Throughout history, many scientists have wondered about the reason for neural pathway decussation in the CNS resulting in contralateral forebrain organization. Hitherto, one of the most accepted theories is the one described by the renowned Spanish physician, Santiago Rámon y Cajal at the end of the 19th century. This Nobel Prize winner, among his many contributions to science, gave us the answer to this question: the key lies in the optic chiasm. Based on the fact that the ocular lenses invert the image formed in the retina, Cajal explained how the decussation of the fibers in the optic chiasm is necessary to obtain a continuous image of the outside in the brain. The crossing of the tactile and motor pathways occurred posteriorly as a compensatory mechanism to allow the cortical integration of the sensory, motor, and visual functions. This theory had a great influence on the scientific community of his time, and maintains its importance today, in which none of the theories formulated to date has managed to entirely refute Cajal’s. In addition, the decussation of neural pathways plays a significant role in different diseases, especially in the recovery process after a hemispheric lesion and in several congenital pathologies. The advantages of cerebral lateralization have also recently been published, although the evolutionary connection between fiber decussation and cortical function lateralization remains a mystery to be solved. A better understanding of the molecular and genetic substrates of the midline crossing processes might result in significant clinical advances in brain plasticity and repair.
Carla Mora, Carlos Velásquez, and Juan Martino
Carlos Velásquez, Elsa Goméz, and Juan Martino
Parietal lobe functions include somesthesia, language, calculation, self-motion perception, and visuospatial awareness. In this video, the authors show the intraoperative mapping of a left parietal lobe for a low-grade glioma resection. Standard sensory and language mapping were performed. Interestingly, by using the “Line Bisection” task, subcortical stimulation of the gyrus angularis was repeatedly associated with ipsilateral spatial neglect, often described in the right parietal lobe. In a similar way, subcortical stimulation in a more posterior point elicited episodes of vertigo, probably due to stimulation of the superior longitudinal fasciculus. Both findings were useful to define the functional limit of the resection.
The video can be found here: https://youtu.be/qgGDRW_6u0A.
Leticia Fernández, Carlos Velásquez, Juan A. García Porrero, Enrique Marco de Lucas, and Juan Martino
The functional importance of the superior temporal lobe at the level of Heschl’s gyrus is well known. However, the organization and function of these cortical areas and the underlying fiber tracts connecting them remain unclear. The goal of this study was to analyze the area formed by the organization of the intersection of Heschl’s gyrus–related fiber tracts, which the authors have termed the “Heschl’s gyrus fiber intersection area” (HGFIA).
The subcortical connectivity of Heschl’s gyrus tracts was analyzed by white matter fiber dissection and by diffusion tensor imaging tractography. The white matter tracts organized in relation to Heschl’s gyrus were isolated in 8 human hemispheres from cadaveric specimens and in 8 MRI studies in 4 healthy volunteers. In addition, these tracts and their functions were described in the surgical cases of left temporal gliomas next to the HGFIA in 6 patients who were awake during surgery and underwent intraoperative electrical stimulation mapping.
Five tracts were observed to pass through the HGFIA: the anterior segment of the arcuate fasciculus, the middle longitudinal fasciculus, the acoustic radiation, the inferior fronto-occipital fasciculus, and the optic radiation. In addition, U fibers originating at the level of Heschl’s gyrus and heading toward the middle temporal gyrus were identified.
This investigation of the HGFIA, a region where 5 fiber tracts intersect in a relationship with the primary auditory area, provides new insights into the subcortical organization of Wernicke’s area. This information is valuable when a temporal surgical approach is planned, in order to assess the surgical risk related to language disturbances.
Mohammed J. Asha, Hirokazu Takami, Carlos Velasquez, Selfy Oswari, Joao Paulo Almeida, Gelareh Zadeh, and Fred Gentili
Transsphenoidal surgery is advocated as the first-line management of growth hormone (GH)–secreting adenomas. Although disease control is defined by strict criteria for biochemical remission, the length of follow-up needed is not well defined in literature. In this report, the authors present their long-term remission rate and identify various predictive factors that might influence the clinical outcome.
The authors conducted a single-institute retrospective analysis of all transsphenoidal procedures for GH-secreting adenomas performed from January 2000 to June 2016. The primary outcome was defined as biochemical remission according to the 2010 consensus criteria and measured at the 1-year postoperative mark as well as on the last recorded follow-up appointment.
Secondary variables included recurrence rate, patterns of clinical presentation, and outcome of adjuvant therapy (including repeat surgery). Subgroup analysis was performed for patients who had biochemical or radiological “discordance”—patients who achieved biochemical remission but with incongruent insulin-like growth factor 1 (IGF-1)/GH or residual tumor on MRI. Recurrence-free survival analysis was conducted for patients who achieved remission at 1 year after surgery.
Eighty-one patients (45 female and 36 male) with confirmed acromegaly treated with transsphenoidal surgery were included. In 62 cases the patients were treated with a pure endoscopic approach and in 19 cases an endoscopically assisted microscopic approach was used.
Primary biochemical remission after surgery was achieved in 59 cases (73%) at 1 year after surgery. However, only 41 patients (51%) remained in primary surgical remission (without any adjuvant treatment) at their last follow-up appointment, indicating a recurrence rate of 31% (18 of 59 patients) over the duration of follow-up (mean 100 ± 61 months). Long-term remission rates for pure endoscopic and endoscopically assisted cases were not significantly different (48% vs 52%, p = 0.6). Similarly, no significant difference in long-term remission was detected between primary surgery and repeat surgery (54% vs 33%, p = 0.22).
Long-term remission was significantly influenced by extent of resection, cavernous sinus invasion (radiologically as well as surgically reported), and preoperative and early postoperative GH and IGF-1 levels (within 24–48 hours after surgery) as well as by clinical grade, with lower remission rates in patients with dysmorphic features and/or medical comorbidities (grade 2–3) compared to minimally symptomatic or silent cases (grade 1).
The long-term surgical remission rate appears to be significantly less than “early” remission rates and is highly dependent on the extent of tumor resection. The authors advocate a long-term follow-up regimen and propose a clinical grading system that may aid in predicting long-term outcome in addition to the previously reported anatomical factors. The role of repeat surgery is highlighted.
María José Mayorga-Buiza, Mónica Rivero-Garvía, Javier Márquez-Rivas, Carlos Velásquez-Rodríguez, and Emilio Gómez-González
Carlos Velásquez, Mónica Rivero-Garvía, Maria Jose Mayorga-Buiza, María de los Ángeles Cañizares-Méndez, Manuel E. Jiménez-Mejías, and Javier Márquez-Rivas
This report describes a reliable and simple technique for securing external ventricular drains (EVDs) to the scalp and avoiding pullout complications. The operative technique consists of fixing the drain between 2 hydrocolloid dressings and securing it with staples. A 10-year retrospective analysis of EVD pullout complications was performed in a series of 435 consecutive patients who were treated at a single institution. The EVD pullout complication rate was 0.4%. No complications related to the fixation technique were found. The median operative time required to fix the drain was 60 seconds. The technique presented here is a simple and reliable procedure to fix the EVD to the scalp, preventing pullout complications and thus reducing the morbidity of EVD reimplantation.
Joao Paulo Almeida, Carlos Velásquez, Claire Karekezi, Miguel Marigil, Mojgan Hodaie, James T. Rutka, and Mark Bernstein
International collaborations between high-income (HICs) and low- and middle-income countries (LMICs) have been developed as an attempt to reduce the inequalities in surgical care around the world. In this paper the authors review different models for international surgical education and describe projects developed by the Division of Neurosurgery at the University of Toronto in this field.
The authors conducted a review of models of international surgical education reported in the literature in the last 15 years. Previous publications on global neurosurgery reported by the Division of Neurosurgery at the University of Toronto were reviewed to exemplify the applications and challenges of international surgical collaborations.
The most common models for international surgical education and collaboration include international surgical missions, long-term international partnerships, fellowship training models, and online surgical education. Development of such collaborations involves different challenges, including limited time availability, scarce funding/resources, sociocultural barriers, ethical challenges, and lack of organizational support. Of note, evaluation of outcomes of international surgical projects remains limited, and the development and application of assessment tools, such as the recently proposed Framework for the Assessment of International Surgical Success (FAIRNeSS), is encouraged.
Actions to reduce inequality in surgical care should be implemented around the world. Different models can be used for bilateral exchange of knowledge and improvement of surgical care delivery in regions where there is poor access to surgical care. Implementation of global neurosurgery initiatives faces multiple limitations that can be ameliorated if systematic changes occur, such as the development of academic positions in global surgery, careful selection of participant centers, governmental and nongovernmental financial support, and routine application of outcome evaluation for international surgical collaborations.
Marco A. Barajas, Guadalupe Ramírez-Guzmán, Carlos Rodríguez-Vázquez, Vinicio Toledo-Buenrostro, Héctor Velásquez-Santana, Ramiro del Valle Robles, Abel Cuevas-Solórzano, and Gabriel Rodríguez-Hernández
Object. The goal of this study was to examine the role of gamma knife radiosurgery (GKS) and adjuvant neuroendoscopic procedures by assessing the outcome in 10 patients with craniopharyngiomas who were treated between 1998 and 2001.
Methods. In 10 consecutive patients (six males and four females, mean age 12 years [range 7–32 years]), there were nine mixed and one solid craniopharyngioma. In the last three cases, neuroendoscopic procedures were conducted. Two cases required insertion of an Ommaya reservoir. In another case partial removal of the cyst wall was performed using an endoscope to create a communication with the cerebrospinal pathways and thereby preclude the need for shunt insertion.
Conclusions. Multimodal management of craniopharyngiomas seems to provide a better rate of survival and greater long-term disease control. It is suggested that GKS combined with adjuvant neuroendoscopy should be used as an alternative in treating recurrent or residual craniopharyngiomas if additional microsurgical removal cannot guarantee a cure.