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Iliac fossa

The iliac fossa is a broad, shallow, concave region on the internal surface of the ilium, forming part of the lateral wall of the pelvis. It accommodates the iliacus muscle and provides a smooth bony surface that contributes to the formation of the pelvic cavity.

In clinical anatomy and imaging, the term is also used topographically to describe the right and left lower abdominal regions overlying the iliac bones, which are important in abdominal examination and radiologic localization.

Synonyms

  • Iliac fossa of the ilium

  • Iliac region (topographic usage)

Location

  • Situated on the medial (internal) surface of the ilium

  • Forms the superior part of the lateral pelvic wall

  • Inferior to the iliac crest

  • Superior to the acetabulum

  • Lateral to the pelvic cavity

  • Deep to the iliacus muscle

Anatomical components

  • Concave bony surface of the ilium

  • Iliacus muscle attachment and bed

  • Bounding landmarks:

    • Iliac crest superiorly

    • Arcuate line medially

    • Anterior inferior iliac spine anteriorly

  • Overlying soft tissues:

    • Iliacus muscle

    • Iliopsoas complex

    • Pelvic fascia

Relations

Superficially (laterally):

  • Gluteal muscles

  • Abdominal wall muscles

Medially:

  • Pelvic cavity

  • External iliac vessels (anterior to iliacus)

Inferiorly:

  • Acetabulum

  • Hip joint capsule

Anteriorly:

  • Anterior abdominal wall

  • Inguinal region

Posteriorly:

  • Sacroiliac joint region

Structures related to the iliac fossa

  • Iliacus muscle

  • Iliopsoas tendon (inferiorly)

  • Femoral nerve (courses between iliacus and psoas)

  • External iliac artery and vein

  • Lymphatic channels and pelvic fascia

X-ray appearance

Pelvic radiographs (AP view):

  • Iliac fossa: Appears as a smooth concave contour on the inner aspect of the iliac wing

  • Cortical margins: Well-defined inner table of the ilium

  • Trabecular pattern: Visible diploic structure of cancellous bone

  • Relationship: Seen superior to the acetabulum and medial to the iliac crest

CT appearance

Pre-contrast CT:

  • Iliac fossa bone: Homogeneous cortical and cancellous bone density

  • Inner table: Smooth concave bony surface

  • Iliacus muscle: Soft-tissue density filling the fossa

  • Fat planes: Preserved between muscle, vessels, and pelvic viscera

  • Bony landmarks: Clear depiction of iliac crest, arcuate line, and acetabular roof

MRI appearance

T1-weighted images:

  • Iliac bone cortex: Low signal intensity

  • Cancellous marrow: High signal intensity due to fatty marrow

  • Iliacus muscle: Intermediate signal

  • Fat planes: High signal outlining neurovascular structures

T2-weighted images:

  • Bone cortex: Low signal

  • Marrow: Intermediate-to-high signal depending on fat content

  • Iliacus muscle: Intermediate signal

  • Pelvic fluid or joint spaces: High signal

STIR:

  • Bone marrow: Suppressed fat signal with dark background

  • Iliac fossa region: Uniform low-to-intermediate signal in normal marrow and muscle

  • Soft tissues: Clear delineation of muscle and fascial planes

CT VRT 3D image

Iliac fossa 3d

CT image

Iliac fossa ct anatomy Location and Imaging Appearance -img-00000-00000