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Parietal veins

The parietal veins, also known as parietal emissary veins, are small venous channels that traverse the parietal bone of the skull. These veins serve as crucial connections between the extracranial veins of the scalp and the intracranial venous sinuses, particularly the superior sagittal sinus. They play an important role in equalizing pressure between the extracranial and intracranial venous systems and may also provide alternative drainage pathways in cases of venous sinus obstruction. Understanding the imaging characteristics of parietal veins is essential, especially in differentiating them from vascular pathologies on neuroimaging.

Synonyms

  • Parietal emissary veins

  • Emissary veins of parietal bone

  • Emissary parietal veins

Function

  • Connect extracranial veins of the scalp (notably the veins of the parietal region) with the superior sagittal sinus inside the cranium.

  • Serve as alternative pathways for venous blood to exit the cranial cavity if the main dural sinuses are obstructed.

  • Help in equalizing intracranial and extracranial venous pressure.

  • May contribute to thermoregulation of the brain via scalp blood flow.

MRI Appearance

  • T2-weighted imaging:

    • Parietal veins appear as small, flow-void structures traversing the parietal bone, often seen as dark (hypointense) channels due to rapid blood flow.

    • Occasionally, slow-flowing or thrombosed veins may appear hyperintense.

  • T1-weighted imaging:

    • Seen as hypointense (dark) linear or dot-like structures within the parietal bone.

    • Not usually well visualized unless there is a flow-related artifact or thrombosis.

  • Phase-Contrast 3D (PC 3D):

    • High sensitivity for demonstrating small venous structures and direction of flow.

    • Parietal veins are seen as small enhancing vessels connecting extracranial and intracranial compartments.

  • Post-contrast T1-weighted imaging:

    • Parietal veins show linear or punctate enhancement as contrast fills the vascular lumen.

    • Enhancement confirms their vascular nature and connection to the superior sagittal sinus.

CT and CTV Appearance

  • CT (Non-contrast):

    • Parietal veins may appear as small lucent (low density) channels within the diploic space of the parietal bone.

    • Sometimes difficult to visualize unless prominent or associated with an emissary foramen.

  • CT Venography (CTV):

    • Better delineation of the parietal veins with intravenous contrast.

    • Visualized as thin, enhancing linear structures traversing the parietal bone, connecting extracranial veins with the superior sagittal sinus.

MRI images

Parietal veins MRI 3T AXIAL IMAGE

MRI images

Parietal veins MRI 3T coronal image

MRI images

Parietal veins MRI 3T sag mip image