Minimal access to deep intracranial lesions using

Authors: Saleh A Almenawer Louis Crevier Naresh Murty Amin Kassam Kesava Reddy

Publish Date: 2012/12/06

Volume: 36, Issue: 2, Pages: 321-330

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Abstract

Surgical access to deep intracranial lesions causing the least amount of iatrogenic trauma to the surrounding brain tissue remains a challenging task In this article we evaluate the use of a set of sequential tubes that dilate and provide retraction of the overlying brain tissue acting as a surgical corridor for deepseated brain lesions resection In addition we conducted a comprehensive review of the literature of previously described techniques using variable brain tubular retractor systems We discuss the adaptation of a system designed for spinal use to intracranial pathologies and evaluate the outcomes for the patients involved in the study Moreover the advantages and limitations of the described technique were presented Between August 2005 and 2011 a total of 30 patients with deep brain lesions were operated on using an incremental increase of tubing size for brain retraction guided by a frameless navigation device Of these seven cases were intraventricular and 23 were intraparenchymal Gross total resection was achieved in 70  of cases and the remaining had planned subtotal resections due to involvement of an eloquent area In conclusion the technique of serial dilatation of the brain tissue can be used in conjunction with a microscope or endoscope to provide satisfactory access to deep intracranial pathologies It appears to minimize the associated retraction injury to the surrounding tissue by gradually dilating the white fiber tracts This operative approach may be considered as an effective and safe alternative for brain tumor resections in selected cases especially deepseated lesionsNone of the authors have any conflicts of interest Amin Kassam is a consultant for Karl Storz Endoscopy and Stryker and has equity interest in the NICO Corporation The authors have no personal financial or institutional interest in any of the materials or devices described in this articleAlmenawer et al present an article entitled Minimal access to deep intracranial lesions using a serial dilation technique caseseries and review of brain tubular retractor systems In this article the authors describe their experience using tubular retractors as a minimally invasive approach to deep cerebral lesions This tubular retractor equipment is commonly used in the spine and is readily available in many neurosurgical centers The article includes stepbystep illustrations experience with 30 cases selected case examples and a thorough literature review The authors should be commended for their workCompared to brain blade retractors tubular retractors distribute external pressure evenly over a larger area potentially minimizing cortical injury They provide a relatively fixed amount of retraction and tamponade adjacent cortex Intuitively their use for focal brain lesion surgery seems like a good idea Almenawer et al describe their experience with a commercially available tubular retractor system originally designed for spinal surgery to resect intracranial tumors in 30 patients over a 6year span They used serial dilatation rather than the singleentry technique previously described and purport that it decreases injury to white matter tracts That is hypothetical there is no radiographic or clinical evidence to validate it Other groups have reported similar success using slightly different iterations of the same concept For intraventricular or subcortical thalamus and basal ganglia lesions or intracerebral hematoma evacuation the fixed surgical path provided by these systems is ideal and may reduce inaccuracies of the navigation system by minimizing the confounding effect of brain shift On the other hand when resecting relatively superficial cortical lesions within 2–3 cm of the pial surface they may be obtrusive There are other limitations The added steps to insert the tube may be cumbersome and the overpass technique described here unwieldy The complex threedimensional morphology of an intraaxial brain tumor requires constant adjustment of the surgical angle and protection or coagulation of adjacent blood vessels Adjusting the trajectory of these opaque rigid tubes may inadvertently inflict injury on adjacent cortex and white matter and they may constrain dexterity required for intracranial surgery The venous structures intimately associated with posterior fossa and pineal lesions require careful consideration and may be at risk with a tubular retractor despite the excellent results demonstrated hereIt is fundamental practice to select the shortest trajectory to a cortical or subcortical lesion that avoids eloquent cortex or essential white matter tracts using intraoperative neuronavigation or in some centers intraoperative magnetic resonance image iMRI guidance A certain amount of normal tissue sacrifice is inherent in this process whether one uses a tubular retractor or not but it is critical to avoid inadvertent injury to adjacent areas not part of the planned surgical tract Creating a surgical path under direct visualization provides a measure of safety especially when adopting transsulcal approaches where cortical vessels are buried in the depths of the sulcus and along the lateral margins of the adjacent gyri In a nonhydrocephalic child or adult the outer margin of the ventricle is generally within 5 cm of the pial surface Hence the outer margin of most cortical lesions would be within 2–3 cm of the pial surface and is easily reached without having to resort to the use of retractors of any kind The popularity of selfretaining planar cortical retractors has waned over the past decade largely because surgeons recognize injury they inflict on adjacent cortex We almost never utilize fixed retractors for intraaxial tumor resections but rather use a handheld Penfield 2 over a soft cotton or telfa patty to gently hold the cortex away and keep the field open — the fatiguing hand of the person holding the Penfield 2 ensures only brief periods of retraction For transsulcal approaches we gently wedge a cottonball in place to keep the surgical path open a nuance Dr Yasargil taught However the dynamic interface between cortical tissue and a tubular retractor is unique They may function as restrainers holding back cortical tissue that would migrate into the surgical path rather than a retractors actively pushing cortical tissue away from the surgical path In the former scenario the pressure effect is inward and a function of intrinsic brain tissue pressure and pulsatility while in the latter case it is an outward pressure and a function of the force applied by the retractor arm human or mechanical A slight difference but important when operating on deep lesions in proximity to essential cortex or white matter tracts such as the internal capsule And there are other considerations when selecting the optimal tubular retractor system The commercially available clear plastic ovoid tubes designed for cranial surgery may have a slight advantage over the system used here and would be iMRI compatible Other adjuncts such as preoperative functional MRI and diffusion tensor imaging data help determine the surgical access point and tract and in some instances electrophysiological or awake cortical mapping would be ideal modalities to preserve neurological function In the end careful case selection based on anatomy and pathology is essential in some instances a stereotactic biopsy may be the best course This is simply a tool that may add a slight advantage to a neurosurgeon’s armamentarium in select circumstances It is not a substitute for surgical skill or judgement and may not determine patient outcome The authors are commended on their excellent results it is possible they may have achieved the same through a conventional approach without the use of this retractorSocalled minimal invasive procedures are already very much used with safety and excellent results in the current practice of many surgical specialties which unfortunately is not a reality for the neurosurgery of intrinsic brain lesions yet despite all efforts and research that has been done in this field as we can appreciate through the extensive list of references of this interesting article Parallel to the notorious appeal of this concept the well known difficulties are more particularly related with the compactness of the brain tissue itself with the dimensions and fragility of the neural and vascular structures and to the magnitude of potential bleedings the brain weights approximately 2  of the body and receives about 10–15  of the cardiac output Even for ventricular and cisternal neurosurgery the currently available technology still allows only very limited surgical interventionsThis article by Almenawer et al propitiates one step ahead within this issue mostly by describing a clever method of serially dilating an introduced tube through which microsurgical procedures can be then done Their also reported experience already with 30 actual surgical cases corroborates its feasibility without significant complications Nevertheless further optical and instrumental developments are still required for us to operate intrinsic brain lesions through minimally invasive approaches more efficiently and with safety and comfortWhile the improvement of our patients care depends very much on further contribution of other fields further development of microneurosurgery itself depends on putting together our current knowledge of morphological and functional brain anatomy together with new technology developments which is achieved mainly through experience and creativity and this article is definitely pointing to this direction Further utilization of this technique proposed by Almenawer et al will evaluate better its use usefulness and/or will provide contributions for development of new similar techniques

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