Abdominal radiographs can be difficult to analyze.  A 
mechanical obstruction is often difficult to differentiate 
from an adynamic ileus.  The goal of this case 
discussion is to help one to have a better understanding 
of a mechanical obstruction versus an adynamic 
(paralytic) ileus, and be able to make a distinction 
between these two conditions.  Sixteen abdominal 
radiographs will be displayed to test your skill in 
distinguishing a bowel obstruction from an ileus.
     It is important to first look at those components that 
are common to all films, such as the stomach, rectum, 
and the hepatic and splenic flexures of the colon.  
These areas are relatively fixed.  Then, one should look 
at the solid abdominal viscera, such as the liver, spleen, 
kidneys, psoas muscles and bladder.  Finally, an 
examination of the lungs (lower portions), diaphragms, 
bony structures and pelvis are important.
     A mechanical obstruction is an impedance to the 
passage of air or intestinal contents secondary to a 
mechanical hindrance.  Examples of this include 
incarcerated inguinal hernia, bowel adhesions, 
intussusception, volvulus, intestinal atresias, 
intraluminal masses (tumors, bezoars, large stool 
masses), and extrinsic bowel compression (Ladd's 
bands, annular pancreas, etc.).  In a paralytic 
(adynamic) ileus, there is a temporary impedance to the 
passage of air or contents secondary to uncoordinated 
peristalsis or hypoperistalsis.
     Adynamic ileus frequently occurs with major 
abdominal, retroperitoneal and spinal surgery.  It also 
occurs frequently with inflammatory processes such as
sepsis, pneumonia, gastroenteritis, appendicitis, 
peritonitis, pancreatitis and urinary tract infection.  One 
may have bowel disturbances and a resultant ileus with 
hypokalemia, electrolyte disturbance, dehydration, 
vasculitis, renal disease, neurogenic shock, sepsis, 
drugs, hypothyroidism and idiopathic intestinal 
pseudoobstruction.  Although the most common cause 
of an ileus is gastroenteritis, an ileus is not necessarily 
a benign condition.
     There are different criteria that one must look at 
when trying to distinguish an ileus from an obstruction 
on an abdominal radiograph.  These include, the fixed 
anatomy, gas distribution, degree of bowel distention, 
air fluid levels, and arrangement of the bowel loops.  It 
should be noted that none of these criteria are 
necessarily definitive in always distinguishing an ileus 
from an obstruction.

Gas distribution:
     A gasless abdomen is usually abnormal.  Only rarely 
is the abdomen truly gasless. However, radiographs 
with an extreme paucity of gas (i.e., almost gasless) 
should be treated with the same degree of suspicion as 
a gasless abdominal radiograph.  Although a gasless 
abdomen is highly suggestive of a high obstruction, this 
can also be seen with excessive vomiting, and/or 
diarrhea.  This picture can also occur in the early 
stages of appendicitis, as well as in Addisonian crisis 
(adrenal crisis).  Occasionally, this occurs in patients 
with marked cerebral depression such that their 
swallowing is impaired.
     In a mechanical obstruction, there is preferentially 
more air proximal to the obstruction than distal to it.  
Thus, in an obstruction, there is either too much gas in 
the small bowel (and not much gas in the large bowel), 
or too much gas in the large bowel (and not much gas 
in the small bowel). In an adynamic ileus, there usually 
is no preferential collection of air.  There is too much air 
or not much air in both the small and large bowel.  This 
pattern of distribution is not necessarily definitive.  
When there is too much air in the small bowel, this may 
be a small bowel obstruction which has been present 
long enough to have allowed the colon gas to clear.  
When there is too much air in the colon, this may be a 
large bowel obstruction (e.g.., sigmoid volvulus) with a 
competent ileocecal valve.  If, however, there is too 
much air in both parts of the bowel, you may have a 
paralytic ileus, or a large bowel obstruction with an 
incompetent ileocecal valve, or a small bowel 
obstruction which is early or intermittent.
     Another important point is that sometimes in a 
mechanical obstruction, there is very little air present 
and the intestinal loops are filled with fluid.  In these 
cases, the loops may appear as opaque sausage-like 
structures in the abdomen or the bowel may be 
isodense with the rest of the abdomen showing a 
paucity of gas.  On the upright view, the air may get 
trapped in the valvulae conniventes (small bowel plicae 
circulares [circular folds]) giving a "string of pearls" gas 
pattern appearance.

Bowel dilatation:
     Bowel dilatation is another important criteria that 
needs to be considered.  In a mechanical obstruction 
one usually sees dilatation proximal to the site of 
obstruction.  In a bowel obstruction, the bowel dilatation 
appearance in children is different from that generally 
seen in adults.  In infants and children, an obstruction 
characteristically shows dilated bowel with SMOOTH 
bowel walls.  The degree of dilatation is not necessarily 
excessive, but the smoothness of the bowel wall is 
most notable.  This smoothness is due to the loss of 
plicae (circular folds) and haustration of the bowel due 
to gaseous distention.  In an obstruction where the 
bowel is dilated, the bowel resembles "hoses" or 
"sausages" where the bowel walls are smooth (the 
normal bowel wall irregularity is lost).
     Determining the level of the obstruction is often 
difficult.  It is often difficult to radiographically 
distinguish small from large bowel in the infant.  In older 
children you may see cross striations which represent 
the valvulae conniventes when the small bowel is 
distended.  These resemble the haustra of the large 
bowel, however, they are more numerous and more 
narrowly spaced.  Haustra appear as indentations 
which do not cross the lumen like these do, and the 
indentations of haustra do not necessarily line up with 
the opposite side.  In paralytic ileus, the bowel loops all 
dilate in proportion to each other.  The colon usually 
remains larger than the small intestine.
     It is worth mentioning here that one can see short 
segments of bowel dilatation adjacent to areas of 
inflammation ("sentinel" loops).  These are areas of 
short segment paralytic ileus and when found in the 
right upper quadrant, can represent cholecystitis, 
pyelonephritis, hepatitis or traumatic disease.  In the left 
upper quadrant these are seen with pancreatitis, 
pyelonephritis, or splenic injury.  In the right lower 
quadrant, it is seen with appendicitis, Meckel's 
diverticulitis, or regional enteritis.  These loops are rare 
in the left lower quadrant, but can be seen with 
salpingitis or cystitis in females.

Air-Fluid levels:
     In mechanical obstruction, air-fluid levels can be 
seen on the upright view.  One can see short air-fluid 
levels in both limbs of what look like hairpin loops of 
intestine.  The heights of the fluid levels are usually 
different in any two limbs of one loop (resembles candy 
canes).  In a paralytic ileus, there may be few to 
numerous sluggish air-fluid levels scattered throughout 
the abdomen.  An obstruction characteristically shows 
many dilated air-fluid levels, while an ileus 
characteristically shows fewer air-fluid levels that are 
not dilated.

Arrangement of Bowel Loops:
     One could also look at how orderly the intestinal 
loops are arranged.  In a mechanical obstruction the 
dilated loops are often stacked one under the other in a 
"step ladder" appearance (in a more orderly fashion) on 
the SUPINE view (not the upright view).  With an ileus, 
the dilated loops tend to be less orderly, scattered 
throughout the abdomen from top to bottom and side to 
side.  Perhaps another way at describing this 
"orderliness", is that an obstruction resembles a bag of 
sausages (a more orderly arrangement), while an ileus 
resembles a bag of popcorn (a less orderly 
arrangement).  The sausages of a bowel obstruction 
are due to dilated bowel while the popcorn of an ileus is 
due to a generalized distribution of bowel gas and 
better preservation of the bowel plicae and haustra.

In summary, one should evaluate abdominal films in a 
stepwise fashion.

1.  Look at the fixed anatomy.  Do not forget the lungs.

2.  Gas Distribution.
     Obstruction:  Too much air in the small bowel (and 
not much gas in the large bowel) or too much air in the 
large bowel (and not much gas in the small bowel).  
Poor gas distribution or gasless.
     Ileus:  Good gas distribution over most of the 
abdomen.  Too much air in both large and small bowel.  
Warning:  This could also appear in large bowel 
obstruction with an incompetent ileocecal valve, or in an 
early or intermittent small bowel obstruction.

3.  Bowel Dilatation.
     Obstruction:  Smooth bowel walls (resembles 
sausages or a hose).  Preferential dilatation of the 
bowel proximal to the obstruction.
     Ileus:  Dilatation of the bowel in proportion to each 
other, so that the colon remains larger than the small 
intestine.  Look for sentinel loops.

4.  Air-fluid Levels.
     Obstruction:  Many dilated air-fluid levels in both 
limbs of a given loop, at different heights (candy canes).
     Ileus:  Fewer and/or smaller (less dilated) air-fluid 
levels scattered throughout the abdomen.

5. Arrangement of loops (supine view only).
     Obstruction:  Dilated loops arranged in "stepladder" 
fashion.  Orderly.  A bag of sausages.
     Ileus:  Disorderly loops scattered throughout the 
abdomen.  A bag of popcorn.

     Remember, presentations are variable, and not 
always clear cut.  Often, it is difficult to distinguish the 
two, especially when there is a mixed paralytic and 
mechanical obstruction.  A high index of suspicion 
should remain when the clinical and radiographic 
information is unclear.  Conditions such as 
intussusception, volvulus, and appendicitis are surgical 
emergencies that require a timely diagnosis and 
intervention.  These conditions may not have definitive 
findings on plain radiographs.  Other diagnostic studies 
or surgical intervention may be necessary if these 
conditions are still suspected after the completion of 
plain film radiographs.

     Now test your skill in distinguishing obstruction from 
ileus in this series of 16 pediatric abdominal 
radiographs.  All of these patients are vomiting with 
varying degrees of abdominal pain.  No histories are 
given here except for the patient's age and sex.  In 
reality, the radiographic findings should be interpreted in 
conjunction with the patient's clinical findings.  Two 
views are shown in each case.  The view on the left is a 
supine view.  The view on the right is an upright view 
unless otherwise specified.


Case A:  18-month old male.

View Case A.





Interpretation of Case A
     Gas Distribution:  There are pockets of gas 
scattered in several areas of the abdomen.  There is 
gas in the small bowel, colon, and rectum.
     Bowel Dilatation:  No excessively dilated bowel.  The 
bowel walls are not smooth.  Haustra and plicae are 
preserved.
     Air-Fluid Levels:  None.
     Arrangement of Loops:  Large loops are not present.
     Impression:  Within normal limits.


Case B:  7-day old female.

View Case B.





Interpretation of Case B
     Gas Distribution:  There are pockets of gas 
scattered in several areas of the abdomen.  There is 
gas in the small bowel, colon, and rectum.
     Bowel Dilatation:  There is mild dilation of the bowel, 
mostly in the colon.  The dilated segment of bowel in 
the left upper quadrant shows relatively smooth bowel 
walls.  However, most of the bowel does not show this.  
In other words, the haustra and plicae of most of the 
bowel are well preserved.
     Air-Fluid Levels:  None.
     Arrangement of Loops:  The loops are not arranged 
in an orderly pattern.
     Impression:  Ileus.


Case C:  17-day old male.

View Case C.





Interpretation of Case C
     Gas Distribution:  There is gas over most of the 
abdomen.  There are loops of bowel mostly in the 
central abdomen.  The dilated loops are mostly small 
bowel.
     Bowel Dilatation:  The bowel walls are smooth 
indicating that the bowel is dilated.  
     Air-Fluid Levels:  There are multiple short air fluid 
levels on the upright film (hair pin loops).  
     Arrangement of Loops:  Orderly, although not truly in 
a stepladder fashion.  The arrangement here resembles 
a bag of sausages more so that a bag of popcorn.
     Impression:  Small bowel obstruction.  In this age, 
the mostly likely cause is an incarcerated inguinal 
hernia.  This is confirmed clinically.


Case D:  1-month old female.

View Case D.





Interpretation of Case D
     Gas Distribution:  There is a lot of gas in the small 
and large bowel distributed throughout the abdomen.
     Bowel Dilatation:  The degree of bowel dilation here 
is proportional throughout.  In other words, the large 
bowel is slightly dilated, as is the small bowel.
     Air-Fluid Levels:  None.
     Arrangement of Loops:  Disorderly arrangement of 
dilated bowel.  This resembles a bag of popcorn rather 
than a bag of sausages.
     Impression:  Ileus.  The differential is extensive, 
including gastroenteritis, urinary tract infection, etc.  
However, an ileus is still compatible with several 
surgical conditions such as appendicitis.


Case E:  3-1/2 year old male.

View Case E.





Interpretation of Case E
     Gas Distribution:  Increased gaseous distribution in 
both small and large bowel, with more colonic 
involvement.  Gas is also present in the rectum.
     Bowel Dilatation:  Note the smooth bowel walls 
resulting in the "sausage-like" appearance of some of 
the loops.  There are several areas of extreme dilation.  
The stomach is also very dilated.
     Air-Fluid Levels:  Multiple loops of bowel with air 
fluid levels.  The typical "candy cane" appearance is not 
very dramatic. 
     Arrangement of Loops:  The loops are stacked in a 
somewhat orderly fashion.  However, this is not definite.  
The "arrangement" should be best determined on the 
supine flat view and not the upright view.  Although this 
arrangement resembles a bag of sausages more so 
than a bag of popcorn, this is not as clear-cut as in 
other cases.
     Impression:  The gas distribution throughout the 
bowel suggests that this is not an obstruction.  
However, the reason for the extreme bowel dilatation is 
uncertain.  This is still suspicious for an obstruction.  
Note the frothy density over the left flank area (supine 
view). This probably represents fecal matter.  Though a 
fecal obstruction is possible, a BE or an UGI series 
would be helpful to evaluate other causes of obstruction 
such as malrotation or Hirshsprung's disease.  A 
contrast enema and an UGI series were performed on 
this patient.  Both were normal.  His symptoms and 
bowel dilation gradually resolved after several enemas 
and bowel movements.


Case F:  7-month old male.

View Case F.





Interpretation of Case F
     Gas Distribution:  Relatively gasless in both large 
and small bowel. This is a poor gas distribution.
     Bowel Dilatation:   In some of the few bowel loops 
that are seen, the bowel walls appear smooth.
     Air-Fluid Levels:  There are no obvious air-fluid 
levels.  However, in the upright view, the central 
abdomen shows the presence of two bowel loops 
resembling arches that are air-fluid levels which do not 
have the typical candy cane appearance.  The candy 
cane appearance of air-fluid levels is usually not seen in 
infants.
     Arrangement of Loops:  It is difficult to comment on 
the arrangement given the minimal gas pattern.
     Impression:  Probable obstruction based mainly on 
the paucity of gas and its distribution.  Since these 
radiographs are highly suspicious, the next 
recommended exam should be an ultrasound and/or a 
BE to evaluate the possibility of intussusception or 
appendicitis.  An intussusception is often the cause of a 
bowel obstruction associated with a paucity of gas on 
plain radiographs  A BE performed in this patient 
demonstrated an intussusception.


Case G:  Newborn male.

View Case G.





Interpretation of Case G
     In this case, only a supine view is shown on the left.  
The image on the right is a contrast enema study.
     Gas Distribution:  There is poor gas distribution with 
only 3 dilated loops of bowel, triple bubbles, probably 
representing high (i.e., proximal) small bowel loops.  
There is some gas in the left lower quadrant.  This 
cannot be the colon since there is no gas in any other 
intervening bowel segments evident.
     Bowel Dilatation:  As noted above, dilation is present 
in the loops seen.  There is no colon gas evident.
     Air-Fluid Levels:  An upright or lateral decubitus view 
is not shown here.
     Arrangement of Loops:  Too few to comment.
     Impression:  This is a proximal small bowel 
obstruction.  The contrast enema on the right shows a 
microcolon indicating the absence of bowel contents 
passing to the colon during gestation.  In a proximal 
small bowel obstruction, a microcolon is usually not 
present.  The presence of a microcolon suggests that 
the distal small bowel is also atretic.  This patient was 
ultimately diagnosed with a long segment small bowel 
atresia.  Note that the contrast enema study also shows 
the cecum in the wrong position.  It should be in the 
right lower quadrant, but it appears to be more medial 
than its expected positions.  Malpositioning of the 
cecum is highly indicative of a malrotation.


Case H:  3-day old female.

View Case H.





Interpretation of Case H
     Gas Distribution:  Generalized presence of gas 
throughout all quadrants.
     Bowel Dilatation:  The degree of  bowel dilatation is 
proportional.  The right lower quadrant may 
demonstrate some smooth bowel walls, but this is 
probably just the descending colon.  Some of the 
haustra in these segments are still preserved.  For the 
remainder of the bowel, the haustra and plicae are well 
preserved.
     Air-Fluid Levels:  None.
     Arrangement of Loops:  Disorderly arrangement 
resembling a bag of popcorn.
     Impression:  Ileus.


Case I:  2-1/2 year old female.

View Case I. 





Interpretation of Case I
     Gas Distribution:  Well distributed throughout all 
quadrants.
     Bowel Dilatation:  There are two dilated regions 
seen on the supine view in both lower quadrants.  
However, the bowel walls do not appear smooth.  The 
typical sausage or hose appearance of dilated small 
bowel is not present.  The haustra and plicae are still 
fairly well preserved.
     Air-Fluid Levels:  The upright view shows many 
small air fluid levels.  The typical hairpin or candy cane 
appearance is not present indicating that these air 
fluid levels are small and not present in large loops.
     Arrangement of Loops:  Disorderly loops resembling 
a bag of popcorn more so than a bag of sausages 
(supine view).
     Impression:  Moderate ileus versus partial 
obstruction.  An ileus is more likely.


Case J:  3-year old female.

View Case J.





Interpretation of Case J

     Gas Distribution:  There is gas distributed 
throughout the abdomen.  Most of the gas present is in 
the colon.
     Bowel Dilatation:  There is moderate dilation of the 
colonic regions.  There is a dilated loop of small bowel 
on the left (supine view) which overlaps the colon.  The 
haustra and plicae are preserved.  No sausages or 
hoses are seen (i.e., no smooth bowel walls are 
present).
     Air-Fluid Levels:  None.
     Arrangement of Loops:  Disorderly arrangement 
resembling a bag of popcorn more so than a bag of 
sausages.
     Impression:  Ileus.


Case K:  9-day old male.

View Case K.





Interpretation of Case K
     Gas Distribution:  Poor distribution.  Although gas is 
present throughout most of the abdomen, its distribution 
appears to be limited to just a few bowel segments.
     Bowel Dilatation:  Marked bowel distention though 
difficult to determine small versus large bowel.  The 
bowel walls are smooth. 
     Air-Fluid Levels:  Multiple air-fluid levels mostly on 
the left.  Hair pins and candy canes are not present.
     Arrangement of Loops:  Not very helpful in this case.  
The arrangement is best evaluated on the supine view 
which is not obviously orderly or disorderly.  In other 
words, it is not easy to say whether this arrangement 
resembles a bag of sausages or a bag of popcorn.
     Impression:  Obstruction based mainly on the gas 
distribution and the degree of bowel dilatation.  This is 
not a normal abdominal series for a 9-day old.  A 
contrast enema demonstrated a transition zone 
consistent with Hirschsprung's disease.


Case L:  12-month old female.

View Case L.





Interpretation of Case L
     Gas Distribution:  Small areas of gas are present 
throughout the entire abdomen.  Many of the areas are 
foamy suggesting the presence of excessive amounts 
of stool.
     Bowel Dilatation:  Most of the bowel is not dilated.  
There is a modest paucity of gas.  There are two dilated 
loops in the RLQ on the supine view (RLQ sentinel 
loops).
     Air-Fluid Levels:  None.
     Arrangement of Loops:  Disorderly.  Despite the 
paucity of gas, the supine view resembles a bag of 
popcorn more so than a bag of sausages.
     Impression:  Ileus.  RLQ sentinel loops raise the 
possibility of appendicitis.


Case M:  7-month old female.

View Case M.





Interpretation of Case M
     Gas Distribution:  There is a definite paucity of gas 
which is poorly distributed.
     Bowel Dilatation:  Nothing obvious.
     Air-Fluid Levels:  None.
     Arrangement of Loops:  Not a useful sign here 
because of the paucity of gas.
     Other comments:  There is a "target sign" in the 
right upper quadrant.  The target sign is discussed in 
detail in Case 2 of Volume 1.  The target is faintly 
visible as a doughnut shape (with the doughnut center 
still present) in the right upper quadrant below the liver 
(supine view).  This is subtle.  You may have to turn 
down the room lights and adjust the contrast and 
brightness on your monitor.  This sign indicates the 
presence of an intussusception.  This radiograph also 
demonstrates the "absent liver edge" sign (liver edge 
not well defined in any view), which is also a sign of 
intussusception (though less specific than the target 
sign).  If you have difficulty identifying the target and 
liver edge findings in this radiograph, review Case 2 of 
Volume 1 for other examples that are easier to identify.
     Impression:  Suggestive of an obstruction based 
mainly on the paucity of gas.  The target sign indicates 
the presence of an intussusception.  A barium enema 
confirmed an intussusception.


Case N:  22-month old.

View Case N.





Interpretation of Case N
     Gas Distribution:  Good distribution except for one 
portion in the LUQ.  Although the upright view appears 
to be somewhat gasless with most of the gas seen 
localized to the upper abdomen only, the supine view 
shows a better distribution of gas.
     Bowel Dilatation:  There are no dilated regions.  The 
haustra and plicae are well preserved.
     Air-Fluid Levels:  None.
     Arrangement of Loops:  Disorderly.
     Other Comments:  The supine view demonstrates 
"thumb printing" suggesting bowel wall edema such as 
that seen in colitis.  This is best seen in the LUQ 
region (or left middle region) where the colon shows 
thumb-shaped indentations into its lumen.
     Impression:  Ileus, colitis.


Case O:  11-month old male.

View Case O.





Interpretation of Case O
     Gas Distribution:  Poorly distributed.  Gas is 
concentrated in the left upper quadrants in both the 
supine and upright views.
     Bowel Dilatation:  There are two dilated bowel 
segments seen on the supine view.  The bowel walls 
are smooth and resemble sausages.
     Air-Fluid Levels:  None.
     Arrangement of Loops:  Orderly.  Note the two 
dilated bowel segments on the supine view are stacked 
on top of each other resembling a step ladder.  Also, 
this view clearly resembles a bag of sausages (only two 
big ones), rather than a bag of popcorn.
     Impression:  Obstruction.  A barium enema in this 
case demonstrated intussusception.


Case P:  6-1/2 year old male.

View Case P.





Interpretation of Case P
     Gas Distribution:  Well distributed except for a 
paucity of gas in the left lower quadrant.
     Bowel Dilatation:  The haustra and plicae are well 
preserved.  No smooth bowel walls are visible.  The 
caliber of the bowel is proportional to the normal bowel 
size.
     Air-Fluid Levels:  None.
     Arrangement of Loops:  Disorderly.  Does not 
resemble a bag of sausages.  Nor does it truly 
resemble a bag of popcorn.  However, there is no order 
to the arrangement.
     Impression:  Ileus.  There is a possible appendicolith 
in the right lower quadrant (spherical density).  This is 
highly suggestive of acute appendicitis.  This again 
stresses the point, that an ileus is not necessarily 
benign.


References
     1.  Swischuk LE.  The Abdomen.  In:  Swischuk LE.  
Emergency Radiology of the Acutely Ill or Injured Child, 
second edition.  Baltimore, Williams & Wilkins, 1986, 
pp. 153-164.
     2.  Swischuk LE.  The Alimentary Tract.  In:  
Radiology of the Newborn and Young Infant, second 
edition.  Baltimore, Williams & Wilkins, 1980, pp. 
487-490.
     3.  Kirks DR.  The Gastrointestinal Tract.  In:  
Practical Pediatric and Diagnostic Radiology of Infants 
and Children.  Boston, Little, Brown and Company, 
1984, pp. 551-553.
     4.  Parker BR.  The Abdomen and Gastrointestinal 
Tract.  In:  Silverman FN, Kuhn JP.  Caffey's Pediatric 
X-Ray Diagnosis, Ninth edition.  St. Louis, Mosby, 
1993, pp. 1059-1089.
     5.  Squire LF, Novelline RA.  The Abdominal Plain 
Film:  Distended Stomach, Small Bowel, Colon, Free 
Fluid and Free Air.  In:  Fundamentals of Radiology, 4th 
edition.  Cambridge, MA, Harvard University Press, 
1988, pp. 194-205.