Bowel perforation with a serendipitous revelation: A case report on a rare developmental anomaly

INTRODUCTION

Peritoneal derived structures that surround the bowel loops act as a protective conduit for neurovascular bundle and also provide structural stability while allowing certain degree of mobility and help in accommodating the long bowel loops in a confined abdominal cavity.^[1] Various names are given to these peritoneal derived structures depending on the location and organ. Peritoneal folds that cover the viscera are usually called ligaments and that cover the small bowel and large bowel are called mesentery and mesocolon, respectively. The parts of the small bowel loops (duodenum) and large bowel loops (right and left colon), which are relatively immobile, are fixed to the posterior abdominal wall and lack peritoneal folds.^[2] Persistent descending mesocolon (PDM) is an underreported and rare congenital anomaly with multiple clinical and surgical implications.^[3]

CASE REPORT

Imaging and intraoperative findings

The patient was subjected to contrast-enhanced computed tomography (CT) scan examination, which revealed small bowel perforation in the form of diffuse edematous wall thickening of the ileal loops, extraluminal air foci, and moderate ascites [Figure 1a and b]. Furthermore, the CT scan revealed a redundant sigmoid colon.

Close

Figure 1:

(a) Axial post-contrast computed tomography (CT) of the abdomen shows bowel wall edema (yellow arrow), extraluminal air foci (blue arrow), and ascites. (b) Axial post-contrast CT of the abdomen in lung window depicts the extraluminal air foci better (arrows). (c) Intraoperative image shows ileal perforation (blue arrow) and (d) shows descending colon (yellow arrow) lying posterior to the small bowel mesentery (blue arrow).

Export to PPT

The patient was taken for emergency laparotomy, and ileal perforation was confirmed [Figure 1c]. Furthermore, the descending colon was found to lie immediate posterior to the small bowel mesentery [Figure 1d]. The review of CT images showed a right-sided sigmoid colon, medialization of the descending colon, medial to the hilum of the left kidney, and posterior to the small bowel mesentery [Figure 2a-f]. These features were suggestive of PDM.^[3,4] Furthermore, inferior mesenteric artery (IMA) was directed to the right of the midline with trifurcation into two sigmoid arteries and superior rectal artery with no definite left colic arterial branch [Figure 2e].

Close

Figure 2:

(a and b) Scannogram images of the patient of interest without (a) and with (b) superimposed schematic graphics show a case of persistent descending mesocolon with medialization of the descending colon (light blue shade), medial to the left renal hilum, right-sided sigmoid colon (light blue shade), and normal position of rest of the colon (dark blue shade). (c) Post-contrast computed tomography (CT) abdomen axial section shows medialized descending colon (yellow arrow), medial to the left renal hilum (white dotted line), absent large bowel in the left lateral aspect of the abdominal cavity (blue arrow). (d) CT axial maximum intensity projection (MIP) reformat depicts medialized descending colon (yellow arrow) sandwiched between small bowel mesentery (blue arrow) and left renal hilum (white star). (e) Coronal MIP reformat shows the right-sided course of the inferior mesenteric artery and three branches, namely two sigmoid branches and superior rectal branch (pink arrows). (f) Sagittal reformat through the left renal hilum (white star) shows the medialized descending colon (yellow arrow).

Export to PPT

DISCUSSION

During embryological development, the entire alimentary tract, from the pharynx to the anus, has a mesentery. As the fetus matures, the mesentery gets resorbed at some parts and persists at some parts of the gastrointestinal tract. The parts of the gastrointestinal tract with persistent derived structures (mesentery, ligament, and mesocolon) in an adult are stomach, small bowel, transverse colon, and sigmoid colon. The dorsal mesentery of the ascending colon and descending colon gets resorbed, and both the right colon and the left colon get attached to the lateral and posterior parietal peritoneum by the process called fixation, which begins around 10 weeks of gestation.^[2] This process of fusion of descending colon with posterior and lateral parietal peritoneum gets completed by the 5^th month of gestation.^[3] The absence of fixation leads to increased mobility in the colon and is called “persistent colonic mesentery.” This anatomical variation was found in 20% of infantile autopsies without intestinal malrotation, 14% of adult autopsies, and 10% of patients with intestinal volvulus.^[2]

PDM is characterized by the presence of residual mesentery that usually extends from the splenic flexure to the sigmoid colon with resultant right-sided sigmoid colon and medialization of the descending colon, medial to the left renal hilum.^[3-5] Complications of PDM include primary intestinal obstruction, colonic volvulus, colonic varices, and intussusception.^[3-6] Altered large bowel course can potentially cause local venous hypertension and can lead to colonic varices.^[5] Furthermore, PDM is known to cause increased surgical time in cases of left hemicolectomy due to variant vascular anatomy and associated multiple congenital adhesions. Furthermore, few studies suggested PDM predisposes for anastomotic failure after left hemicolectomy.^[4]

Altered course of IMA with atypical branching in the form of bear claw was reported in cases with PDM.^[3] To our knowledge, this is the first report of PDM with right-sided course of the IMA. Endoscopy in patients with PDM can be misinterpreted as redundant sigmoid colon because endoscopic examination is an inherently weak modality to assess extramucosal/extramural pathologies of the bowel.^[5] Nevertheless, CT offers exquisite three-dimensional details of the bowel loops and potentially enables the radiologists, to pick up this rare anomaly preoperatively. Hence, radiologists must be aware of such developmental anomalies and prompt recognition of this anatomical variant in pre-operative imaging would help the surgeon in adequately planning the surgery and also could help in assessing the prognosis.^[3-6]

CONCLUSION

PDM is a rare anatomical variant with surgical implications, especially in patients with left colonic cancer and patients who are planned for left hemicolectomy. Medialization of the descending colon, medial to the left renal hilum with right-sided sigmoid colon favors the diagnosis of PDM. Prompt recognition of this anatomical variant in pre-operative imaging will be very useful in surgical planning and prognostication.

TEACHING POINTS

1. Failure of resorption of the mesentery of the left colon during the 5^th month of gestation leads to a rare developmental anomaly called PDM, which is characterized by a redundant course of descending colon marked by medialization of descending colon medial to the left renal hilum and right-sided sigmoid colon

2. PDM is better diagnosed in CT as endoscopy has limitations in characterizing extraluminal pathologies such as altered vascular course and associated other intra-abdominal congenital anomalies

3. Although PDM is a rare developmental anomaly, it is known to predispose the patients to primary intestinal obstruction, colonic volvulus, colonic varices, intussusception, increased surgical time during left colectomy, and anastomotic failure after left hemicolectomy

4. It is essential that radiologists must be aware of this rare yet potentially dangerous anomaly which has many pre-operative, intraoperative, and postoperative implications. Timely recognition of this anomaly and prompt communication with the surgeon would play a vital role in surgical planning and prognostication.