Introduction:
The descending colon is 25 cm long retroperitoneal organ, extending from left colic flexure to the brim of the pelvis; continues as sigmoid colon after passing along the left hypochondriac and lumbar regions.(1) Typical location and position of colon are developmental in origin and if interrupted, may lead to variety of pathological conditions.(2) CT scan of such anatomic variation of colon may confuse a radiologist even though it remains asymptomatic.(3) Most of the earlier studies and case reports mention volvulus, cancer and ulcerative colitis as the pathological conditions related to the colon.(4-7) We report a variant descending colon which was coiled in its lower part and had retained its mesocolon. We also discuss the embryological, functional and clinical aspects related to the anomaly.
Case Report
During dissection classes for first year medical students, we noted multiple variations of descending and sigmoid colons. The descending colon began at the left colic flexure and descended down in front of the left kidney in a usual manner. However, just below the level of kidney, it formed a coil before continuing as the sigmoid colon. The transition between descending and sigmoid colons was difficult to assess because both descending and sigmoid colons had a continuous mesocolon starting at the level of left colic flexure and ending at the level of third sacral vertebral segment. The descending colon did not pass through the left iliac fossa. Instead, after coiling, it shifted to the midline to continue as sigmoid colon. The sigmoid colon had a straight course, almost in the median plane before it continued as rectum. There were no associated vascular variations. The variations can be seen in figures 1-3.
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Figure 1: Photograph of abdomen showing the coiled descending colon (peritoneum and fat has been removed). Note the displaced position of the sigmoid colon. (JJ – jejunum; IL – ileum; TC – transverse colon; DC – descending colon; SC – sigmoid colon; LK – left kidney; PM – psoas major muscle; AA – abdominal aorta; AAW – anterior abdominal wall) |
Figure 2: Photograph of abdomen showing the coiled descending colon. Note the displaced position of the sigmoid colon and the continuity of descending and sigmoid mesocolons. (JJ – jejunum; IL – ileum; ME – mesentery of small intestine; DC – descending colon; SC – sigmoid colon; DMC – descending mesocolon; SMC – sigmoid mesocolon; AAW – anterior abdominal wall) |
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Figure 3: Photograph of abdomen showing the descending mesocolon. The coil of the descending colon has been retracted down by a hook. (JJ – jejunum; IL – ileum; ME – mesentery of small intestine; DC – descending colon; SC – sigmoid colon; DMC – descending mesocolon) |
Discussion
Descending and sigmoid colons develop from the hindgut. In the early stage of development, both of them possess their mesocolons. However, later on during development, the descending colon loses its mesocolon to become retroperitoneal. During embryonic period, failure of disappearance of descending mesocolon may lead to persistence of descending mesocolon in postnatal life (8, 9). In the present case, excessive length of descending colon and the persistence of mesocolon would have resulted in twisting and coiling; because any interruption or arrest of rotation of the intestine during fetal development may result in malrotation, which in turn can lead to volvulus formation.(10)
Numerous cases regarding the variant colon have been reported; however, only a few have been reported regarding the variations of descending colon specifically. Variant position of descending colon lying between the kidney and the psoas major muscle has been reported by Eiref et al.(3) Srivastava et al reported a right sided descending colon.(11) A displaced mesocolon along with sigmoid colon has been reported by Nayak et al (12), in which the descending colon descended in the midline of the abdomen. A redundant loop of descending colon that formed a second hepatic flexure has been reported by Gupta et al.(13) McBrearty et al have reported a case of knot formation in transverse and sigmoid colon due to twisting of a hyperactive bowel segment over a passive segment of bowel, which lead to lower abdominal pain and constipation.(14) Volvulus of colon can occur when there is axial twisting of the colon on its vascular pedicle. Volvulus commonly appears in sites such as sigmoid colon in 75 % of cases, cecum in 22%, transverse colon in 2% and splenic flexure in 1-2% of cases.(4) A case of volvulus formation in descending colon with left hemi-diaphragm elevation has been reported.(15) Torsion and volvulus formation of transverse and descending colon can also be seen in dogs.(16) When compared to the earlier reports on the variations of various parts of colon, present case seems to be unique as descending colon had a coiled nature and the sigmoid colon was unusually straight.
In the present case, the descending colon had mesocolon throughout its extent and its lower part was coiled. It is quite possible that such position of descending colon with presence of mesocolon may lead to formation of volvulus and intestinal obstruction.(9,17) The present case may become a cause of constipation and abdominal pain. Radiographic examinations such as barium enema and CT scan in such variant cases may lead to confusions. During colonoscopy, the colonoscope may find it difficult to pass through a spiral coiled descending colon or may not pass through coiled area at all, thus limiting the visibility beyond the sigmoid colon. Any forced attempt to perform colonoscopy in such cases may even lead to perforation of colon and subsequent complications. Surgeons, while performing segmental resection of the descending colon should be well aware of such variations. Malposition of sigmoid colon may pose problems during diagnosis, intervention and investigation.(11)
Conclusion:
Coiled descending colon with mesocolon can be cause of radiological misinterpretation and may pose difficulty in colonoscopy. It may become a cause of volvulus, intestinal obstruction, constipation and pain in abdomen. Thus radiologists, clinician and surgeons should be aware of such variations.
References
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- Nayak SB, Pamidi N, Shetty SD, Sirasanagandla SR, Ravindra SS, Guru A, et al. Displaced sigmoid and descending colons: a case report. OA Case Reports. 2013 Dec 24;2(17):166.
- Gupta Indrajit, Majumdar Sudeshna, Mandal Subhra. A redundant loop of descending colon and right sided sigmoid colon. Int J Anat Var (IJAV). 2012;5:11–13.
- McBrearty A, Harris A, Gidwani A. Transverse-sigmoid colon knot: a rare cause of bowel obstruction. Ulster Med J. 2011 May;80(2):107–8.
- Marshak JE, Panzarella P, Morim A, Iqbal S, Grendell JH. A "twist" on S1S2: descending colon volvulus causing severe left hemi-diaphragm elevation. J Emerg Med. 2014 Aug;47(2):59-60.
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- Shetty P, Nayak SB. Absence of transverse colon, persistent descending mesocolon, displaced small and large bowels: a rare congenital anomaly with a high risk of volvulus formation. Anat Cell Biol 2014;47:279-281.
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