Human pallidothalamic and cerebellothalamic tracts: anatomical basis for functional stereotactic neurosurgery - PubMed (original) (raw)

Human pallidothalamic and cerebellothalamic tracts: anatomical basis for functional stereotactic neurosurgery

Marc N Gallay et al. Brain Struct Funct. 2008 Aug.

Abstract

Anatomical knowledge of the structures to be targeted and of the circuitry involved is crucial in stereotactic functional neurosurgery. The present study was undertaken in the context of surgical treatment of motor disorders such as essential tremor (ET) and Parkinson's disease (PD) to precisely determine the course and three-dimensional stereotactic localisation of the cerebellothalamic and pallidothalamic tracts in the human brain. The course of the fibre tracts to the thalamus was traced in the subthalamic region using multiple staining procedures and their entrance into the thalamus determined according to our atlas of the human thalamus and basal ganglia [Morel (2007) Stereotactic atlas of the human thalamus and basal ganglia. Informa Healthcare Inc., New York]. Stereotactic three-dimensional coordinates were determined by sectioning thalamic and basal ganglia blocks parallel to stereotactic planes and, in two cases, by correlation with magnetic resonance images (MRI) from the same brains prior to sectioning. The major contributions of this study are to provide: (1) evidence that the bulks of the cerebellothalamic and pallidothalamic tracts are clearly separated up to their thalamic entrance, (2) stereotactic maps of the two tracts in the subthalamic region, (3) the possibility to discriminate between different subthalamic fibre tracts on the basis of immunohistochemical stainings, (4) correlations of histologically identified fibre tracts with high-resolution MRI, and (5) evaluation of the interindividual variability of the fibre systems in the subthalamic region. This study should provide an important basis for accurate stereotactic neurosurgical targeting of the subthalamic region in motor disorders such as PD and ET.

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Figures

Fig. 1

Simplified diagram of the cortico-cerebello-thalamocortical and cortico-basal ganglia-thalamocortical circuitry based on data derived from tracing studies in monkeys. The cerebellar nuclei project to the motor thalamus via the fasciculus cerebellothalamicus (fct), with primary target in the VLp, but also in VLa and VM (projections to medial thalamic nuclei are not included in the schema). Efferent connections of the GPi to the thalamus course through the ansa lenticularis (al) and the fasciculus lenticularis (fl), and the two fibre bulks merge to form the fasciculus thalamicus (ft) which projects primarily to the VLa, VApc, and VM nuclei, with only minor projections to the VLp (projections to the intralaminar nuclei are not shown). Equivalent Hassler’s nomenclature (Hassler 1982) for thalamic nuclei is also indicated. Connections to the thalamus and cortex are represented with different thicknesses according to their relative density and by different gradients in the thalamus. The two major motor pathways are also represented by different colors for clarity. See list of abbreviations

Fig. 2

Series of frontal sections stained for myelin and arranged from anterior (upper left) to posterior (lower right), with corresponding coordinates given in millimeters anterior to the posterior commissural level (Table 1; case Hb4). The pallidothalamic fibres are seen from their emergence from the GPi (al and fl, levels A 21.0–A 13) to their entry into the thalamus (ft, levels A 15–A 12). The cerebellothalamic (fct) tract is shown at its most posterior entrance into the thalamus (near the VPM, level A 6.0) and more anteriorly, into VLp (level A 7.5). Other fibre tracts (mtt, fx, ap, ot, and ac) are also clearly recognizable. Scale bar (in upper left panel): 3 mm

Fig. 3

Representation of the cerebellothalamic (fct) and pallidothalamic (al, fl, ft) tracts on sagittal section of the atlas (panel c) as delimited from myelin (area comprised in the rectangle in a). Thalamic nuclei and STh were best identified on adjacent Nissl section (panel b). Panel d shows PV immunostaining at same sagittal level. The arrows in a and d point to a small gap separating the fct and ft, visible in myelin and PV-ir, respectively. Notice some PV-ir enhanced fibres in the internal capsule near the anterior pole of the STh and presumably corresponding to the fasciculus subthalamicus. Scale bars (a and c): 2 mm

Fig. 4

a Sagittal atlas map and b photomicrographs of adjacent sections stained for myelin, d AChE and c immunoreacted for SMI-32, e CR, and f CB. Case Hb3. Scale bar (upper left panel): 2 mm

Fig. 5

Pallidothalamic (blue) and cerebellothalamic (orange) tracts drawn on the atlas of the human thalamus (case Hb1). The sagittal maps are arranged from medial (L4.5) to lateral (L11.7 mm) with 0.9 mm intervals. The maps are centered on the midcommissural (mcl) and intercommissural (DV0) lines. Scale bar (lower right panel): 2 mm

Fig. 6

Pallidothalamic (blue) and cerebellothalamic (orange) tracts drawn on horizontal sections of the atlas at intercommissural level (DV0) and four levels ventral to DV0 (V0.9, V1.8, V2.7, and V3.6). The horizontal planes are projected on a sagittal section of the atlas 8.1 mm distant from the ventricular border (L8.1) in lower right panel. The pc and mcl levels are represented on the horizontal and sagittal maps by dotted lines. Scale bars (lower right panels): 2 mm

Fig. 7

Series of frontal high-resolution proton density postmortem MRI (left column), myelin sections (middle column), and atlas maps (right column) of the same brain (Table 1; Hb5), at corresponding anteroposterior levels from posterior (lower panels) to middle part of the thalamus (upper panels). Coordinates indicated in the left column (A2.5, A5, and A7.5) correspond to millimeters anterior to the posterior commissural level. The cerebellothalamic tract (fct) can be identified, as well as the RN and several thalamic nuclei. Scale bars (left column): 10 mm

Fig. 8

Anterior continuation of the series shown in Fig. 7 to illustrate MRI correlations of pallidothalamic fibre tracts (al, fl, and ft), thalamic nuclei, and basal ganglia. Same conventions as in Fig. 7. Scale bars (left column): 10 mm

Fig. 9

a Illustration of the pallidal emergence of al in horizontal and b frontal sections stained for myelin. The levels are 4.5 mm ventral to the intercommissural plane (in a) and 22 mm anterior to pc (in b). Note the relatively large anteroposterior extent of the al at the ventral limit of the GPi in a. Cases Hb5 (left panel) and Hb4 (right panel). Scale bars: 3 mm

Fig. 10

Multiarchitectonic characteristics of the pallidal and subpallidal areas on photomicrographs of frontal sections stained for a myelin, b AChE or c immunoreacted for CB and d CR. Note the clear contrast between al (only moderately stained) and the GPi (enhanced in CB, c), and the area underneath the pallidum (or sublenticular area, enhanced for CR, d). A continuity between the sublenticular area and the ansa peduncularis (ap) is seen with CR immunostaining. Case Hb4. Scale bar: 3 mm

Fig. 11

Photomicrographs of adjacent frontal sections 15 mm anterior to the posterior commissure stained for a myelin, c AchE, and b immunostained for the calcium-binding proteins CB and d PV. Pallidothalamic fibres (fl, ft) are darkly stained for myelin, moderately for AChE and PV, and negatively for CB. The STh, thalamic VLp nucleus and the optic tract (ot) are strongly enhanced in PV-ir. The arrow in d points to presumed pallidosubthalamic fibres (fasciculus subthalamicus) crossing the posterior limb of the internal capsule. The asterisks in a, b, and d indicate matching locations in the internal capsule corresponding to striatonigral fibres which are strongly enhanced in CB-ir but unstained for myelin. Case Hb4. Scale bar (a): 2 mm

Fig. 12

Variability of the fibre tracts in the subthalamic area in sagittal (upper panels) and horizontal (lower panel) atlas maps of different brains. In sagittal sections (upper panels, L7 and L8), red contours and filling correspond to brain Hb1 and black contours and gray filling correspond to brain Hb4. In the horizontal section represented in lower panel, red and black thalamic and basal ganglia contours correspond to cases Hb1 and Hb3, respectively (see also Table 1). For reference, the STh is represented in green. In the horizontal section (lower panel), the delineation of fct, ft, and fl in four different cases is represented by different dotted lines and the area of maximal overlap between the tracts in Hb1, Hb2, and Hb5 is depicted in yellow. In all panels, the locations and sizes of the targeted PTT and CTT are represented in dark gray areas. Positions of the horizontal intercommissural (DV0), posterior commissural (AP0) and midcommissural (mcl) planes are also indicated. Midcommissural level in the sagittal maps corresponds to that of case Hb4 (13 mm). Scale bars: 2 mm

Fig. 13

Spatial relationship between the fct, ft, and fl. In each diagram, the x-axis represents the distance (mm) to the posterior commissure and the y-axis, the distance to the medial thalamic border. The distances were measured at three different dorsoventral levels [2 mm ventral (V2) and 1 mm ventral (V1) to intercommissural level, and intercommissural level (DV0)] of two different brains (Hb1 and Hb4) cut in the sagittal plane. For each dorsoventral level, the center of the bulk on the anteroposterior (A-P) axis was measured at medio-lateral (M-L) levels between 0 (ventricular border) and 18 mm

Fig. 14

Targeting in functional neurosurgery. a, b Postoperative T1-weighted axial MRI and c atlas reconstruction of pallidothalamic (PTT) and cerebellothalamic (CTT) tractotomies in two patients with PD and ET, respectively (see text for more detail). The horizontal atlas map is 1.8 mm ventral (V1.8) to the intercommissural plane. Scale bars: 5 mm in a and b, 2 mm in c

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Human pallidothalamic and cerebellothalamic tracts: anatomical basis for functional stereotactic neurosurgery - PubMed (original) (raw)