Internal hernias are defined as protrusion of a viscus through a normal or an abnormal peritoneal or mesenteric aperture within the confines of the peritoneal cavity . Internal hernias account for about 0.5-5.8% of all cases of SBO. Herniation involving the sigmoid mesocolon accounts for about 6% of all internal hernias .
Benson and Killen classified herniation of the sigmoid mesocolon into three types: (1) intersigmoid hernias, (2) transmesosigmoid hernias, and (3) intramesosigmoid hernias . On the basis of this classification, the present case was classified as an intersigmoid hernia (ISH).
The intersigmoid fossa is located in the area where the sigmoid colon turns from an upward direction to the right, where there is an attachment of the mesocolon to the posterior abdominal wall. Although it is a distinct and fairly constant structure, a recent study demonstrated it in 65% of autopsy cases . However, individuals with this structure do not develop internal hernia routinely, because incarceration of the small bowel behind the mesosigmoid is necessary. Therefore, this type of internal hernia may have other causes such as elongation of the mesentery of the small bowel or incarceration of the small bowel within the pelvic space .
A recent report revealed that preoperative differentiation of these three types of hernia involving the sigmoid mesocolon is difficult, and the diagnosis is confirmed only with surgical management in most cases . However, there is a typical formation in ISH that incarcerated small bowel loop and is formed from left lower abdomen to cranial side, because hernia orifice of ISH is located to the attachment of the lateral aspect of the sigmoid mesocolon . Similarly, it is difficult to distinguish ISH from intramesosigmoid hernia (especially lateral type) using only CT findings, because incarcerated small bowel is formed from lower abdomen to cranial side in these two types of hernias . Therefore, it is acceptable that final diagnosis should be defined by using intraoperative findings rather than preoperative CT findings in these two types of hernias.
On the other hand, it is important to distinguish transmesosigmoid hernia from the above two types of hernias because, transmesosigmoid hernia has not only a higher bowel resection rate (50%) than the other two types of hernias (ISH; 18.8%, intramesosigmoid hernia; 13.8%) but also a higher mortality rate (7.1%) (ISH; 0%, intramesosigmoid hernia; 0%) .
Therefore, laparoscopic surgery should be performed for patients with sigmoid mesocolon hernia, except for patients with transmesosigmoid hernia, because it is not difficult to distinguish transmesosigmoid hernia from other two types of hernias. In fact, patients with transmesosigmoid hernia require shorter time from symptom onset to operation (2.2 ± 3.2 days) than those with other two types of hernias (ISH; 7.7 ± 7.0 days, intramesosigmoid hernia; 11.8 ± 8.4 days) .
Thus, laparoscopic surgery is acceptable for patients with ISH, and intraoperative observation is useful to distinguish ISH from intramesosigmoid hernia.
Recently, laparoscopic surgery has been broadly performed for SBO. Laparoscopic surgery has not only high diagnostic value but also minimal invasiveness in comparison with open surgery. In particular, because ISH has few specific clinical findings or symptoms, preoperative diagnosis can be very difficult. Therefore, laparoscopic surgery is recommended for not only treatment but also diagnosis of SBO due to internal hernia, because it is not rare for internal hernia to be diagnosed after laparotomy.
Between 2002 and 2014, a total of 19 cases of ISH were reported from Japan. Among the patients, 7 (37%) were diagnosed before surgery and 3 (16%) underwent bowel resection because of obvious small-bowel necrosis. Therefore, most patients with ISH do not require small-bowel resection . In addition, 15 patients (79%) underwent closure of the hernia orifice for prevention of hernia recurrence.
Therefore, with regard to the indication for small bowel resection, it should be performed when obvious small bowel necrosis was found or the color of small bowel was not so good. However, because intraoperative observation cannot evaluate the intraluminal change of small bowel, we correctly estimate the blood flow of small bowel by using a fluorescence imaging instrument  when we cannot define the indication of small bowel resection on the basis of intraoperative findings.
With regard to the indications for closure of the hernia orifice, we consider that if, on the basis of intraoperative observation, the hernia orifice appears small and there is a possibility that incarceration of the small bowel may recur, the hernia orifice should be closed. On the other hand, if the hernia orifice is large and there is no possibility of the small bowel becoming incarcerated, then it is acceptable not to close the hernia orifice. In the present case, we enlarged the hernia orifice to prevent recurrence of incarceration after mobilization of the sigmoid colon.
In addition, with regard to the reason of small bowel incarceration to the fossa of sigmoid mesocolon, it is supposed that estimating the reason of small bowel incarceration is difficult, because intraoperative observation revealed that there was no concrete evidence to distinguish congenital one from adhesion due to infection in the case.
During operation, we tried to retrieve incarcerated small bowel from intersigmoid fossa by tender operation, and we inserted the tissue pad of power device to the edge of hernia orifice to prevent small bowel injury, because incarcerated small bowel was fixed to the hernia orifice of sigmoid mesocolon.
Moreover, although long-tube insertion for treatment of SBO is not broadly recommended in Western countries, it may be needed in order to perform safe laparoscopic surgery with a sufficient space in the abdominal cavity, since it not only reduces the intraluminal pressure of the dilated small bowel but also facilitates correct preoperative diagnosis using gastrografin contrast enema. Similarly, even if resection of the small bowel is required, sufficient decompression using long-tube insertion is necessary to expedite not only safe anastomosis but also reliable reconstruction.