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Fetal straight sinus

The straight sinus is a dural venous sinus located at the junction of the falx cerebri and tentorium cerebelli. In the fetus, it drains venous blood from the deep cerebral veins (mainly the great cerebral vein of Galen and inferior sagittal sinus) into the confluence of sinuses.

It develops early and is consistently visualized on fetal MRI as a key midline venous structure. Because of its location and reliable appearance, it is an important landmark for assessing midline anatomy and venous drainage of the fetal brain.

Synonyms

  • Tentorial sinus (older term)

  • Sinus rectus

  • Fetal straight dural sinus

Structure and Development

  • Formed by the union of the inferior sagittal sinus and the great cerebral vein (vein of Galen)

  • Courses posteriorly along the line of attachment between the falx cerebri and tentorium cerebelli

  • Terminates at the confluence of sinuses (torcular Herophili)

  • Present from early gestation; lumen gradually enlarges with brain growth and venous maturation

Relations

  • Anteriorly: Confluence of inferior sagittal sinus and vein of Galen

  • Posteriorly: Confluence of sinuses

  • Superiorly: Falx cerebri

  • Inferiorly: Tentorium cerebelli

  • Adjacent structures: Deep cerebral veins, cerebellum, and occipital lobes

Function

  • Drains blood from the deep venous system (vein of Galen, internal cerebral veins, basal veins)

  • Connects deep cerebral circulation with superficial dural sinuses

  • Maintains intracranial venous outflow during fetal development

Clinical Significance

  • Thrombosis: Rare but may occur in utero, associated with maternal/fetal prothrombotic states or infections

  • Malformations: Can be involved in vein of Galen malformations

  • Hemodynamic disturbances: Enlargement may suggest abnormal venous drainage or high-output cardiac states

  • Imaging relevance: Landmark for assessing venous system patency in fetal MRI and ruling out developmental anomalies

MRI Appearance

T2 HASTE (T2 GRE):

  • Straight sinus lumen: flow void, appearing as a dark hypointense linear structure in the midline

  • Occasionally shows flow-related hyperintensity if slow venous flow is present

  • Surrounding CSF and brain parenchyma: bright, giving excellent contrast for sinus identification

T1 GRE:

  • Straight sinus lumen: generally low signal intensity due to flowing blood (flow void)

  • Thrombosed or slow-flow sinus: may appear isointense to hyperintense, depending on stage of clot or flow characteristics

  • Adjacent tentorium and falx: thin low-signal structures outlining the sinus course

MRI image

Fetal straight sinus MRI image