There are two ways to study the mucosal side of colon: radiology and endoscopy. These methods are usually thought to be antithetical, while they are actually complementary.
The introduction of the double contrast methods has corresponded to the advent and the technological advance in endoscopy. The diagnosis of rectal cancer can be supported by radiology as well as by endos-
copy. They are two excellent methods for diagnosis and the choice of either of them is related to the existing social setting and health service standard.
The elective radiologic procedure for the study of colon and rectum is the double contrast enema based on the instillation of a barium sulphate suspension and of its evacuation followed by inflation of air with double contrast examination of the colon. Drug-induced hypotonia is necessary to suspend peristalsis. Intestinal preparation for perfect colonic cleansing is a fundamental prerequisite, its inadequacy being one of the major causes of non-diagnostic exams . The superiority of double contrast enema as compared to the single contrast enema is now well established .
Indications for the procedure are the same as those mentioned for colonoscopy. The only surgical indications are in the neonatal period (intussusceptions).
In cases of acute colonic bleeding, the first choice exam is definitely endoscopy. It should always be performed with double contrast enema with pharma-cologic hypotonia except for the following cases: elderly or non-complying patients, post-operative controls (water-soluble contrast medium) and pseudoobstructions.
Technical limitations are mainly due to faecal residues or artefacts (flocculation of barium, gas bul-lae) which may mimic inflammation, ulceration or polyps. Absolute contraindications for enema are: pregnancy; toxic megacolon; suspected colonic perforation; immediately preceding endoscopic exam, especially if with biopsy; acute diverticulitis or peritonitis; acute colonic obstruction; peritoneal fistulae, anatomical malformations (malrotation, hernia); and ischaemic colitis.
As for the rectum, it can be stated that it is the portion of the entire colon most readily examined by radiology . In a report from the literature  15% of the lesions were missed by rectal exploration and rectoscopy and were detected on doing an enema. However it can be stated that both exams miss some lesions and that in the rectum the two methods show a similar sensitivity in the identification of neoplasms [11, 12]. In our opinion, rectal enema is fundamental in a patient with rectal cancer, especially if pre-operative radiosurgical therapies requiring the exact intra- or extraperitoneal location of the tumour are planned.
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