図１〜図５で遊離ガスを認める（↑）が，図３のｇ は図２の腸管内ガスと重なるので遊離ガスではない．空腸は図７の1から頭側へ展開し図３の10から尾側へ向かうが，図５の13〜図９の17まで壁肥厚（▲）を示している．腸間膜所見も豊富に認められる．図４の△はstranding（streaking：スジ状の濃度上昇）で，図５〜図９の△がinfiltration（浮腫または血液による不均一な，境界不鮮明な濃度上昇）で，図７〜図１１の※は均一な境界鮮明な液貯留で，腸液，血液または血腫（凝血塊）を意味する．従って空腸穿孔との診断となる．遊離ガス像を見落とされ経過観察となったが，翌日腹部単純写真で遊離ガスを認め手術となった．Treitz靱帯から50cmの部位の空腸に穿孔を認め単純閉鎖した．

参考症例（空腸穿孔）：空腸と思われる小腸（J）は他の小腸と比較して明らかな壁肥厚を呈している．図２〜図４で腹水（※）を，図１〜図６で腸間膜または（腹壁直下の）大網の濃度上昇（▲）を，図５と図６で遊離ガス（↑）を認め，空腸穿孔と診断する．図３の△は壁内気腫ではなく，Kerckring 襞間に位置するガスの可能性が高い．壁内気腫はニボーを形成しない線状ガスを示すことが多い．図５の白矢印は図４の腸管内ガスと重なるので遊離ガスではない．手術で空腸穿孔（図A：↑）が確認された．

文献考察：遊離ガスの10％はnon-surgical pneumoperitoneumである．
West J Med. 1999 Jan;170(1):41-6.
Nonsurgical causes of pneumoperitoneum.
Mularski RA, Ciccolo ML, Rappaport WD.

The radiographic manifestation of free air in the peritoneal cavity suggests serious intra-abdominal disease and the need for urgent surgical management. Yet, about 10% of all cases of pneumoperitoneum are caused by physiologic processes that do not require surgical management. We retrospectively reviewed cases of nonsurgical causes of pneumoperitoneum at the 2 teaching hospitals of a university medical center between January 1990 and December 1995. Successful management by observation and supportive care without surgical intervention was defined as the diagnostic feature of nonperforation. Failure of a laparotomy to delineate a surgical cause or to result in a reparative procedure is congruent with a nonsurgical cause of pneumoperitoneum. During this period, 8 patients (6 men and 2 women; mean age, 61 years) were identified with nonsurgical causes of pneumoperitoneum. Two patients underwent negative laparotomy, and the other 6 were successfully managed nonoperatively and discharged from the hospital. In 6 patients, a cause of the pneumoperitoneum was identified. The causes may be grouped under the following categories: postoperatively retained air, thoracic, abdominal, gynecologic, and idiopathic. In our review of the literature, 61 of 139 reported cases underwent surgical treatment without evidence of perforated viscus. To avoid unnecessary surgical procedures, both primary medicine physicians and surgeons need to recognize nonsurgical causes of pneumoperitoneum. Conservative management is warranted in the absence of symptoms and signs of peritonitis.PMID: 9926735