Sigmoid Sinus in a Cut Section of the Skull

Description

Curving along the posterolateral cranial cavity, the sigmoid sinus appears as an S-shaped continuation of the transverse sinus, descending inferiorly and anteriorly within the sigmoid groove of the temporal bone toward the jugular foramen. Superior to it, the superior sagittal sinus runs in the midline within the attached margin of the falx cerebri and drains posteriorly into the confluence of sinuses before distributing into the transverse sinuses. Medially, the tentorium cerebelli forms the dural partition that frames the transverse-sigmoid junction, while the occipital bone and mastoid portion of the temporal bone define the bony contour that the sinus closely follows. Blue venous channels emphasize the dural venous sinus system rather than cortical veins. That transverse-to-sigmoid turn matters because it marks the dominant pathway for cranial venous outflow into the internal jugular vein and sits directly adjacent to surgical corridors of the posterior fossa and mastoid. Injury here is not theoretical. A mastoidectomy, retrosigmoid craniotomy for vestibular schwannoma, or posterior fossa decompression can expose the sigmoid sinus, and its variable caliber and degree of “dominance” influence both risk and strategy. The relationship to the jugular bulb at the jugular foramen also underpins clinical discussions of pulsatile tinnitus, sigmoid sinus diverticulum, and dural arteriovenous fistulas that commonly localize around the transverse-sigmoid complex. Neuroanatomy and head and neck anatomy courses use this cut-section perspective to teach dural reflections, the confluence of sinuses, and the venous drainage route from superior sagittal sinus to transverse and sigmoid sinus into the internal jugular vein. It also fits neurosurgery and otology texts illustrating landmarks for the retrosigmoid approach, mastoid air cell surgery, and radiology correlation for MRV/CTV interpretation of transverse-sigmoid sinus thrombosis or hypoplasia. Anatomical accuracy verified by SciePro's Medical Advisory Board.