X-ray Abdomen
Abdomen AP (Erect)
Region: liver,
spleen, kidney, digestive system, lumbar
vertebrae
Pathology: bowel
obstruction, inflammatory bowel disease, volvulus, organomegaly and
pneumoperitoneum
SID: 100 cm (40
inches)
Central Ray: perpendicular
beam directed at the point 5cm (2 inches) superior to the iliac
crest
Respiration: suspended
Position
1. The patient is in an erect position with the back on the
image receptor (IR).
2. Place the center of the IR 5cm above the center of iliac
crest.
3. Make sure pelvis and
shoulders are not rotated
Collimation: Include
the entire abdomen including the diaphragm.
Evaluation
1. Residual gas in the gastrointestinal tract should be visible
and the residual gas in the lower abdomen should be observed below the
diaphragm.
2. Diaphragm must be included.
3. Outlines of organs in the abdomen should be clearly visible.
4. Pelvis and lumbar
vertebrae should be shown symmetrically without rotation.
5. Bladder must be observed.
kVp-80, mAs-40
Tip
2. If the abdomen is adhered to IR excessively, natural state of abdomen inside cannot be observed.
3. When observing evenly the abdominal organs within abdominal cavity, Abdomen AP Supine Projection is needed.
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.
