Abstract:

Objective　To study the CT manifestations of Milligan’s septum(MS). 　Methods　The pelvic CT images of 172 patients with non-anal disorders were retrospectively analyzed, based on the 1.5 mm thin-slice reconstruction. The CT manifestations of their MS and adjacent fat tissue were observed using multiplanar reconstruction and appropriate window technique. 　Results　The density of upper fat tissue adjacent to MS was lower than that of lower fat tissue, and the difference in CT values between them was statistically significant (P<0.05). Compared with females, the density of fat tissue in the lower anal subcutaneous space was much higher in males (38．37% vs 88．37%), even to the extent that the difference between upper and lower fat tissues could be visually identified; the difference between genders was a statistically significant (P<0.05). The CT direct visualization rate of MS was about 23．26%; the soft tissue density shadows, which could be divided into the relatively symmetrically whole－course linear type, partially linear type and branched type, started from the junction of the subcutaneous and superficial parts of external anal sphincter and travelled to the ischial tuberosity. According to the statistical result of the maximum thickness collected from those showing direct visualization, the average values of left and right sides were（2.50±0.46）mm and（2.89±0.78）mm, and the average values of both sides in males and females were（2.71±0.43）mm and（2.69 ±0.44）mm, respectively. 　Conclusion　Milligan’s septum can be located according to the density difference between the fat tissues in the upper ischiorectal space and the lower anal subcutaneous space, while it can also be directly visualized on CT images in some cases.

Key words: Milligan&rsquo, s septum｜Anatomy｜Computed tomography｜Human