Can you have a pneumoperiteneum under the left hemidiaphragm? If so, is it more common to appear on one side more than the other?
Pneumoperitoneum is basically air in the abdominal cavity. Hence the air will rise to the highest possible spot. On chest xrays which are done with the patient standing, it is much more common to have it under the right aspect of the diaphragm because the right side is higher so the air will go there. Could it be trapped under the left side? Sure it can...the right side is more common however. If the xray or other exam is done in a laying position or on a side then the air will move to the top. So in a supine patient, we may not see the air clearly under the diaphragm because it is not the highest spot. Rather the front of the abdomen will be the highest spot and the air will not be seen easily if the xray is shot with a front to back projection. In a supine patient the air may be seen when the xray is shot from the side of a patient so then we can see air interface kinda like a meniscus...
Hope I didn't confuse you...and it is helpful.