Levator Ani Muscle: Anatomy, Origin, Insertion, Nerve Supply, Function, MRI & CT Imaging

Topic

Levator ani muscle

The levator ani is the principal muscle of the pelvic diaphragm, forming a broad, thin sheet that supports the pelvic organs and maintains continence. It consists of three main components: puborectalis, pubococcygeus, and iliococcygeus. Together, they provide structural and functional integrity of the pelvic floor, assist in urinary and fecal continence, and play an important role during childbirth.

Synonyms

Pelvic diaphragm muscle
Pelvic floor muscle group
Puborectalis–pubococcygeus–iliococcygeus complex

Origin, Course, and Insertion

Origin:
- Arises from the posterior surface of the body of the pubis, the tendinous arch of obturator fascia, and the ischial spine
Course:
- Fibers pass downward, backward, and medially, forming a broad muscular sling across the pelvic floor
- Puborectalis loops around the anorectal junction, pubococcygeus extends toward the coccyx, and iliococcygeus runs more laterally and posteriorly
Insertion:
- Fibers converge to insert into the perineal body, anococcygeal ligament, walls of the prostate or vagina, rectum, and coccyx

Nerve Supply

Nerve to levator ani (branch of sacral plexus, S3–S4)
Inferior rectal branches of pudendal nerve
Contributions from direct branches of S4

Arterial Supply

Inferior gluteal artery
Internal pudendal artery
Inferior vesical artery (in males)
Vaginal artery (in females)

Venous Drainage

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

Function

Supports pelvic organs (bladder, uterus/prostate, rectum)
Maintains urinary and fecal continence by reinforcing urethral and anal sphincters
Puborectalis helps maintain the anorectal angle, critical for continence
Active during forced expiration, coughing, and childbirth

MRI Appearance

T1-weighted images:

Muscle shows low-to-intermediate signal intensity
Fatty infiltration or chronic atrophy appears bright

T2-weighted images:

Normal muscle shows low-to-intermediate signal intensity
Edema, denervation, or injury appears as bright signal intensity

STIR (Short Tau Inversion Recovery):

Muscle baseline is low-to-intermediate signal
Inflammation, strain, or trauma appears bright

Proton Density Fat-Sat (PD FS):

Normal muscle shows low-to-intermediate signal
Pathology (tears, denervation, inflammation) shows bright focal signals

T1 Fat-Sat Post-Contrast:

Normal muscle enhances mildly and homogeneously
Pathological states (myositis, neoplasm, infection) show strong, heterogeneous, or rim enhancement

CT Appearance

Non-Contrast CT:

Muscle appears as soft tissue density
May not be sharply delineated from surrounding pelvic structures without contrast
Hematoma appears as a dense region

Post-Contrast CT: