An Alternative Route to the Posterior Half of the Third Ventricle: The Transoccipital Horn Approach. Technical Note Giovanni Muscas, Francesca Battista, Giancarlo Lastrucci, Alessandro Della Puppa - BACKGROUND: Lesions arising or abutting in the pos- terior half of the third ventricle are approached through established routes to avoid damage of essential brain structures. Occasionally, the features of the lesion require rethinking these traditional routes and tailoring the surgi- cal approach to cause fewer debilitating sequelae to the patient. We introduce a modification of previously described transcortical approaches to lesions of the pos- terior third ventricle. The technique and possible in- dications are discussed. - METHODS: Two cases of posterior third ventricle tumors are presented. In both patients, a small posterior fossa and large tentorial veins located along the surgical route, as well as the position of the lesion underneath the internal cerebral veins, encouraged the concept of a novel trans- occipital horn approach that was developed to access the tumor with less postoperative deficits. - RESULTS: Both lesions were removed with transitory postoperative visual deficits. - CONCLUSIONS: The transoccipital horn approach is a feasible alternative to other surgical routes to the posterior part of the third ventricle in cases of particularly chal- lenging anatomy and tumor characteristics. It allows reaching the lesion along its major axis, fully exploiting the natural space created by the tumor in its growth and avoiding the internal cerebral veins. INTRODUCTION L esions arising or abutting in the third ventricle are a sur- gical challenge because of their deep location and prox- imity to vital anatomic structures. 1,2 Increased surgical experience throughout the years has permitted describing different approaches, tailored to gain safe access to these areas while minimizing damage to the healthy brain, 3-5 and different routes are recommended according to the lesion localization (i.e., in the anterior and mid-third of the posterior part of the ventricle). 5 Tumors located in the posterior part of the third ventricle are approached through established surgical routes neurosurgeons should be familiar with, despite the rarity of these lesions. Ac- cording to the tumor size and shape, its relationship with eloquent structures, the patient’s preoperative neurologic status, and the surgeon’s preference, some options are open, like the infratentorial supracerebellar, occipital transtentorial, posterior interhemispheric transcallosal and retrocallosal, and the posterior transcortical approach through the superior parietal lobule. 3-8 Occasionally, the patient’s anatomy and tumor localization make these surgical approaches unsuited to complete resection, which can be associated with a high risk of severe postoperative defi- cits. 9-11 If deep vessels lie along the surgical path or if the operating corridor is too long and narrow with an inappropriate angle of view for a safe removal through traditional approaches, 12 other routes must be conceived, observing the rule of causing as little harm as possible to the brain. This tenet also applies to cases when large lesions necessitate extensive brain retraction to achieve a sufficient view through transcallosal approaches. 13 Here, we describe a transoccipital horn approach to access the posterior third ventricle, developed for a case in which other common routes were deemed inappropriate or too risky because of the patient’s anatomy and tumor characteristics. The case of a second patient with similar anatomic and pathological features, for which this approach was performed and perfected, is also described. Furthermore, we present the features of this approach and discuss some possible indications. METHODS Case Description 1 A right-handed woman aged 39 years without relevant medical history was admitted to our emergency room after Key words - Surgical approach - Third ventricle - Transcortical - Tumor Departments of Neurosurgery, Neuroscience, Psychology, Pharmacology, and Child Health, University of Florence, Careggi, Florence, Italy To whom correspondence should be addressed: Giovanni Muscas, M.D. [E-mail: muscas.giovanni@gmail.com] Citation: World Neurosurg. (2019) 132:223-229. https://doi.org/10.1016/j.wneu.2019.08.255 Journal homepage: www.journals.elsevier.com/world-neurosurgery Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2019 Elsevier Inc. All rights reserved. WORLD NEUROSURGERY 132: 223-229, DECEMBER 2019 www.journals.elsevier.com/world-neurosurgery 223 Technical Note