The extracranial to intracranial anastomotic channel through the parietal foramen: delineation with magnetic resonance imaging.

Abstract

Parietal foramina (PFs) are openings of fine canals that perforate the parietal bone. However, few studies have investigated the entire canals and their emissary vessels (EVs). Here, we explore the EVs with magnetic resonance imaging. A total of 104 patients who underwent contrast examinations and exhibited an intact scalp, skull, dura mater, and superior sagittal sinus were enrolled in this study. Imaging data were obtained as thin-sliced, seamless sagittal sections and were transferred to a workstation for analysis. A total of 116 EVs passing through the PF and inner canals (parietal canal) were identified in 78 patients (75%). All the EVs were found to perforate each layer of the parietal bone. Of 104 patients, 68% exhibited one EV, 30% two EVs, and 2% three EVs. In 85.3%, the EV was entirely delineated in one sagittal slice, 10.3% were covered by two slices, and 4.3% by three slices. In 68%, the EV connected to the upper surface of the superior sagittal sinus (SSS) with variable courses from near-vertical to horizontal inclinations. EVs perforate the skull with variable inclinations, while showing a highly consistent course in the sagittal dimension. The PF and EV can be used as landmarks of the SSS lying immediately below.