Topics

Topic

design image
Sacral cornu (sacral horn)

The sacral cornua, also called the sacral horns, are paired bony prominences located on either side of the sacral hiatus at the lower end of the sacrum. They represent the inferior articular processes of the fifth sacral vertebra (S5) and project downward to articulate with the coccygeal cornua. These structures serve as palpable and radiological landmarks for the sacral hiatus, which is a key access site for caudal epidural anesthesia.

The sacral cornua are important in clinical anatomy and imaging as they guide safe needle placement into the sacral canal and serve as reliable reference points for identifying the sacral hiatus on MRI, CT, or fluoroscopy.

Synonyms

  • Sacral horns

  • Cornua of sacrum

  • Sacral hiatus landmarks

Location and Structure

  • Location: Situated at the lower dorsal surface of the sacrum, flanking the sacral hiatus

  • Structure:

    • Two small bony projections formed by the inferior articular processes of S5

    • Project downward to articulate with the coccygeal cornua

    • Border the sacral hiatus laterally, creating a palpable landmark on surface examination

Relations

  • Anteriorly: Sacral canal containing filum terminale and sacral nerves

  • Posteriorly: Subcutaneous tissue and skin of lower back near natal cleft

  • Laterally: Gluteal region and sacroiliac ligaments

  • Inferiorly: Coccygeal cornua of the coccyx

  • Superiorly: Laminae of sacrum, continuous with sacral vertebral arches

Function

  • Serve as anatomical landmarks for identifying the sacral hiatus

  • Provide articulation with coccygeal cornua, stabilizing the sacrococcygeal joint

  • Assist clinicians in performing caudal epidural anesthesia by guiding needle placement

  • Act as palpable markers in surface anatomy for locating sacral hiatus in adults and children

Clinical Significance

  • Anesthesia: Landmark for caudal epidural block, commonly used in pediatrics and chronic pain therapy

  • Imaging: Help radiologists confirm the level of the sacral hiatus on MRI and CT

  • Anatomical variations: Size and prominence vary among individuals; hypoplastic cornua can make localization difficult

  • Fractures/trauma: Can be fractured in sacral or coccygeal trauma, altering appearance on imaging

  • Surgical relevance: Used as a guide during sacral canal procedures and sacrococcygeal surgeries

MRI Appearance

T1-weighted images:

  • Sacral cornua appear as low-signal bony structures bordering the sacral hiatus

  • Surrounded by bright fat in the sacral canal and subcutaneous tissue

T2-weighted images:

  • Cornua remain low signal intensity

  • Sacral canal contents (CSF) appear bright, providing contrast against the dark bony cornua

STIR (Short Tau Inversion Recovery):

  • Bony cornua remain dark

  • Adjacent soft tissue or fat suppressed, useful in detecting inflammation or pathology

T1 Fat-Sat Post-Contrast:

  • Cornua do not enhance

  • Surrounding soft tissue or pathologies (abscess, tumor, inflammation) may enhance, highlighting abnormalities around the sacral hiatus

3D T2 SPACE / CISS:

  • Sacral cornua appear as dark bony projections clearly outlining the sacral hiatus

  • CSF in the sacral canal appears very bright, sharply contrasting with the cornua and aiding identification of hiatus boundaries

CT Appearance

Non-Contrast CT:

  • Cornua appear as paired bony projections flanking the sacral hiatus

  • Easily identified in bone window settings as downward projections of S5

  • Variants such as hypoplastic or asymmetric cornua can be well visualized

Post-Contrast CT:

  • Cornua themselves do not enhance

  • Contrast may highlight surrounding vascular or soft tissue structures in cases of pathology

  • Useful in planning interventions such as caudal epidural injections or evaluating traumatic injury

MRI image

Sacral cornu (sacral horn) mri axial anatomy image-img-00000-00000

MRI image

Sacral cornu (sacral horn) mri coronal anatomy image-img-00000-00000

CT image

Sacral cornu (sacral horn) ct axial anatomy image-img-00000-00000