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Transverse ridges

The transverse ridges are a series of four horizontal lines located on the pelvic (anterior) surface of the sacrum. They represent the sites of fusion between the bodies of the five sacral vertebrae. These ridges are subtle elevations separated by shallow grooves and serve as important anatomical landmarks for the identification of sacral segmentation.

They are clinically significant because abnormalities in their development or visualization can indicate congenital anomalies, incomplete sacral fusion, or degenerative changes. In radiology, they are used as reference points when evaluating the anterior surface of the sacrum in MRI, CT, and plain radiographs.

Synonyms

  • Sacral transverse lines

  • Sacral fusion ridges

  • Anterior sacral ridges

Location and Structure

  • Found on the pelvic surface of the sacrum, running transversely

  • Four ridges correspond to the fusion of the five sacral vertebral bodies

  • Small foramina (anterior sacral foramina) lie lateral to the ridges, transmitting anterior rami of sacral nerves

  • Appear more prominent in young adults, gradually smoothing with age

Relations

  • Anteriorly: Pelvic organs (rectum, sigmoid colon in males; uterus, cervix, vagina in females)

  • Posteriorly: Sacral canal and fused sacral bodies

  • Laterally: Anterior sacral foramina and pelvic wall muscles

  • Inferiorly: Coccyx

  • Superiorly: Base of the sacrum and lumbosacral junction

Function

  • Represent anatomical evidence of vertebral fusion

  • Provide strength and stability to the sacrum

  • Serve as landmarks for sacral segmentation in imaging and surgical approaches

  • Indirectly help in transmission of body weight from the vertebral column to the pelvis

Clinical Significance

  • Used in radiology to assess congenital anomalies (sacralization, lumbarization, segmentation errors)

  • Important for surgical planning in pelvic, spinal, and orthopedic procedures

  • May be altered in trauma, degenerative disease, or congenital malformations

  • Serve as key landmarks in MRI/CT interpretation of sacral anatomy

MRI Appearance

T1-weighted images:

  • Transverse ridges appear as low signal intensity lines across the anterior sacrum

  • Adjacent bone marrow shows higher signal

T2-weighted images:

  • Ridges remain low signal intensity, contrasting with higher signal of marrow and pelvic organs

  • Degenerative changes may appear as irregular bright or dark alterations

STIR (Short Tau Inversion Recovery):

  • Normal ridges appear dark (low signal)

  • Bone marrow edema near ridges (trauma, inflammation) appears bright hyperintense

T1 Fat-Sat Post-Contrast:

  • Ridges themselves do not enhance

  • Enhancement may be seen in adjacent marrow or soft tissue in case of pathology (inflammation, tumor, infection)

3D T2 SPACE / CISS:

  • Ridges appear as low-signal transverse lines

  • Provide high-resolution visualization of anterior sacral surface and foramina

CT Appearance

Non-Contrast CT:

  • Ridges visible as thin, dense bony lines across the anterior sacral surface

  • Appear continuous, with foramina lateral to them

  • Variations or interruptions may suggest congenital anomaly or fracture

Post-Contrast CT:

  • Ridges remain unchanged (do not enhance)

  • Surrounding soft tissue pathology (tumor, infection, inflammation) may enhance and distort adjacent anatomy

MRI image

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MRI image

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CT image

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