Background: The cerebellar hemorrhage reported in numerous cases after supratentorial craniotomy has uniformly exhibited the characteristics of hemorrhage associated with venous infarction rather than arterial bleeding. The cause has remained obscure, although previous reports suggested that the cause may be obstruction of flow in the internal jugular vein immediately below the base of the skull.
Methods: The microsurgical anatomy of 36 internal jugular veins in the upper cervical region were defined in adult cadaveric specimens using 3-40x magnification with special attention to the relationship of the vein to the atlas.
Results: In every specimen, the posterior wall of the internal jugular vein rested against the transverse process of the atlas as the vein descended immediately below the jugular foramen. In 14 of 36 specimens, the transverse process indented the posterior wall of the vein, causing the vein to be slightly or moderately angulated as it descended across the anterior surface of the transverse process. Three veins were severely kinked as they descended across the transverse process of the atlas.
Conclusions: Obstruction of flow in the internal jugular vein at the site where the vein descends across the transverse process of the atlas is a likely cause of the venous hypertension that has resulted in the cerebellar hemorrhage reported in numerous cases after supratentorial craniotomy. An examination of the biomechanics of the region confirms that turning the head to the side opposite a supratentorial craniotomy and extending the neck, common practices with unilateral supratentorial craniotomy, further aggravates the angulation and obstruction of the internal jugular vein at the transverse process of C1 on the side ipsilateral to the craniotomy.