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Greater sciatic notch

The greater sciatic notch is a large, deep indentation on the posterior border of the ilium, situated between the posterior inferior iliac spine (PIIS) above and the ischial spine below. Together with the sacrospinous ligament, it forms the greater sciatic foramen, which serves as a major passageway between the pelvis and gluteal region.

The notch is bordered by the ilium superiorly and the ischium inferiorly. It is wider in females than in males, forming part of the sexually dimorphic features of the pelvis.

The piriformis muscle passes through the greater sciatic notch, dividing the greater sciatic foramen into a suprapiriform foramen (above piriformis) and an infrapiriform foramen (below piriformis). These compartments transmit major neurovascular structures, including the sciatic nerve, superior/inferior gluteal nerves and vessels, pudendal nerve, and internal pudendal vessels.

Clinically, the greater sciatic notch is important as a landmark in pelvic surgery, imaging, and trauma. It is also a site where nerve entrapments (piriformis syndrome) and tumor or abscess spread may occur.

Synonyms

  • Greater sciatic foramen (after ligament closure)

  • Incisura ischiadica major

Boundaries

  • Superior: Posterior inferior iliac spine (PIIS)

  • Inferior: Ischial spine

  • Anterior: Body of ilium

  • Posterior: Sacrospinous ligament (converting notch to foramen)

Function

  • Serves as a bony passageway for neurovascular structures between pelvis and gluteal region

  • Landmark for differentiating suprapiriform and infrapiriform compartments

  • Provides surface anatomy for sciatic nerve localization

  • Plays a role in sex determination in anthropology and forensic studies

Structures Passing Through

Suprapiriform Foramen

  • Superior gluteal nerve

  • Superior gluteal artery and vein

Infrapiriform Foramen

  • Sciatic nerve

  • Inferior gluteal nerve, artery, and vein

  • Pudendal nerve

  • Internal pudendal artery and vein

  • Posterior femoral cutaneous nerve

  • Nerve to obturator internus

  • Nerve to quadratus femoris

MRI Appearance

T1-weighted images:

  • Bone cortex: hypointense

  • Bone marrow: intermediate signal

  • Neurovascular structures within notch: intermediate-to-low signal

  • Useful for mapping sciatic nerve course

T2-weighted images:

  • Bone cortex: hypointense

  • Marrow: intermediate to bright depending on fat content

  • Neurovascular bundles: intermediate signal surrounded by fat (hyperintense)

  • Detects nerve compression, tumors, or soft tissue masses

PD Fat-Saturated:

  • Bone cortex: hypointense

  • Marrow edema: hyperintense in trauma or pathology

  • Highlights inflammatory or neoplastic processes in neurovascular bundles

STIR:

  • Suppresses fat, making nerve edema, hematomas, or inflammatory lesions appear bright

  • Sensitive for detecting piriformis syndrome or nerve entrapments

T1 Post-Gadolinium (fat-saturated):

  • Bone cortex: remains hypointense

  • Enhancement: neurovascular structures enhance normally; abnormal enhancement suggests inflammation, tumor, or infection

  • Useful for evaluating nerve sheath tumors or abscesses

3D T2-weighted Imaging:

  • Provides multiplanar reconstruction of the notch and foramen

  • Excellent for visualizing nerve trajectories, piriformis relation, and vascular structures

  • Critical in preoperative surgical navigation

CT Appearance

Non-contrast CT:

  • Bone cortex: sharply hyperdense

  • Marrow: hypodense relative to cortex

  • Best for defining fractures, bone spurs, and notch morphology

  • Used in pelvic trauma assessment

CT Post-Contrast:

  • Bone: unchanged

  • Vessels: opacify brightly, outlining suprapiriform and infrapiriform compartments

  • Useful for vascular pathology, pelvic tumor staging, and surgical planning

  • 3D CT reconstructions can illustrate sex differences in notch width and pelvic morphology

CT VRT 3D image

Greater sciatic notch 3D CT image

CT image

Greater sciatic notch ct axial image

MRI image

Greater sciatic notch MRI axial anatomy image-img-00000-00000