Operative Neurosurgery Advance Access: Microsurgical Anatomy of the Vertical Rami of the Superior Longitudinal Fasciculus: An Intraparietal Sulcus Dissection Study

The superior longitudinal fasciculus (SLF) is the longest dorsal frontoparietal white matter association tract, comprising 3 major subdivisions (SLF-I, SLF-II, and SLF-III). A vertical prolongation of the SLF arising at the level of the supramarginal gyrus and directed vertically toward the superior and inferior parietal lobules (SPL and IPL) has been largely neglected in the anatomic literature.1-4 We have consistently observed this collection of fibers (identified as blue fibers on RGB color-encoded diffusion tensor imaging (DTI) images given their rostro-caudal orientation) during the surgical planning and resection of parietal and periatrial brain tumors, and we have collectively termed these fibers the vertical rami (Vr). These fibers are thought to represent the terminations of the dorsal association tracts as they merge along the banks of the intraparietal sulcus (IPS) and form a rich subcortical network.

Based on extensive study in the human and macaque, the IPS subcortical complex is thought to be a primary multisensory integration center governing functions such as spatial awareness, visuospatial attention, gaze, grasping, numerical cognition, and calculation.5 Apraxia, neglect, optic ataxia, and Gerstmann’s and Balint’s syndromes have been described as the result of parietal lobe dysfunction.6 By their close anatomic association with the IPS, we postulate that the Vr are in fact highly eloquent tracts from a neurosurgical perspective, serving to mediate connectivity between parietal lobe programs (such as praxis, visuospatial integration, attention, and numerical cognition) with motor and language programs residing in the dorsal processing stream (ie, the SLF).

Read more of the first published complete description of the white matter tracts (WMT) of the Vr, their relationship to the intraparietal and parieto-occipital sulci (IPS-POS complex), and their importance in neurosurgical approaches to the parietal lobe.