Neurology India Medknow Publications on behalf of the Neurological Society of India ISSN: 0028-3886 EISSN: 1998-4022 Vol. 58, Num. 6, 2010, pp. 942-944

Neurology India, Vol. 58, No. 6, November-December, 2010, pp. 942-944

Case Report

Cavum septum pellucidum: A feasible route to third ventricle

Kuan-Yin Tseng¹, Hsin-I Ma¹, Dueng-Yuan Hueng¹, Jiann-Her Lin²

¹ Department of Neurological Surgery, Tri-Service General Hospital, Taipei, China
² Department of Neurological Surgery, Taipei Medical University Hospital, Taiwan, China
Correspondence Address: Jiann-Her Lin, No.252, Wuxing St., Xinyi Dist., Taipei City 110, Taiwan, China, de0211tw@yahoo.com.tw

Date of Acceptance: 27-Aug-2010

Code Number: ni10262

PMID: 21150064
DOI: 10.4103/0028-3886.73754

Abstract

Keywords: Anterior third ventricle tumor, cavum septum pellucidum, transcallosal approach

Introduction

The third ventricle is one of the most surgically inaccessible areas in the brain. It is impossible to reach its cavity without incising any neural structure. ^[1] The interhemispheric-transcollosal approach is commonly used to reach the lateral ventricle, where one could choose transforminal, transchoroidal fissure; or interfornical exposure to reach the third ventricle. ^[2] However, these approaches may result in damage to the fornices, internal cerebral veins, posterior medial choroidal arteries, and parietal cortical draining veins. ^[3],[4],[5] Herein, we report a patient with a tumor in the anterior third ventricle and a coincident cavum septum pellucidum (CSP). The transcavum-septum-pellucidum approach anterior to foramen of Monro was utilized to remove the tumor without damaging the critical structures.

Case Report

A 50-year-old man presented with impaired memory and depressed mood of two years duration. Contrast brain magnetic resonance imaging (MRI) showed a contrast-enhancing mass measuring 3.3 Χ 3.5 cm, located in the anterior part of the third ventricle and blocking both the foramen of Monro, causing dilatation of both the lateral ventricles. It also showed a coincident cavum septum pellucidum bounded anteriorly by the genu of the corpus callosum and posteriorly by the column of the fornix. The floor of cavum was lying right over the tumor mass [Figure - 1]. During surgery, the corpus callosum was exposed, and a 1.5-cm oval callosotomy was made. Using retractor to advance the cavity further toward the tumor the boundaries of the cavity could be identified: anteriorly the genu, on either side by septal leaves which extended posteriorly to fuse as a blind end. With the guidance of the navigator system, the cavity was identified as the septal pellucidi, and the floor was found to be lying right over the tumor mass. Anatomically, the CSP has the following boundaries: anteriorly, the genu of the corpus callosum; posteriorly, the columns of fornix; inferiorly, the rostrum of corpus callosum and the anterior commissure. Therefore, it was possible to stay within the CSP without opening the septal leaves and directly open its floor to access the tumor mass between the anterior commissure and column of the fornix. Opening the floor uncovered the tumor mass, which appeared gray in color and firm in consistency with a clear margin between the surrounding third ventricle walls except the anterior wall [Figure - 2]. The tumor seemed to originate from the anterior third ventricle wall. During the removal of the tumor, small cottonoids were placed between the tumor wall and the third ventricle for the dissection of the plane. The attachment to the lamina terminalis was severed using a micro-scissors and a micro-dissector. After the tumor was completely removed, one could visualize the floor of the third ventricle anterior to the orifice of aqueduct of the sylvius posteriorly. Postoperatively patient had transient diabetes insipidus. He had gradual improvement in his memory. The pathology of the tumor revealed choroid glioma. Postoperative MRI demonstrated the route of approach to the tumor, from the interhemispheric fissure through the transcavum septum pellucidum, and confirmed the total excision of the tumor [Figure - 3].

Discussion

The anterior transcallosal approach leads surgeons to the lateral ventricle, where several access routes to the third ventricle are available: the foramen of Monro pathway, the interfornical pathway and the transchoroidal approach. ^[6] The transforaminal approach requires enlargement of the foramen and results in sectioning of the fornix or damage to the anterior nuclei of the thalamus. ^[7] Moreover, removal of the posterior foraminal tissue has the risk of causing uncontrollable venous bleeding from the internal cerebral vein. ^[8] The interfornical approach usually leads to damage to the fornices, the internal cerebral veins and the posterior medial choroidal arteries, especially causing bilateral fornical injury in patients with CSP or cavum vergae (CV). ^[1] The approach via the transchoroidal plane has limitations of exposure of the anterior third ventricle because of the columns of the fornix and the presence of parietal cortical draining veins. ^[5]

This patient had anatomic variation at the fornix-septum pellucidum complex and the cavum septum pellucidum. The boundaries were: anteriorly, the genu of the corpus callosum; superiorly, the body of the corpus callosum; posteriorly, the anterior limbs and columns of the fornix; inferiorly, the rostrum of the corpus callosum and the anterior commissure; laterally, the two leaves of the septum pellucidum. ^[9] Staying within the CSP and opening the floor indicated the availability of a potential avenue into the third ventricle. However, there have been previous reports of confusion usually arising while entering the CSP, due to the absence of familiar ventricular landmarks such as the foramen of Monro, the thalamostriate vein and the choroid plexus in the lateral ventricle. ^[10] In this patient, the tumor located in the anterosuperior third ventricle lifted up the floor of CSP and obstructed the foramen of Monro. Furthermore, it expanded the space between the column of the fornix and the rostrum of the corpus callosum. According to Rhoton, ^[11] the diameter of the space between the anterior commissure and the column of fornix normally ranges between 1.0 and 3.5 mm. Therefore, we propose that the tumor had likely expanded within this space and elevated the floor of CSP. Hence the anteroposterior diameter of the floor was increased by the tumor, which then provided a feasible avenue to third ventricle, making it feasible to pass through the enlarged space anterior to fornix, the internal cerebral vein and the posterior medial choroidal artery. Furthermore, it provided us with a technique to approach the anterior third ventricle directly [Figure - 4]. After the tumor was removed, the entire floor of the third ventricle could be easily visualized using optic recess anterior to the orifice of the aqueduct of sylvius. To the best of our knowledge, in selected cases with a coincident CSP, the transcallosal transcavum-septum-pellucidum approach anterior to the foramen of Monro has never been reported in the literature; however, it may be an appropriate solution for the treatment of the anterior third ventricle tumor.

Acknowledgment

We thank Ryan Lee for English-language editing. This study was supported by grants TSGH-C99-072, TSGH-C99-073, TSGH-C99-074 and TSGH-C99-149 from the Tri-Service General Hospital, Taipei, Taiwan.

References

Copyright 2010 - Neurology India

The following images related to this document are available:

Photo images