1. GI Tract Physiologic Disturbances
In this session, we will be talking about various physiologic processes that may disrupt or affect the GI tract.

2. Intestinal Obstruction
Obstruction to the antegrade flow of intestinal contents
Mechanical
Blockage within the lumen
Blockage from outside of the lumen
Ileus – non mechanical
Paralysis of the intestine
Trauma
Neurologic
Inflammatory
Intestinal obstruction, or the obstruction to the antegrade flow of intestinal contents, can be on a variety of basis’s. A mechanical obstruction can be caused by either a blockage within the lumen or blockage from outside the lumen or something causing a blockage from the outside of the lumen. We can also have an ileus which is a nonmechanical obstruction. This may be the result of paralysis of the intestine, lack of peristalsis because it was paralytic process. This could be on the basis of trauma, it could be neurologic, or could be in the basis of inflammation.

3. Mechanical Obstruction Small Intestine
Small intestine dilated > 3 cm with gas (swallowed air) and fluid (excreted by digestive glands). Forms multiple air/fluid levels
Plain abdominal films (erect and supine view) to confirm the diagnosis
Mechanical obstruction may affect the small intestine with dilatation of the small intestine by greater than 3 cm with gas, swallowed air, or fluid excreted by the digestive glands. This results in the formation of multiple air-fluid bubbles within the visualized small intestine. Plain abdominal films typically an erect and supine film is used to confirm this diagnosis.

4. Mechanical Obstruction Small Intestine
Observing number, location and mucosal pattern of the dilated bowel may roughly indicate the point of obstruction
Commonly due to post-surgical adhesion or hernia
We observe the number, the location, and the mucosal pattern of the dilated segments of bowel in an attempt to roughly identify the point of obstruction. The obstructions are commonly a result of postsurgical adhesions or some type of internal hernia.

5. Mechanical Small Intestine Obstruction
Plain film supine
Distended gas filled loops
: Here is an example of mechanical small intestinal obstruction. On this plain supine film we see multiple distended loops of primarily small intestine. These are identified by the presence of lobular conniventes which you may recall go all the way across various loops.

6. Mechanical Small Intestine Obstruction
Upright film
Multiple air-fluid levels
Step laddering (differential air fluid levels)
Prominent mucosal folds - edema
The upright film corresponding demonstrates the presence of multiple air-fluid levels within the distended loops of small intestine. The liquid within the intestine has gone to the dependent or lower portions. There is a step laddering or the development of differential air-fluid levels. During the early stages of mechanical obstruction peristaltic activity remains within the small intestine forcing fluid from proximal to distal. This results in each adjoining loop with slightly higher fluid levels more distal than proximal. In addition we note some prominence in mucosal fold pattern, prominence of lobular conniventes as result of some mucosal edema.

7. Mechanical Obstruction Large Intestine
Distended colon from cecum to level of obstruction with air and fluid inside
If you have an “Incompetent” ileocecal valve, gas flow retrograde into small intestine
Mechanical obstruction can also involve the large intestine. There may be distention of the colon from the cecum to the level of the obstruction with both air and fluid. If the ileocecal valve is incompetent and does not preclude the retrograde passage of fluid and gas there would be retrograde flow of fluid and gas into the small intestine the small intestine will show evidence of obstruction as well.

8. Mechanical Obstruction Large Intestine
Barium enema to confirm the diagnosis
Commonly due to
Cancer
Volvulus
Child – midgut volvulus
Adults – cecal volvulus
Elderly – sigmoid volvulus
Barium enema can be used to confirm the diagnosis of a mechanical large intestinal obstruction. Causes of large intestinal obstruction include neoplasm volvulus or twisting of the intestine, and in this twisting situation in a child this would be the midgut that is twisted, and in most adults the cecum, and in the very elderly the sigmoid colon will twist upon itself and cause obstruction.

9. Distal Colon Obstruction
Supine
Dilated colon in ascending and proximal transverse portions
Here, an image from plain supine film of the colon demonstrating the presence of dilated colon in its ascending and proximal portions as result of the distal obstruction.

10. Distal Colon Obstruction
Upright view
Multiple air fluid levels
The upright image on the same individual demonstrates the presence of multiple air-fluid levels most marked at the level near the cecum.

11. Paralytic (Adynamic) Ileus
The intestinal lumen is patent
Functional defect
Decreased propulsion, generalized or localized
Large and small intestine dilatation, occasionally stomach dilated
Contrast mechanical obstruction to paralytic or an adynamic ileus. In paralytic or adynamic ileus the intestinal lumen remains patent throughout. This is indeed a functional defect. There is decreased propulsion, which can either be generalized or localized, and may be just decreased for maybe completely stop propulsion. Both the large and small intestine can be dilated and on occasion the stomach may be included as well this dilatation.

12. Paralytic (Adynamic) Ileus
Commonly due to intra-abdominal inflammation, post surgical or post-traumatic reaction, spinal injury
Can be generalized or localized
Common causes for paralytic or adynamic ileus include intra-abdominal inflammation, postsurgical response or respond posttraumatic response of the intestine or spinal injuries. This abnormality can be either generalized or maybe localized.

13. Paralytic (adynamic) Ileus
Supine film
Dilatation of both large and small intestine
Long tube coiled in stomach
In this case of paralytic or adynamic ileus on the supine film, we note dilatation of both large and small intestine. In addition, a long tube has been placed with an attempt to advance this tube into the small intestine to allow decompression.

14. Pneumoperitoneum Free air in the peritoneal cavity Commonly due to:
Perforation of gastrointestinal tract – peptic ulcer
Following surgical procedure – laparotomy
Following laparoscopy
Pneumoperitoneum is another abnormality that can be demonstrated by imaging. The result of free air within the peritoneal cavity, this can be identified as being caused by a variety of conditions including perforation of the gastrointestinal tract, typically by peptic ulcer disease, or following surgical procedures such as laparotomy or laparoscopy.

15. Pneumoperitoneum X-ray signs: On erect abdominal or chest film,
a curvilinear (small amount) or a crescent (moderate amount) of low density beneath the opacity of the dome of the diaphragm and the liver on the right
Most reliable sign
The X-ray signs that we identify for pneumoperitoneum include on the upright or erect abdominal or chest films; we see a curvilinear if there is a small amount or a crescent if there is a moderate amount of low density beneath the opacity of the dome of the diaphragm and between the liver and the diaphragm on the right. This is our most reliable sign.

16. Pneumoperitoneum X-ray signs:
Severely ill patient, one who cannot maintain an erect position
Perform a lateral decubitus film.
The air floats to the top of the peritoneal cavity forming a crescentic lucent area between the abdominal wall and adjacent organs
in severely ill patients, or one who cannot maintain an erect position for whatever reason, will perform a lateral decubitus film. The air close to the top the peritoneal cavity is forming a crescentic lucent area between the abdominal wall in the adjacent organs, including liver or bowel.

17. Pneumoperitoneum X-ray signs:
With no additional gas introduced, or other complicating condition the free air will be absorbed in 7-10 days in adults or much faster 1-2 days in children
If no additional gas is introduced into the peritoneal cavity or if there are no complicating conditions, free air will absorb fairly rapidly in children one or two days and may persist within the abdominal cavity of adults for as much as 7 to 10 days.

18. Pneumoperitoneum PA chest upright
Curvilinear area between right diaphragm and the liver (arrows)
Small amount of free air on the left (single arrow)
Here, this upright chest radiograph demonstrates a crescent of air beneath the right diaphragm between the diaphragm and liver as seen by the small arrows. There is as well some air seen beneath the left diaphragm adjacent to the air within the stomach bubble.