Anococcygeal Body (Anococcygeal Ligament): Anatomy, Attachments, Relations, Function, Clinical Significance, MRI & CT Imaging

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Anococcygeal body (anococcygeal ligament)

The anococcygeal body, also known as the anococcygeal ligament or anococcygeal raphe, is a fibromuscular structure of the pelvic floor. It extends from the posterior wall of the anal canal to the coccyx and serves as a key midline anchoring point for pelvic floor muscles. It is clinically relevant for its role in supporting the anorectal junction, maintaining continence, and as a landmark in colorectal and pelvic floor surgery.

Synonyms

Anococcygeal ligament
Anococcygeal raphe
Median fibrous body of the pelvic floor

Origin, Course, and Insertion

Origin:
- Arises from the posterior wall of the anal canal, between the external anal sphincter and the levator ani muscles
Course:
- Extends posteriorly and superiorly in the midline of the pelvic floor
- Acts as a fibrous raphe, blending with connective tissue and muscle fibers
Insertion:
- Attaches to the coccyx and to the posterior fibers of the levator ani muscles

Relations

Anteriorly: External anal sphincter and posterior wall of the anal canal
Posteriorly: Coccyx and sacrococcygeal ligament
Laterally: Fibers of the levator ani (pubococcygeus)
Superiorly: Pelvic fascia and rectum
Inferiorly: Perianal body and subcutaneous tissues

Nerve Supply

Indirect innervation through branches of the pudendal nerve (S2–S4) supplying the external anal sphincter and levator ani

Arterial Supply

Inferior rectal branches of the internal pudendal artery
Perineal branches of the internal pudendal artery

Venous Drainage

Venous drainage via inferior rectal veins and perineal venous plexus, draining into the internal pudendal vein

Function

Provides midline support for the posterior pelvic floor
Anchors fibers of the levator ani and external anal sphincter
Contributes to anorectal stability and continence
Acts as a fibrous raphe connecting pelvic musculature to the coccyx

Clinical Significance

May be involved in pelvic floor dysfunction or perineal descent
Serves as a surgical landmark in anorectal and pelvic procedures
Can be disrupted during obstetric trauma or pelvic surgeries
Weakness contributes to rectocele and posterior pelvic organ prolapse

MRI Appearance

T1-weighted images:

Appears as a low-signal fibrous band between the anal canal and coccyx
Difficult to distinguish from surrounding connective tissue without high resolution

T2-weighted images:

Shows low-signal intensity as a dense fibrous structure
Surrounding fat and sphincter muscles appear brighter

STIR (Short Tau Inversion Recovery):

Normally remains dark (low signal)
Inflammation or scarring may show localized bright signal

Proton Density Fat-Sat (PD FS):

Visualized as a low-signal fibrous structure
Adjacent edema, trauma, or fibrosis can appear as areas of bright signal

T1 Fat-Sat Post-Contrast:

Normal ligament shows little or no enhancement
Pathological thickening or inflammation may show subtle enhancement

CT Appearance

Non-Contrast CT:

Appears as a thin soft tissue density band extending from the coccyx to the anal canal
Difficult to visualize unless thickened or calcified

Post-Contrast CT:

Generally no significant enhancement under normal conditions
Inflammatory changes or scarring may show mild focal enhancement
Abscess or fistula in adjacent tissues may alter its appearance

MRI image

CT image

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