Morphology of the peritoneal cavity and pathophysiological consequences

The peritoneal cavity (cavum peritonei) is incompletely divided into spaces and recessus (or fossae), which are playing an important role in health and disease. Peritoneal subspaces are determined by the parietal attachments of the abdominal organs, the ligaments and mesenteries. These include the splenorenal, the falciform, the triangular, the gastrosplenic, the phrenicocolic and the gastrocolic ligaments; the greater omentum and the lesser omentum (formed by the gastrohepatic and hepatoduodenal ligaments); the small bowel mesenterium and the mesocolon. These ligaments and mesenteries divide the peritoneal cavity into several distinct anatomic and functional regions. The supramesocolic compartment is divided into a bilateral subphrenic space and a subhepatic space continuing into the lesser sac (bursa omentalis). The inframesolic compartment is divided into a left and right region by the mesentery. The right paracolic gutter communicates with the pelvis and with the right suphrenic space. The left paracolic gutter is separated from the left subphrenic space by the phrenocolic ligament. The peritoneal space is virtual, is completely occupied by the intraabdominal organs and can only be visualized by radiological means in the presence of air (organ perforation), liquid (ascites, pus, bile, gastrointestinal fluids) or tumor invasion. Peritoneal morphology has numerous pathophysiological implications: it impacts on the propagation of intraabdominal infections, determines the spreading of peritoneal metastasis and can cause bowel volvulus. Internal hernias can arise at the junction between intraperitoneal and extraperitoneal bowel segments, in particular into the left paraduodenal recessus. Knowledge of peritoneal morphology is a precondition for developing locoregional therapeutic strategies in peritoneal disease and for effective peritoneal dialysis.

Peritoneal Morphology after Long-Term Peritoneal Dialysis with Biocompatible Fluid: Recent Clinical Practice in Japan

♦BackgroundMorphology changes of the peritoneal membrane after long-term peritoneal dialysis (PD) consist of denudation of peritoneal mesothelial cells, interstitial sclerosis, and hyalinizing vasculopathy. Those changes are considered to be the result of uremia and bioincompatible effects of conventional acidic lactate-buffered dialysate with glucose degradation products (GDPs). In the last decade, biocompatible dialysate with neutral pH and low GDPs has become widely used. Clinical practice has been modified in Japan, especially for anuric patients, and now includes the use of hybrid therapy. The impact on peritoneal morphology has not been well reported.♦ ObjectiveThe aim of the present study was to investigate the long-term effect on peritoneal morphology and function of biocompatible fluid use and current clinical practice in Japan, including hybrid dialysis therapy.♦MethodsWe evaluated peritoneal biopsy specimens from patients who had undergone PD for more than 3 years. We used the average peritoneal thickness (APT) of the submesothelial compact zone as a marker of interstitial sclerosis and the lumen/vessel diameter ratio (L/V ratio) at postcapillary venules as a marker of hyalinizing vasculopathy. Demography and other data for the patients, including dialysate-to-plasma (D/P) ratio of creatinine, were obtained at baseline and every 6 months by peritoneal equilibration test.♦ResultsBetween 2002 and 2009, 110 patients started PD therapy with biocompatible dialysate at Tokyo University Hospital. Among them, 11 patients (8 men, 3 women; age: 54.2 ± 11.8 years; 1 with diabetes mellitus) were enrolled into this morphology study. The mean duration of PD in this group was 61 ± 11.3 months, and the mean time to peritoneal biopsy was 58 ± 15.1 months. The median APT was 180 μm (96 – 1424 μm), and the median L/V ratio was 0.66 (0.46 – 0.74). No obvious correlations between APT, L/V ratio, and PD duration were detected. The D/P creatinine of the 11 patients was maintained at a favorably low value, comparable with that of the other 99 patients.♦ConclusionsPeritoneal dialysis therapy using biocompatible dialysate in conjunction with modification of clinical practice may minimize the progression of peritoneal interstitial sclerosis and hyalinizing vasculopathy, preserving favorable peritoneal function for more than 3 years.

Catheter Patency and Peritoneal Morphology and Function in a Rat Model of Citrate-Buffered Peritoneal Dialysis

BackgroundSingle-dwell studies in rats and humans have shown that supplementing citrate for lactate in peritoneal dialysis (PD) fluids improves ultrafiltration (UF).MethodsThe long-term effects of citrate-substituted PD fluids on PD catheter patency, UF, and peritoneal morphology were evaluated in a rat model over 5 weeks of daily PD fluid exposure. A standard 2.5% glucose 40 mmol/L lactate PD fluid and a corresponding 10/30 mmol/L citrate/lactate PD fluid were compared. In a control group, rats with catheters received no PD fluid.ResultsThe average patency time (% of 36 days) of silicone rubber PD catheters was significantly longer in the citrate PD group (98.8% ± 1.2%) and the control group (100% ± 0%) compared to the lactate PD group (54.7% ± 9.5%). In a separate experiment, heparin-coated polyurethane catheters were used to study peritoneal morphology and fluid transport. The citrate group had a higher net UF than the lactate group at the beginning and at the end of the 5 weeks. During the experiment, both fluid-treated groups suffered from UF loss; the control group showed the highest net UF at the end of the 5 weeks. Peritoneal vascular density and submesothelial thickness, indicators of angiogenesis and fibrosis, were not significantly different among the groups. Fibrosis was significantly negatively correlated to osmotic UF.ConclusionA positive acute effect of citrate on UF was confirmed and conserved over time. Citrate PD strongly improved PD catheter patency time compared with lactate. Both citrate PD and lactate PD induced negative long-term effects on UF compared with control animals.

Does Immunosuppressive Treatment Ameliorate Morphology Changes in Encapsulating Peritoneal Sclerosis?

Encapsulating peritoneal sclerosis (EPS) is a clinical syndrome associated with ileus symptoms and irreversible sclerosis of the peritoneal membrane. Inflammation, fibrosis, and neoangiogenesis are the main features of the pathophysiology. No evidence-based therapy is currently available for EPS. In recent years, anti-inflammatory and immunosuppressive (IS) treatment modalities have become more popular. The aim of the present study was to investigate the effects of various IS treatment strategies—glucocorticosteroid (GC), azathiopurine (AZT), and cyclosporin (CsA)—on regression of EPS. We divided 52 nonuremic Wistar albino rats into six groups: Control group—2 mL isotonic saline injected intraperitoneally (IP) daily for 3 weeks; CG group—2 mL/200 g 0.1% chlorhexidine gluconate (CG) and 15% ethanol dissolved in saline injected IP daily for 3 weeks; Resting group—CG (weeks 1 – 3), plus peritoneal rest (weeks 4 – 6); Corticosteroid (GC) group—CG (weeks 1 – 3), plus 10 mg/L prednisolone in drinking water (weeks 4 – 6); AZT group—CG (weeks 1 – 3), plus 100 mg/L azathioprine in drinking water (weeks 4 – 6); and CsA group—CG (weeks 1 – 3), plus cyclosporin 7.5 mg/kg by subcutaneous injection daily (weeks 4 – 6). At the end of the study, under ketamine HCl anesthesia, the rats were humanely killed by bleeding. Parietal peritoneal samples were then taken from same location (away from the injection site) and changes of parietal peritoneum morphology were examined by a single pathologist. The CG severely disturbed parameters of peritoneal morphology, increasing peritoneal thickness, inflammatory activity, vascularity, and fibrosis score as compared with the Control group ( p < 0.05). No benefit was observed for any parameter in the Resting group as compared withthose parameters in the CG group ( p < 0.05). We observed a lower fibrosis score and less peritoneal thickness in the GC group as compared with the Resting group ( p < 0.05). No beneficial effects of AZT on peritoneal morphology were observed as compared with the effects of peritoneal rest or corticosteroid therapy. Treatment with cyclosporin resulted in more fibrosis, vascularity, and inflammation than was seen with corticosteroid therapy ( p < 0.05). Immunosuppressive therapies, especially those that are corticosteroid-based, may have therapeutic value in the management of EPS. Patients treated with cyclosporin may have a risk for developing EPS.

Simple Peritoneal Sclerosis and Sclerosing Peritonitis: Related or Distinct Entities?

Aim The etiopathogenesis of sclerosing peritonitis is still debated, with some sustaining that it is a rare form of progression of simple peritoneal sclerosis and others that it is a primitive form. The aim of the present research was to clarify this question. Material and Methods 438 peritoneal biopsies from 253 patients were re-examined. 174 were obtained prior to peritoneal dialysis and 224 after various periods of dialysis. Forty biopsies were from peritoneal dialysis patients who developed sclerosing peritonitis. Peritoneal morphology was studied for signs of transition from simple sclerosis to sclerosing peritonitis. Results Evidence was found sustaining the hypothesis that simple sclerosis to sclerosing peritonitis patients have distinct pathologies. Conclusions The results confirm previous observations, excluding the existence of any type of relation between simple peritoneal sclerosis to sclerosing peritonitis.

How Can We Standardize Peritoneal Thickness Measurements in Experimental Studies in Rats?

Objective The various methods of measuring peritoneal thickness in experimental studies in rats have yielded conflicting results. Also, no standard method exists to assess histologic findings in peritoneal morphology. We therefore undertook the present study to create a reproducible and standard method for assessing rat peritoneal histology in experimental studies. Methods Parietal peritoneal samples from 61 Wistar albino rats were used in the study. Excepting the skin, the whole abdominal wall from each rat was cut two-dimensionally (longitudinally and horizontally), fixed in formalin, and processed routinely for light microscopy. Slides were divided into two groups according to the direction of the inner abdominal muscle fibers in the sections. Longitudinal and horizontal sections of abdominal muscle were evaluated. For every section, one histopathology image was captured from a light microscope to an IBM-compatible computer. Peritoneal thickness (mean of the maximum and the minimum) and submesothelial area (SMA) were drawn on the image. A computer program then automatically performed measurements. Two different measurement methods were compared, based on the same sections. Results The mean peritoneal thickness was 91 ± 8 μm in the longitudinal sections and 75 ± 7 μm in the horizontal sections ( p < 0.05). Measurements of the SMA were found to be 47,762 ± 4,374 μm2 for the longitudinal sections and 40,389 ± 3,631 μm2 for the horizontal sections ( p < 0.05). In both types of sections, a positive correlation (96% for longitudinal and 90% for horizontal) was found between the SMA and the peritoneal thickness ( p < 0.01). The SMA measurements correlated significantly with functional properties [ratio of the dialysate concentration of glucose initially and after a 1-hour dwell (D1/D0 glucose), ultrafiltration, and protein loss; p < 0.01]. Conclusion Peritoneal thickness can be measured as a mean of the minimum and maximum values. That measurement strongly correlates with submesothelial area. Both types of sections can be used, but the horizontal and longitudinal sections show systematic differences. All samples in a study should be taken using the same section pattern, either longitudinal or horizontal.