Teaching Case

A 52-year-old man, active smoker with chronic obstructive lung disease, was admitted with pneumonia and influenza. Treated in intensive care unit with mechanical ventilation for nine days.

Post treatment routine chest radiograph taken 7 days after extubation showed a big volume of free air in the peritoneal cavity (Fig. 1). The patient presented no symptoms of acute abdomen. Peritoneal signs, fever and leucocytosis were absent.
Computed Tomography (CT) confirmed free peritoneal air but did not reveal any site of perforation (Fig. 2). No pneumothorax was identified. The patient was discharged from the hospital without any further treatment. Control radiologic examination was recommended.

A common standing chest radiograph can be very sensitive for detection of free air in the peritoneal cavity [1]. The radiographic manifestation of pneumoperitoneum usually suggests a serious intra-abdominal disease such as visceral perforation which invokes a need for emergency surgery. Therefore further imaging such as CT is recommended not only to reveal any potential peritoneal free air, but also to identify the place of perforation.
However, about 10% of all cases of pneumoperitoneum are caused by so-called nonsurgical causes [2]. These generally do not require surgical intervention and may be grouped in the following categories: abdominal, thoracic, gynaecologic and idiopathic [3].

The abdominal causes are most common and include postoperatively retained air, laparoscopy, catheter placement associated to peritoneal dialysis and endoscopic gastrointestinal procedures. Given frequency of abdominal procedures, post surgical pneumoperitoneum is the most frequent cause of nonsurgical pneumoperitoneum. Among inflammatory causes of nonsurgical pneumoperitoneum pneumatosis cystoides intestinalis should be mentioned. [2, 3]

The most frequent thoracic causes in adults are mechanical ventilation, cardiopulmonary resuscitation and pneumothorax. Two competitive mechanisms for the passage of air from thoracic to abdominal cavities have been proposed: a direct passage through pleural and diaphragmatic defects or a passage through mediastinum along perivascular connective tissue to retroperitoneum and peritoneum. Analogous mechanism based on possible existence of microperforations in the diaphragm was proposed for the phenomenon of cirrhotic fluid traversing the diaphragm. [2, 3, 4]

The gynaecologic causes of nonsurgical pneumoperitoneum are rare and occur when air passes through the genital tract via the uterus and fallopian tubes, e.g. vaginal insufflation by orogenital sex, postpartum knee-chest exercises, tubal insufflation in hysterosalpingogram and coitus. [2, 3]

In case of nonsurgical pneumoperitoneum progressive resolution of free air is expected within a few days. In the absence of symptoms and signs of peritonitis conservative management with control abdominal radiographs is recommended. [2, 3, 4]