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Puboanalis muscle

The puboanalis muscle is a subdivision of the levator ani muscle group, forming part of the pelvic diaphragm. It arises from the pubis and extends posteriorly to encircle the anal canal, inserting into the anococcygeal ligament. It plays a crucial role in maintaining anorectal angle, continence, and pelvic floor support. Because of its intimate relationship with the anal canal and rectum, it is of high clinical and radiologic importance in conditions such as incontinence, pelvic floor dysfunction, and anorectal malformations.

Synonyms

  • Pubo-anal part of levator ani

  • Puborectal subdivision (closely related)

  • Pubo-anal sling

Location and Attachments

  • Origin: Posterior surface of the pubic bone, close to the pubic symphysis

  • Course: Fibers pass posteriorly and medially, descending around the anal canal

  • Insertion: Blend with fibers of the external anal sphincter and attach into the anococcygeal ligament behind the anal canal

Relations

  • Anteriorly: Pubic symphysis and bladder base (in males), vagina/uterus (in females)

  • Posteriorly: Coccyx and anococcygeal ligament

  • Superiorly: Rectum and pelvic peritoneum

  • Inferiorly: External anal sphincter and ischioanal fossa

Function

  • Maintains the anorectal angle, which is vital for continence

  • Supports the anal canal and rectum as part of the pelvic floor

  • Contracts with the levator ani to elevate the pelvic diaphragm

  • Assists in defecation by relaxing in coordination with the external anal sphincter

Clinical Significance

  • Weakness or injury contributes to fecal incontinence

  • Involved in pelvic floor dysfunction and obstructed defecation syndrome

  • Target in pelvic floor rehabilitation and physiotherapy

  • Can be injured during childbirth, pelvic surgery, or trauma

  • Evaluated on MRI in pelvic floor dysfunction, rectal prolapse, and fistula mapping

MRI Appearance

T1-weighted images:

  • Appears as a thin, low-signal band extending from pubis to the anal canal

  • Surrounded by high-signal fat planes of the ischioanal fossa

T2-weighted images:

  • Low signal band, clearly outlined against bright pelvic fat and rectal lumen

  • Defects or atrophy appear as focal discontinuity or thinning

STIR (Short Tau Inversion Recovery):

  • Normal muscle shows low signal

  • Pathology (tears, edema, inflammation) appears bright

T1 Fat-Sat Post-Contrast:

  • Normal fibers show minimal or no enhancement

  • Pathological changes (abscess, tumor, inflammation) may show focal enhancement along course

CT Appearance

Non-Contrast CT:

  • Appears as a thin soft tissue density extending posteriorly from pubis to anal canal

  • Surrounded by lower density fat of the ischioanal fossa

Post-Contrast CT:

  • Normal muscle enhances only mildly

  • Pathology (infection, tumor, abscess) shows abnormal focal or rim enhancement

  • May be difficult to isolate on CT without pathology; better seen with MRI

MRI image

Puboanalis muscle MRI axial anatomy image-img-00000-00000

MRI image

Puboanalis muscle MRI axial anatomy image-img-00000-00000_00001

MRI image

Puboanalis muscle MRI axial anatomy image-img-00000-00000_00002