Vertical Hemispherotomy: Contribution of Advanced Three-Dimensional Modeling for Presurgical Planning and Training

Abstract

Vertical hemispherotomy is an effective treatment for many drug-resistant encephalopathies with unilateral involvement. One of the main factors influencing positive surgical results and long-term seizure freedom is the quality of disconnection. For this reason, perfect anatomical awareness is mandatory during each step of the procedure. Although previous groups attempted to reproduce the surgical anatomy through schematic representations, cadaveric dissections, and intraoperative photographs and videos, a comprehensive understanding of the approach may still be difficult, especially for less experienced neurosurgeons. In this work, we reported the application of advanced technology for three-dimensional (3D) modeling and visualization of the main neurova-scular structures during vertical hemispherotomy procedures. In the first part of the study, we built a detailed 3D model of the main structures and landmarks involved during each disconnection phase. In the second part, we discussed the adjunctive value of augmented reality systems for the management of the most challenging etiologies, such as hemimegalencephaly and post-ischemic encephalopathy. We demonstrated the contribution of advanced 3D modeling and visualization to enhance the quality of anatomical representation and interaction between the operator and model according to a surgical perspective, optimizing the quality of presurgical planning, intraoperative orientation, and educational training.

Keywords: augmented reality; epilepsy surgery; three-dimensional modeling; vertical hemispherotomy.

Figure 1

Brain segmentation and 3D rendering using Mimics. The surface contours of the object are overlaid to the 2D MR sequences for a better visualization of the segmentation. (A = anterior, P = posterior, T = top, B = base, L = left, R = right).

Figure 2

(A) Axial (left) and coronal (right) MR sequences showing the segmented gray and WM structures; (B) Comprehensive view of 3D modeling, showing the main brain subcortical structures involved in hemispherotomy procedure, including the corpus callosum (a), ventricles (b), thalamus (c), fornix (d), fimbria and hippocampus (e), putamen (f), caudate (g), main arteries (h), and optic nerves (i); (C) Comprehensive 3D representation of the main inter-hemispheric (i.e., the corpus callosum) and intra-hemispheric (i.e., the corona radiata/CST, OR, IFOF) connection systems interrupted during hemispherotomy. (A = anterior, L = left).

Figure 3

Illustrative Case 1 shows the surgical steps of a right hemispherotomy (first part) in a 2-year-old patient suffering from pharmaco-resistant epilepsy due to multilobar FCD. For each phase, the 3D modeling (left side) and the corresponding post-operative MRI (right side) are shown. (A) Transcortical approach (red dotted rectangle) to the right lateral ventricle (light blue, red arrows); (B) Posterior callosotomy (yellow fibers, red arrows); (C) Interruption of the fimbria (pink)-fornix (violet) complex (red dotted line, red arrow); (D) Unroofing of the vertical (light blue streamlines) and posterior (blue streamlines) connections (red dotted line, red arrow). (A = anterior, L = left).

Figure 4

Surgical steps of a right hemispherotomy procedure (second part). (A) Anterior callosotomy, having as limit the cistern of the pericallosal arteries (red arrows); (B) Frontobasal disconnection having as medial limit the carotid-optic cistern and the intrahemispheric WM connections (e.g., the IFOF) (green streamlines, white dotted line, red arrow); (C) The procedure is completed by frontotemporal, medio-to-lateral separation, passing through the head of the caudate nucleus (red dotted line, red arrow). (A = anterior, L = left).

Figure 5

Illustrative Case 2. A 7-month-old girl was admitted to our Institution for recurrent drug-resistant clustered seizures since the age of 1 month, characterized by sudden flexion of the upper limbs and the head, associated with vertical nystagmus; (A) The interictal wakefulness EEG showed subcontinous altered activity over the right hemisphere, with multifocal slow and sharp waves intermingled with attenuation phases. Epileptiform abnormalities might be expressed also contralaterally; (B) The MRI showed a complex hemimegalencephaly malformation characterized by increased volume of the right hemisphere, diffuse polymicrogyric conformation of the cortex, presence of periventricular heterotopic nodules, alterations of the basal nuclei, and deviation of the right ventricular system; (C–E) The patient underwent a right vertical hemispherotomy. The 3D model was useful to characterize the 3D configuration of the main target structures during each step of disconnection, including transcortical access to the lateral ventricle (D, yellow dotted arrow), posterior callosotomy (C, red dotted arrow), fimbria-fornix complex interruption (C, white dotted arrow), temporal horn unroofing (D, white dotted arrow), anterior callosotomy (E, light blue dotted arrow), frontobasal disconnection (E, red dotted arrow), final mediolateral disconnection (E, white dotted arrow); (F) Postoperative MRI. (A = anterior, L = left)

Figure 6

Illustrative case 3. A 14 years-old boy suffered from pharmacoresistant seizures characterized by staring followed by generalized hypertonus. (A) Interictal sleep EEG showed recurrent slow waves and spike-and-waves over the left parieto-temporal regions and the vertex; (B) The MRI showed a left hemispheric alteration due to post-ischemic perinatal suffering; (C–F) 3D-modeling showing the main steps of vertical hemispherotomy, including transcortical access to lateral ventricle (C, yellow dotted arrow), posterior callosotomy (D, red dotted arrow), fimbria-fornix complex interruption (D, white dotted arrow), temporal horn unroofing (E, white dotted arrow), anterior callosotomy (F, red arrow), fronto-basal disconnection (F, white dotted arrow), mediolateral (F, light blue dotted arrow). (G) Postoperative MRI. (A = anterior, L = left).

Figure 7

Application of AR technology for virtual representation of the 3D model. (A) Operator with glasses; (B) The model is visualized on a real background. The menu allows to select different anatomical structures; (C) AR technology enables a smart and intuitive interaction between the operator and the model, mainly in two ways. (D–G) The first option consists of visualization of different anatomical layers, such as the cortex and the superficial vessels (D,E), the WM pathways (F), and the deep structures, including the corpus callosum, the ventricles, the central core, and the Willis polygon (G); (H) The model can be actively moved by the operator according, for example, to the surgical perspective, to improve the anatomical awareness of the crucial phases of disconnection.