Healing is a complex process not yet completely understood. Soon after tissue damage, the inflammation phase takes place with subsequent migration and proliferation of macrophages, lymphocytes and fibroblasts; thereafter, neoangiogenesis and fibro-plasias lead to wound closure, and finally, contraction of the scar tissue and remodelling complete the healing process. This organised sequence of events can be retarded by many endogenous factors such as ischaemia or poor blood supply, and nutritional deficiencies (common in IBD patients) as well as exogenous ones such as infection, trauma and the use of anti-inflammatory drugs.
Inadequate perfusion or low haemoglobin level, metabolic diseases (e.g. diabetes mellitus) and connective tissue disorders are all systemic factors that contribute to alterations in the healing process. Before focusing on local treatment of an unhealed perineal wound, the surgeon has to correct possible nutritional and circulatory deficiencies, maintain blood glucose within the normal range and control high blood pressure. Radiotherapy, usually performed preoperatively in patients with rectal or anal cancer, represent a further factor that may delay healing and lead to PPS. Microangiosclerosis related to ionising radiation may alter the perfusion at the wound margins, while oedema and subsequent fibro-sis of the pelvic tissues prevent an adequate closure of the pelvic dead space.
Patients with IBD have shown more complications in healing perineal wounds in respect to patients undergoing proctectomy for cancer. In fact, as shown by Manjoney et al.  in their report, at 6 weeks 39% of patients in the IBD group had completely healed in comparison to 64% in the cancer group. Patients affected by Crohn's disease are at higher risk for PPS compared to those with ulcerative rectocolitis. The frequent involvement of the small bowel in Crohn's disease and the constant hypovitaminosis with malabsorption of ascorbate and zinc, both key elements in enzyme activation, involved in the healing process are possible explanations. Furthermore, the inflamed small bowel usually becomes rigid and does not descend to occupy the empty pelvis, leading to a persistent pelvic dead space. The risk of pelvic infection is then very much increased and fistulisation of the remaining bowel is always of great concern. Finally, at the time of operation, the rectal wall, hardened by chronic inflammation, may easily tear with spillage of content into the pelvis. Under these circumstances infection is very likely to occur .
Yamamoto et al.  reviewed the records of 145 patients who underwent proctocolectomy for Crohn's disease between 1970 and 1997 and found that PPS was present in 33 (23%) of the cases. The factors indicated by the authors as contributing to the significantly increased risk included the younger age, the presence of rectal inflammation, perianal sepsis, high fistulous tracts, extra-sphincteric excision of the rectum and fecal contamination of the pelvis. In their experience, the surgical eradication of the perineal sinus gave such poor results as to make them question the usefulness of any aggressive surgical approach for perineal sinus after proctocolecto-my for Crohn's disease. In any case, patients should be thoroughly informed about the possibility that perineal complication may frequently occur . Whitlow et al.  evaluated a series of 195 patients all undergoing proctectomy at the Ochsner Clinic in New Orleans from 1980 to 1996. They reported minor wound complications in 45 (23%) patients and major complications in 13 (7%). Diagnosis of Crohn's disease, neoadjuvant full course radiotherapy, the presence of perineal fistulae or abscesses preoperatively and the direct closure of the peritoneum were all factors that significantly increased the risk of wound complication.
A persistent perineal sinus was the most common late complication in a series of 67 patients who underwent pouch removal after failed restorative proctocolectomy at St. Mark's Hospital between 1977 and 2002 . After 6 months from pouch excision, 40 patients had completely healed while 27 had a PPS that required at least another operation; at 1 year 7 patients were still unhealed.
In order to reduce the risk of perineal wound infection and finally PPS, it is mandatory to avoid any contamination of the pelvis during surgery. Nevertheless, should any spillage of bowel content occur, a generous washing of the pelvic cavity is not a reliable remedy, in this case the perineal wound should be better dressed open. During APR, the laceration of the rectum is more frequent when two surgical teams are operating at the same time; for this reason Keigh-ley  recommends performing the abdominal part of the operation first, and then, while the assistant completes the colostomy, the same surgeon carries out the perineal dissection. The control of haemorrhage is essential as a careful haemostasis prevents the formation of a pelvic haematoma and subsequent infections. Blood pressure needs to be checked throughout the procedure as bleeding or oozing can be difficult to detect if the patient's blood pressure is too low. The obliteration of the pelvic dead space may be useful in preventing later infection. For this reason, an intersphincteric dissection should be considered whenever possible, and the pelvic peritoneum should not be sutured in order to allow the descent of the bowel loops into the pelvis. A suction drainage is useful for preventing the collection of blood and the formation of an haematoma, thus reducing the risk of infection. The drainage is best delivered through the abdominal wall . Primary closure is certainly a choice, provided that pelvic contamination has not occurred and suction drainage has been put in place. Packing should be reserved for those patients in whom contamination has occurred or when intraoperative haemostasis has not been satisfactorily accomplished. According to Jalen et al. , an unhealed perineal wound was present at 6 months after operation in 40% of patients with primary closure and in 60% of patients with perineal packing.
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