Lymph nodes are small bean-shaped structures that are part of the body's immune system. The mesentery is the tissue that holds the small intestines. The retroperitoneal lymph nodes drain lymphatic fluid from the abdominopelvic gastrointestinal system as well as the skin, muscles, organs and deep tissues of the posterior abdominal wall. The main symptom for panniculitis (inflammation of subcutaneous fat), if it is acute, is painful or tender bumps called nodules that form in the layer of fat under your skin. Systemic symptoms may also be present and can include fatigue, fever, a general feeling of being unwell (malaise), joint and muscle pain, abdominal pain, nausea, vomiting, and/or weight loss.