A 43-year-old man visited the emergency room with epigastric pain. According to the patient, he had no significant medical or surgical history, except for hospitalization 20 years ago due to similar abdominal pain that resolved with conservative treatment. The patient's vital signs were stable and mild tenderness was noted on the epigastric area. The bowel gas pattern was non-specific on the initial plain radiographs. The abdominal CT scan was performed with using a 16 row detector CT (Sensation16, Siemens, Erlangen, Germany) at the portal phase after administering intravenous iodinated contrast agent (Ultravist 300, Bayer Schering Pharma, Berlin, Germany). We obtained the axial and coronal reformatted images that were 5 mm thick. A well-demarcated lesion approximately 15×10×6 cm in size with homogeneous fluid attenuation was noted in the pelvic cavity. The lesion was located within the rectovesical pouch, and it mimicked peritoneal inclusion cysts or loculated ascites. The abdominal pain subsided with conservative therapy and the patient was discharged.

Twenty days after the first visit to our hospital, he revisited the emergency room with recurred epigastric pain. He also complained of nausea and vomiting. The blood urea nitrogen and creatinine (42.4 and 2.09 mg/dL, respectively) were slightly more increased than before (14.2 and 1.06 mg/dL, respectively), but the other laboratory results were normal. On physical examination, there was tenderness and rebound tenderness on the epigastric area, with hyperperistaltic bowel sounds. The plain radiograph suggested a markedly distended inverted U-shaped small bowel loop with an air-fluid level (Fig. 1A). A second abdominal CT scan was performed after administering an intravenous contrast agent. A fluid density mass abutting to the small bowel loops was again noted in the pelvic cavity (Fig. 1B). A thin fatty layer between the mass and the small bowel suggested that the mass probably originated from the mesentery rather than from the bowel loop. Whirling of the mesenteric vessels and small bowels around the superior mesenteric artery was disclosed on the axial and coronal reformation images (Fig. 1C-G). The superior part of the cystic mass was insinuated into the whirl. A dilated small bowel was seen tapering with a beaked appearance at the center of the whirling and this continued to the collapsed small bowel that abutted the cystic mass in the pelvic cavity. A markedly distended small bowel loop proximal to the collapsed segment was found, and this corresponded with the distended bowel loop seen on the plain radiographs. All the findings were suggestive of volvulus of the small bowel with closed loop obstruction, and we presumed that the cystic mesenteric mass was the cause of the volvulus.

Diagnostic laparotomy was performed and a large cystic mass arising from the small bowel mesentery at 60 cm distance from the Treitz ligament was found (Fig. 1H). The mass consisted of multiple well-defined locules filled with clear fluid. There was no communication between the cystic mass and the lumen of the small bowel. We observed torsion of this cystic mass that caused volvulus of the connecting mesentery and 55 cm of the small bowel, and this eventually resulted in closed loop obstruction of the small bowel. The volvulus of the small bowel and mesentery was reduced by rotating the mass. There was stricture and luminal narrowing at the twisted small bowel, so segmental resection and end-to-end anastomosis were performed. The mass was pathologically confirmed as being a lymphangioma (Fig. 1I).

Small bowel volvulus is a condition that rarely occurs among adults. There are two distinct categories of small bowel volvulus: the first is the primary type that's defined as torsion of a segment of the small bowel mesentery without evidence of any predisposing anatomical abnormalities, and the secondary type is precipitated by underlying anatomical abnormalities, including postoperative adhesion, malrotation, congenital bands, intussusception, colostomy, fistula, tumors and Meckel's diverticulum (3). Although rare, a large mesenteric mass can rotate and be accompanied by volvulus of the connected mesentery and small bowel, and eventually closed loop obstruction of the involved bowel loop occurs (4-6). In our case, small bowel volvulus and a closed loop obstruction induced by the rotation of the mesenteric lymphangioma brought the patient back to the emergency room again. At the first emergency room visit, the patient's abdominal pain was associated with incomplete small bowel volvulus and the second time his symptoms were induced by complete small bowel volvulus, which made him return to the emergency room. Ischemic damage caused by repeated episodes of torsion by the mass was probably responsible for the stricture of the involved small bowel (7).

Lymphangioma is a congenital malformation of the lymphatic vessels and this is thought to usually be a pediatric disease. Approximately 95% of lymphangiomas are found in the neck and axilla and the other 5% occur in the mediastinum and abdominal cavity, including the mesentery, retroperitoneum and bones (3). The most common symptom of mesenteric lymphangioma is a palpable abdominal mass and abdominal distension (1). Intestinal obstruction related to the mesenteric cysts can be induced by compression or traction by the mass (6, 8). The typical CT feature of mesenteric lymphangioma is a multiloculated fluid-filled mass. The attenuation of the fluid varies according to the internal contents, from that of fluid to that of fat (1). Characteristic thin walls and septa also can be seen on a CT scan (3). MDCT with thin slice multiplanar reformation is helpful to not only diagnosis the lesion, but also to assess the complications such as volvulus, as was noted in our case.

There are two theories explaining the relevance between small bowel volvulus and lymphangioma. The first is that the flaccid and mobile characteristics of a mesenteric lymphangioma cause it to rotate, and this induces small bowel volvulus. The second is that longstanding or intermittent volvulus causes lymphatic obstruction, and this forms lymphatic cysts as a result. The latter case generally forms a unilocular cystic mass without internal septa (9, 10). In our case, a multilocular mesenteric cyst was the primary pathology that secondarily caused volvulus of the small bowel.

The differential diagnosis of a cystic lesion in the pelvic cavity includes reactive ascites, duplication cysts arising from the bowel or bladder, and cystic lesions of the seminal vesicle. In our case, the lesion was present before complete small bowel volvulus and the resultant closed loop obstruction, and this had a relatively unchanged morphology during 20 days. Also, the shape of the margin between the lesion and the adjacent small bowel was convex and lobulated. These findings were suggestive of a cystic mass rather than loculated ascites. In our case, the thin fatty layer between the mass and the small bowel loops told us that the mass did not directly arise from the bowel loops. Furthermore, after the volvulus of a mass and small intestine progresses, the intrusion of a part of the mass into the whirling of the bowel and mesentery reflects the flaccid characteristics of lymphangioma. In adults, mesenteric lymphangioma should be included to the list of rare etiologies of small bowel volvulus. Radiologic evaluation, and especially with MDCT, is critical for making the correct preoperative diagnosis and treatment plan.