The prevalence of renal trauma is ranged 0.3%-3.25% according to literature. Most of them are caused by blunt trauma, the others are occurred with penetrating factors. The common renal trauma classification is the American Association for the Surgery of Trauma (AAST) classification that is classified grade 1–5 (13). Currently, except the hemodynamically unstable grade 4–5 renal trauma, renal injuries are followed up with conservative approach. If some vital changes occur during this time, it can be treated with surgical interventions.
Partial/total nephrectomy or nephrorrhaphy can be preferred according to the type or degree of injury. Usually transperitoneal surgical approach is more preferable because of this route provides some advantages such as the early control of large veins and arteries. Surgery of the renal trauma contains control of the bleeding by sutures, watertight closure of the collecting system and closure of parenchymal injuries. Even preserving kidney capacity in thirty percent can provide adequate kidney function. The renal capsule should be preserved at all possible cases for successfully repairing (14). Sometimes, if renal capsule is not available, a pedicle flap of omentum, free peritoneal grafts or free fat grafts or polyglycolic acid meshes can be used for coverage of large defect. In the technique, omentum is closed to the injured tissue, with superficially with monofilament absorbable sutures (15–17).
The omentum has long been known to have the capacity to migrate to injured organs and facilitate their healing of injuries such as bones, spinal cords, heart, liver, pancreas. Many studies have shown that a reduction in total nephron capacity may cause kidney failure in the future, thus maximum protection of kidney tissue should be the main purpose. Some suture material and surgical techniques can be harmful to kidney tissue. For this reason, alternative techniques have been developed to better protect the kidney tissue especially in the large tissue lose. One of them is using of the omentum or fatty tissue for repairing of renal injury. As we well known, mesenchymal stem cells (MSCs) can be obtained from adipose tissue, peripheral blood or bone marrow. Another alternative source is omentum for repairing of injured tissue. It is a very vascular structure and suitable for use as its healing capacity contains a large number of growth and angiogenic factors and progenitor cells for regeneration (18). MSCs were first isolated from adipose tissue in 2001 by Zuk et al (19). As we know, MSCs features are ability of multipotency, self-renewing, proliferation, regeneration, and differentiation (20).
MSCs can able to accelerate tissue repair by direct migration to the injured sites (21, 22). MSCs may be administered by local or systemic for treatment. It is widely agreed that transplanted MSCs can directly reconstruct impaired organs. They have some specific features as endocrine (growth factors, chemokines, cytokines with paracrine and autocrine activities), immunomodulatory (T-cells, Dendritic cells, Natural Killer cells), anti-inflammatory effects (23). These factors suppress the local immune system, inhibit fibrosis and apoptosis, enhance angiogenesis, stimulate proliferation and differentiation. Firstly, Iwai et al. discovered that local injection of adipose derived MSCs was prone to attenuation of fibrosis (24).
Normal wound healing process includes endothelial injury, myofibroblast activation, macrophage migration, inflammatory signal stimulation, immune activation, matrix deposition and remodeling. Especially in the first 24–28 hours, many molecular reactions occur in the tissue. Fibroblasts are very crucial members at the inflammation process. Moreover, functional microcirculatory bed has been shown of critical importance in the prevention of epithelial loss and fibrosis (25). Fibrosis is one of the most common and refractory pathological processes. Fibrosis is a redundant accumulation of extracellular matrix (ECM) in tissue by the collagen reaction and end of the recovery a thick fibrotic neocapsule can occur. On the other hand, MSCs can directly release HGF and BMP-7, which are important inhibitors of fibrosis. MSCs have been shown to exert anti-fibrotic effects in animal models by matrix metalloproteinase (26). Autologous MSCs are immune compatible unlike synthetic mash and this is an advantage at the remodeling process.
In our research, time dependently, all histopathological scores were decreased in primary kidney repair group and healing in tissue has improved significantly.
Our results showed granulation and inflammation in kidney specimen on kidney repair with omentum groups were lesser than kidney primary repair groups. According to our data, histopathological analysis of degree of inflammation in renal tissue revealed a significant difference between primary kidney repair and First Kidney Repair day 7 and First Kidney Omentum Repair day 7 (p = 0.002), Second Kidney Repair day 18 and Second Kidney Omentum Repair day 18 (p = 0.004). (healing in renal tissue, First Kidney Repair day 7 vs First Kidney Omentum Repair day 7 (p = 0.015)). On the other hand, histopathological analysis of degree of granulation in renal tissue revealed a significant difference between First Kidney Repair day 7 and First Kidney Omentum Repair day 7 (p = 0.002), Second Kidney Repair day 18 and Second Kidney Omentum Repair day 18 (p = 0.015)
In many studies, the histological damage of the kidneys has been evaluated on the tissue with the EGTI scoring system (27). The scoring system consists of histological damage in 4 individual components – Endothelial, Glomerular, Tubular, Interstitial (EGTI Scoring system)– and is scored from 0 to 4. This scoring is performed in renal cortex, especially for glomerular unit. Therefore, we preferred to use a new scoring system for histopathological evaluation, so that it was able to evaluate different components of the regeneration on whole kidney tissue.
Our results showed, there were significant differences among Urea concentration comparison inside groups (p = 0.046, p = 0.026, p = 0.028, p = 0.027) or Creatinine concentration comparison inside groups (p = 0.028, p = 0.042, p = 0.046). Additionally, our results showed there were significant differences among primary kidney repair groups depend on time (on 1st, 7th ,18th day). On the other hand, there were not any significant differences among kidney repair by omentum groups depend on time (on 1st, 7th ,18th day). However, we could not show any significant correlation between biochemical values (U, Cr) and histopathological findings. It can be explained by the fact that we could not produce sufficient nephron damage with our trauma model. In the future, this model should be planned to be repeated with major kidney tissue damage. Contrary to our results, Garcia-Gomez et al reported omentum was effective in treatment of kidney injuries, as was alternative source of adult stem cells. In the context of the use of omentum, progression to CKD (Chronic Kidney Disease) could be reduced in this rat model (11). But in this research kidney injuries were large capacity as like 5/6 subtotal nephrectomy.
According to the our results, granulation and inflammation in kidney specimens were moderately and highly positive correlated with granulation, inflammation, fibrosis and foreign body reaction in surrounding tissue ((r:0.478, p = 0.008), (r:0.591, p = 0.001), (r:0.394, p = 0.031), (r:0.635, p < 0.001)). Healing process completion in kidney was moderately negative correlated with granulation and foreign body reaction in the surrounding tissue ((r:-0.625, p = 0.001), (r:-0.425, p = 0.039)).
As expected, inflammation in surrounding tissue was moderately and highly positive correlated with granulation, fibrosis and foreign body reaction in surrounding tissue ((r:0.490, p = 0.006), (r:0.397, p = 0.030), (r:0.431, p = 0.017)). Moreover, fibrosis in surrounding tissue was moderately and highly positive correlated with inflammation and foreign body reaction ((r:0.397, p = 0.030), (r:0.708, p < 0.001)).
Granulation in kidney specimen was highly possitive correlated with inflammation and foreign body reaction in kidney specimens ((r:0.824, p < 0.001), (r:0.872, p < 0.001)). But it was highly negative correlated with Healing process completion in kidney (r:-0.627, p = 0.001). Moreover, inflammation in kidney specimen was moderately and highly positive correlated with granulation and foreign body reaction in kidney specimens, contrary to negative correlated with Healing process completion in kidney ((r:0.731, p = 0.001), (r:-0.608, p = 0.002)).
Finally, we can suggest that renal and perirenal tissues are healed together due to granulation, inflammation, foreign body reaction and fibrosis. Renal insufficiency could be developed according to loss of nephron capacity.