Puborectalis Muscle: Anatomy, Origin, Insertion, Nerve Supply, Function, Clinical Significance, MRI & CT Imaging

Topic

Puborectalis muscle

The puborectalis muscle is a U-shaped, sling-like muscle that forms part of the levator ani group within the pelvic floor. It arises from the pubic bones and encircles the anorectal junction, maintaining the anorectal angle critical for fecal continence. By creating a muscular sling, the puborectalis acts as a dynamic sphincteric structure, complementing the internal and external anal sphincters.

It is considered one of the most important muscles in the mechanism of continence and defecation, and is frequently evaluated in pelvic floor imaging, anorectal dysfunction, and colorectal surgery.

Synonyms

Puborectal sling
Puboanalis portion of levator ani
Anorectal sling muscle

Origin, Course, and Insertion

Origin:
- Arises from the posterior surface of the body of the pubis, close to the pubic symphysis
Course:
- Fibers sweep posteriorly and inferiorly, looping around the posterior aspect of the anorectal junction
- Forms a U-shaped sling around the rectum, pulling it forward toward the pubis
Insertion:
- Fibers unite behind the rectum, forming a muscular loop, blending with the contralateral puborectalis and connective tissue of the anorectal junction

Relations

Anteriorly: Pubic symphysis and bladder (in males), vagina (in females)
Posteriorly: Rectum and anal canal
Laterally: Pubococcygeus and iliococcygeus muscles (other components of levator ani)
Inferiorly: External anal sphincter
Superiorly: Pelvic viscera (rectum, prostate, uterus, vagina depending on sex)

Nerve Supply

Direct branches from the nerve to levator ani (S3–S4)
Contributions from the pudendal nerve

Arterial Supply

Inferior rectal artery (branch of internal pudendal artery)
Inferior gluteal artery
Internal pudendal artery branches

Venous Drainage

Venous blood drains via the pudendal venous plexus into the internal iliac vein

Function

Maintains the anorectal angle (~80–90° at rest), essential for continence
Contracts to prevent involuntary defecation by tightening the anorectal junction
Relaxes during voluntary defecation, allowing rectal straightening and stool passage
Supports the pelvic floor and contributes to core stability

Clinical Significance

Weakness or injury (e.g., obstetric trauma, pelvic surgery) may cause fecal incontinence
Overactivity or spasm contributes to anismus and obstructed defecation syndrome
Frequently evaluated in defecography, dynamic pelvic floor MRI, and anorectal manometry
Key target in biofeedback therapy and pelvic floor rehabilitation

MRI Appearance

T1-weighted images:

Muscle shows low-to-intermediate signal intensity
Fatty infiltration or atrophy shows higher signal

T2-weighted images:

Low-to-intermediate baseline signal
Hyperintensity may indicate edema, denervation, or inflammation

STIR (Short Tau Inversion Recovery):

Low-to-intermediate baseline signal
Bright signal indicates spasm, strain, or inflammation

Proton Density Fat-Sat (PD FS):

Baseline low-to-intermediate signal intensity
Abnormal bright areas indicate pathology or trauma

T1 Fat-Sat Post-Contrast:

Normal muscle enhances mildly and uniformly
Pathology (abscess, infection, neoplasm) shows focal or rim enhancement

CT Appearance

Non-Contrast CT:

Appears as a symmetric sling-like soft tissue band posterior to the anorectal junction
Hematoma appears as hyperdense region
Fatty degeneration appears as low density

Post-Contrast CT: