**2. Definition and grading severity of colorectal anastomotic leakage (CAL)**

Colorectal anastomotic leakage (CAL) is one of the most serious and feared complications in coloproctology, as said before. Generically, it is a break in the anastomosis between the two intestinal segments performed during colorectal surgery, which means communication between in- and extra-luminal spaces due to a defect in the integrity of the surgical anastomose performed. Therefore, in practical terms, anastomosis's failure must be classified in dimensions, severity, and consequences. However, its precise definition and diagnosis are still the subject of some controversy.

Many CAL definitions have been proposed for decades, but consensus has been proven hard to find. The finding of the lack of consensus on the definition and the subsequent concern to standardize the definition and severity scale common to colorectal surgeons has become more evident in the last decade, with a particular incidence in the last 5 years [1–5]. The use of a CAL consensus survey in some countries [3, 4] and a modified Delphi study that included colorectal surgeons and researchers who had published three or more articles about CAL [5] are evident attempts to use a common language to compare results and define strategies.

According to Helsdingen et al., CAL definition can be standardized into four categories: clinical, laboratory, imaging, and operative findings. Consensual clinical parameters included tachycardia, clinical deterioration, abdominal pain, discharge from the abdominal drain, discharge from the rectum, rectovaginal fistula, and anastomotic defect detected by digital rectal examination. The main laboratory parameters for CAL suspicion are increased plasma CRP or its combination with leukocytosis. The imaging findings valorizing signs of CAL are extravasation of endoluminal water-soluble contrast, collection around the anastomosis, presacral abscess near the anastomosis, perianastomotic air, and intra-abdominal free air on CT scan. Furthermore, indicative re-operative findings of CAL were evidence of necrosis of anastomosis or blind loop, signs of peritonitis, and dehiscence of anastomosis [5].

On the other hand, CAL is an anastomotic failure and must be classified in terms of severity as it has management implications and different outcomes. Rahbari et al. proposed a three-degree (A, B, and C) clinical severity classification, impacting the treatment and consequences. For example, an anastomotic failure type "A" was considered generally sub-clinical and would not require any active therapeutic intervention; type "B" required active management (antibiotic therapy, image-guided drainage, or transanal drainage) with no need for further re-operations; type "C" required further re-operations [1]. This severity classification correlates with the Clavien-Dindo classification [6] and allows us to measure and grade CAL short-term consequences.
