Retrograde WCE is performed with water soluble-contrast introduced in the rectum by a Foley catheter.

The radiologist takes images at different angles inviting the patient to change position during the exam and evaluate the colorectal anastomosis through 360 degrees minimizing the risk of not identifying the radiological leakages.

A positive retrograde WCE study is defined by the presence of contrast outside the bowel lumen or peri-anastomotic fluid collections or a fistula. Anastomotic leakages are clinically identified with the use of both clinical examination and laboratory findings. Retrograde WCE imaging is then used to radiologically identify the leakage [3].

Four morphological types of anastomotic leakage have been described: "saccular type", "horny type", "serpentine type" and "dendritic type" [3].

Each type of leakage has a distinctive morphology:

- "saccular leakages" are identified by their round or oval morphology with a small “collar” of communication with the bowel lumen;

- "horny leakages" protrude as a tubular or elongated blind-ended cavities, similar to an animal’s horn;

- "serpentine leakages" appear as a “snake-like” projection, with a tortuous morphology;

- "dendritic leaks" are described as having multiple foci of leakage in many directions [3].

The authors of this classification observe that dendritic and serpentine types are more frequent in cases with radiologic leak following clinical leakage and that none of the dendritic ones solve spontaneously. On the other hand, saccular and horny type have a better prognosis after the healing of the leak and subsequent stoma restoration since they consist in a cavity that provides a sort of physical barrier to the spread of inflammation [3]. This is the reason why it is important to describe the morphology of the radiological leaks.

In this pictorial review we show a collection of images regarding the different types of radiologic leakages on retrograde WCE: saccular type (Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6), horny type (Fig. 7, Fig. 8, Fig. 9, Fig. 10, Fig. 11, Fig. 12, Fig. 13), serpentine type (Fig. 14, Fig. 15, Fig. 16, Fig. 17, Fig. 18) and dendritic type (Fig. 19, Fig. 20, Fig. 21, Fig. 22), that we selected from our daily experience. We also show images of fistulae (Fig. 23, Fig. 24, Fig. 25, Fig. 26), that represent a possible evolution of leaks.

In addition, we illustrate some images regarding the real challenge in this field: the identification of small and not so clear leakages (Fig. 27, Fig. 28, Fig. 29, Fig. 30, Fig. 31, Fig. 32). Small leaks can be difficult to identify, especially due to false positive findings caused by a “dog ear” of the staple line [4].

In our practice when we suspect the presence of a small leak, we use different tricks to distinguish it from the “dog ear” of the staple line (Fig. 33): first of all during the retrograde WCE study we evaluate the colorectal anastomosis using many radiological projections and we use the maximum possible magnification focused on the suspicious leak. After that, we observe if the suspicious radiological leakage has peristaltic movement. The presence of peristaltic movement allows us to exclude that it is a leak and it directs us to a possible “dog ear” of the staple line.

When we can’t distinguish between the small leaks and the “dog ear” of the staple line despite the tips reported above, we consider all these small findings as leakages, in order to avoid missing a potentially severe complication. We employ a ‘wait and see’ approach to these patients and  re-evaluate them with further radiological imaging, clinical examination and laboratory assessment in collaboration with the medical and surgical teams.