Friday 12 August 2011

Occipital sinus - a normal anatomical variation on MR Venogram

Non contrast 2 D TOF MRI Venogram of brain shows:
Hypoplastic left lateral (transverse sigmoid) sinus.
Occipital sinus as an alternative drainage - a normal anatomical variation.

Occipital sinus

Syn : Sinus occipitalis (Latin)
Occipital sinus is discovered by Guichard Joseph Duverney.

An occipital sinus is an inconstant dural venous sinus, present as an accessory or alternative drainage in case of hypoplastic or congenitally absent  ipsilateral lateral sinus, an unpaired dural sinus commencing at torcula and passing downward to the great foramen and ultimately drains into either of the jugular vein, sometimes even bifurcates to join to both the jugular veins.

Detail Anatomy of occipital sinus, the occipital sinus is formed by the union of two small veins (marginal sinuses) which pass around the lateral margins of the foramen magnum and communicate with the sigmoid portion of the lateral sinus near the jugular foramen and with the posterior spinal veins. It passes along the attached margin of the falx cerebelli to the internal occipital protuberances, where it empties into the torcular Herophili. It may empty into one of the lateral sinuses or into the straight sinus. It receives veins from the tentorium cerebelli and cerebellum, communicating also with the vertebral veins and the anterior spinal plexus. 
Presence of occipital sinus is often associated with hypoplastic or congenitally absent ipsilateral lateral sinus. Lateral sinuses are often asymmetric, the left being more often hypoplastic than the right, pulsations of the right atrium is thought to be responsible for larger capacity of the right jugular system. The jugular foramen on smaller side is correspondingly small as well, helping distinguish developmental hypoplasia from aquired thrombosis. 

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