Bones: spine, ribs, pelvis, and upper femurs. Look for si of arthritis, Fx, and bone lesions
Soft tissues: masses, calcifications.
Air under diaphragm in an upright film or next to the abdominal wall in a lateral decubitus film denotes perforated viscus.
Gastric air bubble. A large air-distended stomach suggests some form of obstruction
Bowel gas pattern. Small volume of air is generally seen in the colon, while the small bowel is generally devoid of air.
Fecal material is often visible in colon. Large amounts may be seen in patient with constipation.
The colon may become greatly distended with air in colonic obstruction (colonic distention proximal to obstruction) or ileus.
Unless the colonic distension is severe, haustral markings are maintained.
Large bowel markings are differentiated from small bowel markings by their wider spacing, and the incomplete crossing of the lumen.
When the ileocecal valve is incompetent, large bowel obstruction may also cause distension of the small bowel.
Distension of the small bowel may be seen in mechanical obstruction and ileus.
Small bowel striations are much more numerous and completely cross the lumen. With mechanical obstruction there is distention proximal to the obstruction and clearing of air distally.
Appearance of ileus is much less distinct. There is discontinuous air in the small and usually large bowel. Distention is less marked and discontinuous
Air-fluid levels do not distinguish mechanical obstruction from ileus. The may be seen in both conditions.