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Atlas Of Operative Microneurosurgery, Vol. 2: Brain Tumors

In the relatively new field of microneurosurgery, the development and use of the transcisternal, transfissural, and transsulcal approaches80,84,85 have established the sulci as fundamental landmarks on the brain surface. The well-known variability in cortical function1,2,17,47,53,75 calls for the aid of cortical mapping techniques to precisely identify specific sites related to cortical function. Nevertheless, detailed knowledge of the structure and form of the cerebral sulci and gyri continues to be mandatory for neuroimaging as well as intraoperative guidance. Once identified, the cerebral sulci can be used by the neurosurgeon either as microneurosurgical corridors or simply as cortical landmarks.61,62

Atlas of Operative Microneurosurgery, Vol. 2: Brain Tumors

Abstract: Breast cancer is the most common malignancy among women worldwide, and the main cause of death in patients with breast cancer is metastasis. Metastasis to the central nervous system occurs in 10% to 16% of patients with metastatic breast cancer, and this rate has increased because of recent advancements in systemic chemotherapy. Because of the various treatments available for brain metastasis, accurate diagnosis and evaluation for treatment are important. Magnetic resonance imaging (MRI) is one of the most reliable preoperative examinations not only for diagnosis of metastatic brain tumors but also for estimation of the molecular characteristics of the tumor based on radiographic information such as the number of lesions, solid or ring enhancement, and cyst formation. Surgical resection continues to play an important role in patients with a limited number of brain metastases and a relatively good performance status. A single brain metastasis is a good indication for surgical treatment followed by radiation therapy to obtain longer survival. Surgical removal is also considered for two or more lesions if neurological symptoms are caused by brain lesions of >3 cm with a mass effect or associated hydrocephalus. Although maximal safe resection with minimal morbidity is ideal in the surgical treatment of brain tumors, supramarginal resection can be achieved in select cases. With respect to the resection technique, en bloc resection is generally recommended to avoid leptomeningeal dissemination induced by piecemeal resection. An operating microscope, neuronavigation, and intraoperative neurophysiological monitoring are essential in modern neurosurgical procedures, including tumor resection. More recently, supporting surgical instruments have been introduced. The use of endoscopic surgery has dramatically increased, especially for intraventricular lesions and in transsphenoidal surgery. An exoscope helps neurosurgeons to comfortably operate regardless of patient positioning or anatomy. A tubular retractor can prevent damage to the surrounding brain tissue during surgery and is a useful instrument in combination with both an endoscope and exoscope. Additionally, 5-aminolevulinic acid (5-ALA) is a promising reagent for photodynamic detection of residual tumor tissue. In the near future, novel treatment options such as high-intensity focused ultrasound (HIFU), laser interstitial thermal therapy (LITT), oncolytic virus therapy, and gene therapy will be introduced.

Complete removal of metastatic brain tumors, termed gross total resection (GTR), is the ideal goal in surgical treatment. According to the latest guidelines published by the Congress of Neurological Surgeons, GTR is recommended over subtotal resection to improve overall survival and prolong the time to recurrence (23). However, recurrence affects about 20% of patients even after treatment with GTR followed by SRS (29). In contrast to diffusely invading tumors such as gliomas, metastatic brain tumors are more often well demarcated masses surrounded by gliotic tissue (26). Several reports have shown that supramarginal resection achieved by additional 5-mm surrounding tissue resection from the tumor edge improved the local control rate compared with conventional GTR (30-32). Even for brain metastasis in eloquent areas, supramarginal resection can be achieved with awake surgery in many cases (33). However, supramarginal resection cannot prevent temporary deficits such as supplementary motor area syndrome even with intraoperative neurophysiological monitoring or awake surgery (34). Therefore, deliberative planning for maximal safe resection with minimal tissue trauma is ideal for both surgeons and patients.

The use of intraoperative neurophysiological monitoring is essential to predict and prevent postoperative neurological deficits. Effective intraoperative mapping and monitoring techniques have developed in the context of glioma surgery (68-71). The purpose of intraoperative monitoring is to reliably identify cortical areas and subcortical pathways including motor, sensory, language, and cognitive functions (72,73), which leads to safe maximal resection of the tumor. A prospective controlled study showed that the use of intraoperative monitoring could achieve an equivalent extent of resection in both eloquent and non-eloquent areas (74). Zhang et al. (71) retrospectively evaluated the long-term functional and survival outcomes of patients with glioma after tumor resection with intraoperative neurophysiologic monitoring and reported that localization of gliomas in eloquent areas should no longer be viewed as a poor prognostic factor. Intraoperative monitoring of the motor systems was recently reported to help reduce surgery-related motor deficits also for surgical resection of metastatic brain tumor (75-77). For metastatic brain tumors, supramarginal resection including additional removal of the adjacent brain tissue is desired to prevent local recurrence (30,32). Therefore, intraoperative neurophysiological monitoring provides important functional information during resection of tumors, especially when the extent of resection reaches an eloquent area (77).

During surgical treatment of deep-seated lesions, obtaining a safe corridor into the tumor and visualizing the interface between the tumor and surrounding structures are important (91). Various kinds of brain retraction systems combined with a microscope or endoscope have been introduced to achieve these goals. The self-retaining retraction system was first introduced by Greenberg (92) in 1981. This system is widely used in brain surgery, although it is associated with a risk of brain infarction and brain damage due to excessive brain retraction pressure (93-95). Many recent reports have indicated the effectiveness of tubular retractors such as the ViewSite (Vycor Medical Inc., Boca Raton, FL, USA) (Figure 1C) (55,96-101). The ViewSite tubular retractor has a plastic body with a tapered end, which allows adjacent tissue to be visualized. Additionally, the ViewSite tubular retractor can be held with a self-retracting arm to prevent shifting of the operative field (101). Moreover, an endoscope and modified surgical instruments for endoscopic surgery can overcome the disadvantage of limited working space by the ViewSite retractor itself (55). The use of tubular retractors with an exoscope has recently shown promising results in the surgical resection of metastatic brain tumors (89,90,102).

Increasing attention has recently been given to 5-aminolevulinic acid (5-ALA) (103-107), a precursor molecule in the heme biosynthetic pathway. Previous studies have demonstrated that both primary and metastatic brain tumors preferentially take up exogenous 5-ALA and store it as protoporphyrin IX (108,109). Several studies have demonstrated the usefulness of 5-ALA for surgical resection of metastatic brain tumors, including breast cancer (110-113). Marbacher et al. (113) assessed the frequency of positive 5-ALA fluorescence in a cohort of patients with metastases and found that 71% of the metastatic brain tumors from breast cancer were 5-ALA fluorescence-positive. Another study showed that the fluorescence intensity of 5-ALA was high in both the sentinel lymph node and primary lesion of breast cancer; thus, 5-ALA shows promise in the detection of metastatic tumors from breast cancer (114). Moreover, the combination of fluorescence and intraoperative monitoring has been shown to be effective with respect to resection radicality and functional preservation (115). 350c69d7ab


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