Abdominal air pocket. Coloured X-ray of air in the abdomen, a condition called pneumoperitoneum. The air (multicoloured, lower left and right) is lying at the top of the abdomen, trapped underneath the diaphragm. The rest of the image shows the lungs and ribcage. Pneumoperitoneum is commonly caused by the perforation of the bowel, or suction of air through the female genital tract. Surgery prevents further air entering and removes the existing air. Free air in the abdomen is best observed below the right-hand side of the diaphragm (lower left).