M02.05.002 Venous Drainage

Learning Objective

By the end of this section, you should be able to:

• Identify the major venous drainage systems of the CNS, including the cerebral, cerebellar, brainstem, and spinal cord veins.
• Describe the structure and function of dural venous sinuses.
• Understand the clinical relevance of venous thrombosis within the CNS, particularly cerebral venous sinus thrombosis (CVST).

Introduction

The central nervous system (CNS) comprises the cerebrum, cerebellum, brainstem, and spinal cord. Its venous drainage is complex and notably does not parallel arterial supply, which is unusual in human anatomy.

• Cerebrum, cerebellum, brainstem: Drained by numerous veins emptying into the dural venous sinuses.
• Spinal cord: Drained via anterior and posterior spinal veins into the internal and external vertebral venous plexuses.

1. Dural Venous Sinuses

The dural venous sinuses are venous channels situated between the periosteal and meningeal layers of the dura mater. They serve as collecting pools for venous blood from the CNS, face, and scalp.

Key Characteristics

• Lack valves (unlike most veins).
• Drain into the internal jugular vein.
• Total: Eleven venous sinuses.

Main Sinuses and Pathway

• Superior, inferior, and straight sagittal sinuses: Located in the falx cerebri, converge at the confluence of sinuses.
• Transverse sinuses: Extend bilaterally from the confluence and curve into the sigmoid sinuses, which drain into the internal jugular vein.
• Cavernous sinuses: Receive ophthalmic veins, situated on either side of the sella turcica.
  • Drain into the jugular vein via the superior/inferior petrosal sinuses.

2. Veins of the Cerebrum

Cerebral veins remove deoxygenated blood from brain tissue and empty into the dural venous sinuses.

Grouped Into:

A. Superficial Cerebral Veins

• Superior cerebral veins → Superior sagittal sinus.
• Superficial middle cerebral vein → Cavernous or sphenoparietal sinus.
• Inferior cerebral veins → Cavernous and transverse sinuses.
• Superior anastomotic vein (of Trolard) → Connects superficial middle cerebral vein to superior sagittal sinus.
• Inferior anastomotic vein (of Labbé) → Connects superficial middle cerebral vein to transverse sinus.

B. Deep Cerebral Veins

• Medullary veins: Arise deep to the cortex; drain into subependymal veins.
• Subependymal veins: Drain into deeper sinuses.
• Great cerebral vein (of Galen): Formed by the union of deep veins; drains into the straight sinus.

3. Venous Drainage of Other CNS Structures

A. Cerebellum

• Superior and inferior cerebellar veins.
• Drain into:
  • Superior petrosal sinus
  • Transverse sinus
  • Straight sinus

B. Brainstem

• Numerous small veins, including:
  • Transverse pontine vein
  • Anteromedian medullary vein
  • Anterior and posterior spinal veins

C. Spinal Cord

• Three anterior and three posterior spinal veins, all valveless.
• Form an anastomotic network on the cord surface.
• Drain into:
  • Internal vertebral plexus (within vertebral canal)
  • External vertebral plexus (outside vertebral column)
  • These plexuses empty into segmental systemic veins and communicate with cranial dural sinuses superiorly.

Clinical Relevance

Cerebral Venous Sinus Thrombosis (CVST)

A condition where a thrombus forms within a dural venous sinus.

Pathophysiology

• Venous occlusion → Backlog of deoxygenated blood → Cerebral venous infarction.
• Impaired cerebrospinal fluid drainage → Raised intracranial pressure.

Symptoms

• Headache
• Nausea and vomiting
• Focal neurological deficits

Diagnosis

• CT or MRI with contrast reveals sinus obstruction.

Treatment

• Anticoagulation therapy to prevent propagation and aid recanalization.

Points to Remember

Bibliography

• Standring, S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed.
• TeachMeAnatomy. www.teachmeanatomy.info
• Osborn AG. Diagnostic Imaging: Brain.