Retroperitoneal: Retroperitoneal Structures, Kidneys, Ureter, Sarcoma, Signs and Symptoms

The region does not have a definitive edge, but most organs are positioned in this compartment.

The retroperitoneal space (retroperitoneum) is located behind the parietal wall of the peritoneum, therefore, in general terms, the organs that lie between the parietal peritoneum and the abdominal wall and have peritoneum on its anterior surface are classified as retroperitoneal.

Retroperitoneal structures

The mainly retroperitoneal structures were retroperitoneal throughout the course of their development:

Urogenital:

  • Kidney glands.
  • Kidneys
  • Ureter.

Vascular system:

  • Aorta.
  • Aena cava inferior.
  • Digestive system.
  • Esophagus (thoracic part, inner part of the abdominal cavity is intraperitoneal).
  • Straight (only middle third, upper third is intraperitoneal, lower third is extraperitoneal).

Secondarily the retroperitoneal structures were initially suspended in the mesentery and later migrated behind the peritoneum at the time of its development.

These structures include:

The head, neck and body of the pancreas , except the tail, the duodenum, except for the first proximal segment, which is intraperitoneal, ascending and descending portions of the colon (but not the transverse colon, the sigmoid or the caecum).

Kidneys

General description

The kidneys are paired organs, each kidney measuring about 4 or 5 inches and is located in the retroperitoneal compartment of the posterior abdominal cavity. There is a kidney on each side that points towards the spine at the top.

The blood supply to the kidneys is ensured by the paired renal arteries, while the blood is drained through the renal veins.

Each kidney excretes urine in an ureter that empties into the bladder. The right kidney is usually smaller and is located lower and slightly closer to the midline as a result of the mass effect of the liver. It is located below the diaphragm and posterior to the liver.

The left kidney is placed at the level of the vertebrae T12 to L3 located below the diaphragm and posterior to the spleen. The ribs 11 and 12 protect the upper parts of the kidneys.

There are two layers of fatty tissue that cover the kidneys. The most superficial layer called perirenal fat is found between the renal fascia and the renal capsule and the deeper fatty tissue layer that is also known as paranephritic fat is found superior to the renal fascia.

Usually, a kidney contains a million nephrons, which filter the blood. The kidneys filter the entire volume of blood several times a day.

Macroscopic anatomy

The kidneys are bean-shaped organs that have a concave and convex edge. The concave border is called the hilum, where the renal artery enters and the renal vein and ureter exit the kidneys. The kidney is surrounded from the inside out by:

  • Renal capsule a resistant fibrous tissue.
  • Perirenal fat (adipose capsule).
  • Fascia renal.
  • Pararenal fat (paranephric body).

The frontal surface is covered by the peritoneum, while the transverse fascia covers the dorsal surface. In men, the kidney weighs 125-170 grams and 115-155 grams in women.

The renal parenchyma is divided into two main structures:

  • External renal cortex.
  • Internal renal medulla.
  • The renal lobe is a functional unit composed of renal pyramids and overlying cortex. The renal medulla is composed of 8-18 cone-shaped renal pyramids (Malpighi) divided by renal columns, which are perpendicular projections of the cortex (Bertin).

Urine produces nephrons that go from the cortex to the marrow. The initial filtration portion is located in the renal corpuscle in the cortex followed by the renal tubule, which goes deep into the medullary pyramids.

The tip of each pyramid is called papilla, which drains the urine in a smaller later in the main chalices and, finally, in the renal pelvis.

The ureter originates in the renal pelvis, this and the renal vein leave the renal artery and enter the kidney in the hilum. The hilum contains fat and lymphatic tissue with lymph nodes. The hilar fat continues to fill the renal sinus as well.

Ureter

General description

The ureters are usually paired with tubular structures 25-30 cm long and 3-4 mm in diameter made of smooth muscle fibers. Its main function is to push urine from the kidneys to the urinary bladder with peristalsis.

The ureters arise from the renal pelvis and descend on the surface of the greater psoas muscle towards the junction of the pelvis in front of the common iliac arteries.

They extend along the sides of the pelvis, curve forward and finally enter the back of the bladder on both sides. The junction between the renal pelvis and the ureters is called the pelvoureteral junction while the junction between the ureter and the bladder is referred to as the vesicoureteric junction.

The ureters enter the bladder through the ureterovesical valves, which prevents the reverse flow of urine. In women, the ureters travel the mesometrium below the uterine arteries.

Blood supply

The ureters receive a segmental arterial supply, which varies throughout their course. The upper part is supplied by the renal arteries.

The middle part is provided by:

  • Common iliac arteries.
  • Direct branches of the abdominal aorta.
  • Gonadal arteries (the testicular artery in men or the ovarian artery in women).

The lower part is provided by:

  • Branches of the internal iliac arteries.
  • Superior bladder artery.
  • Lower bladder artery (in men).
  • Medial rectal artery.
  • Uterine artery (in women).
  • Vaginal arteries (in women).

The periureteral adventitia receives an abundant blood supply through abundant anastomoses that allow surgical mobilization as long as the adventitia is preserved. Lymphatic and venous drainage is usually done in parallel with the arterial supply.

Innervación

The primary sensory fibers to the ureters come from the spinal nerves T12 – L2. This dermatomal arrangement can result in pain radiating to the back and sides of the abdominal wall, the scrotum in men and the labia majora in women and sometimes the upper ventral surface of the thigh.

Histology

The ureter is surrounded by a type of transitional epithelium called the urothelium, which appears as a cylindrical epithelium when relaxed, and squamous epithelium when it is distended. Lamina propria, found below, consists of loose connective tissue with many elastic fibers interspersed with blood vessels, veins and lymphatics.

There are two muscle layers, an internal longitudinal and an outer layer of circular or spiral muscle to provide

  • Reristalsis.
  • Lumbar arteries (segmental).

There are four lumbar arteries, which arise from the posterior part of the aorta at the lumbar level and run parallel to the intercostal arteries.

A fifth pair is small and usually arises from the middle sacral artery. They move laterally and backward over the bodies of the lumbar vertebrae, behind the sympathetic trunk between the adjacent transverse processes and continue towards the abdominal wall.

The arteries on the right side pass behind the inferior vena cava, and the two superior arteries on each side run behind the corresponding pillar of the diaphragm. The arteries on both sides pass under the tendinous arches that give rise to the greater psoas, and then continue behind this muscle and the lumbar plexus.

They cross the lumbar quadrate, the three superior arteries run behind, the last one generally facing the muscle.

On the lateral border of the lumbar quadrate, they perforate the posterior aponeurosis of the transversus abdominis and move between this muscle and the internal oblique. They anastomose with the inferior intercostal, the subcostal, the iliolumbar, the deep iliac circumflex and the inferior epigastric arteries.

Sarcoma retroperitoneal

Sarcoma is a rare cancer that develops in the connective tissues: muscles, bones, nerves, cartilages, tendons, blood vessels and fatty and fibrous tissues.

Retroperitoneal sarcomas occur in the retroperitoneum. This is an area behind the peritoneum, the lining of the abdominal space that covers the abdominal organs.

The retroperitoneum is located inside the abdomen and pelvis, behind the abdominal lining, where organs such as the main blood vessels, the kidneys, the pancreas and the bladder are found.

The main types of sarcoma that occur in the retroperitoneum are:

  • Liposarcoma: cancer of the fatty tissues.
  • Leiomyosarcoma: involuntary muscle cancer.
  • Other less common types in the retroperitoneum include solitary fibrous tumor, pleomorphic sarcoma.
  • Sarcoma de Ewing.
  • Leiomiosarcoma.
  • Liposarcoma.
  • Malignant tumor of the peripheral nerve sheath (MPNST).
  • Sarcoma sinovial.

Signs and symptoms

The symptoms of retroperitoneal sarcoma may vary depending on the size and location of your tumor. They can include:

  • A noticeable bulge in the abdomen.
  • Increase in abdominal circumference.
  • Deaf pain in the abdomen or back.
  • Severe abdominal pain with bleeding.
  • Other rare symptoms include early satiety (that is, feeling full after eating a small amount of food), weight loss, hernia or anemia .

Types of diagnostic scans

The diagnosis of retroperitoneal sarcoma can begin with a visit to your GP that will refer you to a specialist doctor. Some retroperitoneal sarcomas are discovered through research for another medical condition or diagnosed after surgery because of a different problem.

A specialist doctor will diagnose sarcoma through a series of tests. These may include:

  • Physical examination: observe and feel any lump.
  • An exploration: taking pictures of the inside of the body with ultrasound, x-rays, CT, EUS, PET or magnetic resonance.
  • A biopsy: take and analyze a sample of tissue.