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Fetal sigmoid sinus

The fetal sigmoid sinus is a paired dural venous sinus located in the posterior cranial fossa. It is the continuation of the transverse sinus and curves in an “S” shape toward the jugular foramen, where it drains into the internal jugular vein.

In the fetus, the sigmoid sinus is proportionally large relative to the cranial cavity because of its role in venous drainage of the rapidly growing brain. It is a major pathway for venous outflow, connecting superficial and deep cerebral venous systems to extracranial circulation.

Synonyms

  • Dural sigmoid sinus

  • S-shaped sinus

  • Fetal posterior dural venous sinus

Structure and Development

  • Formed by the splitting of the dura mater layers

  • Continuation of the transverse sinus, curving posteroinferiorly in the posterior fossa

  • Terminates at the jugular foramen, becoming the internal jugular vein

  • Present and functional early in fetal life as part of the developing dural venous sinus system

Relations

  • Superiorly: Transverse sinus (from which it continues)

  • Inferiorly: Jugular bulb and internal jugular vein

  • Anteriorly: Temporal bone (petrous portion) and posterior cranial fossa structures

  • Posteriorly: Occipital bone

Function

  • Provides major venous drainage pathway of fetal brain into systemic circulation

  • Connects intracranial venous blood to extracranial venous system (internal jugular vein)

  • Regulates venous outflow during rapid fetal brain growth

  • Serves as an anatomical landmark in prenatal neuroimaging

Clinical Significance

  • Thrombosis: Rare but may occur prenatally or neonatally; can cause venous infarction or hemorrhage

  • Maldevelopment: Abnormal sinus development may impair cerebral venous drainage

  • Hemodynamic disorders: Altered flow patterns may indicate high-output states or arteriovenous malformations

  • Imaging: Fetal MRI assesses sinus patency, flow voids, and possible thrombosis

MRI Appearance

T2 HASTE (T2 GRE):

  • Flowing blood in the sinus produces a flow void (dark signal)

  • When flow is sluggish or turbulent: may show mixed hypointense and hyperintense areas

  • Thrombosed sinus: loss of flow void with intraluminal bright hyperintensity

T1 GRE:

  • Flowing venous blood: typically dark (low signal intensity)

  • Acute thrombus: may appear isointense to hyperintense depending on stage of clot evolution

  • Normal dural walls: thin and not well distinguished on T1

MRI image

Fetal sigmoid sinus MRI coronal anatomy image-img-00000-00000