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Pontomedullary sulcus

The pontomedullary sulcus is an important anatomical landmark located at the junction between the pons and the medulla oblongata on the anterior (ventral) surface of the brainstem. It marks the superior border of the medulla and the inferior border of the pons. This shallow transverse groove is easily identified in anatomical dissections and imaging studies and serves as the origin point for several cranial nerves.

Synonyms

  • Pontomedullary groove

  • Sulcus pontomedullaris

  • Groove between pons and medulla

Function

  • Serves as an anatomical landmark for the separation of the pons and medulla oblongata

  • Acts as the point of emergence for the abducens nerve (cranial nerve VI), facial nerve (VII), and vestibulocochlear nerve (VIII)

  • Important reference in neurosurgical and neuroradiological procedures

Arterial Supply

  • Primarily supplied by the branches of the basilar artery, which runs along the ventral surface of the brainstem and ends at the pontomedullary sulcus

  • Additional supply from the anterior inferior cerebellar artery (AICA) and small perforating branches from the vertebral arteries

Venous Drainage

  • Drained by the anterior pontomesencephalic veins and the anterior spinal vein

  • These veins empty into the larger basal vein of Rosenthal and the inferior petrosal sinus

MRI Appearance

  • T2-weighted imaging:

    • The pontomedullary sulcus is seen as a hyperintense (bright) thin line or cleft at the junction of the pons and medulla, due to the presence of CSF, which is bright on T2.

    • This bright line distinguishes the border between the lower pons and upper medulla.

    • Surrounding brainstem tissue appears relatively hypointense (darker) compared to the CSF in the sulcus.

  • T1-weighted imaging:

    • The sulcus appears as a hypointense (dark) line at the pontomedullary junction, as CSF is dark on T1.

    • The border between pons and medulla is less conspicuous than on T2.

  • FLAIR imaging:

    • The pontomedullary sulcus appears as a hypointense (dark) line, since FLAIR suppresses the signal from free CSF.

    • This can make the sulcus appear more subtle compared to T2, but it still defines the anatomical separation.

CT Appearance

  • Not well visualized on non-contrast CT; may appear as a subtle cleft due to tissue interfaces, but is generally not a distinct feature.

MRI images

pontomedullary sulcus MRI 3T axial image