Diagnosis
Cats are often classified as having megacolon in studies if they have constipation that is refractory to medical therapy for more than 3 months, had three of more bouts of constipation, and subsequently required subtotal colectomy (Trevail et al.
2011). The most common clinical sign is tenesmus, but other signs include, lethargy, dehydration, anorexia, and occasionally vomiting. This includes cats with idiopathic mega-colon, and known etiologies including pelvic fractures with malunion causing hypertrophic mega-colon or dysautonomia. Clinical features of dysautonomia, include mydriasis with depressed direct and consensual pupillary light reflex, dysuria with distended urinary bladder, dry mucous membranes, prolapsed third eyelid, and dysphagia (Sharp, Nash, and Griffiths 1984). The predominant clinical signs of hypertrophic mega-colon in the dog are tenesmus, weight loss, anorexia, and vomiting (Nemeth et al. 2008). Some dogs had reported anemia, or elevated packed cell volume (Nemeth et al. 2008).Investigation should include a thorough physical examination with careful attention of abdominal palpation, minimum database that includes hematology, biochemistry, fecal analysis, and urinalysis. A rectal examination, conscious in the dog or under anesthesia in the cat or painful dog, can be helpful in gauging the pelvic canal size in the case of a malunion, or if there are other rectal pathologies including stricture, masses, rectal diverticula, foreign body, or inflammation (Washabau 2003). Although the role of hypothyroidism and obesity in the pathogenesis of mega-colon is tenuous, it has been described in several cases and should warrant consideration. A full neurological examination should be conducted. If neurological disease is found, this may warrant further diagnostics including advanced imaging studies, cerebrospinal fluid analysis, infectious disease screen, or electrophysiologic studies to characterize and confirm the pathology. Abdominal and pelvic radiography serves two purposes, first to confirm the dilated colon (Figure 18.1) and second to exclude pelvic or spinal malformations or injuries, but orthopedic diseases may require computed tomography.
Mega-colon in cats is confirmed radiographically after appropriate history and clinical findings support a suspicion.