Topics

Topic

design image
Pyramids of the medulla oblongata

The pyramids of the medulla oblongata are two prominent longitudinal structures located on the anterior (ventral) surface of the medulla oblongata, a part of the brainstem. These paired, white matter elevations are formed by the corticospinal tracts, which carry voluntary motor fibers from the cerebral cortex to the spinal cord. The pyramids are clinically significant because they contain the site of the decussation of the pyramids, where the majority of corticospinal fibers cross to the opposite side, thus contributing to contralateral motor control. Their distinct appearance and anatomical relationships make them key landmarks in neuroimaging and neuropathology.

Synonyms

  • Medullary pyramids

  • Pyramidal tracts (when referring to the corticospinal fibers within)

  • Ventral medullary pyramids

Arterial Supply

  • Supplied primarily by branches of the anterior spinal artery.

  • Additional blood supply from the vertebral arteries and, to a lesser extent, branches of the posterior inferior cerebellar artery (PICA).

Venous Drainage

  • Drained by medullary veins, which empty into the anterior spinal vein and veins of the lateral medulla.

  • Ultimately, venous blood from the pyramids drains into the internal jugular vein via the larger medullary venous plexus.

Function

  • The pyramids transmit the corticospinal tracts, which are responsible for:

    • Voluntary motor control of the limbs and trunk.

    • Conveying motor impulses from the cerebral cortex to the spinal cord.

  • The decussation of the pyramids (crossing over of fibers) results in the contralateral control of motor function, meaning the left side of the brain controls the right side of the body, and vice versa.

MRI Appearance

  • T1-weighted images:

    • Pyramids appear as isointense to slightly hypointense linear structures relative to the surrounding medullary tissue.

  • T2-weighted images:

    • Pyramids are slightly hyperintense compared to the adjacent medulla, especially when myelination is prominent.

  • FLAIR (Fluid-Attenuated Inversion Recovery):

    • Pyramids are usually isointense, though may appear hyperintense in pathological conditions (e.g., demyelination, infarct).

  • Location:

    • Seen on axial and sagittal images as paired, ventral, elongated structures on either side of the midline in the anterior medulla.

CT Appearance

  • On non-contrast CT, the pyramids are not distinctly visualized as separate from the surrounding medullary tissue due to limited soft tissue contrast.

  • May be inferred as low-density, longitudinal bulges on the ventral medulla, most apparent in high-resolution or thin-slice images.

  • Better appreciated in pathological states (e.g., infarcts, calcifications, or mass effect) when there is loss of normal tissue architecture.

MRI images

pyramids of the medulla oblongata mri 3t coronal image

MRI images

pyramids of the medulla oblongata mri 3t axial image