Objective:

To evaluate the normal anatomy of perianal muscles using high-resolution magnetic resonance imaging (MRI) with phased array coil.

Methods:

A total of 38 normal adults [16 males and 22 female

media age (56.319.7) years

]

underwent anal MRI with an abdominal phased array coil. The relationship among puborectalis muscle

levator ani muscle and external anal sphincter

fiber bundles of external anal sphincter and comp

onents of conjoint longitudinal muscle were analyzed. The length of anal canal

external anal sphincter and puborectalis muscle

the thickness of puborectalis muscle

external anal sphincter and internal anal sphincter were measured. The differences between males and females were compared.

Results:

Optimal image quality of puborectalis muscle

levator ani muscle

internal anal sphincter and external anal sphincter was obtained in all cases. Puborectalis muscle was an independent structure

with fat spaces separating among the superior levator ani muscle and inferior external anal sphincter. External anal sphincter had three separated muscular fiber bundles: deep

superficial and subcutaneous. Two longitudinal muscle layers were in the space between external anal sphincter and internal anal sphincter. The thickness of external anal sphincter in males [(4.10.7 mm)

]

was greater than that in females [(3.40.6) mm

]

(

P

=0.003). There was no significant difference in the length of anal canal

external anal sphincter and puborectalis muscle

and the thickness of puborectalis muscle

internal anal sphincter and external anal sphincter between males and females (

P

＞0.05).

Conclusion:

High-resolution mri with phased-array coil can display the anal canal and perianal structures in great detail

which will provide valuable information for the diagnosis and treatment of anal diseases.