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In the human abdomen, a thin membrane called the visceral peritoneum covers most organs, such as the kidneys and liver. A second membrane, called the parietal peritoneum, forms a type of bag around the organs. When a tumor or cyst grows behind the visceral peritoneum, but within the parietal peritoneum, it is called a retroperitoneal mass. In some cases, doctors are not able to determine the precise cause of a retroperitoneal mass. Most often, however, they are caused by kidney disorders, including kidney stones, polycystic kidney disease, nephrotic syndrome, and tumors.
Kidney stones can result in a condition called hydronephrosis. Patients with this condition have kidneys that don't properly pass urine to the bladder. As a result, the kidneys become swollen with urine and a peritoneal mass can result. Although kidney stones are the most common cause of hydronephrosis, the condition can also be caused by a tumor, a prostate condition or a congenital defect.
Polycystic kidney disease is a condition in which fluid-filled sacs form in and on the kidneys. Although these sacs are not cancerous, they may spread to the liver or other organs in the abdominal cavity. Peritoneal growths are often associated with these sacs.
Patients with nephrotic syndrome have an excess of urinary protein. The condition is normally due to injury or scarring of the blood vessels in one or both kidneys. If a clot forms in one of the primary veins of the kidney, the condition is called renal vein thrombosis. Renal vein thrombosis is sometimes linked to the formation of a retroperitoneal mass.
There are a number of tumors that can form on or near the retroperitoneal organs. One of the most common types of tumors that can also result in a retroperitoneal mass forms in the kidney and is called a mesoblastic nephroma. Most cases of mesoblastic nephroma are congenital, and the condition is normally discovered during first 90 days following birth.
Although a retroperitoneal mass may develop due to disease or injury to any of the retroperitoneal organs, the kidneys tend to cause the most problems. Occasionally, however, the growth may be related to diseases of the pancreas, colon or adrenal glands. Left untreated, some growths may spread to the intraperitoneal organs, such as the liver, ovaries, uterus and spleen.
Treatment for a peritoneal mass depends primarily on its cause. Sometimes, correcting the underlying disorder that has resulted in the growth is sufficient; relief may be found through medication or surgery to remove a blockage. In other cases, the peritoneal mass itself may need to be surgically removed. Rarely, a diseased kidney may need to be removed, but this is not considered a viable option if both kidneys are damaged.