Having to do with the area outside or behind the peritoneum (the tissue that lines the abdominal wall and covers most of the organs in the abdomen). Lymphatic vessels outside or behind the peritoeum.
Some patients have dilated (almost varicose) valveless megalymphatics which allow the reflux of lymph (often chyle) against the expected direction of flow. These dilated lymphatics often end in cutaneous vesicles which are visible in the skin or which may rupture into body cavities such as the pleura (see Section 35.9) 67, peritoneum, kidney (see Section 41.16) 68, bladder, uterus, and vagina. Rupture results in the accumulation of lymph or chyle in the relevant cavity (chylothorax, hydrothorax, chylous ascites, chyluria) and chylous discharge on to the skin surface or mucosa can also occur. Accumulation of chyle in the pleural and peritoneal cavities produces severe symptoms, and patients often become dyspnoeic and very distended. Patients with megalymphatics often also have a protein-losing enteropathy which can cause weight loss and exacerbate accumulation of fluid in the body cavities and tissues. This results from leakage of lymph from the mucosal surface of the bowel; associated lymphatic leakage from the serosal surface may exacerbate the accumulation of ascites.