Intraventricular meningiomas require a cautious surgical preoperative planning in an attempt to avoid unwanted postoperative neurological déficits. Despite that better surgical approaches exist, the posterior parietal transcortical approach to intraventricular trigonal lesions, with its unavoidable damage to the posterior parietal white matter pathways, is still popular in clinical practice, at times,like in the following case report, without any electrophysiological support.

Keywords: surgical approach, optic ataxia, hemianopsia, optic radiation

Intraventricular meningiomas are found infrequently in clinical practice^1,2 and, although the development of neuro-imaging technology has enabled its non-invasive diagnosis, their delayed clinical expresión, which is usually vague and at times intermittent, allows these lesions to reach a significant size by the time of their detection.³ Because the cerebral ventricles are surrounded by eloquent neural structures, the surgical approach taken for the resection of these lesions must be individualized, taking into account the lesion´s location within the ventricular system, it´s size and blood supply, in an attempt to reduce to a mínimum the occurrence of unwanted postoperative neurological déficits.⁴

A careful literature search under the titles of “meningioma”and “Intraventricular tumors” was carried out and the reference lists of the publications thus gathered was reviewed in order to augment the data on the surgical aspects concerned with these lesions and their potential complications.

An elderly right handed male, with a personal and family history of migraine, reported that, for the previous few years, he had been experiencing recurrent episodes of flicker scotoma in his right homonymous visual fields. It was not triggered by any particular stimulus, it was colorless and showed no movement. It lasted a few minutes and cleared spontaneously, only to recur after variable periods of time. The flicker scotoma was not associated with any change in his mental status, headache, convulsions nor with any auditory components. Through these years the patient did not notice any visual field defect nor any deterioration in his visual acuity. Later on, when he developed some mood changes and gait imbalance, a neurological consultation was obtained and a magnetic resonance imaging was done,which revealed a right intraventricular meningioma (Figure 1).

Figure 1 Contrasted MRI depicting a rightsided intraventricular meningioma.

He was transferred to a tertiary neurosurgical referal center where his neurological examination and visual field testing by confrontation revealed no abnormalities. Surgery was undertaken via a right posterior parietal transcortical approach with image guidance assistance. Under the operating microscope the tumor was visualized and a biopsy taken which revealed a meningioma grade 2. The mass was debulked by ultrasonic aspiration and it was completely resected.

Post-operatively the patient presented a left homonymous hemianopsia and optic Ataxia,¹ which caused him difficulty reaching and grasping of objects and playing his guitar and piano. Moreover he also experienced trouble in shifting gaze to the next text line while reading which caused difficulties in his work at the computer and Reading subtitles while watching a movie or televisión. His pre-existing gait imbalance also worsenned somewhat. Four months after the surgery a magnetic resonance scan with contrast enhancement revealed a small left parietal cortical defect (Figure 2A) and the surgical track from the posterior parietal área into the right lateral ventricle (Figure 2B) but showed no evidence of residual or recurrent tumor.

Figure 2A Contrasted MRI depicting the small postsurgical cortical defect.

Figure 2B Contrasted MRI in sagital view showing the surgical track into the lateral ventricle..

 An EEG revealed a right parietal delta focus without epileptiform activity. Nevertheless and because the clinically sugestive epileptic nature of the flicker scotoma, which did not seem to be directly related to the rightsided tumour, treatment with Pregabaline 100 mg/day was initiated and shortly thereafter the flicker scotoma ceased and did not recur. Through a three year follow-up period, the gait imbalance gradually improved to his preoperative level, the difficulty in reaching and grasping objects and his difficulty playing guitar and piano also gradually improved, but the left homonymous hemianopia and the reading difficulties remained unchanged.

The initial challenge posed by intraventricular meningiomas was their timely diagnoses, a difficulty that has been significantly subserved with the advent of imaging technologies. A second challenge remained and consisted in the selection of the optimal surgical technique that would allow for the safe and complete resection of these lesions, a persuit that benefited with the development of microneurosurgery. A third, and still ongoing quest, is the one posed by the selection of the optimal surgical approach that could provide for the shortest avenue to the lesión and enable its complete resection.^2,5 The current surgical planning is usually based on the location of specific cortical sulci to determine the point of entry, with no consideration been paid to the underlying white matter pathways.

Despite that functional MRI, and whole-brain difusión tensor imaging have improved this preoperative planning,⁶ most of the current publications on that topic focus on the identification and anatomical location of the optic radiation in its relation to the ventricular system, but ignore^7–10 other important white matter pathways that should also be considered in such a plan. For instance, identifying the white matter ventral and dorsal visual streams emanating from the striate cortex^11,12 deserve being included in such a preoperative planning since their disruption could cause significant neurological déficits.¹³

At the present time, the posterior parietal transcortical approach to the lateral ventricular atrium is still a popular one in neurosurgical practice, and, although the cortical damage it causes may be restricted, a significant disruption of the subcortical white matter pathway network is unavoidable. Moreover, this approach also places visual function itself in double jeopardy: a.-By dysrupting the white matter dorsal visual stream, that connects the striate cortex to the posterior parietal lobe, this approach can cause Optic Ataxia,¹³ a disfunction at a more integrative sensorymotor level that results in difficulty completing reaching and grasping tasks guided by peripheral visión, as well as other related disabilities¹⁴ in the absence of a primary motor or sensory déficit. b.- By damaging fibers of the optic radiation, either at the surgical point of entry into the atrium^8,9 or by trans-ependymal optic radiation trauma caused during tumor removal¹⁵ it could result in an homonymous visual field defect. Because of these significant postoperative problems, a different surgical approach have been sugested in an attempt to improve the surgical results.^16,17

With this objective in mind, the use of preoperative non-invasive functional neuroimaging and electrophysiological monitoring have also been incorporated to the preoperative planning. Nevertheless for most of these rechniques,the identification of white matter eloquent pathways remains problematic. As a consequence, the use of intraoperative real-time direct electrical cortical and subcortical stimulation has been recommended^18–20 as a method that could allow for a safer tumor resection. The case reported herein exemplify the current situation where even at a neurosurgical tertiary referral center this quest remains unsolved.

The transcortical approach to the lateral ventricle through the posterior parietal cortex, should be avoided and replaced by the interhemispheric transcallosal approach in order to minimize potential operative neurological injury. In those cases where the transcortical parietal approach must be used, it should be carried out with the support of the adjuncts herein outlined, ideally by intraoperativeelectrical cortical and subcortical mapping.

The author wish to thank Mrs. Paola D.Vermeer PhD and Ms Elizabeth Gonzalez for their bibliographic support and to Ms.Pascal Prado y Mr. Samuel Abogabir for heir technical assistance.

The author declares that there is no conflicts of interest.

1. CBTUS statistical report: Primary brain tumors in the United States. Hindsdale. IL. 2002.
2. Grujicic D, Cavallo LM, Somma T, et al. Intraventricular meningiomas.A series of 42 patients at a single institution and literatura review. World Neurosurgery. 2017;97:178–188.
3. Pendl G, Ozturk E, Haselberger C. Surgery of tumors of the lateral ventricle. Acta Neurochir (Wien). 1992;116(2-4):28–36.
4. Yasargil MG. Microneurosurgery of CNS tumors. Suttgart. Georg Thieme. 1996.
5. Drapkin AJ. The choice of the best surgical approach remains critical despite the technological revolution. Rev Chil Neurocirugia. 2020;46(1):45–46.
6. Agarwal V, Malcom JG, Padilla G, et al. Tractography for optic radiation preservation in transcortical approaches to intracerebral lesions. Cureus. 2017;9(9):e1722.
7. Hofer S, Karaus A, Frahm J. Reconstruction and dissection of the entire human visual pathway using difusión tensor MRI. Front Neuroanat. 2010;4:15.
8. Mahaney KB, Abdulrauf SJ. Anatomic relationship of the optic radiations to the atrium of the lateral ventricle:description of a novel entry point to the trigone. Neurosurgery. 2008;263(4):195–203.
9. Peltier J, Traqvers N, Destrieux C. Optic radiations:a microsurgical anatomical study. J Neurosurg. 2006;105(2):294–300.
10. Yamamoto T, Yamada K, Kishimura T, et al. Tractography to depict three layers of visual field trajectories to the calcarin gyri. Am J Ophthalmol. 2005;140(5):781–785.
11. Goodale MA, Milner AD. Separate visual pathways for perception and action. Trends Neurosci. 1992;15(1):20–25.
12. Ungerleider LG, Mishkin M. Analysis of visual behavior. In: Ingle DJ, Goodale MA, Mansfield RJW, editors. MIT Press. 1982;549–586.
13. Andersen RA, Andersen KN, Hwang EJ, et al. Optic ataxia: from Balint´s síndrome to the parietal reach región. Neuron. 2014;81(5):967–983.
14. Ffyche DH, Blom D, Catani M. Disorders of visual perception. J Neurol Neurosurg Psychiat. 2010;81(11):1280–1287.
15. Piepmeier JM, Spencer DD, Sass KJ, et al. Lateral ventricular masses,in Apuzzo LMJ editor. Brain Surgery: complication avoidance and management. New York Churchill Livingstone. 1993;581–599.
16. Kempe LG, Blaylock R. Lateral-trigonal intraventricular tumors. A new operative approach. Acta Neurochir (Wien). 1976;35(4):233–242.
17. Yasargil MG, Türe U, Yasargil DCH. Surgical anatomy of supratentorial midline lesions. Neurosurg Focus. 2005;18(6B):E1.
18. Berger MG. Lesions in Functional (eloquent”) cortex and subcortical white matter. Clin Neurosurg. 1994;41:444–463.
19. Duffau H, Chapelle L, Denvil D, et al. Usefulness of intraoperative electrical subcortical mapping during surgery for low grade gliomas located within eloquent brain regions: functional results in a consecutive series of 103 patients. J Neurosurg. 2003;98:764–778.
20. Eisner W, Burtscher J, Bale R, et al. Use of neuronavegation and electrophysiology in surgery for subcortically located lesions in the sensorymotor strip. J Neurol Neurosurg Psychiat. 2002;72:378–381.