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Transverse perineal muscle

The transverse perineal muscles are paired structures of the perineum that provide support to the pelvic floor and stabilize the perineal body. They are divided into two distinct components: the superficial transverse perineal muscle and the deep transverse perineal muscle. Both are small but clinically important in maintaining pelvic floor integrity, continence, and support of the urogenital diaphragm.

These muscles are frequently encountered in urogynecological and colorectal surgery, and they are well evaluated in pelvic floor imaging, especially MRI.

Synonyms

  • Superficial transverse perineal muscle

  • Deep transverse perineal muscle

  • Perineal transverse muscle

Origin, Course, and Insertion

  • Superficial transverse perineal muscle

    • Origin: Ischial tuberosity

    • Course: Fibers run medially and anteriorly across the posterior aspect of the urogenital triangle

    • Insertion: Perineal body (central tendon of the perineum)

  • Deep transverse perineal muscle (inconstant in some individuals)

    • Origin: Medial surface of the ischial ramus

    • Course: Fibers pass medially, lying superior to the perineal membrane

    • Insertion: Perineal body, blending with fibers of the external urethral sphincter and opposite side muscle

Relations

  • Anteriorly: Perineal membrane and external genital structures

  • Posteriorly: Anal canal and external anal sphincter

  • Superiorly: Pelvic diaphragm (levator ani muscles)

  • Inferiorly: Superficial perineal pouch and perineal fascia

Function

  • Provides support to the perineal body and pelvic floor

  • Stabilizes the central tendon of the perineum, especially during defecation, micturition, and childbirth

  • Contributes to urogenital diaphragm integrity

  • Assists in voluntary control of continence

  • Provides muscular attachment site for pelvic and perineal connective tissues

Clinical Significance

  • May be damaged in childbirth, leading to pelvic floor weakness or prolapse

  • Involved in perineal tears and episiotomy repairs

  • Important landmark in urogynecologic and colorectal surgery

  • Atrophy or scarring may be identified in pelvic floor dysfunction on imaging

  • Can be affected by trauma, infection, or perineal abscesses

MRI Appearance

T1-weighted images:

  • Muscle appears as a low-to-intermediate signal band in the perineal region

  • Surrounded by high-signal fat planes, enhancing visibility

T2-weighted images:

  • Normal muscle demonstrates intermediate signal

  • Pathology (edema, trauma, infection) shows bright signal

STIR (Short Tau Inversion Recovery):

  • Normal muscle: low signal

  • Edema, inflammation, or abscess: bright hyperintensity

T1 Fat-Sat Post-Contrast:

  • Normal muscle enhances mildly and uniformly

  • Pathological muscle shows focal, diffuse, or rim enhancement depending on etiology

3D T2 SPACE / CISS:

  • Muscle appears with intermediate signal compared to pelvic floor muscles

  • Surrounded by bright fat or pelvic fluid, providing sharp contrast

  • Useful for delineating fine pelvic floor structures and perineal body integrity

CT Appearance

Non-Contrast CT:

  • Muscle appears as soft tissue density bands in the perineal region

  • Fat planes provide definition against adjacent pelvic structures

  • Hematoma or scarring may appear as localized density changes

Post-Contrast CT:

  • Normal muscle enhances mildly and homogeneously

  • Inflammation, infection, or tumor involvement may cause irregular or heterogeneous enhancement

  • Perineal abscess: rim enhancement with central low attenuation

MRI image