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Transsulcal Parafascicular Surgery Using Brain Path® for Subcortical Lesions

2017; Lippincott Williams & Wilkins; Volume: 64; Issue: CN_suppl_1 Linguagem: Inglês

10.1093/neuros/nyx324

1524-4040

J. D. Day,

Neurosurgical Procedures and Complications

DTI: diffusion tensor imaging DWI: diffusion-weighted imaging ICH: intracerebral hemorrhage MRI: magnetic resonance imaging Subcortical neoplasms present a particularly challenging problem for surgical resection. The lesions are, by nature, deep in the brain tissue, and therefore access is limited by the morbidity that is inherent in dissecting white matter to reach the lesion. Traditionally, a corticotomy with blunt white matter separation and placement of fixed blade retractors to access the lesion has been practiced. Dissecting through white matter with bipolar forceps likely is damaging to the tracts. Combined with retraction by fixed blade retractors that apply pressure to the tracts, especially at the edge of the retractor blades, it is likely that significant damage to white matter can occur with this method. Further compounding the problem is the necessity of enhancing vision with the surgical microscope, which has its own inherent limitations when viewing down a narrow corridor in terms of light delivery and depth of field. Owing to these factors, this traditional method has not been satisfactory to a number of our colleagues. Different methods have been proposed to improve upon our ability to access such deep lesions while minimizing morbidity.1,2 The method that is discussed in this presentation utilizes a combination of imaging technology (diffusion tensor imaging[DTI]), a tubular retraction device (Brain Path®, Nico Corp, Indianapolis, Indiana), a high-definition visualization platform (Vitom®, Karl Storz Endoscopy America Inc, El Segundo, California), and a specially designed resection device (Myriad®, Nico Corp)3,4 to mitigate against excessive damage to white matter tracts while accessing deep lesions. PATIENT SELECTION As with most every situation in which neurosurgeons are called to intervene, patient selection for the particular method proposed is critical to a successful outcome. Even the most technically well-done operation can fail if the lesion is not amenable to the approach. This technique is certainly and particularly no exception to that rule. This surgical technique is appropriate for subcortical neoplasms, intracerebral hematomas, and selected intraventricular lesions. This discussion will focus on appropriate use for neoplasms. Both primary and secondary subcortical neoplasms may be considered for resection with this technique. There are a number of considerations to take into account based upon preoperative imaging. Though lesions of any depth may be considered, a lesion that presents to the surface is not an ideal candidate for this technique. These, of course, can be well handled through a small, targeted (ie, image guided) craniotomy, and microsurgically removed. In general, lesions that are below the cortical surface are good candidates for the technique, especially if deeply located. Tumors involving the basal ganglia, those that are periventricular, or deep within lobar white matter are ideal (Figure 1). Lesions in a cerebellar hemisphere may also be considered. Lesions that arise from, or extend to, the skull base are probably better treated via an alternative strategy. The technique utilizes technology that is all approved by the US Food and Drug Administration for these indications; therefore, special consent or approval by the local Investigational Review Board is not necessary. PREOPERATIVE PREPARATION AND PLANNING When considering utilization of this technique for subcortical tumors, complete imaging information is critical. Magnetic resonance imaging (MRI) must include diffusion-weighted imaging (DWI) and DTI with tractography studies to assist in surgical planning (Figure 2). The essential importance of these studies cannot be overstated.FIGURE 1: Pre- and postoperative MRI films of a case example utilizing the technique in a 50-yr-old female patient with a history of malignant melanoma. A, Preoperative MRI T1 with DTI mapping demonstrating the left basal ganglia mass with displacement of the corticospinal tract. B, Preoperative T2-weighted image demonstrating significant peritumoral edema. C, Postoperative axial T1 with contrast image demonstrating gross total resection. D, Postoperative sagittal T1 with contrast image demonstrating resection and the approach path through white matter.FIGURE 2: DTI generated 3-dimensional tractography of the patient in Figure 1. The corticospinal tract (red) on the left is distorted by the tumor (orange circle). Tracts outlined are the corticospinal (red), arcuate (green), uncinate (orange), inferior fronto-occipital fasciculus (light blue), inferior longitudinal fasciculus (dark blue).DWI studies help to determine the character of the neoplasm in terms of water content, which helps predict the density and firmness of the tumor. This is particularly important in planning whether to penetrate the Brain Path® device (Nico Corp) into the tumor, a so-called depth cannulation, or to target the surface of the tumor, a so-called surface cannulation. The technical considerations of this will be discussed later in the discussion. In general, lesions that appear to be soft will be best approached by targeting a point in the depth of the tumor. More dense, firm lesions are planned to place the Brain Path® retractor at the surface of the lesion. Careful study of the MRI data is critical in this technique. The Brain Path® is inserted in a trans-sulcal manner, and therefore this is an important planning aspect. A combination of the DTI data and the surface anatomy of the brain is considered in planning the approach (Figure 3). A cannulation that is as parallel as possible to any major white matter fascicular bundle is optimal. Also of consideration is the shape of the lesion. As much as possible, the long axis of a lesion should be the trajectory of approach. A combination of these 2 factors is a primary consideration in surgical planning.FIGURE 3: Image guidance system planning of approach trajectory to the lesion. The trajectory was planned specifically considering the relationship of the corticospinal tract fibers to the tumor.Patients may be operated either under general anesthesia or awake with conscious sedation. The selection of anesthetic method depends upon a number of factors, both patient and lesion location-specific. SURGICAL TECHNIQUE The patient is positioned according to the preoperative plan with respect to approach trajectory. This may call for positioning either supine, lateral, or park bench. Prone positioning may present particular problems owing to the image guidance platform requirements for registration. Therefore, in our experience, the prone position presents particular challenges with this technique. Once the patient is in position, the position of the various necessary equipment is arranged. Arrangement of the operating room is of particular importance for this technique. Whatever the patient position, care is taken to place the viewing monitor and the image guidance monitor within direct view of the surgeon. It is not optimal, or comfortable, to have these monitors in a position that the surgeon has to turn his/her head while working. The monitors must be in the direct view of the operating surgeon. Also of importance, optimal positioning of the Vitom (Karl Storz Endoscopy America Inc.) on the Mitaka® pneumatic arm (Mitaka USA Inc, Denver, Colorado) is of vital importance. Particular care is taken to place the arm at an optimal position to hold the imaging device along the projected viewing angle, and in a comfortable position for the surgeon (Figure 4).FIGURE 4: The arrangement of equipment in the operating room is important for maximal efficiency and surgeon comfort. The video monitor and image guidance monitor are placed in direct view of the surgeon. The Mitaka® (Mitaka USA Inc) arm is also positioned to be in the most comfortable position and avoiding interference with the reference arm for the image guidance system.With the patient positioned and the equipment arranged in the optimal position, the patient is registered in 3-dimensional space with the image guidance system. A trajectory-centric system is preferred. The preplanned entry point is marked on the scalp and it is important to test the preplanned trajectory to make sure it is attainable as the patient is positioned. After confirming that it is an attainable trajectory as the patient is positioned, the incision is planned. Typically, a slightly curved, “Lazy S,” incision is optimal. The craniotomy required is approximately 2 cm in diameter; therefore, no more than a 4-cm incision is typically required. Depending upon the approach trajectory, the craniotomy may be necessarily shifted to accommodate the trajectory of the Brain Path® (Nico Corp). A minimum of hair removal is necessary, typically a thin strip along the line of incision. The incision and craniotomy are made. It is best to retract the scalp with low-profile blunt scalp hooks. The dural opening is limited to just larger than the diameter of the Brain Path® (13 mm). It may be advisable to utilize the ultrasound to confirm the position of the planned sulcus for entry prior to dural opening. The dural flaps are tacked up with suture. The Vitom (Karl Storz Endoscopy America Inc) is brought into place to view the cortical surface with magnification. The sulcal entry point is confirmed with the image guidance probe and adjusted as necessary. The arachnoid over the sulcus is opened using microsurgical technique. A wide opening of the arachnoid is not necessary, approximately 3 to 6 mm is sufficient for introduction of the Brain Path®. The Brain Path® device is then advanced through the opening in the arachnoid into the sulcus and to the preplanned depth (Figure 5). The obturator tip is 10 mm beyond the rim of the retractor tube; therefore, the tube is advanced over the obturator to the preplanned depth and the obturator removed. In cases of depth cannulation, the Brain Path® will be within the lesion. For surface cannulation cases, a cuff of white matter typically is retained over the lesion and is visible. This will be removed to expose the lesion.FIGURE 5: A, The Brain Path® (Nico Corp) is passed transsulcal along the preplanned approach trajectory to the target lesion. B, The tumor resection proceeds with the video screen in comfortable view of the surgeon.The lesion is then resected utilizing a combination of suction, bipolar cautery, and the Myriad device (Nico Corp; Figure 6). Owing to the small diameter of the Brain Path®, other devices, such as an ultrasonic aspirator, are not small enough to utilize with this device. The optimal technique for resection is a “2-handed” technique whereby the surgeon uses the Myriad for suction and resection in 1 hand and the bipolar cautery for hemostasis simultaneously in the other. The Myriad device provides a small diameter suction tube with adjustable pressure in combination with a tissue cutting function that can be turned off and on. The small diameter of the device is key to allowing adequate visualization owing to the limited working diameter of the Brain Path® device.FIGURE 6: The surgeon works through the Brain Path® (Nico Corp) with instruments designed for a low profile due to the narrow working channel.Once hemostasis is obtained, the Brain Path® is withdrawn from the brain. This is carefully inspected to insure hemostasis. A small piece of Gelfoam is then placed over the exposed brain and the dura closed with suture. The bone flap is replaced and secured with miniplates and screws. The scalp is then closed and a dressing applied. Our general practice is to admit the patient to our regular inpatient unit after postanesthesia recovery. Patients are observed closely by the nursing staff with neurological exam every 2 h until 12 to 18 h after surgery. Hospital length of stay varies between 1 and 3 d in general (See Video, Supplemental Digital Content, demonstrating the technique for a metastatic tumor). RESULTS The author's experience with the technique now numbers 49 patients. Forty-three patients have been operated with neoplastic lesions and 6 patients with intracerebral hemorrhage (ICH) over an 18-mo period (2014-2016). Patient diagnosis, lesion location, extent of resection, and complications are detailed in Table. The distribution between primary and secondary tumors is roughly equivalent. The ability to obtain a gross total resection of radiographically enhancing tissue was better in metastatic lesions than in primary tumors (95% vs 65%). Removal of greater than 90% of ICH volume was accomplished in 5 of the 6 patients (83%). The minimum follow-up time was 3 mo. The majority of complications occurred in patients with primary brain tumors, primarily gliomas. One patient with a metastatic lesion suffered a postoperative hemorrhage in the cavity that did not require evacuation. The other patient that suffered a postoperative hemorrhage in the cavity required repeat craniotomy to evacuate the clot. Five patients suffered a new motor deficit after tumor resection. Fortunately, this was temporary in 3 of the 5 patients. Two of these 5 patients had a supplementary motor area syndrome that improved slowly over the following 3 mo, but neither realized a full recovery. One patient had a small cortical infarct owing to a small sulcal artery branch avulsion from passing the Brain Path® that was demonstrated on the postoperative MRI. Fortunately, this was asymptomatic. There were no surgical site infections. One patient with a large metastatic nonsmall cell lung carcinoma suffered severe pulmonary complications after surgery and expired.TABLE: Summary of Cases Over 18-mo Period (2014-2016)DISCUSSION Accessing selected neoplastic and hemorrhagic subcortical lesions via a trans-sulcal parafascicular approach using the Brain Path® (Nico Corp) retractor device is a viable and generally safe alternative to a traditional transcortical microsurgical approach. A number of pathologies may be considered to utilize this strategy. However, experience with the technique is necessary to make a sound judgment regarding the suitability of this approach for any particular case. This discussion will focus on particular surgical pearls that have been gained from the author's experience with various lesions. Primary Brain Tumors Glial tumors located in a subcortical location are reasonable candidates for utilization of this strategy. High-grade tumors that are generally soft in consistency are well suited based upon the ability to resect the tumor essentially from the inside-out. Abnormal tumor tissue that is readily discernible from surrounding white matter can be well resected with suction or the Myriad® device (Nico Corp). Adjustments in viewing angle and toggling the Brain Path® appropriately to resect the tumor in all quadrants can result in a gross total resection of the enhancing portion of the lesion. The ability to obtain a gross total resection is dependent upon the location, size, and experience with this technique. Metastatic Tumors Aside from location, a particularly important element of preoperative evaluation in cases of metastatic tumors is an analysis of the DWI. Predicting the character of the tumor tissue with respect to its firmness based upon water content is helpful in terms of selecting the depth of cannulation with the Brain Path®. As in high-grade primary lesions, a soft lesion is amenable to a so-called depth cannulation, targeting the tube depth to a point within the tumor. This results in a resection strategy characterized by an inside-out resection, stopping at the white matter borders of the lesion. This is not an appropriate strategy with this method in the case of a firm tumor. In the case of a firm tumor, a so-called surface cannulation is appropriate, targeting the capsule of the mass and not penetrating the tumor tissue. This can be of particular importance in smaller lesions, as a firm tumor may be displaced by the Brain Path® if firm and a depth cannulation is attempted. This is a result of the tumor “rolling” out of the field of view by displacement during cannulation. Awareness of this particular potential pitfall will help mitigate the possibility of difficulty localizing the mass. In general, our experience demonstrates that a gross total resection, while minimizing tissue disruption is possible with this technique. Intraventricular Lesions Intraventricular lesions may be well suited to this technique when ventricular size is sufficient to allow entrance of the diameter of the Brain Path®. When the ventricular caliber is less than or equal to the diameter of the retractor tube, it is not advisable to utilize this technique. Especially in the case of a third ventricular colloid cyst, there is substantial risk of damage to the caudate head and/or the fornix if the frontal horn of the lateral ventricle does not have enough width to comfortably accommodate the diameter of the tube. Therefore, primary consideration must be attended to the caliber of the ventricle that must be entered by the Brian Path®. Visualization of the ventricular anatomy is at least equivalent to that obtained endoscopically. A particular advantage in visualization with the exoscope through the Brain Path® is if any significant bleeding is encountered. The ability to isolate and coagulate the bleeding point we find to be superior in this technique vs the endoscopic technique when blood in cerebrospinal fluid can greatly obscure vision. Intracerebral Hemorrhage Deep ICH constitutes one of the best indications for this technique. Cannulation of the ICH, ie, a “deep cannulation,” works well to evaluate the clot. Since the intracranial pressure is elevated, a substantial amount of clot delivers into the Brain Path® and can be easily evacuated by suction. This initial release of pressure can be significant. The remainder of the ICH is then carefully removed with the aid of suction and/or the Myriad device to remove firm clot. As in tumor surgeries, toggling the Brain Path® to accommodate different trajectories and depths results in the ability to inspect the cavity for sources of bleeding. Control of small bleeding vessels is best handled with bipolar cautery forceps that are low profile and designed for keyhole microsurgery. A recent multicenter investigation has provided safety data for utilizing this approach in ICH and suggests utility to more widespread application of this approach in the treatment of ICH patients.5 CONCLUSION The current armamentarium of minimally invasive techniques in cranial surgery includes a number of strategies that take advantage of our current state of technology in advanced imaging, high-definition viewing platforms, and innovative instrumentation. The Brain Path® device for access to subcortical lesions is being adopted across multiple centers as an attractive alternative to traditional microsurgical transcortical techniques utilizing a corticotomy. Accumulated experience with this technique will lead to further refinements in defining the indications for this approach, as well as improvements in instrumentation and operative technique. Disclosure The author has no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.