Letter to the Editor: Approaches to the ventricular atrium

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TO THE EDITOR: We read with interest the recent article by Jeelani and colleagues3 (Jeelani Y, Gokoglu A, Anor T, et al: Transtentorial transcollateral sulcus approach to the ventricular atrium: an endoscope-assisted anatomical study. J Neurosurg [epub ahead of print June 24, 2016. DOI: 10.3171/2016.3.JNS151289]).

In this interesting laboratory investigation, Jeelani et al. describe the well-known supracerebellar transtentorial transcollateral approach (STTS)2,4 to the atrium through a retrosigmoid craniotomy in cadaveric specimens. They also include the use of the endoscope to enter and identify the regional anatomy of the atrium in order to augment visibility and enhance surgical maneuverability. Undoubtedly, by introducing the three-quarter prone position coupled with the retrosigmoid corridor and the use of the endoscope to perform the STTS approach for accessing atrial lesions, the authors make a valuable contribution to the current neurosurgical armamentarium, since, at least theoretically, the risk of air embolism is greatly reduced. They also, very prudently, at the end of the article comment on the limitations of their study, clearly stating that the extrapolation of this approach to real clinical settings should be done with great caution. Obviously, it should also only be done by surgeons with vast clinical experience and thorough neuroanatomical knowledge.

However, there are a few surgical and anatomical issues that need to be stressed in order to enhance the clarity of the current study. When using normal cerebral sulci as surgical corridors to access deep-seated lesions, one should consider 2 important facts. 1) The morphology and topography of the cerebral sulci in terms of their continuity and branching pattern are highly variable,6 rendering the proper identification of the relevant sulcus challenging. 2) It is almost always mandatory to open the sulcus widely along its length so as to minimize the ill effects of adjacent normal parenchyma retraction, preserve sulcal vascular anatomy, and maximize the surgeon's operative view and maneuverability.1,8 The latter is especially crucial when dealing with intraventricular pathologies with rich blood supply, such as meningiomas, papillomas, and AVMs, where frequently shifting the operative angle is of paramount importance for the safe resection of the lesion and for meticulous hemostasis. Therefore, a considerable extent of the sulcus needs to be exposed in order to meet the aforementioned objectives. In this context, the working area that the STTS approach offers through the retrosigmoid corridor is quite limited not only for a wide spreading of the collateral sulcus but also for the safe identification of the posterior mediobasal temporal lobe surface anatomy, factors that, as previously stressed, interfere with a safe and effective surgical exploration of atrial lesions.

Additionally, in the event that the surgeon needs to switch from endoscopically assisted surgery to traditional microneurosurgery, it seems quite challenging and time consuming to optimally align the microscope's light through the small cortical opening made on the collateral sulcus, with the difficulty being augmented by the steep angle of the surgical trajectory to the ventricular atrium achieved through the retrosigmoid pathway. This challenge could be significant and could potentially increase the surgical risk of postoperative complications when inadvertent intraventricular bleeding has to be tackled with the traditional use of the surgical microscope and bimanual dexterity.

Furthermore, in Table 2 of their Discussion section, the authors provide a very useful summary of the different surgical routes to the ventricular atrium and their potential complications, thus orienting the reader with respect to the different surgical variants. However, in their list of approaches, although the main transgyral operative corridors to the atrium are mentioned, there is a lack of reference to the relevant transsulcal transventricular routes, which shorten the surgical distance while minimizing normal brain transgression-retraction.1,7,8 In this context, apart from the collateral sulcus, the surgeon can gain access to the atrium through the intraparietal sulcus by performing the relevant transsulcal approach.1,7 A wide opening of the intraparietal sulcus followed by a subcortical dissection along the longitudinal axis of the fundus of the sulcus allows a short, direct, and effective access to the atrium through its roof, thus avoiding the optic radiation, which courses on its lateral wall, and preserving eloquent motor sensory and speech areas, which are located further anteriorly and laterally. Ideally, the entire process can be assisted by image-guided stereotaxy and/or ultrasonography. When compared to STTS, the intraparietal transsulcal approach provides a more straightforward and wider working corridor for surgical manipulations; avoids tentorial incision, with possible venous bleeding or infarct from the tentorial sinus; and allows for quicker and easier positioning of the patient. Potential postoperative complications, such as visuospatial neglect and some forms of ataxia, that result from injury to the parietal lobe are greatly reduced, since normal brain transgression and retraction are kept to minimal through the transsulcal trajectory.

Lastly, in the Results section, where the authors describe the regional anatomy identified through the endoscope, they write the following: “Focusing the endoscope on the lateral wall of the atrium, the tapetum was visualized.” At this point, it has to be emphasized that in order to study and illustrate the subcortical white matter fiber tract anatomy and architecture in the context of a microneurosurgery laboratory one has to apply Klingler's method (freeze-thaw process) to formalin-fixed hemispheres followed by the well-known fiber microdissection technique.5 This is the only procedure through which subcortical fiber tracts can be dissected and identified in a neuroanatomy laboratory. Particularly, the fibers of the tapetum, due to their deep location and elegant configuration, are very difficult to demonstrate, even with the implementation of the aforementioned techniques.5

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Disclosures

The authors report no conflict of interest.

Response

We appreciate the insightful comments from Koutsarnakis et al. and we agree with their observations about the topographic variability of the cerebral sulci on the basal occipitotemporal surface. They have also alluded to an alternative way to get to the ventricular atrium, namely through the intraparietal sulcus, which provides a wide working corridor and eliminates the necessity of transgressing the tentorium. Our transtentorial approach is intended to provide a medial corridor to selected lesions that might be difficult to access using standard supratentorial exposures.

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Article Information

INCLUDE WHEN CITING Published online February 17, 2017; DOI: 10.3171/2016.7.JNS161766.

© AANS, except where prohibited by US copyright law.

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