CHAPTER 117 Surgical Complications of Brain Tumors and Their Avoidance
Craniotomy for resection of intrinsic brain tumors is performed with the goals of establishing a tissue diagnosis, improving neurological symptoms, and prolonging survival. Cytoreductive surgery has been favorably associated with survival in patients with low-grade astrocytoma, malignant glioma, and a single metastasis to the brain.1–3 Surgical management of these tumors has also evolved significantly, including the routine use of cortical mapping, frameless stereotaxis, and intraoperative magnetic resonance imaging (MRI), all of which have improved our ability to localize and radically remove intrinsic brain tumors. Thus, it is important to understand the risks associated with cytoreductive surgery so that patients can be selected who may be candidates for aggressive tumor resection and be properly counseled regarding the expected outcomes of brain tumor surgery. This chapter focuses on the complications associated with craniotomy for resection of intrinsic brain tumors (e.g., glioma, metastasis), with an emphasis on how to avoid these adverse events.
Defining a Complication
Significant disagreement exists regarding what constitutes a complication. All neurosurgeons recognize that an outcome must be unwanted to be considered a complication of surgery. Whether a particular event is undesirable may differ for the neurosurgeon, the patient, and the patient’s family. For example, development of frontalis paresis after frontotemporal craniotomy would be considered an undesirable outcome by most neurosurgeons, whereas this deficit may go unnoticed by the patient. Another essential feature of a surgical complication is the unexpected nature of the outcome; that is, the complication does not occur commonly. Most surgical procedures have a range of anticipated outcomes, and complications are the outcomes that deviate from this norm. However, this feature introduces a degree of subjectivity into the classification of surgical outcomes. For example, a patient undergoing removal of a glioma located within the dominant supplementary motor area generally experiences predictable postoperative neurological deficits (e.g., hemiparesis, mutism) that improve with time and rehabilitation. Should such a deficit be considered an expected (although undesirable) outcome of surgery or a neurological complication? Despite little consensus on this matter, most surgical series document all adverse events without regard to whether they are expected.4–7 In practice, however, the neurosurgeon must have intimate knowledge of the complications and risk factors associated with craniotomy and engage in careful discussions with the patient and family regarding expected (although undesirable) outcomes lest they be viewed as complications.
Classification Schemes
Various schemes have been introduced to classify neurosurgical complications, with significant overlap among them. Some investigators view all complications as potentially avoidable and attributable to one of three main causes: (1) lack of information (e.g., failure to recognize a preexisting medical condition), (2) incorrect judgment (e.g., suboptimal surgical approach), or (3) incorrect execution (e.g., excessive brain retraction).8 This classification system assumes that complications are generally under the neurosurgeon’s control, which does not apply to most medical complications.
An alternative classification distinguishes among neurological, regional, and systemic complications and provides a rational framework for categorizing complications associated with brain tumor surgery (Table 117-1).6 In this system, neurological complications are events that directly produce motor, sensory, language, or visual deficits (e.g., edema, vascular injury, hematoma). Regional complications are related either to the wound (e.g., infection, pseudomeningocele) or to the brain (e.g., seizures, hydrocephalus) but are not associated with neurological deficits. Systemic complications include more generalized medical conditions (e.g., thromboembolism, pneumonia). These main categories can be subdivided on the basis of the degree of severity. Major complications include events that are permanent, significantly affect quality of life, or require surgical intervention. Minor complications are transient events without significant functional impact that resolve without surgery.
| NEUROLOGICAL | REGIONAL | SYSTEMIC |
|---|---|---|
| Motor or sensory deficit |
Data from Sawaya R, Hammoud M, Schoppa D, et al. Neurosurgical outcomes in a modern series of 400 craniotomies for treatment of parenchymal tumors. Neurosurgery. 1998;42:1044-1056.
Patient Selection and Avoidance of Complications
The overall incidence of complications associated with intrinsic brain tumor resection ranges from 20% to 35% and includes all adverse events (expected and unexpected), regardless of severity.4–69 The complication rate in a particular series depends on the definition of a complication, the type of study (retrospective versus prospective), and the referral base of the institution. In general, higher complication rates are reported by investigators at tertiary neurosurgical centers, who prospectively analyze complications and include all adverse events (expected and unexpected).6 Therefore, complication rates among neurosurgical centers may not be directly comparable because of differences in the classification of complications and data collection methods.
Neurological Complications
The risk for a new neurological deficit (minor or major) after craniotomy for intrinsic tumor ranges from 10% to 25% in modern surgical series.4–69 The following risk factors have been shown to predict an adverse neurological outcome: age older than 60 years, Karnofsky Performance Scale score less than 60, deep tumor location, and tumor in proximity to eloquent brain areas.4–7 Although there is concern that aggressive tumor resection could lead to greater neurological morbidity, two studies have demonstrated the opposite, namely, that gross total resection of intrinsic tumors (particularly malignant gliomas) is associated with fewer neurological complications than subtotal resection is.4,6 This finding is probably explained by the risk for postoperative edema and hemorrhage when a glioblastoma is incompletely removed.10 Recognition of the previously mentioned risk factors allows the neurosurgeon to estimate the risk for a neurological complication developing in an individual patient.6 In one clinical scenario, a 42-year-old patient with a normal neurological examination and a tumor not located in an eloquent brain region would have a predicted complication rate of approximately 5% (Fig. 117-1A). In contrast, a 66-year-old patient with significant hemiparesis caused by a glioblastoma in a region controlling motor function would have a predicted complication rate as high as 26% (Fig. 117-1B). Thus, the surgical approach must be individualized according to factors related to the patient (age, neurological status, preference) and the tumor (size, location, presumed histology).
Neurological complications result from one of the following causes: (1) direct injury to normal brain structures, (2) brain edema, (3) vascular injury, or (4) hematoma. Inadvertent injury to normal brain structures may occur as a result of incorrect localization of the tumor in relation to adjacent eloquent brain areas. Avoidance of this problem begins with intimate knowledge of the normal structural and functional anatomy of the operative field and the relationship of the tumor borders to adjacent critical brain structures. For tumors located in the posterior frontal lobe, the motor strip can be identified by cortical mapping techniques so that the subcortical motor pathways can be preserved during tumor resection.9,11 Similarly, craniotomy using speech mapping with the patient awake allows the neurosurgeon to maximally resect dominant temporal lobe tumors while minimizing the risk for a postoperative language deficit.9,11 The introduction of frameless stereotactic techniques has revolutionized the practice of neurosurgery by providing an easy, intuitive, and accurate method for intracranial navigation.12 Frameless stereotaxis enables precise localization of superficial tumors and provides the neurosurgeon with the ability to plan optimal trajectories to approach deeply seated tumors, thereby minimizing the tissue injury associated with brain dissection (Fig. 117-2). Normal structures (e.g., motor cortex) can be readily identified and preserved. Last, the extent of tumor resection can be monitored throughout the operation to prevent inadvertent resection of normal brain tissue. However, the neurosurgeon should not overly rely on image guidance to determine the extent of tumor resection because the accuracy of this information decreases as brain shifts occur during surgery. The intraoperative feedback provided by frameless stereotaxis must be integrated with conventional techniques to assess the extent of resection (including visual inspection), measurement of the tumor cavity, and identification of normal adjacent structures (e.g., falx, skull base, sulci). More recently, intraoperative MRI has been used to provide real-time guidance during intrinsic brain tumor resection, thus allowing maximal tumor resection while minimizing injury to normal brain tissue.13
Brain edema is a common cause of neurological morbidity and, in its extreme form, may result in herniation and death. Factors that contribute to postoperative edema include excessive brain retraction and subtotal resection of malignant tumors, especially glioblastomas. Injury caused by excessive brain retraction can be minimized by proper patient positioning, hyperventilation, high-dose corticosteroids, diuretics, and intermittent retractor placement (Fig. 117-3). Frameless stereotaxis can be used to determine the optimal surgical trajectory and to reduce the need for prolonged retraction. However, hyperventilation and diuretics are often omitted during frameless stereotactic procedures, possibly resulting in excessive retraction and postoperative edema. Most important, craniotomy and resection of malignant glioma should be undertaken with the goal of either gross total or radical subtotal resection. Limited debulking leaves residual vascular tumor that has the propensity to produce brain edema and intratumoral hemorrhage (“wounded glioma syndrome”) (Fig. 117-4). Several studies have established that patients with malignant glioma who undergo partial resection experience greater neurological morbidity than do patients who undergo gross total resection.4,6,10
