Topics

Topic

design image
Anterior sacral foramina

The anterior sacral foramina are paired openings located on the pelvic (anterior) surface of the sacrum, usually four on each side. They represent the points where the ventral rami of the sacral spinal nerves (S1–S4) exit the sacral canal to form part of the sacral plexus. These foramina lie in a line lateral to the midline sacral bodies and are separated by the transverse ridges.

Each foramen transmits a ventral ramus of a sacral spinal nerve along with accompanying branches of the lateral sacral arteries and veins. The foramina open anteriorly into the pelvic cavity and are clinically significant in neurosurgery, orthopedics, and interventional radiology because they serve as access points for nerve blocks, neuromodulation, and sacral fracture fixation.

Synonyms

  • Ventral sacral foramina

  • Anterior foramina of sacrum

Function

  • Provide passage for ventral rami of sacral nerves (S1–S4)

  • Transmit branches of the lateral sacral vessels

  • Serve as neurovascular gateways to the pelvis

  • Key anatomical landmarks in sacral nerve stimulation, pelvic surgery, and imaging

Nerve Supply Through Foramina

  • S1–S4 ventral rami, contributing to the sacral plexus

  • Nerves emerging supply the pelvic organs, perineum, gluteal region, and lower limbs

Arterial Supply

  • Lateral sacral arteries (branches of internal iliac artery) send branches through foramina to supply nerve roots and sacral structures

Venous Drainage

  • Lateral sacral veins drain into the internal iliac veins

  • Form connections with the internal vertebral venous plexus

MRI Appearance

T1-weighted images:

  • Foramina appear as low-signal circular openings within the sacral bone

  • Nerve roots show intermediate signal intensity against hyperintense surrounding fat

T2-weighted images:

  • Foramina remain dark, with nerve roots appearing as intermediate signal

  • CSF signal is usually absent (unlike in spinal canal)

STIR:

  • Suppresses fat signal, enhancing visibility of nerve roots and perineural pathology

  • Useful for detecting nerve inflammation, edema, or tumor infiltration

T1 Fat-Saturated Pre-Contrast:

  • Nerve roots appear as intermediate signal against suppressed fat planes, aiding identification

T1 Fat-Saturated Post-Contrast (Gadolinium):

  • Normal nerves show minimal enhancement

  • Abnormal enhancement indicates tumor, perineural spread, or infection

  • Highlights small vessel enhancement in the foramina

MRI Non-Contrast 3D Imaging:

  • Provides 3D reconstructions of foraminal size and orientation

  • Valuable in surgical planning, congenital anomaly assessment, and tumor mapping

CT Appearance

CT Pre-Contrast:

  • Foramina appear as bony circular openings aligned in vertical rows

  • Excellent for assessing bony margins, fractures, and congenital variations

CT Post-Contrast:

  • Enhances visualization of vessels and any abnormal soft-tissue within foramina

  • Useful for tumor invasion, vascular lesions, or inflammatory processes

MRI image

Anterior sacral foramina MRI axial anatomy image -img-00000-00000

CT image

Anterior sacral foramina ct axial image

CT VRT 3D image

Anterior sacral foramina ct 3d coronal image