Case study of megacolon in a cat

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1 Vet Times The website for the veterinary profession Case study of megacolon in a cat Author : Gareth Richardson Categories : Vets Date : September 5, 2011 Gareth Richardson discusses the examination, diagnosis and treatment of a constipated cat that had been previously unresponsive to medical therapy Summary Megacolon in the cat is encountered relatively frequently in practice and medical treatment is usually unsuccessful. Surgical management by total or sub-total colectomy results in a more favourable clinical outcome. Key words megacolon, mesenteric, colorectal, colectomy AN eight-year-old male, neutered, domestic shorthair cat weighing 4.7kg initially presented with a two-year history of chronic constipation that had become refractory to medical management. Treatment with lactulose and sodium citrate and enemas had become increasingly ineffective. The client had become discouraged by these poor results, so the cat was no longer receiving any form of treatment. It had exhibited clinical symptoms of tenesmus and had vomited once on the day of presentation. Clinical examination 1 / 6

2 On clinical examination, the cat was found to be slightly depressed. The colon was easily examined by transabdominal palpation and found to be full of hard material, which was consistent with impacted faeces. The neurological examination was unremarkable and no other abnormalities were detected. Colonic inertia or mechanical obstruction were identified as the main problems in this patient, and a list of differential diagnoses for each was considered. Colonic inertia can result from idiopathic megacolon, colonic neoplasia secondary to prolonged colonic distention, or from neuromuscular dysfunction. Neuromuscular dysfunction can be as a result of spinal cord disease processes, including congenital or acquired lumbosacral disease, cauda equina syndrome or sacral spinal cord abnormalities. Trauma to colonic innervation or feline dysautonomia can also lead to colonic neuromuscular dysfunction. Mechanical obstruction to defaecation can occur secondary to pelvic fracture malunions, colonic, rectal or anal strictures, intrapelvic extraluminal masses, such as prostatic diseases or neoplasia, anal or rectal diverticula, atresia or even perineal herniation. Other causes of mechanical obstruction include inflammatory causes, such as perianal fistulation, proctitis, and bite wounds to the perineal region. Metabolic or endocrine disturbances, such as dehydration, obesity, hypokalaemia or hypothyroidism, can also lead to mechanical constipation, as can foreign bodies, such as hair or stones. Following clinical examination the investigation was continued by obtaining and analysing serum biochemistry and haematology profiles, but these were found to be unremarkable ( Table 1 ). The cat was sedated with medetomidine and butorphanol, and right-lateral and ventrodorsal abdominal radiographic projections were obtained ( Figures 1 and 2 ). These revealed a distended colon containing dense, mottled, radio-dense material and no evidence of pelvic canal injury or stenosis. Rectal examination detected hard faecal matter at the pelvic entrance. These findings were consistent with a diagnosis of feline idiopathic megacolon. Surgery Due to the cat s previous history of poor response to medical management of the condition, two days later it was decided to proceed with surgical treatment. The patient was induced with intravenous propofol, and anaesthesia was maintained with isoflurane in oxygen. It was also treated with the intravenous administration of cefazolin sodium at a dose of 20mg/kg, given at induction and six hours later. The cat was administered meloxicam for analgesia and placed on to intravenous fluid therapy (Hartmann s solution). 2 / 6

3 The ventral abdomen was aseptically prepared for surgery, and a subtotal colectomy with end-toend ileocolic anastomosis was performed. A ventral midline celiotomy incision was made from umbilicus to pubis. The distal ileum, caecum and colon were exteriorised and isolated with salinesoaked laparotomy sponges. Ileal, ileocolic and caudal mesenteric arteries and veins were identified and then double ligated with 1.5M polyglactin 910 prior to transection ( Figure 3 ). Care was taken to ensure that the cranial rectal artery was preserved. Faecal matter was milked into the segment to be resected. Doyen clamps were placed 3cm proximal and distal to the resection site, and Carmalt clamps were then placed at the transection site. An incision, perpendicular to the long axis of the colorectal area, was made close to the crushing forceps. At the ileocaecal region, the ileum was incised at a 45 angle and the antimesenteric border left shorter than the mesenteric one. The colon was removed and samples were taken for histopathology ( Figure 4 ). The intestinal ends were cleaned with moistened gauze sponges and reapposed with simple interrupted 2M polydioxanone sutures incorporating all layers commencing at the mesenteric border, followed by a suture at the antimesenteric border. The edges were gently apposed and additional sutures placed between the first two sutures. The lumen was moderately distended with sterile saline and gentle digital pressure applied to detect leakage at the anastomosis site. The mesentery was apposed with simple interrupted 2M polydioxanone sutures. The isolated intestine was lavaged with sterile saline and the laparotomy pads removed. The abdomen was lavaged with one litre of lukewarm sterile saline, which was removed by suction, and the omentum was wrapped around the anastomosis sites. Gloves, drapes and instruments were then changed. Celiotomy closure was routine, with simple interrupted 3M polyglactin 910 sutures in the linea alba. The subcutis was closed with a simple continuous 3M polyglactin 910 suture and the skin was closed with simple interrupted 3M polymerised caprolactam sutures. Postoperative treatment Fluid therapy was continued for 24 hours postoperatively, and analgesia was maintained with 0.01mg/kg subcutaneous buprenorphine six-hourly for 48 hours. Twice-daily administrations of 20mg/kg subcutaneous cefalexin and 10mg/kg intravenous metronidazole maintained antibiosis until discharge five days later. The patient was drinking 12 hours postoperatively and eating after 24 hours. It had also passed 3 / 6

4 liquid stools by then. It was hospitalised to monitor defaecation for a further five days before being discharged with a bland diet small amounts to be fed four times daily for one week before gradually being reintroduced to a normal diet. Skin sutures were removed 14 days postoperatively, at which time the cat was producing semiformed faeces. It was clinically normal with soft-formed faeces 44 days postoperatively and this situation had been maintained when it was re-examined six months later with successful resolution of the constipation. Megacolon Megacolon is not a specific disease, but a clinical sign associated with failure to normally void faeces (Hedlund, 2002; White, 2002). It may be primary (idiopathic or congenital) or secondary (pelvic fracture malunion or neurological dysfunction) (Ryan et al, 2006). Congenital megacolon has not been rigorously documented in dogs or cats (Holt and Brockman, 2003). In humans, Hirschsprung s disease is familiar, resulting from congenital absence of inhibitory neurones in Meissner s submucosa and Auerbach s myenteric plexuses in the distal colon and rectum. Aganglionosis has been reported in colonic tissue from two affected cats and myenteric ganglia were absent in another two. The significance of this is unclear because these cats were mature, making congenital megacolon unlikely (Holt and Brockmann, 2003; White, 2002). Histologically, no consistent lesions explain the aetiology of megacolon (Bright et al, 1986; Hedlund, 2002; Rosin et al, 1988; Washabau and Holt, 2003). Radiographically, the diameter of a normal colon should be less than the length of the seventh lumbar vertebra (Biery, 1998). An enlargement beyond oneand a-half times this indicates megacolon (O Brien, 1978), as was the case in this patient. The history, age, histopathological and radiographic findings suggested idiopathic megacolon in this patient. Feline idiopathic megacolon accounts for 60 to 70 per cent of cases seen (Bertoy, 2002; Ryan et al, 2006). The aetiology of feline megacolon is unclear, but an abnormality of intrinsic or extrinsic innervation to the lower large intestine, the myoneural junction or smooth muscle seems likely (Bertoy, 2002; Hedlund, 2002; Holt and Brockmann, 2003; Washabau and Holt, 1999). Medical management is unrewarding in most cases, and total or subtotal colectomy, with or without preservation of the ileocolic valve, is the recommended treatment (Rosin, 1993; Ryan et al, 2006). Healing of the large intestine is delayed compared to the small intestine. Optimal healing at the colorectal anastomosis depends on good blood supply. Preserving the cranial rectal artery to avoid ischaemic necrosis is, therefore, very important (Washabau and Holt, 1999), as are accurate 4 / 6

5 mucosal apposition, minimal surgical trauma, tensionfree closure and omentalisation of the anastomosis sites. The omentum enhances healing of ischaemic rectal anastomosis and increases bursting strength (Holt and Brockman, 2003). Anastomosis may be performed using full thickness sutures, staples or biofragmentable anastomosis rings with equal success (Ryan et al, 2006). Colectomy with colocolonic, ileocolonic or jejuno-colonic anastomosis has been described for feline megacolon (Washabau and Holt, 1999). Preserving the ileocolic junction is controversial (White, 2002). Preservation does not result in continued constipation (Washabau and Holt, 1999), but resection may be associated with increased incidence and severity of diarrhoea (Bright, 1991; Sweet et al, 1994). Resection allowed for greater tension-free anastomosis in this patient (Bertoy, 2002). Stool storage and water absorption are altered after subtotal colectomy. The distal small intestine adapts, increasing its storage capacity and ability to absorb water (Bertoy et al, 1989). More than 90 per cent of cats have uncomplicated recovery and good enteric function post-surgery (Bertoy, 2002; Gregory et al, 1990; Rosin, 1993). Metronidazole and firstgeneration cephalosporins are useful for colonic surgery (Hedlund, 2002), as the risk of infection after colorectal surgery is high. Antibiotic use with colorectal surgery reduces morbidity and mortality associated with infection justifying their use in this patient. References Bertoy R W (2002). Megacolon in the cat, Veterinary Clinics of North America, Small Animal Practice 32(4): Bertoy R W, MacCoy D M, Wheaton L G et al (1989). Total colectomy with ileorectal anastomosis in the cat, Veterinary Surgery 18: Biery D N (1998). The large bowel. In Thrall D E (ed), Textbook of Veterinary Diagnostic Radiology (3rd edn), W B Saunders, Philadelphia: Bright R M (1991). Idiopathic megacolon in the cat, subtotal colectomy with preservation of the ileocolic valve, Veterinary Medicine Report 3: Bright R M, Burrows C F, Goring R et al (1986). Subtotal colectomy for treatment of acquired megacolon in the dog and cat, JAVMA 188(12): 1,412-1,416. Gregory C R, Guilford W G, Berry C R et al (1990). Enteric function in cats after subtotal colectomy for treatment of megacolon, Veterinary Surgery 19(3): Hedlund C S (2002). Surgery of the large intestine. In Fossum T W (ed), Small Animal Surgery (2nd edn), Mosby, Philadelphia: Holt D E and Brockman D (2003). Large intestine. In Slatter D (ed), Textbook of Small Animal Surgery (3rd edn) W B Saunders, Philadelphia: O Brien T R (1978). Large intestine. In Radiographic Diagnosis of Abdominal Disorders in 5 / 6

6 Powered by TCPDF ( the Dog and Cat, W B Saunders, Philadelphia: Rosin E (1993). Megacolon in cats the role of colectomy, Veterinary Clinics of North America, Small Animal Practice 23(3): Rosin E, Walshaw R, Mehlhaff C et al (1988). Subtotal colectomy for treatment of chronic constipation associated with idiopathic megacolon in cats: 38 cases ( ), JAVMA 193(7): Ryan S, Seim H, MacPhail C et al (2006). Comparison of biofragmentable anastomosis ring and sutured anastomosis for subtotal colectomy in cats with idiopathic megacolon, Veterinary Surgery 35: Sweet D C, Hardie E M and Stone E A (1994). Preservation versus excision of the ileocolic junction during colectomy for megacolon: a study of 22 cats, JSAP 35: Washabau R J and Holt D (1999). Pathogenesis, diagnosis and therapy of feline idiopathic megacolon, Veterinary Clinics of North America, Small Animal Practice 29(2): Washabau R J and Holt D (2003). Pathophysiology of gastrointestinal disease. In Slatter D (ed), Textbook of Small Animal Surgery (3rd edn) W B Saunders, Philadelphia: White R N (2002). Surgical management of constipation, Journal of Feline Medicine and Surgery 4: / 6