Retroperitoneum

Background

Boundaries

• The retroperitoneum can be described as the entirety of the structures contained:
  • Anteriorly by the posterior reflection of the peritoneum
  • Posteriorly by the abdominal wall
  • Cranially by the diaphragm
  • Caudally by the extraperitoneal pelvic structures (bladder, rectum, vagina, uterus)
    • Extraperitoneal pelvic structures is different from extraperitoneal space; the latter includes the retroperitoneum and the space that circumferentially surrounds the abdominal cavity

Contents

Organs

• Primarily retroperitoneal (3):
  1. Kidneys
  2. Ureters
  3. Adrenal glands
• Secondarily retroperitoneal (4):
  1. 2nd and 3rd portions of the duodenum
  2. Ascending colon
  3. Descending colon
  4. Pancreas

Vessels

• Abdominal aorta (and its branches)
• Inferior vena cava (and its tributaries)
• Ascending lumbar veins
• Portal vein
• Lumbar lymph nodes
• Lumbar lymphatic trunks
• Cisterna chyli

Nerves

• Branches of the lumbosacral plexus
• Sympathetic trunk
• Autonomic plexuses
• Autonomic ganglia

Posterior abdominal wall

• Table for Musculature of the Posterior and Lateral Abdominal Wall
• Flank muscles
  • Layers:
    • Skin
    • Subcutaneous fascia
    • External oblique
      • Inferior border of the aponeurosis of the external oblique forms the inguinal ligament
    • Internal oblique
    • Transversus abdominus
      • Named because of the transverse direction of its muscle fibers
    • Transversalis fascia
      • Crosses the midline anteriorly and fuses with the lumbodorsal fascia posteriorly
      • Continuous with the endopelvic fascia
  • External oblique, internal oblique, and transversalis fascia are each invested in a layer of fascia
  • These flank muscles function to flex, extend, and rotate the trunk and provide compression of the abdominal contents.
• Psoas, Iliacus, Quadratus Lumborum, and Erector Spinae
  • Psoas major
    • Travels along the pelvic brim posterior to the inguinal ligament
  • Psoas minor
    • Functions in flexion of the thigh at the hip joint
    • Innervated by the anterior rami of L1, L2, and L3
    • May be absent in some individuals
  • Iliacus
    • Functions in flexion of the thigh at the hip joint
  • Quadratus lumborum
    • Lies posterior and medial to the psoas muscle
  • Erector spinae (sacrospinalis)
    • Large group of back muscles
  • Insert figure

• Spine
  • Consists of:
    • 7 cervical vertebrae
    • 12 thoracic vertebrae
    • 5 lumbar vertebrae
    • Sacrum
    • Coccyx
  • The spinal cord terminates in the cauda equina at spinal column level L2
    • In the adult,
      • The lumbar cord is situated between T9 and T11 vertebrae.
      • The sacral cord is situated between the T12 to L2 vertebrae
  • Spinal cord segmental levels are defined by their roots but are not always situated at the corresponding vertebral levels
    • When discussing spinal cord injury, one must be careful to specify vertebral column level versus spinal segmental level
      • For example, the C8 cord segment is situated in the C7 vertebra while the T12 cord segment is situated in the T8 vertebra.
      • In this distal end of the spinal cord (conus medullaris), the spinal cord segments are named for the vertebral body at which the nerve roots exit the spinal canal.
        • Thus, although the sacral spinal cord segment is located at vertebral segment L1, its nerve roots run in the subarachnoid space posterior to the L2 to L5 vertebral bodies until reaching the S1 vertebral body, at which point they exit the canal.
        • Therefore, all of the sacral nerves that originate at the L1 and L2 spinal column levels run posterior to the lumbar vertebral bodies until they reach their appropriate site of exit from the spinal canal. This group of nerve roots running at the distal end of the spinal cord is commonly referred to as the cauda equina.
        • Conus medullaris vs. cauda equina
          • The most distal bulbous part of the spinal cord is called the conus medullaris, and its tapering end continues as the filum terminale. Distal to this end of the spinal cord is a collection of nerve roots, which are horsetail-like in appearance and hence called the cauda equina (Latin for horse's tail)§
• 10th, 11, and 12th ribs
  • The lower ribs function to protect the retroperitoneal structures from traumatic injury. Fracture of these lower ribs should lead to a high clinical suspicion for injury to the retroperitoneal structures
  • The 11th and 12th ribs must be distinguished from the other ribs because they have no anterior connection with the sternum and are often referred to as floating ribs. These ribs are of clinical significance during palpation for the marking of a surgical incision
  • The intercostal vessels and nerves travel between the internal intercostal and innermost intercostal muscles, within the costal groove on the caudal margin of the superior rib

Lumbodorsal fascia

• Merges anterolaterally with the transversus abdominis muscle, [and posteriorly with transversalis fascia]
• Composed of 3 layers that cover the posterior abdominal wall musculature.
  • The posterior lamella originates medially from the spinous process of the lumbar vertebrae and covers the erector spinae muscles.
  • The middle lamella separates the erector spinae muscles from quadratus lumborum.
  • The anterior lamella covers the ventral surface of quadratus lumborum. Extending medially, the anterior lamella attaches to the vertebral transverse process and is continuous with the fascia that invests the psoas muscle
• The retroperitoneum can be entered without incising muscle using a dorsal lumbotomy incision. This approach uses a vertical incision through the lumbodorsal fascia lateral to the erector spinae and quadratus lumborum muscles

Retroperitoneal fasciae and spaces

• See Kidney Anatomy Chapter Notes

Gastrointestinal viscera

• The non-urologic viscera within the retroperitoneum includes the pancreas, 2nd and 3rd parts of the duodenum, and the colon

Pancreas

• Head lies anterior to the IVC and is surrounded by the 2nd portion of the duodenum.
  • This portion is at risk of injury during right kidney procedures
• The neck connects the head to the body, which crosses the abdomen anterior to the aorta to the origin of the superior mesenteric artery.
• The tail of the pancreas is closely associated with the spleen
  • This portion is at risk of injury during left kidney procedures because of its proximity to the upper pole of the left kidney and left adrenal.
  • In addition, the stomach is anterior to the upper pole of the left kidney and must be accounted for during transperitoneal left renal surgery

Duodenum

• 20-25 cm in length
• May be mobilized medially using a Kocher maneuver to expose these right-sided retroperitoneal structures
• Can be divided into 4 distinct parts:
  1. First (superior) portion
     • Intraperitoneal
     • Extends from the pylorus to the neck of the gallbladder
  2. Second (descending) portion
     • Retroperitoneal
     • Critically important to the urologist because of its proximity to the right renal hilum
     • The common bile duct and the main pancreatic duct combine to enter the 2nd portion at the ampulla of Vater (hepatopancreatic ampulla).
  3. Third (horizontal or inferior) portion
     • Retroperitoneal
     • Crosses the body from right to left and lies posterior to the SMA and anterior to the aorta
  4. Fourth (ascending) portion
     • Intraperitoneal
     • Ascends and becomes intraperitoneal as it transitions into the jejunum

Colon

• The ascending colon and hepatic flexure overlie the right-sided retroperitoneal structures, and the splenic flexure and descending colon cover the left-sided retroperitoneal structures.
• To gain access to the kidneys transperitoneally, the ipsilateral colon must be reflected medially in most instances. This can be performed by mobilizing the colon at the white line of Toldt (see above). Care must be taken to divide the hepatocolic and splenocolic ligaments sharply when necessary to avoid iatrogenic injury to the liver and spleen, which is often due to excessive retraction during attempts to obtain adequate exposure.

Arterial Vasculature

• Arterial structures have 3 layers (innermost to outermost):
  • Tunica intima (intima)
  • Tunica media (media)
  • Tunica externa (tunica adventitia or adventitia)
• Abdominal aorta
  • See CW11 Table 33-3 for Branches of the Abdominal Aorta
  • Branches from superior to inferior
    1. Inferior phrenic arteries (paired)
       • Supply inferior surface of the diaphragm
       • The superior adrenal arteries branch off the inferior phrenic arteries to supply the ipsilateral adrenal gland
    2. Celiac artery
       • Branches (3):
         1. Gastric
         2. Splenic
         3. Common hepatic
         • The splenic vessels course on the cephalad aspect of the body and tail of the pancreas
         • Right gastric arises from common hepatic arteries
       • Supplies the abdominal esophagus, stomach, duodenum, spleen, liver, and pancreas
    3. Middle adrenal (suprarenal) arteries (paired)
       • Supply the ipsilateral adrenal gland
       • [May be above or at level of SMA]
    4. Superior mesenteric artery
       • Arises anteriorly in the midline at approximately the level of the middle adrenal arteries at L1-L2
       • Supplies the pancreas, small intestine, and most of the large intestine
       • Branches (4)
         1. Inferior pancreaticoduodenal
         2. Ileocolic
         3. Right colic
         4. Middle colic
         • The middle colic artery anastomoses with the left colic artery off the inferior mesenteric artery (IMA) via the marginal artery of Drummond. This anastomosis forms an important SMA-to-IMA collateral circulation that allows for the IMA to be sacrificed without colonic ischemia. However, despite the presence of this collateral circulation, injury to the SMA during left-sided retroperitoneal surgery may lead to severe bowel ischemia.
    5. Renal arteries (paired)
       • At L1 vertebral level
       • The inferior adrenal arteries branch off the renal arteries to supply the ipsilateral adrenal gland
    6. Gonadal arteries (paired)
       • Called testicular arteries in males and ovarian arteries in females.
         • The testicular arteries typically run anterior to the psoas, IVC, genitofemoral nerve, and ipsilateral ureter as they travel toward the internal inguinal ring.
         • The ovarian arteries travel anterior to the ureter and course medially as they pass through the infundibulopelvic ligament (suspensory ligament of the ovary) to the ovary
       • There are extensive collaterals to the gonads in both sexes, allowing for ligation of the testicular and ovarian arteries without gonadal ischemia.
    7. Lumbar arteries (paired)
       • 4 paired arteries
       • Arise posteriorly, adjacent to the bodies of the upper 4 lumbar vertebrae
       • Supply the posterior body wall and spine
    8. Inferior mesenteric artery (IMA)
       • Arises from the anterior aorta
       • Supplies the colon from the splenic flexure to the upper rectum
       • Branches (3)
         1. Left colic
         2. Sigmoid
         3. Superior rectal (hemorrhoidal)
         • The sigmoid artery branches into 2-3 inferior left colic arteries.
         • The superior rectal artery has anastomoses with (2)
           1. Middle rectal artery (arises from anterior branch of internal iliac).
           2. Inferior rectal artery (arises from internal pudendal, which arises from anterior branch of internal iliac).
           • These collaterals for an important internal iliac-to-IMA that provides blood supply to the rectum and prevent ischemia during IMA ligation.
    9. Middle sacral artery
       • Arises from the posterior aspect of the aorta before bifurcation.
    10. No named branches are given off as these arteries enter the pelvis and divide to form the internal and external iliac arteries.

Venous Vasculature

• Inferior vena cava
  • Formed from the confluence of the common iliac veins, inferior and to the right of the aortic bifurcation
  • The venous system is more variable than the arterial system; however, many venous structures run parallel with their arterial equivalent.
  • Tributaries
    • Median (middle) sacral vein
      • Runs with its respective artery and typically drains into the left common iliac vein
    • Ascending lumbar veins (paired)
      • Drain the posterior abdominal wall and run posterior to the psoas muscle and lateral to the spinal column
      • Connect with the ipsilateral lumbar veins, which are variable in number and location compared with their arterial equivalents. These veins may assume a plexiform arrangement anterior to the vertebral bodies.
      • As the ascending lumbar veins enter the thorax, they become the hemiazygos vein on the left and the azygos vein on the right.
    • Gonadal veins
      • In males, the gonadal veins (testicular veins) receive drainage from the pampiniform plexus, which is the venous complex that emerges from the testes. The testicular veins ascend through the retroperitoneum medially, running lateral to the respective artery and anterior to the ipsilateral ureter.
        • The left testicular vein typically enters the inferior aspect of the left renal vein at a right angle; however, it may enter the IVC directly.
        • The right testicular vein typically enters into the right anterolateral aspect of the IVC;however, it may enter into the right renal vein in 10% of cases.
        • Clinical significance:
          • The increased length and perpendicular entry of the left testicular vein into the left renal vein may result in some element of increased back pressure and explain the higher incidence of left-sided varicoceles compared with the right side.
          • With the relative rarity of unilateral right-sided varicocele, a sudden-onset right varicocele should increase suspicion for a renal or retroperitoneal malignancy causing obstruction and poor venous outflow (e.g., right side renal cell cancer with venous thrombus). This clinical scenario should warrant retroperitoneal imaging to rule out malignancy.
      • The ovarian veins receive drainage from the pampiniform plexus adjacent to the ovarian hilum and travel through the infundibulopelvic ligament. As with the gonadal veins in males, the left ovarian vein enters the left renal vein, and the right ovarian vein empties into the anterolateral wall of the vena cava.
    • Renal veins
      • Course anteriorly to the renal arteries and empty into the lateral aspects of the vena cava at the level of L1
      • The right and left renal veins differ in length and tributaries
        • Right is shorter and typically has no tributaries
        • Left is longer and typically receives (3):
          1. The left gonadal vein at its inferior margin.
          2. At least one lumbar vein at or near the ostia of the gonadal vein.
          3. The left adrenal vein at its superior margin and in most patients inserts into the renal vein just medial to the gonadal vein.
    • Gastrointestinal venous drainage
      • Does not mirror the arterial system
      • The portal venous system receives venous blood from the bowel, spleen, pancreas, and gallbladder to be emptied into the liver
      • Splenic vein
        • Receives the venous drainage from the colon distal to the splenic flexure
        • Tributaries include the short gastric, left gastro-omental, pancreatic, and typically inferior mesenteric veins.
      • Superior mesenteric vein (SMV)
        • Receives venous drainage from the small intestine and the large intestine proximal to the splenic flexure.
        • Tributaries include the right gastro-omental, anterior and posterior inferior pancreaticoduodenal, jejunal, ileal, ileocolic, right colic, and middle colic veins.
      • The SMV combines with the splenic vein to form the hepatic portal vein
      • Insert figure
      • Portal vein
        • Splits into right and left branches, and the venous blood enters the endothelial lined hepatic sinusoids. After passing through these sinusoids, the venous blood leaves the liver through the hepatic veins
        • Hepatic veins
          • Enters the anterior aspect of the IVC before it crosses the diaphragm into the thorax
          • Two groups of hepatic veins: upper group, typically larger in caliber vs. lower group, which are typically smaller.
          • Occlusion can lead to Budd-Chiari syndrome, which is a form of progressive liver failure that often manifests rapidly with jaundice, ascites, abdominal pain, and hepatomegaly

Lymphatic system

• Lymph generally flows cephalad from right to left until it returns to the venous circulation at the left innominate (brachiocephalic) vein.
  • Lymphatic fluid from the head, neck, right thorax, right arm, and right heart drains into the right innominate vein
• The lymphatic fluid from the pelvis and lower extremities drains into the internal iliac, external iliac, common iliac, obturator, and sacral nodes. These nodal regions then drain cephalad toward the lumbar nodes
• The efferent lymphatics of the lateral lumbar nodes coalesce to form the right and left lumbar trunks. Posterior to the right side of the abdominal aorta and anterior to the L1 and L2 vertebrae, these trunks come together at a saccular dilated structure known as the cisterna chyli. This marks the beginning of the thoracic duct, which runs cephalad posterior to the aorta and empties into the left innominate vein.

Nervous system

• Divided into the autonomic nervous system and the somatic nervous system:
  • The autonomic system supplies efferent and afferent innervation to the abdominal viscera, blood vessels, and smooth muscle
  • The somatic system supplies efferent and afferent innervation to skeletal muscle, skin, and peritoneum

Autonomic nervous system

• General structure of the autonomic nervous system consists of two nerves with two cell bodies.
  • The pre-ganglionic neuron has a cell body within the central nervous system and an axon that extends into the peripheral nervous system, synapsing with another neuron within a ganglion.
  • The second neuron is referred to as a post-ganglionic neuron, and its axon enters the structure in which it provides innervation.
  • An exception to this general structure is the adrenal gland where the pre-ganglionic fibers synapse directly with the cells of the adrenal medulla resulting in release of catecholamines
• Parasympathetic nervous system
  • Pre-ganglionic fibers originate from:
    • Cranial nerves III, VII, IX, and X
      • The vagus nerve (cranial nerve X) provides preganglionic parasympathetic fibers to the thoracic, abdominal, and pelvic viscera
    • Ventral rami of the S2, S2, and S4
      • The S2-S4 preganglionic fibers form the pelvic splanchnic nerves, which provide parasympathetic innervation to the pelvic and abdominal viscera
  • Post-ganglionic parasympathetic fibers are often within the walls of the viscera
• Sympathetic nervous system
  • The pre-ganglionic fibers originate from:
    • T1 to L2 and exit through the ventral root and course through the corresponding spinal nerve and anterior rami into the ipsilateral sympathetic trunk.
      • The fibers then run medial to the psoas muscle along the anterolateral aspect of the spine. The paired sympathetic trunks are in close proximity to the lumbar arteries and veins, which cross them perpendicularly.
  • The pre-ganglionic fibers can
    1. Synapse within the ganglia of the sympathetic trunk and send forth post-ganglionic fibers to the body wall and lower extremities
    2. Leave the trunk as splanchnic nerves to synapse with ganglia from one of autonomic plexuses of the aorta (3):
       1. Celiac plexus
          • First and largest of these plexuses
          • Contains paired ganglia that lie lateral to the celiac artery.
          • Much of the autonomic innervation to the kidney, adrenal, renal pelvis, and ureter runs through this plexus.
       2. Superior hypogastric plexus
          • Originates at the caudal extent of the abdominal aorta and extends to the anterior surface of the 5th lumbar vertebra.
            • Clinical significance: extensive retroperitoneal dissection that causes disruption of these plexuses may result in loss of seminal vesicle emission or failure of bladder neck closure resulting in retrograde ejaculation.
       3. Inferior hypogastric plexus
       • Much of the sympathetic innervation to the pelvic viscera travels through the superior and inferior hypogastric plexuses, which are contiguous.
• Confusion may arise with the term splanchnic used for nerves of both the parasympathetic and the sympathetic systems. For clarification, the thoracic splanchnics (greater, lesser, and least), lumbar splanchnics, and sacral splanchnics carry sympathetic fibers from the paired sympathetic trunks to the autonomic plexuses, whereas the pelvic splanchnics carry parasympathetic fibers from the sacral outflow

Somatic nervous system

• See Table in Male Pelvis Anatomy Chapter Notes
• The somatic sensory and motor nerves of the lower abdomen and lower extremities originate in the retroperitoneum. They form the lumbosacral plexus from the anterior rami of the lumbar and sacral nerves along with T12
• The subcostal nerve (T12) runs inferior to the 12th rib.
• The sciatic nerve receives input from L4-S3 and provides the bulk of motor and sensory input to the lower extremities, including motor innervation to the posterior thigh compartment and all muscles in the leg and foot.
  • Injury to this nerve may occur secondary to prolonged hip hyperflexion used during a high lithotomy position for vaginal and urethral procedures.

References

• Wein AJ, Kavoussi LR, Partin AW, Peters CA (eds): CAMPBELL-WALSH UROLOGY, ed 11. Philadelphia, Elsevier, 2015, chap 33