Morphometry of the adult sigmoid colon and relation to volvulus

METHOD: Ninety five sigmoid colons (fifty male subjects) were harvested at autopsy. The following measurements were made: length of the sigmoid colon, length of the mesocolon root, height of the mesocolon. The sigmoid length. mesocolic root length ratio and sigmoid length: mesocolic height ratios were also calculated. All means and ratios were compared for gender using the Student t-test. P < 0.05 was considered statistically significant.


Introduction
The sigmoid colon is the commonest site for volvulus formation.The incidence of sigmoid volvulus shows both gender and population disparities being more common in males and in several developing countries (1)(2)(3)(4).In Africa, epidemiological studies indicate a higher incidence of sigmoid volvulus in males than females with a male to female ratio ranging from 9:1 in South Africa (5,6) to 13.5:1 in Ethiopia (7).Elsewhere, similar gender pattern is documented and is thought to be due to anatomical factors (1,2).Sigmoid loops with tall mesocolons (dolichomesocolic) show a male predominance while loops with short mesocolons (brachymesocolic) depict a female predominance among Indians (1) and Caucasians (3).The literature on the morphometry of the sigmoid colon among Africans is limited (8).
This study describes the morphometric features of the sigmoid colon in adult Kenyans autopsied at a University and a city council mortuary in Nairobi.

Materials and Methods
Ninety fi ve sigmoid colon specimens were obtained during autopsy examinations performed at the Chiromo and Nairobi city mortuaries.Ethical approval was obtained from the Kenyatta National Hospital Ethical Review Committee (KNH-ERC) before specimen retrieval from fi fty adult males and forty fi ve adult females.The ages of the subjects used Morphometry of the adult sigmoid colon and relation to volvulus ranged from twenty one to fi fty six years.The effects of post mortem shrinkages were limited by taking measurements from subjects that had died within forty eight hours.
The colons were accessed through midline abdominal incisions used at autopsy.After refl ection of the small intestines and the bladder (uterus in females), the sigmoid colons were identifi ed and both the root and vertical lengths of sigmoid mesocolon measured in situ (Figure 1).The length of the sigmoid colon at the antimesenteric border was also estimated (in centimeters) using a tape measure.
Two indices relating the total length of the sigmoid colon and the vertical height of the mesocolon to the length of the mesocolon root were calculated as shown; • Index 1 = sigmoid colon length/mesocolon root length (S 1/S3) • Index 2 = mesocolon vertical height mesocolon root length (S2/S3) The results of the measurements were tabulated and analyzed using computer software and statistical package of social sciences (SPSS) for windows version 11.50, Chicago Illinois, 2002.The means and the calculated ratios were compared for males and females using the Student t-test.The level of signifi cance was set at P < 0.05.

Results
The length of the sigmoid colon in the studied sample ranged from 27.6cm to 46.7cm in males and 27.1cm to 40.2cm in females.Most sigmoid colons measured 30-34.9cm in length (41.7%).
The range of the mesocolic vertical height was 3.1cm to 26.4cm in males and 9.5cm to 18.1cm in females.The mean vertical height was 15.1 ± 4.3 cm and 13.4 ± 2.6cm in males and females respectively (Table 1, Figure 3).
The average value of index 1 (sigmoid colon length/mesocolon root length) was 2.68 in males and 1.76 in females (p = 0.004).The average value of index 2 (mesocolon vertical height/mesocolon root length) was 1.22 in males and 0.74 in females (p = 0.024).
Male subjects generally had longer sigmoid loop length, shorter mesocolic root lengths and longer mesocolic heights.Female subjects possessed shorter sigmoid loops, longer mesocolic root lengths and shorter mesocolic heights (Figures 2, 3 and 4).Population studies have shown that sigmoid volvulus is more common in males than in females (1,3) implicating a morphometric basis in the susceptibility to this pathology.The longer sigmoid loop in males may be the anatomic factor.Morphometric dimensions of the sigmoid mesocolon studied here also showed signifi cant gender difference.The root length was 14.3cm for males and 18.4cm for females (average, 16.0cm) (P = 0.012).Previous studies suggest that individuals with a long sigmoid colon length and short mesocolon root length are more susceptible to volvulus (1).From indices calculated in this study, taking account of these colon and mesocolon dimensions, index 1 was 2.68 for males and 1.76 for females while index 2 was 1.22 for males and 0.74 for females.
Both indices indicated that males in the studied population are more prone to volvulus formation than females.The current results therefore extend the observation that the sigmoid mesocolon in the male is dolichomesocolic (longer than wide), whereas the female mesocolon is brachymesocolic (wider than long) (1).Accordingly, the narrower mesocolic root and a longer vertical length of the mesocolon make the male sigmoid colon more prone to volvulus (3).
In conclusion the adult male sigmoid colon is longer in males than in females with a shorter root length.This pattern, added to a longer mesocolic height forms the anatomical basis for higher prevalence of sigmoid volvulus in males in Africa.

Figure 3 :Figure 4a :
Figure 3: Short mesocolon height of a thirty two year old female.The height was 3cm, the lowest recorded mesocolic parameter