflammation of a congenital cecal diverticulum mimicking appendicitis. Medical Sci. Monitor. 9, CS107-109. in a 12-year-old girl with diverticulectomy only (Ciftci et al. 1998). In a prospective study of Meckel’s diverticulum in Holcomb, G.W. 3rd, Gheissari A., O’Neill J.A. Jr, Shorter, N.A. and Bishop, H.C. (1989) Surgical management of alimentary tract human patients, there was no difference in post operative duplications. Ann. Surg. 209, 167-174. complications or mortality when patients underwent a Jeppesen, G.A. and Willerth, M. (2002) Perforated congenital diverticulectomy vs. an intestinal resection and anastomosis diverticulum of the sigmoid colon. J. Pediatr. Surg. 37, E35. (McKay 2007). Further, prophylactic resection was Krishnamurthy, S., Kelly, M.M., Rohrmann, C.A. and Schuffler, M.D. recommended in patients aged <50 years because they are (1983) Jejunal diverticulosis. A heterogenous disorder caused by a more likely to become symptomatic compared to patients of variety of abnormalities of smooth muscle or myenteric plexus. >50 years (McKay 2007). There have been no studies Gastroenterol. 85, 538-547. investigating Meckel’s diverticulum in horses; however, this McKay, R. (2007) High incidence of symptomatic Meckel's author would recommend resection of the affected intestinal diverticulum in patients less than fifty years of age: an indication for resection. Am. Surg. 73, 271-275. segment and anastomosis of adjacent bowel ends in cases showing clinical signs as well as prophylactically if a McPherson, A.G., Trapnell, J.E. and Arith, G.R. (1969) Duplications of the colon. Br. J. Surg. 56, 138-142. diverticulum was recognised incidentally at surgery. Ravitch, M.M. (1953) Hind gut duplication. Ann. Surg. 137, 588-601. Oesophageal pulsion diverticula in horses are usually managed surgically with diverticulectomy or introversion of Robert, M.P., Benamou-Smith, A.E., Cadore, J.L., Rosengarten, M.S. and Lepage, O.M. (2008) Recurrent colics in a 9-year-old Arabian the mucosa and submucosa of the diverticulum. The latter is stallion due to several congenital anomalies. Equine vet. Educ. 20, recommended because of the lower risk of leakage, infection, 567-571. and fistula formation post operatively (Stick 2006) compared Simstein, N.L. (1986) Congenital gastric anomalies. Am. Surg. 52, to diverticulectomy. Oesophageal resection and anastomosis is 264-268. associated with a high complication rate and is not Sisil Kumara, P.D.R., Jayawardane, G.L.D.P. and Aluwihare, A.P.R. recommended. (2001) Complete colonic duplication in an infant. Ceylon. Med. Information on survival and complication rates following J. 46, 69-70. surgical treatment of other gastrointestinal diverticula has not Sprinkle, T.P., Swerczek, T.W. and Crowe, M.W. (1984) Meckel’s been obtained for the horse because of the low incidence. diverticulum in the horse. J. equine vet. Sci. 4, 175-179. However, based on the information in the human literature as Stick, J.A. (2006) Esophagus. In: Equine Surgery, Eds: J.A. Auer and well as our limited clinical experience, resection of the entire J.A. Stick, W.B. Saunders Co., Philadelphia. pp 351-386. affected segment is recommended if it is technically possible Tappenden, J. and Shrestha, B.M. (2007) Colonic diverticular disease: Current perspectives. J. Napal. Med. Ass. 46, 206-213. based on the location of the diverticulum. We recently had a case of multiple acquired jejunal diverticula in a mature horse. van Twisk, R.A. (1984) Congenital diverticulum of the small intestine; Meckel’s diverticulum or duplication? Netherlands J. Surg. 36, 107- The affected jejunal segment was resected and the horse had 111. a favourable outcome. Varghese, T.K., Marshall, B., Chang, A.C., Pickens, A., Lau, C.L. and Mesodiverticular bands should be identified and resected Orringer, M.B. (2007) Surgical treatment of epiphrenic diverticula: at surgery because there are almost no complications or A 30-year experience. Ann. Thorac. Surg. 84, 1801-1809.