Imaging the operated colon using water-enema multidetector CT, with emphasis on surgical anastomoses
Water-enema multidetector CT (WE-MDCT) provides a detailed multiplanar visualisation of mural, intra- and extraluminal abnormalities of the large bowel, relying on preliminary bowel cleansing, retrograde luminal distension, pharmacological hypotonisation and intravenous contrast enhancement. In patients with a history of colorectal surgery for either carcinoma or Crohn’s disease (CD), WE-MDCT may also be performed via a colostomy, which allows depicting the anatomy and position of the residual large bowel and evaluates the calibre, length, mural and extraluminal features of luminal strictures. Therefore, WE-MDCT may prove useful as a complementary technique after incomplete or inconclusive colonoscopy to assess features and suspected abnormalities of the surgical anastomosis, particularly when endoscopic or surgical interventions are being planned. This pictorial essay presents the WE-MDCT technique and pitfalls, the expected appearances after different colic surgeries and the imaging features of benign anastomotic disorders (fibrotic stricture, kinking, inflammatory ulcer) and of locally recurrent tumours and CD.
• Water-enema multidetector CT (WE-MDCT) effectively visualises the operated colon
• Complementary to endoscopy, WE-MDCT may helpfully depict abnormalities of surgical anastomoses
• WE-MDCT allows assessment of strictures’ features and abnormalities of the upstream bowel
• Technical pitfalls, normal postsurgical findings and benign anastomotic disorders are presented
• WE-MDCT allows detecting relapsing Crohn’s disease, recurrent and metachronous tumours
KeywordsComputed tomography (CT) Colonoscopy Colorectal surgery Anastomosis Stricture Colorectal carcinoma Crohn’s disease
Since the first description by Gossios et al. , water-enema multidetector CT (WE-MDCT) has developed into a technique dedicated to visualising the large bowel, which relies on a combination of preliminary bowel cleansing, retrograde fluid-attenuation luminal distension, pharmacological hypotonisation and intravenous contrast enhancement. Although relatively simple to perform and interpret, WE-MDCT is increasingly considered the most accurate imaging technique to comprehensively stage colorectal carcinoma (CRC) and has very high sensitivity (98.6–99%) for lesions measuring at least 1 cm and good agreement between CT features and histopathology [2, 3, 4, 5]. Moreover, WE-MDCT has been effectively adopted to diagnose bowel endometriosis [6, 7, 8], colonic diverticular disease  and chronic inflammatory bowel diseases (IBD) [9, 10, 11, 12, 13].
Following colorectal surgery for either benign or malignant processes, optical colonoscopy remains the gold standard technique to assess the anastomotic site and residual large bowel and to identify recurrence of resected disease. However, in operated patients endoscopy is often hampered by postsurgical adhesions, sharp bowel angulations, bowel kinking, poor bowel preparation and anastomotic strictures (AS). WE-MDCT allows reliable measurement of the colonic wall thickness in normal and pathological conditions, and provides a detailed multiplanar assessment of mural, intra- and extraluminal abnormalities of the large bowel. Therefore, its use is appealing to investigate the operated colon, particularly after unsuccessful, incomplete or inconclusive endoscopy.
Based upon personal experience at a tertiary hospital that performs IBD and oncologic surgery, this pictorial essay presents the WE-MDCT technique and pitfalls, the expected appearances after various colon surgeries and the imaging features of benign anastomotic disorders, recurrent tumours and Crohn’s disease (CD).
Water enema multidetector CT technique and interpretation
Retrograde colonic distension is contraindicated in the presence of high-grade bowel obstruction, when a standard contrast-enhanced CT acquisition reliably investigates the site and cause of obstruction, thanks to the pre-existent bowel dilatation with intraluminal fluid. Before WE-MDCT, bowel cleansing is obtained using an iso-osmolar non-absorbable laxative solution (typically 4–6 doses of polyethylene glycol dissolved in 500 ml water per dose) the day before the examination, in association with a low-fibre diet for 3 days. Patients fast for 12 h after a liquid dinner the evening before the scheduled examination .
Rationale and comparison with other CT techniques
In patients with a history of partial colonic resection for CRC, Neri et al. used CT colonography (CTC) after incomplete endoscopy to assess the colonic mucosa and pericolic tissues searching for local recurrence, metachronous polyps and tumours. Although the residual colon was always entirely visualised with 100% sensitivity for AS, in their experience CTC findings were not sufficiently reliable to differentiate fibrotic from neoplastic strictures. Furthermore, in patients with right hemicolectomy retrograde insufflation of the anastomosed ileum may cause suboptimal distension of the residual colon .
Compared with full-dose contrast-enhanced CTC, WE-MDCT has a shorter learning curve for radiologists, is less cumbersome for the patient without the need for rotation from the prone to supine position and generates a lower radiation dose because it involves a single CT acquisition during contrast medium injection. Although no studies compared the comfort between the two different techniques, Ridereau-Zins et al. observed that the retrograde introduction of warm water was well, moderately and poorly tolerated by 86.2%, 12.2% and 1.7% of patients, respectively . Furthermore, WE-MDCT does not seem to suffer from the occasional but potentially severe complications associated with air or carbon dioxide CTC, including a 0.04% perforation rate . At our centre, the vast majority of patients do not experience side effects and consistently feel WE-MDCT is less disagreeable than those receiving colonic distension using litres of air . After WE-MDCT, Paparo et al. reported four (1.3%) mild adverse events (nausea, abdominal discomfort) and one episode of diarrhoea in a cohort of 30 patients with a high proportion of underlying bowel disorders. In the same study, the frequency of side effects with WE-MDCT was the lowest compared with peroral CT enterography (CTE), CT enteroclysis with intubation and combined CTE plus WE-MDCT .
Although prospective trials comparing accuracy for lesion detection between CTC and WE-MDCT are lacking, some authors have compared the degree of colonic distension between the two techniques, concluding that the sigmoid and left colon were better assessed using both WE-MDCT and prone CTC compared with the supine CTC acquisition . Therefore, we started to use WE-MDCT to assess diverticular disease and chronic inflammatory bowel diseases  and suspected abnormalities of surgical anastomoses. Together with the two leading French groups, we believe that—compared with CTC—retrograde filling using water does not overdistend the colonic lumen and thus allows a better assessment of the true mural thickness of the irregular external edges that define T3-stage CRC and of peritumoral lymph nodes [2, 3, 4, 5].
In the setting of chronic IBD, WE-MDCT has been validated by the Genoa group, consistently provides superior distension of the large bowel compared with CTE and optimally reproduces the well-known mural and extraluminal features of CD [10, 11, 12]. Furthermore, without the patient having to ingest polyethylenglycole solution, WE-MDCT achieves adequate luminal filling of the neoterminal ileum in a high proportion of patients with ileocecal resection (ICR) [9, 10, 11, 12].
Similarly to the preoperative setting , interpretation of CT studies focused on the large bowel benefits from multiplanar image review: therefore, WE-MDCT images should be routinely reconstructed along the axial, coronal and sagittal planes. We suggest that radiologists should review the study on a workstation to save oblique or curved-planar reconstruction images focused on the key findings, such as surgical anastomoses and strictures.
Interpretation of WE-MDCT scans benefits from the excellent contrast between the intraluminal water, enhanced colonic wall and normal fat-attenuation perivisceral planes. In surgically treated patients, WE-MDCT allows depicting the anatomy and position of the residual large bowel in arbitrary planes, including the coronal orientation, which is most appealing for surgeons. Study interpretation benefits from precise knowledge of the type of resection and reconstruction performed and of recent endoscopic findings. Surgical anastomoses should be evaluated for site, configuration, patency and mural features. Ileo-colic and colo-colic anastomoses can be either manual (hand-sewn) or mechanical, with the latter clearly identified by the presence of hyperattenuating circular or linear staple lines. Focused maximum-intensity projection (MIP) images may be helpful to assess the configuration and integrity of a stapled anastomosis (Fig. 3, image c). Known or indeterminate strictures should be assessed for length, configuration, mural thickness, entity and pattern of enhancement (homogeneous or stratified) and associated extraluminal changes.
Expected CT appearances after colorectal surgery
Local anastomotic complications
The development of a benign colorectal AS is an increasingly common postsurgical problem. Strictures may form after open or laparoscopic surgical treatment of either benign or malignant diseases, with a higher incidence in stapled compared with hand-sewn anastomoses. Although causes are still not clearly understood, AS may result from ischaemia, disruption or leakage at the anastomotic site. Symptoms such as pain, distension, nausea and vomiting are reported in up to one-third of patients after colorectal surgery and reflect the degree of luminal stenosis [21, 22, 23].
In our experience, WE-MDCT is particularly helpful when repeated surgery or endoscopic treatment of AS is being contemplated. Balloon dilatation with or without endoscopic incision using laser or argon plasma is successful in 88% of benign AS cases. Alternatively, refractory ASs are increasingly treated with fully covered stents to achieve a prolonged clinical success and to obviate the high morbidity from revisional surgery [22, 23, 25, 26, 27, 28].
Following CRC resection, patients are at risk for local anastomotic or extraluminal tumour recurrence and may develop adenomatous polyps and metachronous tumours in the residual bowel. At endoscopic surveillance, abnormal findings are found within 2 years from surgery in up to 18.5% of patients [31, 32]. Recurrent malignancies generally require repeated surgery or palliative endoscopic stenting [24, 25].
Crohn’s disease recurrences
failure to achieve retrograde colonic distension because of incontinence at either the rectum or colostomy;
segmental non-distension or spasm, which most commonly occurs at the sigmoid or the nondependent transverse colon and generally mimics a segmental mural thickening (Fig.16A–C); this phenomenon often disappears with further water inflow and repeated hypotonisation
presence of faecal residues from insufficient bowel cleansing (Fig.16D–E), which may obscure intraluminal processes but generally does not impede identification of strictures and assessment of mural thickness.
In our experience, WE-MDCT is a rapid, easy-to-perform and well-tolerated technique that provides multiplanar high-resolution visualisation of the operated large bowel, with the drawback of ionising radiation. In selected patients with a history of colorectal surgery, WE-MDCT may prove useful as a complementary technique to endoscopy to assess suspected abnormalities at the anastomosis. Furthermore, WE-MDCT allows assessing the calibre, length, mural and extraluminal features of luminal strictures and evaluating the bowel upstream to an endoscopically impassable tract and is therefore particularly helpful when endoscopic procedures or surgical interventions are being planned.
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