Abdominal Wall Reconstruction–Diagnostic and Therapeutic Algorithm

Due to its complex structure, the abdominal wall is vital as it serves to protect the internal organs, maintain the upright position and regulate the intraabdominal pressure. Complex abdominal defects are a major health problem, with challenging treatment, many complications and risks. It is not a completely elucidated pathology as there is no consensus in literature regarding the defi nition and classifi cation. Although there are various reconstruction techniques, there is no sistematic protocol in literature that allows the surgeon to choose the best treatment suitable for each patient. Therefore, the fi rst step to manage these patients is a carefull assesment of the patient background and only after that, a complete analysis of the actual wound should be made. Second step is appropriate abdominal wall closure. After the analysis of current data from international literature, we identifi ed a decision-making algorithm to offer guidance in surgical management in order to obtain an optimal functional outcome. The foundation of the algorithm is the idea of gradually improving the local tissue status, in order to deal with a clean wound as much as possible. This way, the success rate of the surgical reconstruction improves.

wall defect the failure of prior attempt at closure 5 while A. Leppaniemi refers to the patients where simple repair of abdominal hernia is not possible due to large size of the defect 6 . Other authors consider as complex defect any abdominal defect that cannot be closed primary without tension 7 .
Although there is not a consensus on the defi nition there are some common features that are mentioned by all authors when describing a complex abdominal wall defect. Th ese include a possible concomitant infection or a visceral fi stula, multiple failed attempts of repair and lack of enough local skin to cover the defect. Th ese defects are often a result of trauma, including burn injury, radiation necrosis, local infection with multiple excisional debridement, or tumor resection 5 . Th ere are multiple tumors that can occur on the abdominal wall, but the most common one is desmoid tumor. Although the tumor is histologically benign, it is very invasive in the local tissue and has a high rate of recurrence (40%-50%) thus leading to multiple resections. Th e most common malignant tumors of the abdominal wall are sarcomas and beside aggressive resection, the treatment is also completed by radiation therapy which aff ects even more local structures 1 . Regarding that the complex abdominal wall defects are often large both in diameter and depth, they may aff ect multiple layers of the abdominal wall and result in complex neuromuscular deformities or evisceration with loss of domain.
Th e Italian Consensus Conference on "Complex abdominal wall management" held in June 2015 has divided the defi nition in two major entities, one for emergency and one for chronic patients. Th e defi nition of complex abdomen in emergency referes to the situation where there is an increased risk for occurence of compartment syndrome, early reintervention or suture dehiscence. Th ey defi ne the complex abdomen in elective surgery when there is at least one of the following situations: loss of domain grater than 20%, surgical wound class III or IV infection, non-healing wound, the presence of fi stula, recurrent hernia, previous mesh infection, full thickness wall defects, necessity of intraperitoneal mesh extraction 8 .

Classifi cation of complex abdominal wall defects INTRODUCTION
Due to its complex structure, the abdominal wall is vital as it serves to protect the internal organs, maintain the upright position and regulate the intraabdominal pressure. Th e last function mentioned allows the performance of certain actions that require the execution of Valsalva, such as defecation, urination, coughing and vomiting 1 . Some authors also suggest that the integrity of the abdominal wall is related to satiety and patients with abdominal wall defects are prone to gain weight 2 . Up to 20% of the patients that had elective median laparotomy develop an incisional hernia. Th ere are several risk factors for incisional hernia formation such as wound infection, immunosupression, extreme obesity, age, malnutrition, multiple abdominal surgery, Ehlers-Danlos syndrome or aneurysmal disease 3 . Aging of the population, increase of diabetes rate and obesity, increase of abdominal cancer survival rate and the progress of medicine and patient-centered treatment are factors that lead to the annual increase in the number of patients with complex abdominal wall defects. Considering this, we believe that a more detailed study of this pathology is important and for start there are a few goals to achieve: establish a consensual defi nition, elaborate a classifi cation and create a reconstruction algorithm.

BACKGROUND-ACTUAL STATE OF KNOWLEDGE IN COMPLEX ABDOMINAL DEFECT RECONSTRUCTION Anatomy
Th e abdominal wall has a multilayered structure that comprises the skin, subcutaneous tissue, the fascial layer, abdominal muscles (fi ve pairs of muscles), preperitoneal adipose tissue and peritoneum 4 . A good understanding of the abdominal wall structures along with its neurovascular anatomy is decisive for abdominall wall reconstruction.

Defi nition of complex abdominal wall defect
To date, there is no widley accepted defi nition of the complex abdominal wall defect. Analyzing existing literature data, we observed diff erent approaches for abdominal wall defects evaluation, infl uenced by each center experience. For example, S J Mathes et al consider as the main particularity of a complex abdominal presentation. Each of these variables can be divided in three severity classes: Minor, Moderate, Major. Th is classifi cation was created to guide the surgical management and assess the fi nancial costs of it 10 .

Goals of abdominal wall reconstruction
Th e goals to be achieved in abdominal wall reconstruction may vary depending whether the surgery is perfomed in emergency or in elective fashion. For emergency surgery, the main goal is rather to relief incarceration or strangulation of viscera 11 . For patients without such critical status, the surgeon has to obtain a strong and dynamic abdominal wall, to prevent recurrence and to achieve a satisfactory esthetic appearance. Th e ultimate sifi cation for surgeons is the "Ventral Hernia Working Group" grading sistem for risk of complications at the surgical site. Th e last modifi ed VHWG grading sistem was updated since 2012 (Figure 1   In order to minimize the SSO (surgical site occurences -dehiscence, seroma, hematoma, skin necrosis, fi stula, etc) and hernia reccurence, a careful prehabilitation must be done. In general, patients that are poor candidates for a surgical procedure should be delayed until the risk factors are assessed and the modifi able ones are optimized. Th e main risk factors for complications are obesity, infection, hernia size, smoking, chronic resipratory disease, poor wound healing, failure of previous reconstruction with mesh. Th ere are two particular risk factors that are directly related to increased rate of reccurence. Th ese are a BMI (body mass index) > than 30 kg/ m 2 and defect size > 8-10 cm. Sauerland S et al. suggest that there is a 10% increase in hernia reccurence risk with every unit of BMI 15 . Many surgeons use a BMI equal to 40kg/m 2 as a cutoff before declining elective abdominal wall reconstruction. At the opposite pole of obesity, protein malnutrition, mainly the lack of methionine and arginine, is associated with higher mortality 16 . Also, low albumine increases the risk of infection 17 . Poorly controlled diabetes is also a risk factor for SSO. Preoperatively, the level of glucose should be kept below 160 mg/ dL, otherwise the risk of infection and dehiscence is highly increased 18 . Smoking cessation should occur at least 4 weeks before and after surgery for a signifi cantly decrease of infectious risk, as it is well known that tobacco decreases tissue perfusion 19 .
Treating complex abdominal wall defects may be very challenging for the reconstructive surgeon. In case of skin loss alone, the defect can be treated with skin graft, tissue exapnders or soft-tissue fl aps. For myofas-goal of all these is to increase the quality of life 12 and for that the surgeon must always choose the best treatment option for each patient.
Th ere are many closure techniques available to the reconstructive surgeon. Choosing the surgical approach should always follow the reconstructive ladder, starting with simple approach if possible and moving to more complicated ones as previous options fail or do not seem to be suitable from the beginning 13 .
A model of the reconstructive ladder can be the following (Figure 3) 14 .

DIAGNOSTIC AND THERAPEUTIC ALGORITHM FOR EVALUATION AND TREATMENT OF PATIENTS WITH ABDOMINAL WALL DEFECTS
Considering that choosing the best option for treatment of the complex abdominal wound defects is a real challenge, as there is no protocol yet for this pathology, we identifi ed, after the analysis of current data from international literature-an algorithm that could guide the surgeon through decision making in order to obtain an optimal functional outcome ( Figure 4).

DISCUSSION
Performing an eff ective abdominal wall reconstruction requires some basic principles: Correct patient selection and optimization of risk factors, choosing the right procedure, preserve skin and subcutaneous tissue, careful postoperative management 14 . by up to 50% 21 . Sometimes it is unvoidable to leave the fascia open due to trauma, vascular emergences or compartment syndrome, and a staged repair is needed. Usually a skin graft or a vacuum therapy can be applied to temporize the fi nal repair 6 . Also, temporary abdominal closure with mesh and vacuum assisted therapy has been described 22 .
If there is a partial myofascial loss, a single rectus abdominis muscle is enough to reconstruct the abdominal wall, but if both muscles are absent a functional cial defects, all eforts must be done to primary close the fascia, after propper excision of non-viable tissue. Th is is mandatory in order to achieve a stable abdominal wall, that is able to resist strain and stress. If primary fascial closure is not possible, component separation should be performed 20 . For fascial defects larger than 16 cm, bilateral component separation is required, often with a mesh reinforcement. Some surgeons constantly use mesh reinforcement even when primary fascial closure is possible as it is proven to lower the recurrence rate When the defect is complicated by an enterocutaneous fi stula, the fi rst step is to treat the infectious source and prevent sepsis 26 . Th is often requires an intestinal repair, gastro-intestinal diversion and formation of an ostomy, with the disadvantage that the site of ostomy may interfere with potential options of local soft tissue fl aps. Unfortunately, this a procedure indicated in order to convert a complicated wound to contaminated and further to clean wound for a future abdominal closure 23 .

CONCLUSIONS
Complex abdominal defects are a major health problem and treating is really challenging with many pifalls and risks. It is not a completely elucidated pathology as there is nor consensus in literature regarding the defi nition and classifi cation, neither an approved protocol of treatment. Th e method of abdominal wall reconstruction needs to be individually tailored and that is why we consider that the algorithm proposed can be useful for planning and decision making, in order to achieve an optimal functional outcome.
Compliance with ethics requirements: Th e authors declare no confl ict of interest regarding this article. Th e authors declare that all the procedures and experiments of this study respect the ethical standards in the Helsinki Declaration of 1975, as revised in 2008(5), as well as the national law. Informed consent was obtained from all the patients included in the study. reconstruction has to be done with soft tissue fl aps. For the upper two thirds of the abdomen, local fl ap options include the latissimus dorsi, internal oblique, external oblique, rectus abdominis, inferior epigastric perforator, and superior epigastric perforator fl aps. Reconstruction of the lower two thirds of the abdomen with local fl aps can be achieved with tensor fascie latae (TFL), rectus abdominis, vastus lateralis fl aps, antero-lateral thigh (ALT) and gracillis fl aps. Free tissue transfer is preferred when the motor function of the abdominal wall is severly altered. Th e best situation to use a free fl ap is when there is a full-thickness defect that comprises the upper third of the abdomen 6 . Th e best fl aps suitable for microvascular reconstruction are ALT, TFL and rectus femoris fl aps 23 .
It is often possible that due to severe traumatic injury, or wide tumoral resection, patients with complex defects of the abdominal wall also need a visceral transplantation. Th ese are the ideal candidates for vascularized composite allotransplant of the abdominal wall. For now, this is also an ultimate solution when conventional treatment techniques are exhausted 24 . Th is technique provides immediate coverage of viscera. Levi et al described reconstructing the abdominal wall with partial abdominal wall transplants and fi ve out of eight patients had a functioning and viable abdominal wall at a 23 months follow-up 25 . When abdominal wall transplantation is combined with organ transplantation it is possible that the morbidity rate is the lowest on long term follow-up, due to the fact that additional immunosuppression is not needed.