Department of Radiology, Tri-Service General Hospital, National Defense Medical Center, No 325, Sec. 2, Cheng-Gung Road, Nei-Hu 114, Taipei, Taiwan, Republic of China 2 Department of Internal Medicine, Tri-Service General Hospital, National Defense Medical Center, No 325, Sec. 2, Cheng-Gung Road, Nei-Hu 114, Taipei, Taiwan, Republic of China 3 Department of Surgery, Tri-Service General Hospital, National Defense Medical Center, No 325, Sec. 2, Cheng-Gung Road, Nei-Hu 114, Taipei, Taiwan, Republic of China
We present a rare case of strangulated closed loop small bowel obstruction secondary to a transmesosigmoid hernia to emphasize the diagnostic role of computed tomography in patients with no history of previous surgery. The characteristic computed tomographic features showed a cluster of dilated, ﬂuid-ﬁlled, U- and C-shaped loops of small bowel entrapped the left posterior and lateral to the sigmoid colon through a defect in the mesosigmoid, which caused anterior and medial displacement of the sigmoid colon.
An 81-year-old female presented to the emergency room with a 12-h history of diffusely cramping, abdominal pain chieﬂy focused below the umbilicus. She experienced occasional nausea, vomiting, and diarrhea for several days before arrival. There was no history of abdominal surgery, but she had been admitted once for “bowel obstruction” 1 year before. Physical examination showed her to be well developed and well nourished but in acute distress. Body temperature was 36.5°C, pulse rate was 84 beats/min, and blood pressure was 160/80 mmHg. The abdomen was slightly distended with diffuse tenderness, more marked in the left lower quadrant, but no peritoneal sign or shifting dullness could be elicited. Bowel sounds were hyperactive. Laboratory studies showed a white blood cell count of 9500/L, with neutrophil predominance (neutrophil:lymphocyte, 93:7). Blood sugar, serum urea nitrogen, and serum levels of creatinine, amylase, calcium, phosphorus, and potassium were within normal limits. Plain abdominal radiography showed dilatation of continuous loops of the small intestine but without air in the colon, indicating mechanical small bowel obstruction. Axial spiral CT (Somatom Hi-Q, Simens Medical System, Germany) through the entire abdomen and pelvis was performed with intravenous and oral contrast but without rectal contrast administration. CT images were obtained at the portal venous phase and demonstrated marked dilatation of the proximal small intestine. Three consecutive CT scans in the upper pelvis delineated ﬁxed radial distribution of ﬂuid-ﬁlled distended loops of the small bowel occupying the left upper pelvis. This encapsulation of bowel loops converged medially toward a rent between the sigmoid colon and the left psoas muscle, which signiﬁed a defect of the sigmoid mesocolon (Fig. 1A). The sigmoid colon showed
Key words: Internal hernia—Transmesosigmoid hernia— Small bowel obstruction—Computed tomography
Internal hernia through the sigmoid mesocolon is a rare clinical manifestation and accounts for approximately 6% of all internal hernias . Preoperative diagnosis is difﬁcult and has been established mainly by surgical exploration [2, 3]. Only eight cases of transmesosigmoid hernia have been published in the English-language literature, but all lack computed tomographic (CT) ﬁndings [2– 6] or reported uncertain diagnosis even after CT evaluation . Our case was an elderly female with sudden onset mechanical small bowel obstruction. CT demonstrated internal herniation of the small bowel through a mesosigmoid defect, which then caused closed loop obstruction and ischemic change. To our knowledge, the CT appearance of closed loop small bowel obstruction and strangulation secondary to a trans-mesosigmoid hernia has not been described in the radiologic literature. Correspondence to: J.-C. Yu; email: [email protected]
C.-Y. Yu et al.: Strangulated trans-mesosigmoid hernia
Fig. 1. A CT section at the level of the upper pelvis shows distended ﬂuid-ﬁlled loops of small bowel (B) locking into the left posterior lateral aspect of the sigmoid colon (arrow) through the mesosigmoid defect (arrowhead). This defect is between the sigmoid colon and the left psoas muscle (P). B CT section 1 cm cranial to the view shown in A shows Ushaped dilated small bowel loops (B) with prominent mesenteric vessels (arrowhead), which indicate closed loop obstruction. The sigmoid colon (arrow) shows anterior and medial displacement. C CT section 1 cm cranial to the view shown in B shows C-shaped closed loop obstruction with wall thickening (short arrow) and mesenteric fat obliteration, which represent ischemic change. The sigmoid colon (long arrow) also shows anterior and medial displacement.
anterior and medial displacement by a distended U- and C-shaped loop of small bowel, which represented closed loop obstruction (Fig. 1B,C). In addition, the loop showed wall thickening and attached mesenteric fat obliteration, strongly suggestive of strangulation (Fig. 1C). Emergency laparotomy through a midline incision of the lower abdomen and pelvis was carried out. A mesosigmoid defect of approximately 5 cm was found in the posterior aspect of the sigmoid colon, trapping a closed loop of ileum (140 cm distal to the Treitz ligament) with incarceration (Fig. 2). The ring of the sac was incised, and a 20-cm segment of ileum was released. Grossly, it showed twisting with gangrenous change. The hernia defect was repaired with suture ligation, and the gangrenous portion of the small intestine was resected. The patient recovered uneventfully.
Discussion Internal hernias involving the sigmoid mesocolon may present in one or both mesenteric leaves and are divided into three distinct categories: intersigmoid; intra-mesosigmoid, and trans-mesosigmoid [2, 3]. The most common type is the intersigmoid hernia, which arises in the congenital fossa located in the attachment of the lateral aspect of the sigmoid mesocolon and reaches the
posterior abdominal wall . Only 32 cases have been reported in the English-language literature since 1885 . Intra-mesosigmoid hernia occurs when the defect in the sigmoid mesocolon affects only the left leaf of the peritoneum, and the hernia sac lies within the sigmoid mesocolon itself. Only one case has been reported . Trans-mesosigmoid hernia develops when loops of intestine pass through a defect in the sigmoid mesocolon and the defect involves both layers of the sigmoid mesentery. This hernia is demonstrated to be without an actual hernia sac . Seven cases have been reported in the English-language literature but without CT images [2– 6]. One case reported CT evaluation but did not offer a deﬁnite preoperative diagnosis . In our case, CT was performed in the acute obstruction state, and the key CT ﬁndings for diagnosis included (a) a cluster of dilated ﬂuid-ﬁlled loops of small bowel entrapped in the left posterior and lateral aspect of the sigmoid colon through a mesosigmoid defect; (b) the defect located between the sigmoid colon and the left psoas muscle; (c) the sigmoid colon showed anterior and medial displacement; (d) these encapsulated loops of small bowel showing U- and C-shaped conﬁgurations and wall thickening representing closed loop obstruction and ischemic change; (e) attached mesentery with vessel engorgement and fat obliteration in-
C.-Y. Yu et al.: Strangulated trans-mesosigmoid hernia
ing closed loop obstruction remains critical to preserve bowel viability . Some have recommended direct surgical exploration for all acute onset, high-grade small bowel obstructions, which renders mandatory preoperative CT equivocal . Nevertheless, correct surgical incision requires detailed anatomic information before any procedure. Early diagnosis with CT may decrease a time-consuming and unnecessary procedure such as laparoscopy . A mesosigmoid defect associated with an internal herniation is very rare. Our case demonstrated that CT is a valuable imaging tool for preoperative diagnosis of closed loop small bowel obstruction and strangulation secondary to a trans-mesosigmoid hernia. References
Fig. 2. Diagrammatic illustration of the course of the transmesosigmoid hernia with closed loop small bowel (B) obstruction and torsion (arrow). The sigmoid colon (S) shows anterior and medial displacement.
dicating strangulation; and (f) proximal small intestine showed dilatation. In a patient without obstruction, trans-mesosigmoid hernia may be diagnosed on the postevacuation ﬁlm of barium enema showing sacculated ileal loops occupying the left lower abdomen with elevation and right lateral displacement of the sigmoid colon . However, this imaging study would not be useful when this type of hernia is associated with closed loop obstruction. In mechanical high-grade small bowel obstruction, the limitations of small bowel followthrough for emergency use may relate to the long time for barium to progress to the obstruction transition zone, dilution of contrast material in the intestinal contents, and inability to produce the clearcut images necessary for diagnosis . Enteroclysis can be performed more quickly, and it has been shown to have 85% accuracy in the evaluation of small bowel obstruction . However, it is contraindicated in patients with high-grade closed loop obstruction and in those with suspected strangulation . Recently, CT has demonstrated importance for the preoperative evaluation of patients with suspected intestinal obstruction [10, 11]. Its speed and ability to visualize the cause of obstruction makes it particularly valuable in the acute setting. CT can not only differentiate high- from lowgrade small bowel obstruction  but also offers speciﬁc features for the diagnosis of closed loop obstruction . The small aperture of a hernia sac with bowel loop entrapment is especially dangerous because of its potential for rapid development of strangulation. Early recognition of strangulat-
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