Pneumoperitoneum – supine versus erect radiograph

Case contributed by Maher Khazem

Presentation

Post total abdominal hysterectomy for a cystic pelvic mass presenting with abdominal discomfort.

Patient Data

Age: 40 years
Gender: Female

In the first study shown, the patient is supine. The general findings of the image above are sub optimal inspiration leading to decreased lung volumes and bibasilar atelectasis. There is a slight area of increased lucency over the liver.

The study was repeated with the patient in the semi-erect position which is shown in the above image. The study has better inspiration and shows markedly decreased airspace opacities bilaterally. More importantly, the study being in the semi-erect position shows a clear and impressive pneumoperitoneum. 

Case Discussion

Given the patient's clinical history. This is most likely a case of post-operative pneumoperitoneum. However, this does demonstrates the difference in appearance of pneumoperitoneum between a supine and erect x-ray.

This case is extremely important, especially for those beginning their radiology training, for a variety of reasons:

1. Technique is important - Going off the first study, you might call this atelectasis and focus on the pulmonary findings or etiologies. The second study highlights the importance of positional variance and inspiratory effort. The better inspiration aerates the entire lung widening the area of x-ray. This gives a better interpretation of pulmonary vessels, airspace opacities, and cardiomegaly. The second study shows no acute cardiopulmonary findings. Even more important than this, the erect position of the patient in the second study makes a very tough call on radiograph into a glaring one. The comparison of both studies looking at pneumoperitoneum is shocking and is changed by a simple technique. 

2. If something looks just slightly off, investigate it - It would be easy for a novice radiologist to write off the just slightly increased lucency of the liver, especially being that the spleen is covered by bowel gas on the opposite side so there is less to compare it to. This case is a great example of noticing something in a study that looks or feels off and investigating it further. Once again, pneumoperitoneum is considered a surgical emergency, it is a shouldn't miss the diagnosis. It is important to recognize this patient did have an abdominal surgery 2 days prior and this can be a common finding postoperatively which may resolve on its own. The due diligence to pursue a "hunch" and obtain another x-ray in an erect position helped this patient and will help many others. Understanding this patient had a recent abdominal surgery could raise your awareness more to that increase in lucency over the liver. This would lead to further investigation and better treatment of the patient. 

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