Original Article Schwalbe’s Triangular Fossa: Normal and Pathologic Anatomy on Frozen Cadavers. Anatomo-Magnetic Resonance Imaging Comparison and Surgical Implications in Colloid Cyst Surgery Pasqualino Ciappetta1, Maria Pia Tropeano2, Lorenzo Gitto3, Lorenzo Pescatori4 - BACKGROUND: The fornix is a region of greatest - CONCLUSIONS: The anatomy of the TR influences the neurosurgical interest in regards to its complex anatomy growth pattern of CC within the ventricular cavity and and surgical approaches to this area. The objective of this determines the surgical strategy for their removal. study was to evaluate the morphology of the triangular recess (TR) and its role in the growth pattern of the colloid cysts (CC) within the third ventricle and in the choice of the surgical approach for their removal. Furthermore, to compare the results of the dissections with measurements INTRODUCTION performed on a magnetic resonance imaging scan. he fornix represents the main efferent system of the hip- pocampal formation and is the main component of the - In the anatomic study, 20 cadaveric speci- METHODS: Papez circuit, a complex neural network comprising other mens were dissected and analyzed. In the radiologic study, T neural structures such as the hippocampus, mammillary bodies, a magnetic resonance imaging scan was performed in 20 the Vicq d’Azyr fasciculus, and the cingulus involved in the genesis healthy volunteers. In the clinical study, a retrospective of the factual content of memories.1-5 The complex anatomic analysis of all the patients affected with CCs micro- conformation of the fornix is of pivotal importance from a surgically removed at our institute between 2010 and 2018 neurosurgical point of view, because this structure contributes to was conducted. constitute the roof and anterior wall of the third ventricle and is commonly encountered in most of the surgical approaches to this - RESULTS: In the anatomic study, the width, height, and area.1-7 the area of the TR were respectively 0.31 cm, 0.33cm, and In correspondence of the third ventricle anterior wall, the col- 2 0.051 cm . In the radiologic study, 3 different typologies of umns of the fornix tend to diverge passing mainly behind the TR were identified: open recess in ventriculomegaly (7 anterior commissure to reach the mammillary bodies.1-5,8,9 The patients); open recess in physiologic ventricular system (3 triangular area identified by the column of the fornix and the patients); closed or blind recess (10 patients). Three anterior commissure has been the subject of anatomic debates 10,11 different growth patterns of CCs were identified: type 1) regarding its anatomic boundaries and its denomination. The CCs localized at the foramen of Monro growing behind the terms used by neuroanatomists to describe this portion of the fornix and below the third ventricular roof; type 2) CCs third ventricle anterior wall varied throughout history. They include triangular recess (TR), Schwalbe’s triangular fossa, and growing rostrally between the column of fornix; and even vulva cerebri.11 The dimension of this triangular area is type 3) CCs growing above the plane of the third ven- characterized by a significant interindividual variability, and is tricular roof. influenced by pathologic conditions such as hydrocephalus or Key words From the 1Department of Neurosciences, Section of Neurosurgery, University of Bari Medical 2 - Colloid cyst School, Bari, Italy; Department of Neurosurgery, Humanitas University, Rozzano, Italy; 3 - Fornix Department of Pathology, State University of New York Upstate, Medical University, 4 ’ - Surgery Syracuse, New York, USA; and Department of Neurosurgery, Ca Foncello Hospital, Treviso, - Third ventricle Italy - Triangular recess To whom correspondence should be addressed: Maria Pia Tropeano, M.D. [E-mail: [email protected]] Abbreviations and Acronyms Citation: World Neurosurg. (2019) 128:e116-e128. CC: Colloid cysts https://doi.org/10.1016/j.wneu.2019.04.058 MRI: Magnetic resonance imaging Journal homepage: www.journals.elsevier.com/world-neurosurgery TR: Triangular recess Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2019 Elsevier Inc. All rights reserved. e116 www.SCIENCEDIRECT.com WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2019.04.058 ORIGINAL ARTICLE PASQUALINO CIAPPETTA ET AL. SCHWALBE’S TRIANGULAR FOSSA intraventricular mass.2,10,12,13 However, the individual width of the of the column of fornix. Eventually, the genu and the splenium of triangle in each subject, which mainly depends on the distance the callosum were removed and we were able to follow both the between the columns of fornix, can in turn influence the growth postcommissural and the precommissural components of the pattern of lesions located within the third ventricle such as colloid column of fornix to the mammillary bodies and the septal, lateral cysts (CC).10,12-14 preoptic and anterior thalamic nuclei, as well as the bed nucleus of In this work, we performed an anatomic study of the TR by the stria terminalis. performing dissections and measurements of this region on brains In addition, in the remaining 10 hemispheres, coronal sections fixed according to Klingler’s technique. The measurements have centered at the anterior wall of the third ventricle were obtained. also been performed on magnetic resonance imaging (MRI) In these sections, the relationships between the columns of fornix (volumetric sequences) and compared with the results of the and anterior commissure as well as the morphology of the TR dissections. were analyzed. Morphometric data of the recess were obtained A historical excursus regarding the etymology of the term from these hemispheres. “fornix” and the various denominations given to this region is also given.11,15-52 Finally, we analyzed the neurosurgical applications of our MRI Study anatomic study by illustrating how the distance between the col- Twenty healthy volunteers (10 men and 10 women; mean age 55 umn of fornix, and consequently the dimension and the years ranging from 37e77) were enrolled for this study. morphology of the TR, can influence the growth pattern of the CC In all the patients, a volumetric brain 3T MRI-scan was per- within the third ventricle and the choice of the surgical approach formed, acquiring both T1- and T2-weighted sequences. Given for their removal. With this purpose, some illustrative cases of their capacity to detect the white matter tracts, the fluid attenuated operated CC are presented. inversion recovery (FLAIR) sequences were found to be particularly suitable for the aim of this study. The sequences obtained had the following characteristics: voxel size 0.43 Â 0.43 Â 0.9 mm, TR METHODS (repeat time) 1.570 ms, TE (echo time) 3.29 ms, TI (inversion time) All procedures performed in studies involving human participants 800 ms, flip angle 15, field of view 416 Â 512 voxels (178.9 Â 220.1 were in accordance with the ethical standards of the institutional mm), coronal plane of acquisition. and/or national research committee and with the 1964 Declaration In all the MRI performed, the dimension of the ventricular of Helsinki and its later amendments or comparable ethical system was analyzed according to the Evan’s index. standards. We applied the term “ventriculomegaly” according to the following criteria:53 Klingler’s Dissection Twenty human cerebral hemispheres were placed in a 10% - Evan’s index superior to 0.30 (men, women) in patients <65 formalin solution for at least 40 days. Ten hemispheres were years; dissected with the aim to expose all the components of the fornix. - ’ The first step was the removal of the arachnoidal and vascular Evan s index superior to 0.34 (men)/0.32 (women) in patients of age comprised between 65e69; structures under microscopic magnification. The hemispheres were frozen at e15 C for at least 14 days, and dissections were - Evan’s index superior to 0.36 (men)/0.33 (women) in patients of carried out through different sized wooden spatulas. The Klin- age comprised between 70e74; gler’s dissection was performed with the aim to expose all the - Evan’s index superior to 0.37 (men)/0.34 (women) in patients of main components of the limbic system. age comprised between 75e79; Starting from the basal surface, we were able to progressively expose the floor of the lateral ventricle with the head of the hip- - Evan’s index superior to 0.37 (men)/0.36 (women) in patients of pocampus, the collateral eminence, the alveus, the dentate gyrus, age comprised between 80e84. and the initial part of the fimbria hippocampi. Subsequently, the dissection was continued following a mediolateral orientation. As the first step, the cortex from the medial surface of the ce- Measurements rebral hemispheres was removed starting at the cingulate sulcus In the 10 coronal sections of frozen hemispheres centered at the following the cingulate gyrus until the cingulate isthmus. In the anterior wall of the third ventricle through the aid of a Vernier second phase, the dissection was continued by removing the calliper we performed measurements of the TR dimensions by cortex of the parahippocampal gyrus and exposing the remaining selecting the following parameters: portion of the fimbria and the crura of the fornix until the psal- terium fornices. The exposure of the body fornix was accom- - Width of the recess (distance between the column of fornix in plished by cutting the body and the splenium of the corpus correspondence of the anterior commissure); callosum, and the lateral wall of the frontal horn, body, and atrium - Height of the recess (distance between the superior margin of of the lateral ventricle. This maneuver allowed to visualize the the middle point of the anterior commissure and the meeting neural layer of the third ventricular roof composed by the body point of the column of fornix); fornix separated from the thalamus by the choroidal fissure. The roof of the third ventricle was entirely exposed until the initial part - Area of the recess.