Left mesocolic hernia presenting as an abdominal lump in an adult

To the Editor: Mesocolic hernias are rare congenital abnormalities caused by malrotation of the midgut and entrapment of the major part of the small gut within a peritoneal sac formed by the developing mesentry of the descending colon.¹ They present with chronic digestive symptoms or with acute intestinal obstruction, gangrene or perforation of the gut.² They are mostly diagnosed incidentally at laparotomy for other conditions or at autopsy.³

We describe an adult male with left-sided mesocolic hernia, presenting with chronic atypical abdominal pain and dyspeptic symptoms along with a very unusual finding of a fairly large and extremely mobile abdominal lump. A 40-year-old man presented with acute colicky abdominal pain along with bilious vomiting for 12 hours and a history of episodic abdominal pain and dyspepsia since childhood. For the last 3 months he could feel a lump in the left upper abdomen, mostly during the episodes of pain. Physical findings included an extremely mobile, globular, slightly tender mass about 10 cm in diameter, in the left upper quadrant (LUQ) of the abdomen. Total blood count and biochemical parameters were normal. Straight x-ray of the abdomen showed dilated loops of small gut in the LUQ. An upper GI barium study, done after conservative management and which relieved his obstructive symptoms, revealed conglomerated loops of small gut in the LUQ of the abdomen, a caecum at a higher level than normal and to the left of midline (Figure 1). Exploration revealed almost ⅔ of the small gut encapsulated in the LUQ within a peritoneal sac formed by the descending mesocolon, after gaining entry through a ring below the fourth part of the duodenum. An engorged inferior mesenteric vein (IMV) formed the anterior border of the neck of the sac while the inferior mesenteric artery coursed along the left side of the sac. The ascending colon did not show retroperitoneal fixation.

Figure 1.

Barium-filled loops of small gut in the left upper quadrant of the abdomen.

The entrapped, viable small gut was brought to the right side through the hernial ring after skeletonizing the IMV; the redundant sac was excised after closing the hernial ring. Appendicectomy was also performed. Postoperative recovery was uneventful.

Mesocolic hernias are a rare congenital internal hernia arising from an error of rotation of the midgut when the small bowel invaginates into the mesocolon as the later undergoes rotation and retroperitoneal fixation. Failure of rotation of the pre-arterial segment of the midgut around the superior mesenteric artery in the presence of normal rotation of the post-arterial segment results in right mesocolic hernia, where the small gut remains trapped behind the right mesocolon, in the right upper quadrant of the abdomen.⁴ On the other hand, left mesocolic hernia, as in our case, results when the small bowel rotates to the left superior portion of the abdominal cavity between the IMV and the retropritoneum, and during this process invaginates an avascular portion of the descending mesocolon before the later gets fixed to the retroperitoneum.⁴ Thus the IMV forms the anterior margin of the narrow hernial ring.

Congenital mesocolic hernias and herniations into one of the paraduodenal fossae are two distinct clinical entities. The later results from herniations into small peritoneal recesses formed due to abnormal fixation of the fourth part of duodenum.⁴ In either case, preoperative diagnoses of these internal hernias are difficult.^2,3

Though in this reported case the herniated loops of small gut could be reduced easily, it may not be so easy. Sometimes the hernial orifice may be difficult to identify and the engorged IMV may make the reduction potentially dangerous.⁴ Sometimes it may be necessary to sacrifice the inferior mesenteric vessels to reduce the hernia⁵ though most of the time this is unnecessary,^1,2 provided the IMV is properly skeletonized on the right margin and then reduction is attempted. Following reduction the IMV returns to the left of the base of the mesentry of small bowel. Appendicectomy is always performed to avoid any future diagnostic confusion arising from the abnormal position of the caecum.