White Matter-Governed Superior Frontal Sulcus Surgical Paradigm: A Radioanatomic Microsurgical Study—Part I

BACKGROUND Frontal subcortical and intraventricular pathologies are traditionally accessed via transcortical or interhemispheric-transcallosal corridors. OBJECTIVE To describe the microsurgical subcortical anatomy of the superior frontal sulcus (SFS) corridor. METHODS Cadaveric dissections were undertaken and correlated with magnetic resonance imaging/diffusion-tensor imaging-Tractography. Surgical cases demonstrated clinical applicability. RESULTS SFS was divided into the following divisions: proximal, precentral sulcus to coronal suture; middle, 3-cm anterior to coronal suture; and distal, middle division to the orbital crest. Anatomy was organized as layered circumferential rings projecting radially towards the ventricles: (1) outer ring: at the level of the SFS, the following lengths were measured: (A) precentral sulcus to coronal suture = 2.29 cm, (B) frontal bone projection of superior sagittal sinus (SSS) to SFS = 2.37 cm, (C) superior temporal line to SFS = 3.0 cm, and (D) orbital crest to distal part of SFS = 2.32 cm; and (2) inner ring: (a) medial to SFS, U-fibers, frontal aslant tract (FAT), superior longitudinal fasciculus I (SLF-I), and cingulum bundle, (b) lateral to SFS, U-fibers, (SLF-II), claustrocortical fibers (CCF), and inferior fronto-occipital fasciculus, and (c) intervening fibers, FAT, corona radiata, and CCF. The preferred SFS parafascicular entry point (SFSP-EP) also referred to as the Kassam-Monroy entry point (KM-EP) bisects the distance between the midpupillary line and the SSS and has the following coordinates: x = 2.3 cm (lateral to SSS), y ≥ 3.5 cm (anterior to CS), and z = parallel corona radiata and anterior limb of the internal capsule. CONCLUSION SFS corridor can be divided into lateral, medial, and intervening white matter tract segments. Based on morphometric assessment, the optimal SFSP-EP is y ≥ 3.5 cm, x = 2.3 cm, and z = parallel to corona radiata and anterior limb of the internal capsule.

Locating the Acupoint Baihui (GV20) Beneath the Cerebral Cortex with MRI Reconstructed 3D Neuroimages

Baihui (GV20) is one of the most important acupoints of the Du meridian (the government vessel) and is commonly used in neurology and psychiatry and as a distal point of anorectal disorders by general practitioners. The anatomical relationship between the scalp region of the acupoint and the underlying corresponding cortex remains obscure. In this study, we first prepared the indicator for MRI scanning on a GE 1.5 T excite machine in a mode suitable for 3D reconstruction. The 3D Avizo software system (version 6.0, Mercury Computer Systems, Inc., Germany) was then used for image processing and the resulting data subsequently analyzed using descriptive statistics and analysis of variance (ANOVA). The mean distance from the Baihui anterior to the central sulcus in the adult group was greater than that in the child group (22.7 ± 2.2 and 19.7 ± 2.2 mm, resp.,P= .042), whereas in the child group the distance between the Baihui anterior and the precentral sulcus was greater than in the adult group (6.8 ± 0.8 and 3.8 ± 0.8 mm, resp.,P< .001). This MRI presentation demonstrates that the location of Baihui (GV20) can be identified using the distance from the central or precentral sulcus.

Surgical Anatomy of Microneurosurgical Sulcal Key Points

OBJECTIVE: The brain sulci constitute the main microanatomic delimiting landmarks and surgical corridors of modern microneurosurgery. Because of the frequent difficulty in intraoperatively localizing and visually identifying the brain sulci with assurance, the main purpose of this study was to establish cortical/sulcal key points of primary microneurosurgical importance to provide a sulcal anatomic framework for the placement of craniotomies and to facilitate the main sulci intraoperative identification. METHODS: The study was performed through the evaluation of 32 formalin-fixed cerebral hemispheres of 16 adult cadavers, which had been removed from the skulls after the introduction of plastic catheters through properly positioned burr holes necessary for the evaluation of cranial–cerebral relationships. Three-dimensional anatomic and surgical images are displayed to illustrate the use of sulcal key points. RESULTS: The points studied were the anterior sylvian point, the inferior rolandic point, the intersection of the inferior frontal sulcus with the precentral sulcus, the intersection of the superior frontal sulcus with the precentral sulcus, the superior rolandic point, the intersection of the intraparietal sulcus with the postcentral sulcus, the superior point of the parieto-occipital sulcus, the euryon (the craniometric point that corresponds to the center of the parietal tuberosity), the posterior point of the superior temporal sulcus, and the opisthocranion, which corresponds to the most prominent point of the occipital bossa. These points presented regular neural and cranial–cerebral relationships and can be considered consistent microsurgical cortical key points. CONCLUSION: These sulcal and gyral key points can be particularly useful for initial intraoperative sulci identification and dissection. Together, they compose a framework that can help in the understanding of hemispheric lesion localization, in the placement of supratentorial craniotomies, as landmarks for the transsulcal approaches to periven-tricular and intraventricular lesions, and in orienting the anatomic removal of gyral sectors that contain infiltrative tumors.

Functional Properties of Brain Areas Associated With Motor Execution and Imagery

Imagining motor acts is a cognitive task that engages parts of the executive motor system. While motor imagery has been intensively studied using neuroimaging techniques, most studies lack behavioral observations. Here, we used functional MRI to compare the functional neuroanatomy of motor execution and imagery using a task that objectively assesses imagery performance. With surface electromyographic monitoring within a scanner, 10 healthy subjects performed sequential finger-tapping movements according to visually presented number stimuli in either a movement or an imagery mode of performance. We also examined effects of varied and fixed stimulus types that differ in stimulus dependency of the task. Statistical parametric mapping revealed movement-predominant activity, imagery-predominant activity, and activity common to both movement and imagery modes of performance (movement-and-imagery activity). The movement-predominant activity included the primary sensory and motor areas, parietal operculum, and anterior cerebellum that had little imagery-related activity (−0.1 ∼ 0.1%), and the caudal premotor areas and area 5 that had mild-to-moderate imagery-related activity (0.2 ∼ 0.7%). Many frontoparietal areas and posterior cerebellum demonstrated movement-and-imagery activity. Imagery-predominant areas included the precentral sulcus at the level of middle frontal gyrus and the posterior superior parietal cortex/precuneus. Moreover, activity of the superior precentral sulcus and intraparietal sulcus areas, predominantly on the left, was associated with accuracy of the imagery task performance. Activity of the inferior precentral sulcus (area 6/44) showed stimulus-type effect particularly for the imagery mode. A time-course analysis of activity suggested a functional gradient, which was characterized by a more “executive” or more “imaginative” property in many areas related to movement and/or imagery. The results from the present study provide new insights into the functional neuroanatomy of motor imagery, including the effects of imagery performance and stimulus-dependency on brain activity.