Intraoperative Mapping and Monitoring of Brain Functions
Intraoperative Mapping and Monitoring of Brain Functions
Low-grade gliomas ([LGGs] WHO Grade II) are slow-growing intrinsic cerebral lesions that diffusely infiltrate the brain parenchyma along white matter tracts and almost invariably show a progression toward malignancy. The treatment of these tumors forces the neurosurgeon to face uncommon difficulties and is still a subject of debate. At the authors' institution, resection is the first option in the treatment of LGGs. It requires the combined efforts of a multidisciplinary team of neurosurgeons, neuroradiologists, neuropsychologists, and neurophysiologists, who together contribute to the definition of the location, extension, and extent of functional involvement that a specific lesion has caused in a particular patient. In fact, each tumor induces specific modifications of the brain functional network, with high interindividual variability. This requires that each treatment plan is tailored to the characteristics of the tumor and of the patient. Consequently, surgery is performed according to functional and anatomical boundaries to achieve the maximal resection with maximal functional preservation. The identification of eloquent cerebral areas, which are involved in motor, language, memory, and visuospatial functions and have to be preserved during surgery, is performed through the intraoperative use of brain mapping techniques. The use of these techniques extends surgical indications and improves the extent of resection, while minimizing the postoperative morbidity and safeguarding the patient's quality of life.
In this paper the authors present their paradigm for the surgical treatment of LGGs, focusing on the intraoperative neurophysiological monitoring protocol as well as on the brain mapping technique. They briefly discuss the results that have been obtained at their institution since 2005 as well as the main critical points they have encountered when using this approach.
Resection of LGGs, here understood as Grade II gliomas according to the WHO classification, forces the neurosurgeon to face uncommon difficulties and is still a subject of considerable debate. First, these tumors, which comprise Grade II astrocytoma (fibrillary and protoplasmic), Grade II oligoastrocytoma, and Grade II oligodendroglioma, are relatively rare; according to the Central Brain Tumor Registry of the United States, the various histological classes of LGGs have incidences varying between 0.10 and 0.46 per 100,000 population, and a cumulative incidence of ~ 0.9 per 100,000 people. By comparison, high-grade gliomas (WHO Grade III or IV) have a cumulative incidence of 3.7 per 100,000 population. Second, the tumors mainly affect young people (median age at diagnosis 35 years) and especially males (male/female ratio 1.5) with active professional and social lives. Third, LGGs present predominantly with seizures. Clinical symptoms are usually subtle, and the neurological examination findings are negative, although these tumors tend to occur in eloquent areas. Lastly, some of these lesions may show an apparently slow pattern of growth. If the patients do not undergo appropriate serial MR imaging, it may be difficult to prove the tumor's volumetric increase.
In the recent past, the aforementioned characteristics have caused a large part of the neurosurgical community to consider LGGs as indolent tumors, deserving a cautious and conservative diagnostic and therapeutic approach (wait and see, open/needle biopsy) to preserve the functional integrity of the patient. Currently, however, there is growing evidence that Grade II gliomas are aggressive neoplasms, with a constant growth rate of ~ 4 mm/year, which diffusely infiltrate the brain parenchyma along white matter tracts, and which almost invariably show a progression toward malignancy. They also frequently induce pharmacoresistent seizures, especially large and/or insular tumors. Furthermore, larger lesions are associated with a greater risk of malignant progression and with shorter patient survival. Finally, although LGGs have produced overt neurological deficits in only a few cases, they frequently present with more subtle symptoms affecting complex neurological functions (memory, language, character, visuospatial orientation, and so on), which require specific testing performed by a neuropsychologist to be detected.
The rationale of the surgical treatment is based, first of all, on the ability to provide an adequate specimen for histological diagnosis and genetic and molecular analysis (1p19q loss of heterozygosity, MGMT methylation), whose results have fundamental therapeutic and prognostic implications. Moreover, surgery may contribute to control the frequency of seizures or to decrease the burden of drugs, as well as to improve the neurological symptoms that are directly related to the mass effect of the tumor on the cortex or on the functional fiber bundles. Finally, as shown by the most recent contributions in the literature, the extent of the resection is able to influence the overall survival and the time to malignant transformation. However, since the natural history of the tumor can be relatively long (with or without surgery), the conservation of simple and complex neurological functions of the patients is mandatory.
For these reasons, at our institution resection is the first option in the treatment of LGGs, with the goal to maximally resect the tumor mass, while at the same time minimize the postoperative morbidity. This allows the patient's quality of life to be safeguarded and allows for prompt reintegration in professional and social lives, which is of primary importance considering the young age of the majority of these patients.
The identification of the eloquent cerebral areas, which are involved in motor, language, memory, and visuospatial functions and have to be preserved during surgery, is performed through the intraoperative use of brain mapping techniques.
In this paper we present our paradigm for the surgical treatment of LGGs, focusing on the intraoperative monitoring protocol as well as on the brain mapping technique. In the end, we briefly discuss the results that have been obtained at our institution since 2005 as well as the main critical situations we have encountered using this approach.
Abstract and Introduction
Abstract
Low-grade gliomas ([LGGs] WHO Grade II) are slow-growing intrinsic cerebral lesions that diffusely infiltrate the brain parenchyma along white matter tracts and almost invariably show a progression toward malignancy. The treatment of these tumors forces the neurosurgeon to face uncommon difficulties and is still a subject of debate. At the authors' institution, resection is the first option in the treatment of LGGs. It requires the combined efforts of a multidisciplinary team of neurosurgeons, neuroradiologists, neuropsychologists, and neurophysiologists, who together contribute to the definition of the location, extension, and extent of functional involvement that a specific lesion has caused in a particular patient. In fact, each tumor induces specific modifications of the brain functional network, with high interindividual variability. This requires that each treatment plan is tailored to the characteristics of the tumor and of the patient. Consequently, surgery is performed according to functional and anatomical boundaries to achieve the maximal resection with maximal functional preservation. The identification of eloquent cerebral areas, which are involved in motor, language, memory, and visuospatial functions and have to be preserved during surgery, is performed through the intraoperative use of brain mapping techniques. The use of these techniques extends surgical indications and improves the extent of resection, while minimizing the postoperative morbidity and safeguarding the patient's quality of life.
In this paper the authors present their paradigm for the surgical treatment of LGGs, focusing on the intraoperative neurophysiological monitoring protocol as well as on the brain mapping technique. They briefly discuss the results that have been obtained at their institution since 2005 as well as the main critical points they have encountered when using this approach.
Introduction
Resection of LGGs, here understood as Grade II gliomas according to the WHO classification, forces the neurosurgeon to face uncommon difficulties and is still a subject of considerable debate. First, these tumors, which comprise Grade II astrocytoma (fibrillary and protoplasmic), Grade II oligoastrocytoma, and Grade II oligodendroglioma, are relatively rare; according to the Central Brain Tumor Registry of the United States, the various histological classes of LGGs have incidences varying between 0.10 and 0.46 per 100,000 population, and a cumulative incidence of ~ 0.9 per 100,000 people. By comparison, high-grade gliomas (WHO Grade III or IV) have a cumulative incidence of 3.7 per 100,000 population. Second, the tumors mainly affect young people (median age at diagnosis 35 years) and especially males (male/female ratio 1.5) with active professional and social lives. Third, LGGs present predominantly with seizures. Clinical symptoms are usually subtle, and the neurological examination findings are negative, although these tumors tend to occur in eloquent areas. Lastly, some of these lesions may show an apparently slow pattern of growth. If the patients do not undergo appropriate serial MR imaging, it may be difficult to prove the tumor's volumetric increase.
In the recent past, the aforementioned characteristics have caused a large part of the neurosurgical community to consider LGGs as indolent tumors, deserving a cautious and conservative diagnostic and therapeutic approach (wait and see, open/needle biopsy) to preserve the functional integrity of the patient. Currently, however, there is growing evidence that Grade II gliomas are aggressive neoplasms, with a constant growth rate of ~ 4 mm/year, which diffusely infiltrate the brain parenchyma along white matter tracts, and which almost invariably show a progression toward malignancy. They also frequently induce pharmacoresistent seizures, especially large and/or insular tumors. Furthermore, larger lesions are associated with a greater risk of malignant progression and with shorter patient survival. Finally, although LGGs have produced overt neurological deficits in only a few cases, they frequently present with more subtle symptoms affecting complex neurological functions (memory, language, character, visuospatial orientation, and so on), which require specific testing performed by a neuropsychologist to be detected.
The rationale of the surgical treatment is based, first of all, on the ability to provide an adequate specimen for histological diagnosis and genetic and molecular analysis (1p19q loss of heterozygosity, MGMT methylation), whose results have fundamental therapeutic and prognostic implications. Moreover, surgery may contribute to control the frequency of seizures or to decrease the burden of drugs, as well as to improve the neurological symptoms that are directly related to the mass effect of the tumor on the cortex or on the functional fiber bundles. Finally, as shown by the most recent contributions in the literature, the extent of the resection is able to influence the overall survival and the time to malignant transformation. However, since the natural history of the tumor can be relatively long (with or without surgery), the conservation of simple and complex neurological functions of the patients is mandatory.
For these reasons, at our institution resection is the first option in the treatment of LGGs, with the goal to maximally resect the tumor mass, while at the same time minimize the postoperative morbidity. This allows the patient's quality of life to be safeguarded and allows for prompt reintegration in professional and social lives, which is of primary importance considering the young age of the majority of these patients.
The identification of the eloquent cerebral areas, which are involved in motor, language, memory, and visuospatial functions and have to be preserved during surgery, is performed through the intraoperative use of brain mapping techniques.
In this paper we present our paradigm for the surgical treatment of LGGs, focusing on the intraoperative monitoring protocol as well as on the brain mapping technique. In the end, we briefly discuss the results that have been obtained at our institution since 2005 as well as the main critical situations we have encountered using this approach.
