Topics

Topic

design image
Iliococcygeus muscle

The iliococcygeus muscle is a thin but important part of the levator ani group, which also includes the pubococcygeus and puborectalis. It forms part of the pelvic diaphragm, supporting the pelvic organs and contributing to continence. Though thinner and less muscular than the pubococcygeus, it plays a key role in reinforcing the pelvic floor and is closely related to pelvic viscera. It is clinically significant in pelvic floor dysfunction, prolapse, and during pelvic imaging.

Synonyms

  • Iliococcygeal part of levator ani

  • Pelvic diaphragm component

  • Iliococcygeus portion of pelvic floor

Origin, Course, and Insertion

  • Origin: Arises from the ischial spine and the posterior part of the tendinous arch of the obturator internus fascia (arcus tendineus levator ani)

  • Course: Fibers pass posteromedially in a thin sheet, blending with fibers of the pubococcygeus and meeting the contralateral iliococcygeus

  • Insertion: Attaches into the coccyx and the anococcygeal body (raphe) posterior to the anal canal

Relations

  • Superiorly: Peritoneum of the pelvic cavity and pelvic viscera (rectum, vagina, bladder)

  • Inferiorly: Ischiorectal (ischioanal) fossa filled with fat

  • Anteriorly: Pubococcygeus muscle

  • Posteriorly: Coccygeus muscle and sacrospinous ligament

  • Medially: Meets opposite iliococcygeus in midline raphe

Function

  • Provides support for pelvic viscera, particularly the bladder, rectum, and uterus (in females)

  • Contributes to continence by maintaining closure of the anal canal and supporting the urogenital hiatus

  • Resists intra-abdominal pressure during activities like coughing, lifting, or straining

  • Forms part of the pelvic diaphragm, maintaining pelvic floor integrity

Clinical Significance

  • Weakness or atrophy contributes to pelvic organ prolapse and urinary/fecal incontinence

  • Injured or thinned in childbirth trauma, pelvic surgery, or neurological disease

  • Important landmark in MRI pelvic floor evaluation and dynamic studies (defecography, prolapse assessment)

  • May be asymmetrically thinned or replaced by fibrous tissue in chronic pelvic floor dysfunction

MRI Appearance

T1-weighted images:

  • Appears as a thin band of low-to-intermediate signal muscle between obturator internus laterally and midline raphe medially

  • Surrounded by bright fat of the ischioanal fossa

T2-weighted images:

  • Low-to-intermediate signal intensity band

  • Thinning, asymmetry, or discontinuity indicates pelvic floor injury

  • Fat of ischioanal fossa appears bright, outlining the muscle clearly

STIR (Short Tau Inversion Recovery):

  • Normal muscle shows low-to-intermediate signal intensity

  • Edema, acute injury, or inflammation appear as bright hyperintense regions

T1 Fat-Sat Post-Contrast:

  • Normal iliococcygeus enhances mildly and uniformly

  • Pathological enhancement may occur in inflammation, infection, or tumor infiltration of pelvic floor

CT Appearance

Non-Contrast CT:

  • Appears as a thin, soft-tissue density band forming part of the pelvic diaphragm

  • Difficult to delineate unless surrounded by fat planes of ischioanal fossa

  • Atrophy may present as thinning with increased fat density in region

Post-Contrast CT:

  • Enhances mildly and uniformly in normal state

  • Pathological thickening or abnormal enhancement may indicate infection, abscess, or infiltration by pelvic malignancy

MRI image

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

CT image

Iliococcygeus muscle CT axial anatomy image-img-00000-00000

CT image

Iliococcygeus muscle CT axial anatomy image-img-00000-00000_00001