Microsurgical approaches to the pulvinar: A comparative analysis.

OBJECTIVE: To compare the area of exposure to the cisternal thalamus associated with four surgical techniques: supracerebellar-infratentorial (SCIT), occipital interhemispheric (OI), transchoroidal (TC) and subtemporal before and after parahippocampal resection (ST and STh, respectively). METHODS: All approaches were performed on both sides of three heads. Qualitative anatomical analyses were performed to understand anatomical limits, advantages, and flaws of each technique. Quantitative analyses for multiple repeated dependent variables assessed significant differences between areas of exposure. RESULTS: Exposure area was significantly more extensive using TC and STh approaches compared to ST, OI, and SCIT. STh achieved a significantly wider exposure compared to ST. Regarding dissection angle, surrounding structures and limitations, ST approaches do not provide adequate exposure, nor alignment with the thalamic axis. The OI and STh may provide a better field of exposure, but without adequate alignment and challenging deeper dissections. TC provides better exposure of the cisternal pulvinar with access to lateral pulvinar at the atrium's anterior wall but is a transcortical route that disrupts non-pathological tissue. SCIT provides an adequate area of exposure with the possibility of alignment with the thalamus axis, thus allowing an easier dissection of deeper lesions. CONCLUSIONS: For lesions at the pulvinar surface, OI and STh are adequate. For lesions restricted to medial pulvinar and deep along the thalamus axis, SCIT approaches are recommended. Lesions extending to the lateral pulvinar and ventricular atrium are best removed through TC approaches. The ST approach was not suitable to the cisternal pulvinar due to its limited angular exposure.

Tractography of the ansa lenticularis in the human brain.

The aim of this study was to make a thorough investigation of the trajectory of the ansa lenticularis (AL) and its subcomponents using high-resolution fiber-tracking tractography. The subcomponents of the AL were reconstructed from one region of interest (ROI) in the area of the globus pallidus combined with another ROI in the red nucleus, substantia nigra, subthalamic nucleus, or thalamus. This fiber-tracking protocol was tested in an HCP-1065 template, 35 healthy subjects from Massachusetts General Hospital (MGH), and 20 healthy subjects from the human connectome project (HCP) using generalized q-sampling imaging (GQI)-based tractography. Quantitative anisotropy and fractional anisotropy were also computed for the AL subcomponents. The subcomponents of the AL could be reconstructed in the HCP-1065 template, 35 MGH healthy subjects, and 20 HCP healthy subjects. The AL descends from the globus pallidus and joins the ansa peduncularis for a short distance, subdividing later into fibers that continue separately to the red nucleus, substantia nigra, subthalamic nucleus, and thalamus. The study demonstrated the trajectory of the ansa lenticularis and its subcomponents using GQI-based tractography, improving our understanding of the anatomical connectivity between the globus pallidus and the thalamo-subthalamic region in the human brain. One Sentence Summary The investigation of the ansa lenticularis and its subcomponents using high-resolution diffusion images based tractography.

Microsurgical anatomy of the central core of the brain.

OBJECTIVE The purpose of this study was to describe in detail the cortical and subcortical anatomy of the central core of the brain, defining its limits, with particular attention to the topography and relationships of the thalamus, basal ganglia, and related white matter pathways and vessels. METHODS The authors studied 19 cerebral hemispheres. The vascular systems of all of the specimens were injected with colored silicone, and the specimens were then frozen for at least 1 month to facilitate identification of individual fiber tracts. The dissections were performed in a stepwise manner, locating each gray matter nucleus and white matter pathway at different depths inside the central core. The course of fiber pathways was also noted in relation to the insular limiting sulci. RESULTS The insular surface is the most superficial aspect of the central core and is divided by a central sulcus into an anterior portion, usually containing 3 short gyri, and a posterior portion, with 2 long gyri. It is bounded by the anterior limiting sulcus, the superior limiting sulcus, and the inferior limiting sulcus. The extreme capsule is directly underneath the insular surface and is composed of short association fibers that extend toward all the opercula. The claustrum lies deep to the extreme capsule, and the external capsule is found medial to it. Three fiber pathways contribute to form both the extreme and external capsules, and they lie in a sequential anteroposterior disposition: the uncinate fascicle, the inferior fronto-occipital fascicle, and claustrocortical fibers. The putamen and the globus pallidus are between the external capsule, laterally, and the internal capsule, medially. The internal capsule is present medial to almost all insular limiting sulci and most of the insular surface, but not to their most anteroinferior portions. This anteroinferior portion of the central core has a more complex anatomy and is distinguished in this paper as the "anterior perforated substance region." The caudate nucleus and thalamus lie medial to the internal capsule, as the most medial structures of the central core. While the anterior half of the central core is related to the head of the caudate nucleus, the posterior half is related to the thalamus, and hence to each associated portion of the internal capsule between these structures and the insular surface. The central core stands on top of the brainstem. The brainstem and central core are connected by several white matter pathways and are not separated from each other by any natural division. The authors propose a subdivision of the central core into quadrants and describe each in detail. The functional importance of each structure is highlighted, and surgical approaches are suggested for each quadrant of the central core. CONCLUSIONS As a general rule, the internal capsule and its vascularization should be seen as a parasagittal barrier with great functional importance. This is of particular importance in choosing surgical approaches within this region.