Optimizing Outcomes With Maximal Surgical Resection of Malignant Gliomas

Stephen J. Hentschel, MD, Raymond Sawaya, MD

Disclosures

Cancer Control. 2003;10(2) 

In This Article

Surgical Techniques and Adjunctive Technologies

The stages of a craniotomy to resect a malignant glioma should include appropriate preoperative and postoperative imaging, preoperative planning including location and size of the craniotomy, and intraoperative decision making. Intraoperative ultrasound and neuronavigation systems are also available to identify anatomical structures and dissection planes, as well as aid in the determination of the extent of resection.

High-quality imaging is necessary and should include MRI. The detail obtained with MRI is far superior to computed tomography (CT) in determining the exact anatomic location of the lesion, particularly the relationship with eloquent structures. Also, the high definition provided by MRI allows the surgeon to identify cystic or necrotic portions of the tumor that may not be visible on enhanced CT. This high definition can assist in the tumor dissection by allowing correlation of such structures on imaging with what is seen at open surgery. As well, MRI can identify residual tumor postoperatively more accurately than CT (Fig 1).[21] Adjunctive imaging techniques such as functional MRI, spectroscopy, and positron emission tomography can aid in identifying the relationship of the tumor to eloquent areas and in the separation of tumor from edema from normal brain (Fig 2). The use of these adjuncts varies depending on their availability and the location of the tumor mass.

(A) Preoperative and (B) postoperative contrast-enhanced MRI images demonstrating complete resection of a glioblastoma.

MR spectroscopy with (A) the tumor and superimposed grid, and (B) the resulting spectrographic profile. The first large peak best initially seen in box 3 represents choline, which is elevated in brain tumors but not in other processes such as edema or infarction. The ratio between choline and creatinine is more sensitive for neoplasia than the absolute height of the choline peak. N-acetyl aspartate (NAA) is decreased in tumors and elevated in neurodegenerative processes.

Standard operative exposures are performed with or without utilizing neuronavigation for the location of the bone flap. Linear or curvilinear incisions as well as flaps are acceptable with regard to blood supply, cosmesis, and possible reoperation. A cortical incision or a corticectomy, depending on the location and size of the lesion, is made if the lesion is superficial. For deeper or smaller lesions, entrance through a sulcus, if possible, is preferred. Determining the location for such an incision into the brain requires knowledge of the anatomy of the region that may be significantly altered due to the distortion caused by the mass of tumor. Various surgical adjuncts are available to assist the surgeon is determining the pathologic anatomy, including ultrasound,[22] neuronavigation,[23] intraoperative CT[24] or MRI,[25,26] and somatosensory-evoked potential (SSEP) mapping 27 (Fig 3). When the lesion is near speech or motor areas, the procedure can be performed with the patient awake to permit intraoperative stimulation mapping.[28]

Somatosensory-evoked potential (SSEP) mapping demonstrating (A) the grid over the motor (M) and sensory (S) cortex, and (B) the resulting potentials. There is a clear reversal of phase between the second and third lines, indicating that one corresponding electrode is over the sensory cortex while the other is over the motor cortex.

Regardless of the depth of the lesion, the dissection should be in the white matter plane outside of the lesion with the goal of circumferential dissection.[29] Subpial dissection is a useful technique around the margins as even malignant gliomas respect pial borders.[30] In some cases, identifying the correct plane can be challenging and requires a combination of the above surgical adjuncts. However, the surgeon's interpretation of the color and consistency of the tissue, together with knowledge of anatomy, is most important in determining where the resection will cease. The main goal of surgery is removal of the enhancing tissue, which should be possible even in functionally critical areas as there should be no neurons within the tumor itself. While this is generally true, approximately 7% of gliomas will have invaded eloquent areas without altering function, thus rendering aggressive resections potentially threatening to critical functions such as speech and motor areas.[31,32] In most cases, an effective technique of tumor resection utilizes the suction and bipolar cautery since usually these tumors are soft and amenable to resection in this manner.[30] However, when the tumor is firm or fibrous, the ultrasonic aspirator is useful. A potential drawback with the ultrasonic aspirator is that it may aerosolize tumor cells, thus distributing them some distance from the original site, but the clinical significance of this is uncertain.[33]

With the advances in surgical techniques and perioperative technology, it is now possible to maximally resect malignant intrinsic glial neoplasms, even within functionally critical areas, without increased morbidity. Studies have demonstrated a survival advantage with 98% or greater resection of these lesions, particularly in younger patients with good Karnofsky scores.

The print version of this article was originally certified for CME credit. For accreditation details, contact the publisher. H. Lee Moffitt Cancer Center & Research Institute, 12902 Magnolia Drive, Tampa, FL 33612. Telephone: (813) 632-1349. Fax: (813) 903-4950. Email: ccjournal@moffitt.usf.edu.

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