Principles of Surgical Treatment

Preoperative surgical evaluation

The initial evaluation of a patient with suspected glioblastoma includes history and physical examination, anatomic imaging, and symptom management with seizure medications and corticosteroids. Clinical presentation of glioblastoma is highly variable, depending on tumor size, location, and the amount of peritumoral edema. Glioblastomas are rarely discovered incidentally (3.8% of patients). Seizures and neurocognitive changes are the most common presenting symptom, occurring in more than 70% of patients. Blunted affect, changes in personality, and neurocognitive dysfunction may be more prevalent in patients with frontal tumors. Speech and language deficits occur in 58% of patients from tumors affecting cortical or subcortical language pathways in the dominant hemisphere. Additional symptoms include headaches, memory loss, sensory dysfunction, and visual field deficits.

Initial imaging of patients with suspected glioblastoma begins with brain MRI with and without enhancement. T1-weighted images with and without gadolinium enhancement are critical, because they allow the estimation of anatomic localization, tumor necrosis, vascularity, and amount of mass effect. T2-weighted, fluid-attenuated inversion recovery (FLAIR) images and diffusion-weighted MRI sequences show the extent of surrounding vasogenic edema. Glioblastomas are typically avidly enhancing on FLAIR signals outside of tumor boundaries, showing the degree of surrounding peritumoral edema. Structural and functional imaging, such as functional MRI (fMRI), diffusion tensor imaging (DTI), and magnetoencephalography (MEG), may be useful when evaluating tumors within presumed functional areas.

Corticosteroids are commonly used to control tumor-associated vasogenic edema. Dexamethasone is commonly used, with doses ranging between 2 and 24 mg daily. Corticosteroids may improve focal neurologic deficits and level of consciousness, and relieve headaches. Major side effects of corticosteroids include depression, osteoporosis, and immunosuppression; therefore, they should be administered only if necessary and at the lowest dose possible. Recent data suggest that higher doses of corticosteroids may lead to resistance to alkylating chemotherapy such as temozolomide. Patients presenting with seizures should be started on an anticonvulsant while balancing side-effect profiles and drug-to-drug interactions. Phenytoin was historically the first-line antiepileptic agent; however, levetiracetam is now commonly used because of its low toxicity, lack of need to monitor serum levels, and minor side-effect profile.

Preoperative planning

Management of intrinsic brain tumors begins with surgery intended to establish the diagnosis and maximal safe resection. In order to minimize perioperative risk, careful planning should occur before the patient is taken to the operating room. High-quality contrast MRI scans with and without enhancement are vital for developing the optimal operative plan. Preoperative imaging provides knowledge about glioblastoma location as well as its relationship to vascular structures and potential functional areas. Structural MRI and fMRI can be reconstructed to create three-dimensional models to establish a safe surgical corridor during surgery. fMRI, DTI tractography, and MEG MRI provide valuable information regarding the interface of tumor tissue with adjacent functional cortical and subcortical pathways ( Fig. 12.1 ). fMRI produces the blood oxygenation level–dependent (BOLD) signal, which marks cortical regions associated with task performance (motor, expressive language, receptive language). DTI tractography establishes white matter tracts surrounding the glioblastoma and can be helpful in determining whether functional pathways are infiltrated or displaced by tumor mass effect. DTI of white matter pathways is particularly important for language pathways, including corticospinal tract, superior longitudinal fasciculus, arcuate fasciculus, uncinate fasciculus, inferior orbitofrontal fasciculus, and optic pathways. Preoperative clinical evaluation should include baseline language and sensorimotor assessment performed 24 to 48 hours before surgery. Many glioblastomas are within or adjacent to potential functional areas, making it difficult to balance achieving an excellent extent of resection with minimizing postoperative deficits. Preoperative planning must therefore take into consideration the range of available approaches, including awake language and motor brain mapping craniotomy, asleep motor mapping craniotomy, image-guided resection, and use of the intraoperative MRI (iMRI).

Intraoperative standards of resection

Over the past 2 decades, numerous studies have enhanced the understanding of the impact of extent of resection on overall and progression-free survival in patients with glioblastoma. The decision to offer maximal safe resection depends on factors such as performance status, patient age, and tumor location and size. There are several intraoperative tools and strategies that have been developed to both enhance safety and improve the extent of tumor resection. These options include neuronavigation, intraoperative brain mapping, use of iMRI, and fluorescence-guided surgical resection.