MRI OF ABDOMEN
PREPARATION
- X-ray or MRI or CT Scan or USG Films/Images with Reports
- Blood for Serum Creatinine (If Contrast)
- FNAC/Biopsy Test Reports
- Old Documents
- Operation Note (If Post Operation)
- Empty Stomach (08 Hoiurse)
PROTOCOL
- SURVEY BFFE_COR
- T2W_TSE_BH_TRA
- T2W_SPAIR_BH_ TRA
- Dual_FFE_BH_TRA
- T2W_TSE_BH_TRA
- BTFE_TRA
- DWI_3b_RT_TRA
- e-THRIVE_BH_PRE_TRA
- 2D_BOLUSTRAK_BOLUS
- e-THRIVE_BH ART 1_TRA
- e-THRIVE_BH ART 2_TRA
- 1e-THRIVE_BH VENO_TRA
- e-THRIVE_del_5min_TRA
Indications for MRI of Abdomen Multiphase
- Obstructed vena cava
- Renal vein thrombosis
- Renal arterial obstruction
- Hydronephrosis (kidney enlargement from reflux of urine)
- Glomerulonephritis (inflammation of the kidney glomeruli)
- Acute tubular necrosis
- Extent of tissue damage in organ (kidney) transplant rejection
- Pancreatic cancer
- Adrenal masses
- Mass (tumor) of the gallbladder
- Other tumors or masses
- Differentiates cancer from other types of lesions
- Staging of prostate, uterine, or bladder cancer
- Lymphadenopathy (abnormalities of the lymph nodes)
- Portal vein obstruction (liver)
- Enlarged spleen or liver
- Distended gallbladder or bile duct
- Gallstones, bile duct stones
- Focal diseases such as abscess, hemangiomas, or others
Anatomy Stomach
The stomach, is an intraperitoneal digestive organ located between the oesophagus and the duodenum.
It has a ‘J’ shape, and features a lesser and greater curvature. The anterior and posterior surfaces are smoothly rounded with a peritoneal covering.
In this article, we shall look at the anatomy of the stomach – its position, structure and neurovascular supply.
Anatomical Position
The stomach lies within the superior aspect of the abdomen. It primarily lies in the epigastric and umbilical regions, however, the exact size, shape and position of the stomach can vary from person to person and with position and respiration.
Anatomical Structure
Fig 1 – The parts of the stomach.
The stomach has four main anatomical divisions; the cardia, fundus, body and pylorus:
Cardia – surrounds the superior opening of the stomach at the T11 level.
Fundus – the rounded, often gas filled portion superior to and left of the cardia.
Body – the large central portion inferior to the fundus.
Pylorus – This area connects the stomach to the duodenum. It is divided into the pyloric antrum, pyloric canal and pyloric sphincter. The pyloric sphincter demarcates the transpyloric plane at the level of L1.
Greater and Lesser Curvatures
The medial and lateral borders of the stomach are curved, forming the lesser and greater curvatures:
Greater curvature – forms the long, convex, lateral border of the stomach. Arising at the cardiac notch, it arches backwards and passes inferiorly to the left. It curves to the right as it continues medially to reach the pyloric antrum. The short gastric arteries and the right and left gastro-omental arteries supply branches to the greater curvature.
Lesser curvature – forms the shorter, concave, medial surface of the stomach. The most inferior part of the lesser curvature, the angular notch, indicates the junction of the body and pyloric region. The lesser curvature gives attachment to the hepatogastric ligament and is supplied by the left gastric artery and right gastric branch of the hepatic artery.
Fig 2 – The greater and lesser curvatures of the stomach
Anatomical Relations
The anatomical relations of the stomach are given in the table below:
Anatomical Relation | Structures |
Superior | Oesophagus and left dome of the diaphragm |
Anterior | Diaphragm, greater omentum, anterior abdominal wall, left lobe of liver, gall bladder |
Posterior | Lesser sac, pancreas, left kidney, left adrenal gland, spleen, splenic artery, transverse mesocolon |
Sphincters of the Stomach
There are two sphincters of the stomach, located at each orifice. They control the passage of material entering and exiting the stomach.
Inferior Oesophageal Sphincter
The oesophagus passes through the diaphragm through the oesophageal hiatus at the level of T10. It descends a short distance to the inferior oesophageal sphincter at the T11 level which marks the transition point between the oesophagus and stomach (in contrast to the superior oesophageal sphincter, located in the pharynx). It allows food to pass through the cardiac orifice and into the stomach and is not under voluntary control.
Pyloric Sphincter
The pyloric sphincter lies between the pylorus and the first part of the duodenum. It controls of the exit of chyme (food and gastric acid mixture) from the stomach.
In contrast to the inferior oesophageal sphincter, this is an anatomical sphincter. It contains smooth muscle, which constricts to limit the discharge of stomach contents through the orifice.
Emptying of the stomach occurs intermittently when intragastric pressure overcomes the resistance of the pylorus. The pylorus is normally contracted so that the orifice is small and food can stay in the stomach for a suitable period. Gastric peristalsis pushes the chyme through the pyloric canal into the duodenum for further digestion.
Fig 3 – The peristaltic ejection waves of the stomach
Greater and Lesser Omenta
Within the abdominal cavity, a double layered membrane called the peritoneum. supports most of the abdominal viscera and assists with their attachment to the abdominal wall.
The greater and lesser omenta are two structures that consist of peritoneum folded over itself (two layers of peritoneum – four membrane layers). Both omenta attach to the stomach, and are useful anatomical landmarks:
Greater omentum – hangs down from the greater curvature of the stomach and folds back upon itself where it attaches to the transverse colon It contains many lymph nodes and may adhere to inflamed areas , therefore playing a key role in gastrointestinal immunity and minimising the spread of intraperitoneal infections.
Lesser omentum– continuous with peritoneal layers of the stomach and duodenum, this smaller peritoneal fold arises at the lesser curvature and ascend to attach to the liver. The main function of the lesser omentum is to attach the stomach and duodenum to the liver.
Together, the greater and lesser omenta divide the abdominal cavity into two; the greater and lesser sac. The stomach lies immediately anterior to the lesser sac. The greater and lesser sacs communicate via the epiploic foramen, a hole in the lesser omentum.
Fig 4 – The greater and lesser omenta.
Neurovascular Supply
The arterial supply to the stomach comes from the celiac trunk and its branches. Anastomoses form along the lesser curvature by the right and left gastric arteries and along the greater curvature by the right and left gastro-omental arteries:
Right gastric – branch of the common hepatic artery, which arises from the coeliac trunk.
Left gastric – arises directly from the coeliac trunk.
Right gastro-omental – terminal branch of the gastroduodenal artery, which arises from the common hepatic artery.
Left gastro-omental – branch of the splenic artery, which arises from the coeliac trunk.
The veins of the stomach run parallel to the arteries. The right and left gastric veins drain into the hepatic portal vein. The short gastric vein, left and right gastro-omental veins ultimately drain into the superior mesenteric vein.
Fig 5 – Arterial supply to the stomach
Innervation
The stomach receives innervation from the autonomic nervous system:
Parasympathetic nerve supply arises from the anterior and posterior vagal trunks, derived from the vagus nerve.
Sympathetic nerve supply arises from the T6-T9 spinal cord segments and passes to the coeliac plexus via the greater splanchnic nerve. It also carries some pain transmitting fibres.
Lymphatics
The gastric lymphatic vessels travel with the arteries along the greater and lesser curvatures of the stomach. Lymph fluid drains into the gastric and gastro-omental lymph nodes found at the curvatures.
Efferent lymphatic vessels from these nodes connect to the coeliac lymph nodes, located on the posterior abdominal wall.
Clinical Relevance: Disorders of the Stomach
Gastro-Oesophageal Reflux Disease
This is a digestive disorder affecting the lower oesophageal sphincter. It refers to the movement of gastric acid and food into the oesophagus.
GORD is a common condition, affecting 5-7% of the population. Symptoms include dyspepsia, dysphagia, and an unpleasant sour taste in the mouth.
There are three main causes of reflux disease:
Dysfunction of the lower oesophageal sphincter
Delayed gastric emptying
Hiatal hernia (see below)
Treatment involves lifestyle changes, medication such as a PPI to reduce stomach acid, and as a last resort, surgery.
Hiatus Hernia
A hiatus hernia occurs when a part of the stomach protrudes into the chest through the oesophageal hiatus in the diaphragm. There are two main types of hiatal hernias; sliding and rolling:
Sliding hiatus hernia – The lower oesophageal sphincter slides superiorly. Reflux is a common complication, as the diaphragm is no longer reinforcing the sphincter.
Rolling Hiatus Hernia – The lower oesophageal sphincter remains in place, but a part of the stomach herniates into the chest next to it. This type of hiatus hernia is more likely to require surgical correction to prevent strangulation of the herniated pouch.
Fig 6 – Classifications of hiatus hernias. A is the normal anatomy, B is a pre-stage, C is a sliding hiatal hernia, and D is a rolling type.
Anatomy small intestine
The small intestine is an organ located within the gastrointestinal tract. It is approximately 6.5m in the average person and assists in the digestion and absorption of ingested food.
It extends from the pylorus of the stomach to the ileocaecal junction, where it meets the large intestine at the ileocaecal valve. Anatomically, the small bowel can be divided into three parts: the duodenum, jejunum, and ileum.
In this article, we shall examine the anatomy of the small intestine – its structure, neurovascular supply, and clinical correlations.
Fig 1 – The anatomical divisions of the small intestine.
The Duodenum
The most proximal portion of the small intestine is the duodenum. Its name is derived from the Latin ‘duodenum digitorum’, meaning twelve fingers length. It runs from the pylorus of the stomach to the duodenojejunal junction.
The duodenum can be divided into four parts: superior, descending, inferior and ascending. Together these parts form a ‘C’ shape, that is around 25cm long, and which wraps around the head of the pancreas.
D1 – Superior (Spinal level L1)
The first section of the duodenum is known as ‘the cap’. It ascends upwards from the pylorus of the stomach, and is connected to the liver by the hepatoduodenal ligament. This area is most common site of duodenal ulceration.
The initial 3cm of the superior duodenum is covered anteriorly and posteriorly by visceral peritoneum, with the remainder retroperitoneal (only covered anteriorly).
D2 – Descending (L1-L3)
The descending portion curves inferiorly around the head of the pancreas. It lies posteriorly to the transverse colon, and anterior to the right kidney.
Internally, the descending duodenum is marked by the major duodenal papilla – the opening at which bile and pancreatic secretions to enter from the ampulla of Vater (hepatopancreatic ampulla).
D3 – Inferior (L3)
The inferior duodenum travels laterally to the left, crossing over the inferior vena cava and aorta. It is located inferiorly to the pancreas, and posteriorly to the superior mesenteric artery and vein.
D4 – Ascending (L3-L2)
After the duodenum crosses the aorta, it ascends and curves anteriorly to join the jejunum at a sharp turn known as the duodenojejunal flexure.
Located at the duodenojejunal junction is a slip of muscle called the suspensory muscle of the duodenum. Contraction of this muscle widens the angle of the flexure, and aids movement of the intestinal contents into the jejunum.
Fig 2 – The different parts of the duodenum. The liver, gall bladder and transverse colon have been removed.
Clinical Relevance: Duodenal Ulcers
A duodenal ulcer is the erosion of the mucosa in the duodenum. It may also be described as a peptic ulcer (although this term can also be used to refer to ulcerations in the stomach). Duodenal ulcers are most likely to occur in the superior portion of the duodenum.
The most common causes of duodenal ulcers are Helicobacter pylori infection and chronic NSAID therapy.
An ulcer in itself can be painful, but is not particularly troublesome and can be treated medically. However, if the ulcer progresses to create a complete perforation through the bowel wall, this is a surgical emergency, and usually warrants immediate repair. A perforation may be complicated by:
Inflammation of the peritoneum(peritonitis) – causing damage to the surrounding viscera, such as the liver, pancreas and gall bladder.
Erosion of the gastroduodenal artery – causing haemorrhage and potential hypovolaemia shock.
Jejunum and Ileum
The jejunum and ileum are the distal two parts of the small intestine. In contrast to the duodenum, they are intraperitoneal.
They are attached to the posterior abdominal wall by mesentery (a double layer of peritoneum).
The jejunum begins at the duodenojejunal flexure. There is no clear external demarcation between the jejunum and ileum – although the two parts are macroscopically different. The ileum ends at the ileocaecal junction.
At this junction, the ileum invaginates into the cecum to form the ileocecal valve. Although it is not developed enough to control movement of material from the ileum to the cecum, it can prevent reflux of material back into the ileum (if patent, see below).
Fig 3 – The ileocecal junction
Clinical Relevance: Characteristic Features of the Jejunum and Ileum
During surgery, it is often necessary to be able to distinguish between the jejunum and ileum of the small intestine:
Jejunum | Ileum |
Located in upper left quadrant | Located in lower right quadrant |
Thick intestinal wall | Thin intestinal wall |
Longer vasa recta (straight arteries) | Shorter vasa recta |
Less arcades (arterial loops) | More arcades |
Red in colour | Pink in colour |
Vasculature and Lymphatics
Duodenum
The arterial supply of the duodenum is derived from two sources:
Proximal to the major duodenal papilla – supplied by the gastroduodenal artery (branch of the common hepatic artery from the coeliac trunk).
Distal to the major duodenal papilla – supplied by the inferior pancreaticoduodenal artery (branch of superior mesenteric artery).
This transition is important – it marks the change from the embryological foregut to midgut. The veins of the duodenum follow the major arteries and drain into the hepatic portal vein.
Lymphatic drainage is to the pancreatoduodenal and superior mesenteric nodes.
Jejunum and Ileum
The arterial supply to the jejunoileum is from the superior mesenteric artery.
The superior mesenteric artery arises from the aorta at the level of the L1 vertebrae, immediately inferior to the coeliac trunk. It moves in between layers of mesentery, splitting into approximately 20 branches. These branches anastomose to form loops, called arcades. From the arcades, long and straight arteries arise, called vasa recta.
The venous drainage is via the superior mesenteric vein. It unites with the splenic vein at the neck of the pancreas to form the hepatic portal vein.
Lymphatic drainage is into the superior mesenteric nodes.
Fig 4 – Arterial supply to the jejunum and ileum of the small intestine
Clinical Relevance: Ileocaecal valve
The ileocaecal valve represents the separation between the small and large intestine. Its main function is to prevent the reflux of enteric fluid from the colon into the small intestine. It is also used as an landmark during colonoscopy, indicating that the limit of the colon has been reached and that a complete colonoscopy has been performed.
The ileocaecal valve is also important in the setting of large bowel obstruction. Should the ileocaecal valve be competent, a closed loop obstruction can occur and cause bowel perforation. Should the ileocaecal valve be incompetent (i.e. allow backflow of enteric contents into the small bowel) then the situation is less emergent and the trajectory of the obstruction less rapid.
Anatomy Abdomen
The peritoneal cavity is a potential space between the parietal and visceral peritoneum.
It normally contains only a thin film of peritoneal fluid, which consists of water, electrolytes, leukocytes and antibodies. This fluid acts as a lubricant, enabling free movement of the abdominal viscera, and the antibodies in the fluid fight infection.
While the peritoneal cavity is ordinarily filled with only a thin film of fluid, it is referred to as a potential space because excess fluid can accumulate in it, resulting in the clinical condition of ascites (see clinical applications).
In this article, we shall look at the anatomy of the peritoneal cavity – its subdivisions, structure and clinical correlations.
Subdivisions of the Peritoneal Cavity
The peritoneal cavity can be divided into the greater and lesser peritoneal sacs. The greater sac comprises the majority of the peritoneal cavity. The lesser sac (also known as the omental bursa) is smaller and lies posterior to the stomach and lesser omentum.
Greater Sac
The greater sac is the larger portion of the peritoneal cavity. It is further divided into two compartments by the mesentery of the transverse colon (known as the transverse mesocolon):
Supracolic compartment – lies above the transverse mesocolon and contains the stomach, liver and spleen.
Infracolic compartment – lies below the transverse mesocolon and contains the small intestine, ascending and descending colon. The infracolic compartment is further divided into left and right infracolic spaces by the mesentery of the small intestine.
The supracolic and infracolic compartments are connected by the paracolic gutters which lie between the posterolateral abdominal wall and the lateral aspect of the ascending or descending colon.
Fig 2 – The greater sac can be subdivided into the supracolic and infracolic compartments.
Clinical Relevance: Subphrenic Abscesses
The subphrenic recesses are potential spaces in the supracolic compartment of the greater sac. They are located between the diaphragm and the liver. There are left and right subphrenic spaces, separated by the falciform ligament of the liver.
Subphrenic abscesses refer to an accumulation of pus in the left or right subphrenic space. They are more common on the right side due to the increased frequency of appendicitis and ruptured duodenal ulcers (pus from the appendix can track up to the subphrenic space via the right paracolic gutter).
Lesser Sac (Omental Bursa)
The lesser sac lies posterior to the stomach and lesser omentum. It allows the stomach to move freely against the structures posterior and inferior to it.
The omental bursa is connected with the greater sac through an opening in the omental bursa – the epiploic foramen (of Winslow).
The epiploic foramen is situated posterior to the free edge of the lesser omentum (the hepatoduodenal ligament).
Fig 3 – Sagittal view of the peritoneal cavity.
Fig 4 – The lesser omentum removed to show the epiploic foramen of Winslow.
Structure of the Peritoneal Cavity in the Pelvis
Due to the presence of different pelvic organs, the peritoneal cavity differs in structure between the sexes. The primary difference in structure is the location of the most distal portion of the cavity.
When humans stand or sit upright, any superfluous fluid (which could be blood, pus, or infected fluid) is likely to collect in the most inferior portion of the peritoneal cavity. Thus, it is clinically important to be aware of the differences between males and females.
Male
In males, the rectovesical pouch is a double folding of peritoneum located between the rectum and the bladder. The peritoneal cavity is completely closed in males.
Fig 5 – The rectovesical pouch is the most distal portion of the peritoneal cavity in males.
Females
In females, there are two areas of note:
Rectouterine pouch (of Douglas) – double folding of the peritoneum between the rectum and the posterior wall of the uterus.
Vesicouterine pouch – double folding of peritoneum between the anterior surface of the uterus and the bladder.
The peritoneal cavity is not completely closed in females – the uterine tubes open into the peritoneal cavity, providing a potential pathway between the female genital tract and the abdominal cavity. Clinically, this means that infections of the vagina, uterus, or uterine tubes may result in infection and inflammation of the peritoneum (peritonitis).
Actual passage of infectious material into the peritoneum, however, is rare due to the presence of a mucous plug in the external os (opening) of the uterus which prevents the passage of pathogens but allows sperm to enter the uterus.
Fig 6 – The vesicouterine and rectouterine pouches
Clinical Relevance: Sampling of Peritoneal Fluid
Culdocentesis
Culdocentesis involves the extraction of fluid from the rectouterine pouch (of Douglas) through a needle inserted through the posterior fornix of the vagina. It can be used to extract fluid from the peritoneal cavity or to drain a pelvic abscess in the rectouterine pouch.
Paracentesis
Paracentesis is a procedure used to drain fluid from the peritoneal cavity. A needle is inserted through the anterolateral abdominal wall into the peritoneal cavity. The needle must be inserted superior to the urinary bladder and the clinician must take care to avoid the inferior epigastric artery.
It is used to drain ascitic fluid, diagnose the cause of ascites and to check for certain types of cancer which may metastasise via the peritoneum, e.g. liver cancer.
Clinical Relevance: Disorders of the Peritoneal Cavity
Ascites
Ascites refers to an accumulation of excess fluid within the peritoneal cavity. It is typically caused by portal hypertension (secondary to liver cirrhosis).
Other causes include malignancy of the GI tract, malnutrition, heart failure, and mechanical injuries which result in internal bleeding.
Clinical features of ascites include abdominal distension, abdominal discomfort, nausea, and dyspnoea due to pressure on the lungs from the enlarged abdominal cavity.
Fig 7 – Ascites; an accumulation of excess fluid in the peritoneal cavity.
Peritonitis
Peritonitis refers to infection and inflammation of the peritoneum. It can occur as a result of bacterial contamination during a laparotomy (open surgical incision of the peritoneum) or it can occur secondary to an infection elsewhere in the GI tract, for example a ruptured appendix, acute pancreatitis or a gastric ulcer eroding through the wall of the stomach.
Exudation of fluid into the peritoneal cavity causes the cavity to expand, and due to the somatic innervation of the parietal peritoneum, results in pain
Clinical features include pain and tenderness of the overlying skin and the anterolateral abdominal muscles contract to protect the viscera (known as guarding). Other symptoms include; fever, nausea, vomiting, and constipation. Patients may lie with their knees flexed in an effort to relax the anterolateral abdominal wall muscles.
Anatomy Colon.
The colon (large intestine) is the distal part of the gastrointestinal tract, extending from the cecum to the anal canal. It receives digested food from the small intestine, from which it absorbs water and electrolytes to form faeces.
Anatomically, the colon can be divided into four parts – ascending, transverse, descending and sigmoid. These sections form an arch, which encircles the small intestine.
In this article, we shall look at the anatomy of the colon – its anatomical structure and relations, neurovascular supply, and clinical correlations.
Anatomical Position
The colon averages 150cm in length, and can be divided into four parts (proximal to distal): ascending, transverse, descending and sigmoid.
Ascending Colon
The colon begins as the ascending colon, a retroperitoneal structure which ascends superiorly from the cecum.
When it meets the right lobe of the liver, it turns 90 degrees to move horizontally. This turn is known as the right colic flexure (or hepatic flexure), and marks the start of the transverse colon.
Transverse Colon
The transverse colon extends from the right colic flexure to the spleen, where it turns another 90 degrees to point inferiorly. This turn is known as the left colic flexure (or splenic flexure). Here, the colon is attached to the diaphragm by the phrenicocolic ligament.
The transverse colon is the least fixed part of the colon, and is variable in position (it can dip into the pelvis in tall, thin individuals). Unlike the ascending and descending colon, the transverse colon is intraperitoneal and is enclosed by the transverse mesocolon.
Descending Colon
After the left colic flexure, the colon moves inferiorly towards the pelvis – and is called the descending colon. It is retroperitoneal in the majority of individuals, but is located anteriorly to the left kidney, passing over its lateral border.
When the colon begins to turn medially, it becomes the sigmoid colon.
Sigmoid Colon
The 40cm long sigmoid colon is located in the left lower quadrant of the abdomen, extending from the left iliac fossa to the level of the S3 vertebra. This journey gives the sigmoid colon its characteristic “S” shape.
The sigmoid colon is attached to the posterior pelvic wall by a mesentery – the sigmoid mesocolon. The long length of the mesentery permits this part of the colon to be particularly mobile.
Paracolic Gutters
The paracolic gutters are two spaces between the ascending/descending colon and the posterolateral abdominal wall.
These structures are clinically important, as they allow material that has been released from inflamed or infected abdominal organs to accumulate elsewhere in the abdomen.
Anatomical Structure
The large intestine has a number of characteristic features, which allows it to be distinguished from the small intestine:
Attached to the surface of the large intestine are omental appendices – small pouches of peritoneum, filled with fat.
Running longitudinally along the surface of the large bowel are three strips of muscle, known as the teniae coli. They are called the mesocolic, free and omental coli.
The teniae coli contract to shorten the wall of the bowel, producing sacculations known as haustra.
The large intestine has a much wider diameter compared to the small intestine.
These features cease at the rectosigmoid junction, where the smooth muscle of the teniae coli broaden to form a complete layer within the rectum.
Fig 2 – The macroscopic features of the large intestine.
Anatomical Relations
The colon has numerous important anatomical relations in the abdomen, as shown in Table 1:
Anterior | Posterior | |
Ascending colon | Small intestine Anterior abdominal wall | Iliacus and quadratus lumborum Right kidney Iliohypogastric and ilioinguinal nerves |
Transverse colon | Greater omentum Anterior abdominal wall | Head of the pancreas |
Descending colon | Small intestine Greater omentum Anterior abdominal wall | Iliacus and quadratus lumborum Left kidney Iliohypogastric and ilioinguinal nerves |
Sigmoid colon | Urinary bladder | Sacrum Ileum |
Neurovascular Supply
The neurovascular supply to the colon is closely linked to its embryological origin:
Ascending colon and proximal 2/3 of the transverse colon – derived from the midgut.
Distal 1/3 of the transverse colon, descending colon and sigmoid colon – derived from the hindgut.
Arterial Supply
As a general rule, midgut-derived structures are supplied by the superior mesenteric artery, and hindgut-derived structures by the inferior mesenteric artery.
The ascending colon receives arterial supply from two branches of the superior mesenteric artery; the ileocolic and right colic arteries. The ileocolic artery gives rise to colic, anterior cecal and posterior cecal branches – all of which supply the ascending colon.
The transverse colon is derived from both the midgut and hindgut, and so it is supplied by branches of the superior mesenteric artery and inferior mesenteric artery:
Right colic artery (from the superior mesenteric artery)
Middle colic artery (from the superior mesenteric artery)
Left colic artery (from the inferior mesenteric artery)
The descending colon is supplied by a single branch of the inferior mesenteric artery; the left colic artery. The sigmoid colon receives arterial supply via the sigmoid arteries (branches of the inferior mesenteric artery).
Marginal Artery of Drummond
The marginal artery (of Drummond) is a clinically important vessel that provides collateral supply to the colon – thereby maintaining arterial supply in the case of occlusion or stenosis of one of the major vessels.
As the terminal vessels of the superior mesenteric and inferior mesenteric artery approach the colon, they split into many branches, which anastomose with each other. These anastomoses form a continuous arterial channel which extends the length of the colon – the marginal artery. Long, straight arterial branches (called vasa recta) arise from the marginal artery to supply the colon.
Venous Drainage
The venous drainage of the colon is similar to the arterial supply:
Ascending colon – ileocolic and right colic veins, which empty into the superior mesenteric vein.
Transverse colon – middle colic vein, which empties into the superior mesenteric vein.
Descending colon – left colic vein, which drains into the inferior mesenteric vein.
Sigmoid colon – drained by the sigmoid veins into the inferior mesenteric vein.
The superior mesenteric and inferior mesenteric veins ultimately empty into the hepatic portal vein. This allows toxins absorbed from the colon to be processed by the liver for detoxification.
Fig 3 – The major arteries and veins supplying the colon.
Innervation
The innervation to the colon is dependent on embryological origin:
Midgut-derived structures (ascending colon and proximal 2/3 of the transverse colon) receive their sympathetic, parasympathetic and sensory supply via nerves from the superior mesenteric plexus.
Hindgut-derived structures (distal 1/3 of the transverse colon, descending colon and sigmoid colon) receive their sympathetic, parasympathetic and sensory supply via nerves from the inferior mesenteric plexus:
Parasympathetic innervation via the pelvic splanchnic nerves
Sympathetic innervation via the lumbar splanchnic nerves.
Lymphatic Drainage
The lymphatic drainage of the ascending and transverse colon is into the superior mesenteric nodes. The descending colon and sigmoid drain into the inferior mesenteric nodes.
Most of the lymph from the superior mesenteric and inferior mesenteric nodes passes into the intestinal lymph trunks, and on to the cisterna chyli – where it ultimately empties into the thoracic duct.
Anatomy Abdomen wall ( anterolateral)
The abdominal wall encloses the abdominal cavity and can be divided into anterolateral and posterior sections. The abdominal wall:
Forms a firm, yet flexible boundary which keeps the abdominal viscera in the abdominal cavity and assists the viscera in maintaining their anatomical position against gravity.
Protects the abdominal viscera from injury.
Assists in forceful expiration by pushing the abdominal viscera upwards.
Is involved in any action (coughing, vomiting, defecation) that increases intra-abdominal pressure.
The anterolateral abdominal wall consists of four main layers (external to internal): skin, superficial fascia, muscles and associated fascia, and parietal peritoneum.
In this article, we shall look at the anatomy of the anterolateral abdominal wall – its musculature, surface anatomy and clinical correlations.
Superficial Fascia
The superficial fascia is connective tissue. The composition of this layer depends on its location:
Above the umbilicus – a single sheet of connective tissue. It is continuous with the superficial fascia in other regions of the body.
Below the umbilicus – divided into two layers; the fatty superficial layer (Camper’s fascia) and the membranous deep layer (Scarpa’s fascia).
The superficial vessels and nerves run between these two layers of fascia.
Fig 1 – The layers of the anterolateral abdominal wall. Below the umbilicus, there are two layers of superficial fascia – Camper’s and Scarpa’s.
Muscles of the Abdominal Wall
The muscles of the anterolateral abdominal wall can be divided into two main groups:
Flat muscles – three flat muscles, situated laterally on either side of the abdomen.
Vertical muscles – two vertical muscles, situated near the mid-line of the body.
Flat Muscles
There are three flat muscles located laterally in the abdominal wall, stacked upon one another. Their fibres run in differing directions and cross each other – strengthening the wall and decreasing the risk of abdominal contents herniating through the wall.
In the anteromedial aspect of the abdominal wall, each flat muscle forms an aponeurosis (a broad, flat tendon), which covers the vertical rectus abdominis muscle. The aponeuroses of all the flat muscles become entwined in the midline, forming the linea alba (a fibrous structure that extends from the xiphoid process of the sternum to the pubic symphysis).
External Oblique
The external oblique is the largest and most superficial flat muscle in the abdominal wall. Its fibres run inferomedially.
Attachments: Originates from ribs 5-12, and inserts into the iliac crest and pubic tubercle.
Functions: Contralateral rotation of the torso.
Innervation: Thoracoabdominal nerves (T7-T11) and subcostal nerve (T12).
Internal Oblique
The internal oblique lies deep to the external oblique. It is smaller and thinner in structure, with its fibres running superomedially (perpendicular to the fibres of the external oblique).
Attachments: Originates from the inguinal ligament, iliac crest and lumbodorsal fascia, and inserts into ribs 10-12.
Functions: Bilateral contraction compresses the abdomen, while unilateral contraction ipsilaterally rotates the torso.
Innervation: Thoracoabdominal nerves (T7-T11), subcostal nerve (T12) and branches of the lumbar plexus.
Fig 2 – The muscles of the anterolateral abdominal wall. Note how the flat muscles form aponeuroses medially.
Transversus Abdominis
The transversus abdominis is the deepest of the flat muscles, with transversely running fibres. Deep to this muscle is a well-formed layer of fascia, known as the transversalis fascia.
Attachments: Originates from the inguinal ligament, costal cartilages 7-12, the iliac crest and thoracolumbar fascia. Inserts into the conjoint tendon, xiphoid process, linea alba and the pubic crest.
Functions: Compression of abdominal contents.
Innervation: Thoracoabdominal nerves (T7-T11), subcostal nerve (T12) and branches of the lumbar plexus.
Vertical Muscles
There are two vertical muscles located in the midline of the anterolateral abdominal wall – the rectus abdominis and pyramidalis.
Rectus Abdominis
The rectus abdominis is long, paired muscle, found either side of the midline in the abdominal wall. It is split into two by the linea alba. The lateral borders of the muscles create a surface marking known as the linea semilunaris.
At several places, the muscle is intersected by fibrous strips, known as tendinous intersections. The tendinous intersections and the linea alba give rise to the ‘six pack’ seen in individuals with a well-developed rectus abdominis.
Attachments: Originates from the crest of the pubis, before inserting into the xiphoid process of the sternum and the costal cartilage of ribs 5-7.
Functions: As well as assisting the flat muscles in compressing the abdominal viscera, the rectus abdominis also stabilises the pelvis during walking, and depresses the ribs.
Innervation: Thoracoabdominal nerves (T7-T11).
Pyramidalis
This is a small triangular muscle, found superficially to the rectus abdominis. It is located inferiorly, with its base on the pubis bone, and the apex of the triangle attached to the linea alba.
Attachments: Originates from the pubic crest and pubic symphysis before inserting into the linea alba.
Functions: It acts to tense the linea alba.
Innervation: Subcostal nerve (T12).
Rectus Sheath
The rectus sheath is formed by the aponeuroses of the three flat muscles and encloses the rectus abdominis and pyramidalis muscles. It has an anterior and posterior wall for most of its length:
The anterior wall is formed by the aponeuroses of the external oblique, and of half of the internal oblique.
The posterior wall is formed by the aponeuroses of half the internal oblique and of the transversus abdominis.
Approximately midway between the umbilicus and the pubic symphysis, all the aponeuroses move to the anterior wall of the rectus sheath. At this point, there is no posterior wall to the sheath; the rectus abdominis is in direct contact with the transversalis fascia.
The demarcation point where the posterior layer of the rectus sheath ends is the arcuate line.
Surface Anatomy
Many of the organs in the abdominal cavity can be palpated through the abdominal wall, or their position can be visualised by surface markings.
The umbilicus is the most visible structure of the abdominal wall and is the scar of the site of attachment of the umbilical cord. It is usually located midway between the xiphoid process and the pubis symphysis.
The rectus abdominis muscle gives rise to abdominal markings. The lateral border of this muscle is indicated by the linea semilunaris, a curved line running from the 9th rib to the pubic tubercle. The linea alba is a fibrous line that splits the rectus abdominis into two. It is visible as a vertical groove extending inferiorly from the xiphoid process.
The abdomen is a large area, and so it split into nine regions – these are useful clinically for describing the location of pain, location of viscera and describing surgical procedures. The nine regions are formed by two horizontal and two vertical planes:
Horizontal planes:
Transpyloric plane – halfway between the jugular notch and the pubic symphysis, approximately the level of the L1 vertebrae.
Intertubercular plane – horizontal line that runs between the superior aspect of the right and left iliac crests.
Vertical planes – run from the middle of the clavicle to the mid-inguinal point (halfway between the anterior superior iliac spine of the pelvis and the pubic symphysis). These planes are the mid-clavicular lines.
Fig 3 – The nine regions of the abdomen.
Clinical Relevance: Surgical Incisions in Abdominal Wall
Midline
An incision that is made through the linea alba. It can be extended the whole length of the abdomen by curving around the umbilicus. The linea alba is poorly vascularised, so blood loss is minimal, and major nerves are avoided. It can be used in any procedure that requires access to the abdominal cavity.
Paramedian
Similar to the median incision, but is performed laterally to the linea alba, providing access to more lateral structures (kidney, spleen and adrenals). This method ligates the blood and nerve supply to muscles medial to the incision, resulting in their atrophy.
Kocher
A Kocher incision ③ begins inferior to the xiphoid process and extends inferolaterally in parallel to the right costal margin. It is mainly used to gain access for gall bladder and/or biliary tree pathology.
Two modifications and extensions of the Kocher incision are possible:
Chevron / rooftop incision or modification ④ – the extension of the incision to the other side of the abdomen. This may be used for oesophagectomy, gastrectomy, bilateral adrenalectomy, hepatic resections, or liver transplantation
Mercedes Benz incision or modification ⑤ – the Chevron incision with a vertical incision and break through the xiphisternum. This may be used for the same indications as the Chevron incision, however classically seen in liver transplantation.
McBurney
A McBurney is a called a ‘grid iron’ incision, because it consists of two perpendicular lines, splitting the fibres of the muscles without cutting them – this allows for excellent healing. McBurney incision is performed at McBurney’s point (1/3 of the distance between the ASIS and the umbilicus) and is used in an open appendicectomy.
Fig 4 – Common abdominal incisions. ① Midline incision, ② Paramedian incision, ③ Kocher incision, ④ Rooftop modification and ⑤ Mercedes Benz modification.
Anatomy posterior abdominal wall
The posterior abdominal wall is a complex region of anatomy. It is formed by the lumbar vertebrae, pelvic girdle, posterior abdominal muscles and their associated fascia. Major vessels, nerves and organs are located on the inner surface of the posterior abdominal wall.
In this article, we shall look at the muscles and fascia of the posterior abdominal wall.
Posterior Abdominal Muscles
There are five muscles in the posterior abdominal wall: the iliacus, psoas major, psoas minor, quadratus lumborum and the diaphragm. We shall look at the attachments, actions and innervation of these muscles in more detail.
Quadratus Lumborum
Fig 1.0 – The quadratus lumborum of the posterior abdominal wall.
The quadratus lumborum muscle is located laterally in the posterior abdominal wall. It is a thick muscular sheet which is quadrilateral in shape. The muscle is positioned superficially to the psoas major.
Attachments: It originates from the iliac crest and iliolumbar ligament. The fibres travel superomedially, inserting onto the transverse processes of L1 – L4 and the inferior border of the 12th rib.
Actions: Extension and lateral flexion of the vertebral column. It also fixes the 12th rib during inspiration, so that the contraction of diaphragm is not wasted.
Innervation: Anterior rami of T12- L4 nerves.
Psoas Major
The psoas major is located near the midline of the posterior abdominal wall, immediately lateral to the lumbar vertebrae.
Attachments: Originates from the transverse processes and vertebral bodies of T12 – L5. It then moves inferiorly and laterally, running deep to the inguinal ligament, and attaching to the lesser trochanter of the femur.
Actions: Flexion of the thigh at the hip and lateral flexion of the vertebral column.
Innervation: Anterior rami of L1 – L3 nerves.
Fig 1.2 – Muscles of the posterior abdominal wall.
Psoas Minor
The psoas minor muscle is only present in 60% of the population. It is located anterior to the psoas major.
Attachments: Originates from the vertebral bodies of T12 and L1 and attaches to a ridge on the superior ramus of the pubic bone, known as the pectineal line.
Actions: Flexion of the vertebral column.
Innervation: Anterior rami of the L1 spinal nerve.
Iliacus
The iliacus muscle is a fan-shaped muscle that is situated inferiorly on the posterior abdominal wall. It combines with the psoas major to form the iliopsoas – the major flexor of the thigh.
Attachments: Originates from surface of the iliac fossa and anterior inferior iliac spine. Its fibres combine with the tendon of the psoas major, inserting into the lesser trochanter of the femur.
Actions: Flexion and lateral rotation of the thigh at the hip joint.
Innervation: Femoral nerve (L2 – L4).
Diaphragm
The posterior aspect of the diaphragm is considered to be part of the posterior abdominal wall. It is described in detail here.
Clinical Relevance: Psoas Sign
The psoas sign is a medical sign that indicates irritation to the iliopsoas group of muscles. The sign is elicited by flexion of the thigh at the hip. The test is positive if the patient reports lower abdominal pain.
A right sided psoas sign is an indication of appendicitis. As the iliopsoas contracts, it comes into contact with the inflamed appendix, producing pain.
Fascia of the Posterior Abdominal Wall
A layer of fascia (sheet of connective tissue) lies between the parietal peritoneum and the muscles of the posterior abdominal wall. This fascia is continuous with the transversalis fascia of the anterolateral abdominal wall.
Whilst the fascia is one continuous sheet, it is anatomically correct to name the fascia according to the structure it overlies.
Psoas Fascia
The psoas fascia covers the psoas major muscle. It is attached to the lumbar vertebrae medially, continuous with the thoracolumbar fascia laterally and continuous with the iliac fascia inferiorly
Thoracolumbar fascia
The thoracolumbar fascia consists of the three layers; posterior, middle and anterior. Muscles are enclosed between these layers:
Quadratus lumborum – between the anterior and middle layers.
Deep back muscles – between the middle and posterior layers.
The posterior layer extends between the 12th rib and the iliac crest posteriorly. Laterally the fascia meets the internal oblique and transversus abdominis muscles, but not the external oblique. As it forms these attachments it covers the latissimus dorsi.
The anterior layer attaches to the anterior aspect of the transverse processes of the lumbar vertebrae, the 12th rib and the iliac crest. Laterally the fascia is continuous with the aponeurotic origin of the transversus abdominis muscle. Superiorly the fascia thickens to become the lateral arcuate ligament, which joins the iliolumbar ligaments inferiorly.
Fig 1.2 – The layers of thoracolumbar fascia.
Clinical Relevance - Referred Pain
Pain from the viscera is poorly localised. As described earlier, it is referred to areas of skin (dermatomes) which are supplied by the same sensory ganglia and spinal cord segments as the nerve fibres innervating the viscera.
Pain is referred according to the embryological origin of the organ; thus pain from foregut structures are referred to the epigastric region, midgut structures are to the umbilical region and hindgut structures to the pubic region of the abdomen.
Foregut – oesophagus, stomach, pancreas, liver, gallbladder and the duodenum (proximal to the entrance of the common bile duct).
Midgut – duodenum (distal to the entrance of the common bile duct) to the junction of the proximal two thirds of the transverse colon with the distal third.
Hindgut – distal one third of the transverse colon to the upper part of the anal canal.
Pain in retroperitoneal organs (e.g. kidney, pancreas) may present as back pain.
Irritation of the diaphragm (e.g. as a result of inflammation of the liver, gallbladder or duodenum) may result in shoulder tip pain.
Referred Pain in Appendicitis
Initially, pain from the appendix (midgut structure) and its visceral peritoneum is referred to the umbilical region. As the appendix becomes increasingly inflamed, it irritates the parietal peritoneum, causing the pain to localise to the right lower quadrant.
By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
Fig 4 – Referred pain oracic, abdominal and pelvic organs.
