Abdominal cavity

The abdominal cavity is located between the thoracic cavity and pelvic cavity. It is lined by the parietal and visceral peritoneum, and the space between these two layers forms the peritoneal cavity. The peritoneal cavity develops from the intraembryonic coelom, which arises within the lateral plate mesoderm. The abdominal organs (e.g., spleen, kidneys) and structures of the gastrointestinal tract are covered by the peritoneum. The visceral peritoneum folds upon itself to form peritoneal folds, which suspend organs and divide the peritoneal cavity into various compartments (e.g., the greater sac, lesser sac, and subphrenic space). Organs that are completely covered by the visceral peritoneum are referred to as intraperitoneal organs and those that are only partially covered are called retroperitoneal organs. The retroperitoneal space lies between the peritoneal cavity and the posterior abdominal wall. It contains the following structures: abdominal aorta, inferior vena cava, portal vein, abdominal prevertebral plexus, lymph node clusters, lymphatic trunks, and cisterna chyli.

• Location: between the thoracic cavity and the pelvic cavity
• Boundaries
  • Superior: diaphragm
  • Ventral and lateral: muscles of the anterior abdominal wall
  • Posterior: muscles of the posterior abdominal wall
  • Inferior: pelvic inlet
• Divisions
  • Intraperitoneal space: space within the abdominal cavity completely lined by the peritoneum
  • Retroperitoneal space: space within the abdominal cavity located between the peritoneal cavity and posterior abdominal wall
• Contents
  • Organs
    • Gastrointestinal tract
    • Liver
    • Gallbladder
    • Pancreas
    • Spleen
    • Kidneys and ureters
    • Adrenal glands
  • Arteries: abdominal aorta and its branches
  • Veins
    • Inferior vena cava and its tributaries
    • Portal vein and its tributaries
  • Nerves
    • Sympathetic nervous system
    • Parasympathetic nervous system
    • Enteric nervous system
    • Abdominal prevertebral plexus
  • Lymphatics
    • Lymph node clusters of the abdominal cavity
    • Intestinal lymphatic trunk
    • Lumbar lymphatic trunks
    • Cisterna chyli

Overview of peritoneum

Peritoneum is a serous mesothelial membrane that lines the abdominopelvic cavity and encloses most intraabdominal and pelvic organs. It consists of two layers, the parietal peritoneum and visceral peritoneum.

Parietal peritoneum

• Definition: the layer of peritoneum that lines the abdominopelvic cavity
• Nerve supply
  • Receives somatic innervation corresponding to the region of the abdominal wall that it lines ^[1]
  • Supplied by the phrenic nerves, lower intercostal nerves, subcostal nerves, ilioinguinal nerves, and iliohypogastric nerves

Visceral peritoneum

• Definition: the layer of peritoneum that covers the intraperitoneal organs as serosa and also forms the mesentery, omentum, and peritoneal ligaments
• Nerve supply: receives visceral innervation corresponding to the organs it covers ^[1]

Omentum

Omentum is a double layer of visceral peritoneum arising from the stomach and proximal part of duodenum to various abdominal organs.

• Greater omentum
  • Attachments
    • Arises from the greater curvature of the stomach and proximal part of the duodenum
    • Folds back on itself, allowing it to lie anterior to the intestines (four layered)
    • Attaches to the posterior abdominal wall after fusing with the peritoneum of the transverse colon
  • Functions
    • Contains macrophages and lymphoid tissue that regulate peritoneal inflammation and immunity ^[2]
    • Limits the spread of infection (e.g., acute appendicitis)
• Lesser omentum
  • Attachments: extends from the lesser curvature of the stomach and proximal part of the duodenum to the liver
  • Functions
    • Forms the anterior wall of the lesser sac
    • Free edge (hepatoduodenal ligament) contains the portal triad.

Peritoneal ligament

Definition: a collection of folds of visceral peritoneum connecting certain gastrointestinal organs to one another and/or to the abdominal wall

Mesentery

Definition: : a contiguous double-layered fold that anchors bowel to the posterior abdominal wall and allows for passage of neurovascular structures.

Parietal peritoneum of the lower anterior abdominal wall

• Peritoneal folds are described in relation to the umbilicus.
  • Median umbilical fold
    • Single midline peritoneal fold formed by the median umbilical ligament, which is the obliterated urachus
    • Runs between the umbilicus and apex of the bladder
  • Medial umbilical folds
    • Pair of peritoneal folds formed by the medial umbilical ligaments, which are the obliterated umbilical arteries
    • Lie on either side of the median umbilical fold
  • Lateral umbilical folds
    • Pair of peritoneal folds formed by the underlying inferior epigastric artery and vein
    • Lie on either side of the medial umbilical folds
• Fossae: depressions created by the umbilical folds ^[1][9]
  • Supravesical fossa
    • Lies between median and medial umbilical folds
    • Its level rises and falls according to filling and emptying of the bladder.
  • Medial inguinal fossa (Hesselbach triangle)
    • Lies medial to lateral umbilical fold
    • Common site for direct inguinal hernia
  • Lateral inguinal fossa
    • Lies lateral to lateral umbilical fold
    • Common site for indirect inguinal hernia

Peritoneum of the pelvis

See “Ligaments of the female pelvis” and “Pelvic spaces.”

Function

• Compartmentalization of the abdominal cavity to give rise to distinct recesses (e.g., subphrenic recess)
• Allows for free movement of organs in relation to each other
• Provides ligament support to organs (e.g., stomach, liver, spleen)
• Absorption of peritoneal fluid ^[9]

Peritoneal cavity

• Definition: the potential space between the parietal and visceral layers of peritoneum in the abdomen and pelvis
• Anatomy
  • In males, the peritoneal cavity is a closed sac.
  • In females, the lateral ends of the fallopian tube are not covered by peritoneum, making it an open cavity.
• Content: peritoneal fluid containing water, electrolytes, and proteins
• Clinical significance
  • Abdominal paracentesis: removal of excess fluid in the peritoneal cavity in patients with ascites
  • Culdocentesis: extraction of fluid (e.g., blood, pus) from the peritoneal cavity through an incision in the rectouterine pouch
  • Hysterosalpingography: Injection of radioopaque dye into the uterine cavity with spillage into the peritoneal cavity indicates that the fallopian tubes are patent.
  • Peritoneal dialysis: Dialysate placed into the peritoneal cavity allows for exchange of waste products through the semipermeable peritoneal membrane.
  • Ventriculoperitoneal shunt: Excess CSF from the ventricles is shunted to the peritoneal cavity for absorption.

Peritoneal spaces

• Definition: group of potential spaces between adjacent organs or between an organ and the abdominal wall in which intraperitoneal fluid can accumulate

Disease can rapidly spread through the peritoneal cavity, e.g., in metastatic ovarian cancer or peritonitis. Paracentesis and analysis of peritoneal fluid can help to diagnose diseases affecting the peritoneal cavity.

Fluid from the abdominal cavity can also collect in the pelvic spaces, e.g., the pouch of Douglas. (See “Pelvic spaces.”)

Bowel perforation can lead to pneumoperitoneum. Since gas is not normally present in the peritoneal cavity, this can be detected with an abdominal x-ray.

Peritoneal folds

• Superior duodenal fold ^[12]
  • Fold of peritoneum with a free lower edge closely related to the fourth part of the duodenum
  • Surrounds the superior duodenal recess and overlies the inferior mesenteric vein
  • Used as a reference point in abdominal surgery to mark the end of the duodenum and the beginning of the jejunum
• Inferior duodenal fold ^[13]
  • Fold of peritoneum with a free upper edge closely related to the fourth part of the duodenum
  • Surrounds the inferior duodenal recess
• Gastropancreatic fold ^[9]
  • Fold of peritoneum that runs between the lesser curvature of the stomach and the neck of the pancreas
  • Divides the lesser sac into superior and inferior recess
  • The upper part of the fold overlies the left gastric artery and the lower part overlies the common hepatic artery.

Definition

• An anatomical space in the abdominal cavity that is located between the parietal peritoneum and the transversalis fascia of the posterior abdominal wall

Boundaries

• Superior: diaphragm
• Anterior: parietal peritoneum of posterior abdominal wall
• Posterior: posterior abdominal wall muscles (e.g., quadratus lumborum)
• Lateral: fuses with the extraperitoneal connective tissue of the anterolateral abdominal wall
• Inferior: pelvis

Content

• Paired viscera
  • Kidney and ureters
  • Adrenal gland
• Unpaired viscera
  • Duodenum (except for the first part)
  • Pancreas
  • Ascending colon
  • Descending colon
• Other structures
  • Abdominal aorta
  • Inferior vena cava
  • Origin of the azygos and hemiazygos vein
  • Preaortic lymph nodes and paraaortic lymph nodes
  • Cisterna chyli and origin of thoracic duct
  • Diaphragmatic crura
  • Lumbar plexus
  • Lumbosacral trunk
  • Autonomic plexus of the abdomen
  • Paraaortic bodies (organ of Zuckerkandl)
    • Mass of chromaffin tissue derived from the neural crest that is closely related to the abdominal prevertebral plexus
    • Site of extraadrenal pheochromocytoma (on rare occasions)

Clinical significance

• Retroperitoneal hematoma
• Retroperitoneal fibrosis

SAD PUCKER for the retroperitoneal and secondary retroperitoneal organs: Suprarenal (adrenal) glands, Aorta/IVC, Duodenum (except for the first part), Pancreas (except for the tail), Ureters, Colon (ascending and descending parts), Kidneys, Esophagus, Rectum.

Development of peritoneal cavity ^[9]

Peritoneum and related structures develop from the lateral plate mesoderm. See “Embryology of the gastrointestinal tract”, “Development of the reproductive system”, and “Kidney embryology” to know more about the development of specific organs of the abdominal cavity.

• Appearance of lateral plate mesoderm: : In the third week of development, the mesoderm divides into paraxial, intermediate, and lateral plate mesoderm on either side of the notochord.
• Formation of intraembryonic coelom
  • Small cavities develop within the lateral plate mesoderm.
  • Cavities coalesce to form a large horse-shoe shaped intraembryonic coelom with midline and lateral portions.
• Splitting of lateral plate mesoderm: The intraembryonic coelom divides the lateral plate mesoderm into two layers.
  • Somatopleuric coelomic epithelium: adjacent to the ectoderm and forms the parietal layer of pericardial, pleural, and peritoneal cavities
  • Splanchnopleuric coelomic epithelium: adjacent to the endoderm and forms the visceral layer of pericardial, pleural, and peritoneal cavities
• Formation of body cavities
  • The intraembryonic coelom gives rise to the pericardial, pleural, and peritoneal cavities.
  • The midline portion of intraembryonic coelom surrounding the heart forms the pericardial cavity.
  • As the headfold develops, the pericardial cavity and the lateral portions of intraembryonic coelom communicate to form the right and left pericardioperitoneal canals.
  • Lung buds arising from the respiratory diverticulum grow into the pericardioperitoneal canals to form the pleural cavity.
  • Pleuroperitoneal membranes and the septum transversum (later forming the diaphragm) separate the peritoneal cavity from the pericardial and pleural cavities.

Development of lesser sac

• Rotation of the stomach
  • The ventral and dorsal mesogastrium connect the stomach to the anterior and posterior abdominal walls, respectively.
  • The peritoneal cavity associated with the foregut is divided into the right and left pericardioperitoneal canals.
  • The right and left pericardioperitoneal canals give rise to the lesser sac and greater sac, respectively.
  • After rotation of the stomach, its posterior border (greater curvature) faces the left and anterior border (lesser curvature) faces the right.
  • The right pericardioperitoneal canal lies posterior to the stomach.
• Formation of pneumatoenteric recess
  • Multiple clefts arise within the paraesophageal mesenchyme, which coalesce to form the right pneumatoenteric recess.
  • The right pneumatoenteric recess extends between the lung bud and foregut.
  • The caudal end of the pneumatoenteric recess gives rise to the hepatoenteric recess.
  • The hepatoenteric recess expands the splanchnopleuric layer between the stomach and the liver to form the bilaminar lesser omentum.
  • The space behind the lesser omentum forms the upper part of the lesser sac.
  • The lesser sac opens towards the right into the greater sac through the epiploic foramen.
• Formation of recess in the dorsal mesogastrium: Multiple cavities arising within the dorsal mesogastrium coalesce to form the lower part of the lesser sac, which is made up of two parts.
  • Retrogastric: behind the stomach
  • Greater omental
    • The greater omentum elongates and folds upon itself before fusing with the posterior abdominal wall.
    • The space enclosed between the two leaves of the greater omentum forms the inferiormost recess of lesser sac.

Development of greater sac

• It arises from the left pericardioperitoneal canal and joins with the peritoneal cavity associated with the midgut and hindgut.

Development of mesentery ^[9]

• Origin: The medial walls of the intraembryonic coelom fuse to form the mesentery.
• Content: composed of two layers of visceral peritoneum, mesenchymal tissue, and neurovascular structures
• Type
  • Dorsal mesentery: runs between the posterior margin of the gut and posterior abdominal wall
  • Ventral mesentery: runs between the anterior margin of the gut and anterior abdominal wall
• Mesentery of foregut
  • Contains both dorsal and ventral mesentery
  • Structures arising from ventral mesentery
    • Lesser omentum
    • Falciform ligament
  • Structures arising from dorsal mesentery
    • Greater omentum
    • Splenorenal ligament
• Mesentery of midgut and hindgut
  • Contains dorsal mesentery only
  • Initially, all structures of the midgut and hindgut are suspended by the dorsal mesentery.
  • After rotation of the gut, the mesentery of some structures (e.g., the ascending colon) fuses with the posterior abdominal wall and becomes fixed to form secondary retroperitoneal organs.

Abdominal organs and peritoneum are supplied by the branches of abdominal aorta.

Overview ^[9]

• Source: continuation of thoracic aorta after passing through the aortic hiatus of the diaphragm (at the level of T12)
• Course: retroperitoneal
  • Left of the midline
  • Ventral to the spine
  • Divides at the aortic bifurcation, located at the level of the navel (L4), into the common iliac arteries
• Branches (cranial to caudal)
  • Inferior phrenic arteries
  • Celiac trunk
  • Left and right middle suprarenal artery
  • Superior mesenteric artery
  • Right and left renal artery
  • Right and left ovarian artery/testicular artery
  • Right and left lumbar arteries
  • Inferior mesenteric artery
  • Median sacral artery
• Supply
  • Paired branches: abdominal wall, kidneys, adrenal glands, and gonads
  • Unpaired branches: spleen and gastrointestinal organs

The abdominal aorta bifourcates at the level of L4.

Paired aortic branches

Unpaired aortic branches

Celiac trunk

The celiac trunk emerges approximately at the level of T12 ; and divides into the three following branches to supply the foregut.

A penetrating peptic ulcer or tumor in the posterior duodenal wall can erode into the gastroduodenal artery, leading to torrential hemorrhage.

Superior mesenteric artery

The superior mesenteric artery emerges from the aorta approx. at the level of L1; and then runs anteriorly and inferiorly, dividing into the following branches to supply the midgut.

Inferior mesenteric artery

The inferior mesenteric artery emerges at the level of L3 and supplies the hindgut with the following branches.

All unpaired branches of the abdominal aorta form an anastomosis to ensure continued perfusion of organs in the event of vascular occlusion.

• Sites of anastomosis
  • Duodenum
    • Celiac artery: superior pancreaticoduodenal artery
    • Superior mesenteric artery: inferior pancreaticoduodenal artery
  • Distal third of transverse colon
    • Superior mesenteric artery: middle colic artery
    • Inferior mesenteric artery: left colic artery
  • Rectum
    • Inferior mesenteric artery: superior rectal artery
    • Internal iliac artery: middle rectal artery
• Examples
  • Marginal artery of Drummond ^[9][20]
    • Anastomosis between the terminal branches of the superior and inferior mesenteric artery
    • Runs along the inner mesenteric border of the colon
    • Extends from ileocecal junction to the rectosigmoid junction
    • Poorly developed in the splenic flexure and rectosigmoid region (watershed areas)
  • Riolan anastomosis (part of the marginal artery of Drummond) ^[9][21]
    • Anastomosis between branches of middle colic artery and left colic artery
    • Provides collateral blood supply to the splenic flexure

Nutcracker syndrome

• Pathology: compression of left renal vein between the aorta and superior mesenteric artery
• Clinical features
  • Hematuria (rupture of thin-walled varices due to elevated venous pressure)
  • Abdominal/flank pain that may radiate to the thigh or buttock
  • Left-sided varicocele in men
  • In female individuals: chronic pelvic pain, dyspareunia, dysuria, and dysmenorrhea
• Diagnosis
  • Urinalysis: microscopic/macroscopic hematuria and orthostatic proteinuria ^[22]
  • Doppler ultrasonography
• Treatment
  • Conservative management with ACE inhibitors for mild cases ^[22]
  • Endovascular stenting in severe cases of hematuria ^[23]

Celiac artery compression syndrome (median arcuate ligament compression syndrome) ^[24]

• Pathology: compression of the celiac trunk by the median arcuate ligament of the diaphragm
• Clinical features
  • Postprandial epigastric pain
  • Weight loss
  • Abdominal bruit
• Diagnosis
  • Doppler ultrasonography
  • CT/MR angiography
• Treatment
  • Surgery: median arcuate ligament release and celiac trunk reconstruction
  • Endovascular stenting of celiac trunk

Splenic artery aneurysm ^[25][26][27]

• Pathology: abnormal dilatation of the vessel wall of the splenic artery
• Risk factors
  • Pregnancy and history of multiple pregnancies in women
  • Hypertension
  • Atherosclerosis
  • Fibromuscular dysplasia
  • Connective tissue disease
  • Vasculitis (e.g., granulomatosis with polyangiitis)
  • Pancreatitis
  • Portal hypertension with splenomegaly
• Clinical features
  • Asymptomatic
  • Abdominal and flank pain
  • Hematemesis
  • Hematochezia
• Diagnosis
  • Doppler ultrasonography
  • CT/MR angiography
• Treatment ^[28]
  • If dilation < 3 cm: annual surveillance using CT or ultrasound
  • If dilation > 3 cm or presence of risk factors: surgical ligation or endovascular therapy due to high risk of rupture
  • Splenectomy: in case of rupture and hemodynamic instability

Other conditions

• Superior mesenteric artery syndrome
• Acute mesenteric ischemia
• Chronic mesenteric ischemia
• Ischemic colitis
• Abdominal aorta aneurysm
• Anterior spinal artery syndrome

There are two systems responsible for venous drainage of the abdominal spaces that merge just before the heart, the inferior vena cava and portal hepatic vein.

• Source: confluence of the common iliac veins (L5)
• Course
  • Runs retroperitoneally and to the right of the abdominal aorta
  • Passes the diaphragm through the vena cava foramen (T8)
  • Drains into the right atrium in the thorax
• Tributaries
  • Four lumbar veins
  • Renal vein
  • Right gonadal vein
  • Right suprarenal vein
  • Right, left, and middle hepatic veins
  • Inferior phrenic veins
• Area of drainage
  • Lower extremities
  • Abdominal wall
  • Pelvic wall
  • Pelvic organs (except for the proximal rectum)
  • Kidneys and ureters
  • Adrenal glands

Overview ^[9]

• Source: formed by the confluence of the splenic vein and the superior mesenteric vein behind the neck of the pancreas (at the level of L1–L2)
• Course
  • Runs within the hepatoduodenal ligament toward the porta hepatis
  • Divides into right and left branches at the hilum of the liver
• Area of drainage: : spleen and gastrointestinal organs (except for the rectum below the pectinate line)
• Function
  • Provides most of the blood supply to the liver (∼ 70–80%) ^[1]
  • Carries nutrient-rich blood from the gastrointestinal organs and spleen to the liver
  • Portocaval anastomosis in patients with portal hypertension

Main tributaries ^[1][32][33]

The hepatic portal vein receives blood directly from smaller veins as well as the splenic vein and the superior and inferior mesenteric vein.

Direct tributaries from smaller veins

Indirect tributaries via large veins

Overview

• Caval system: veins that drain directly/indirectly into the superior or inferior vena cava
• Portal system: veins that drain directly/indirectly into the portal vein

Cavocaval anastomoses ^[9][37][38]

• Definition: valveless anastomotic connections between the superior vena cava and inferior vena cava
• Function: provide an alternative route for venous drainage in the event of occlusion of the superior/inferior vena cava (e.g., due to tumor)
• Sites of anastomosis
  • Anterior abdominal wall
    • Internal thoracic pathway: inferior vena cava ↔︎ common iliac vein ↔︎ external iliac vein ↔︎ inferior epigastric vein ↔︎ superior epigastric vein ↔︎ internal thoracic vein ↔︎ subclavian vein ↔︎ brachiocephalic vein ↔︎ superior vena cava
    • Lateral thoracic pathway: inferior vena cava ↔︎ common iliac vein ↔︎ external iliac vein ↔︎ femoral vein ↔︎ superficial epigastric vein ↔︎ thoracoepigastric veins ↔︎ lateral thoracic vein ↔︎ axillary vein ↔︎ subclavian vein ↔︎ brachiocephalic vein ↔︎ superior vena cava
  • Posterior abdominal wall
    • Azygos/hemiazygos pathway: inferior vena cava ↔︎ lumbar veins ↔︎ ascending lumbar vein ↔︎ azygos vein (right)/hemiazygos vein (left) ↔︎ superior vena cava
    • Vertebral pathway: inferior vena cava ↔︎ lumbar veins ↔︎ vertebral venous plexus (Batson's) ↔︎ posterior intercostal veins ↔︎ azygos vein (right)/hemiazygos vein (left) ↔︎ superior vena cava

In the event of IVC obstruction, venous blood can still enter the SVC and right atrium of the heart via the azygos/hemiazygos system or alternative pathways.

Portocaval anastomoses ^[29]

• Definition: valveless anastomotic connections between the portal vein and the caval system (SVC or IVC)
• Function: provide an alternative route for venous drainage in patients with portal hypertension (e.g., liver cirrhosis)
• Sites of anastomosis
  • Distal esophagus: gives rise to esophageal varices
    • Portal vein ↔︎ left gastric vein ↔︎ distal esophageal veins ↔︎ azygos vein (right)/hemiazygos vein (left) ↔︎ superior vena cava
    • Portal vein ↔︎ left gastric vein ↔︎ left inferior phrenic vein ↔︎ inferior vena cava
  • Anterior abdominal wall: gives rise to caput medusae (a pathognomonic sign of portal hypertension characterized by the presence of engorged, tortuous paraumbilical veins that resemble the head of Medusa)
    • Portal vein ↔︎ paraumbilical veins ↔︎ superior epigastric vein ↔︎ internal thoracic vein ↔︎ brachiocephalic vein ↔︎ superior vena cava
    • Portal vein ↔︎ paraumbilical veins ↔︎ thoracoepigastric vein ↔︎ axillary vein ↔︎ subclavian vein ↔︎ brachiocephalic vein ↔︎ superior vena cava
    • Portal vein ↔︎ paraumbilical veins ↔︎ inferior epigastric vein ↔︎ external iliac vein ↔︎ common iliac vein ↔︎ inferior vena cava
  • Rectum and anal canal (gives rise to anorectal varices): portal vein ↔︎ inferior mesenteric vein ↔︎ superior rectal vein ↔︎ middle and inferior rectal veins ↔︎ internal iliac vein ↔︎ inferior vena cava
  • Colon: portal vein ↔︎ superior/inferior mesenteric vein ↔︎ colonic vein ↔︎ lumbar veins and ascending lumbar veins ↔︎ inferior and superior vena cava

Patients with portal hypertension can develop varices of the gut (distal esophagus), butt (rectum and anal canal), and caput (medusae).

Inferior vena cava thrombosis ^[39]

• Etiology
  • Congenital IVC anomaly ^[40]
  • Prothrombotic state (e.g., thrombophilia, malignancy)
  • Renal cell carcinoma
  • Abdominal masses causing extrinsic compression (e.g., large uterine fibroid)
  • Abdominal trauma or surgery
  • Thrombotic occlusion of IVC filter
• Clinical features
  • Acute IVC thrombosis
    • Low back and/or buttock pain
    • Flank pain
    • Hematuria
    • Oliguria/anuria
    • Dilated veins over abdomen or legs
  • Chronic IVC thrombosis
    • Dull aching pain in legs
    • Lower limb swelling
    • Postthrombotic syndrome
• Diagnosis
  • Duplex ultrasonography: shows noncompressible veins with monophasic waveform
  • CT/MRI venography: shows filling defect
• Treatment: depends on etiology, presentation (acute or chronic), and patient factors
  • Medical management: anticoagulant therapy (e.g., LMW heparin, fondaparinux)
  • Endovascular therapy: for thrombolytic injection or stent placement
  • Surgery: thrombectomy

Other conditions

• Portal hypertension
• Transjugular intrahepatic portosystemic shunt
• Budd-Chiari syndrome
• Splenic vein thrombosis
• Portal vein thrombosis
• Anorectal varices
• Esophageal variceal bleeding

Lymphatic drainage of the abdominal cavity occurs via lymph nodes around the individual organs, lymph node clusters, and, finally, into one of the large lymphatic trunks, which merge at the cisterna chyli to form the thoracic duct.

Lymph node clusters of the abdominal cavity ^[9][33]

They lie along the course of major blood vessels and are divided into three main groups: preaortic nodes, paraaortic nodes, and iliac lymph nodes. For more information on the lymphatic drainage of these lymph nodes, see “Abdominal lymph nodes.”

Lymphatic trunks ^[9]

The three major lymphatic trunks drain into the cisterna chyli.

• Lumbar lymphatic trunks (right and left): drain the paraaortic lymph nodes
• Intestinal lymphatic trunk: drains the preaortic lymph nodes

Cisterna chyli ^[9]

• Origin: confluence of intestinal lymphatic trunk and left lumbar lymphatic trunk (less commonly, the right lumbar lymphatic trunk)
• Location
  • At L1–L2 level
  • Posterior to right crus of diaphragm
  • Right of the abdominal aorta
• Area of drainage
  • Abdominal and pelvic viscera
  • Abdominal wall (below umbilicus)
  • Lower limbs
• Termination: thoracic duct

Clinical significance

• Chylous ascites
• Retroperitoneal lymph node dissection
• See “Lymph node clusters” for differential diagnosis of lymphadenopathy.

The visceral organs are innervated by sympathetic nervous system, parasympathetic nervous system, and enteric nervous system.

Sympathetic innervation ^[9][33]

• Origin: : cell bodies in the lateral horn of gray matter in the T1–L2 (or T1–L3) spinal segments
• Preganglionic fibers: exit the spinal cord through ventral roots, ventral rami, and white rami communicantes to take the following routes:
  • Pass through the paravertebral ganglia without synapsing and form the splanchnic nerves, which synapse in the prevertebral ganglia
  • Pass through the paravertebral and prevertebral ganglia to directly synapse in the chromaffin cells of the adrenal medulla
• Postganglionic fibers: form a plexus around the vessels to innervate organs and provide inputs to the enteric nervous system
• Function
  • Decreases visceral smooth muscle motility and glandular secretions
  • Induces sphincter contraction
  • Vasoconstriction
  • Release of catecholamines from the adrenal medulla
  • Carries visceral afferent fibers to convey sensory information (e.g., pain)

Parasympathetic innervation ^[9][33]

• Origin: CN X and lateral horns of S2–S4 spinal segments (anterior rami form pelvic splanchnic nerves)
• Preganglionic fibers: : pass through the prevertebral plexus without synapsing and synapse within the ganglia located in the bowel wall
• Postganglionic fibers: provide inputs to the enteric nervous system
• Function
  • Increases visceral smooth muscle motility and glandular secretions
  • Induces sphincter relaxation
  • Carry visceral afferent fibers to convey sensory information (e.g., mechanical distention, chemical composition of secretions)

The Cannon point (at the left colic flexure) is where parasympathetic innervation transitions from the vagus nerve to the pelvic splanchnic nerves.

The left vagus nerve is anterior to the stomach, and the right vagus is posterior to it. This can be remembered with the mnemonic LARP: Left Anterior, Right Posterior.

Prevertebral ganglia and autonomic nerve plexus ^[9]

• Abdominal prevertebral plexus: a collection of sympathetic and parasympathetic nerve fibers closely related to the abdominal aorta and its branches
• Prevertebral ganglia: a collection of sympathetic ganglia closely related to the abdominal aorta and its branches

Clinical significance

• Diabetic autonomic neuropathy
• Celiac plexus block
• Neuroblastoma