- Email: [email protected]
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY
0733-8619 /98 $8.00
IATROGENIC DISORDERS
+ .OO
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY Douglas Kondziolka, MD, FRCS (C), FACS, Andrew D. Firlik, MD, and L. Dade Lunsford, MD, FACS
Stereotactic surgery refers to an image-guided neurosurgical procedure in which a three-dimensional guidance stereotactic system is used to facilitate a diagnostic or therapeutic goal in the brain. A surgical complication is defined as an adverse event that occurs either during surgery or within a 30-day postoperative interval. Such a complication must arise as a direct consequence of the surgery or its associated administration of anesthesia. Traditionally, stereotactic surgery uses a stereotactic head frame to register accurately high-resolution neurodiagnostic brain images for use in neurosurgery. Most frame-based stereotactic procedures involve accessing brain targets using probes, electrodes, or catheters through small cranial openings. The use of closed-skull, single treatment session radiation to treat brain disease (stereotactic radiosurgery) is an important and increasingly used treatment. Invisible radiation beams replace rigid surgical instruments. More recently, both frame-based and frameless stereotactic systems have proven helpful during conventional craniotomy procedures. These techniques use external cutaneous fiducial markers to correlate preoperative brain imaging with the surgical approach. Image-guided craniotomies are stereotactic procedures because of their use of a three-dimensional localizing system, but postoperative complications are mainly those associated with the craniotomy itself, rather than with the stereotactic technology. This article discusses only complications associated with stereotactic frame-based procedures that involve minimal or no opening of the cranial vault, including diagnostic brain biopsy, cyst or abscess management, ablative movement disorder surgery, and stereotactic radiosurgery. DIAGNOSTIC STEREOTACTIC BIOPSY
Before 1980, stereotactic brain biopsy was usually performed using either freehand brain needle aspiration techniques or less sophisticated stereotactic devices. From the Department of Neurological Surgery, University of Pittsburgh, and Center for Image-guided Neurosurgery, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania. NEUROLOGIC CLINICS OF NORTH AMERICA VOLUME 16 *NUMBER 1 * FEBRUARY 1998
35
36
KONDZIOLKA et a1
The target was localized by cerebral angiography, radioisotope scintigraphy, ventriculography, or early generation computed tomography (CT), none of which provided high-resolution brain mapping. The field of stereotactic surgery was considered complex, risky, and backroom (i.e., not in the forefront). Most patients who underwent these procedures were either considered too old or too medically ill to undergo the preferred craniotomy for resection of their brain lesion. A biopsy was frequently requested so that palliative chemotherapy or radiation could be offered. Stereotactic technology did maintain a dominant role in functional neurosurgery with a history dating back to the 1940s. With the advent of high-resolutionCT and magnetic resonance (MR),imaging over the past two decades, new stereotactic frame systems were introduced. The two most popular stereotactic devices in North America are the Leksell (Elekta Instruments, Atlanta, GA) and the Brown-Roberts-Wells (BRW) (Radionics, Burlington, MA) systems (Fig. l). With the availability of spatially accurate brain parenchymal imaging (as CT quality improved), the role of stereotactic biopsy entered a renaissance. For the first time, brain lesions could be imaged and specific targets selected for sampling. The surgeon could choose a safe trajectory from the skull to the lesion that avoided critical brain regions, blood vessels, or the ventricular system. Most surgeons recognized that the bony opening need only be slightly larger than the diameter of the inserted probe. The opportunity to sample defined brain lesions through minute cranial openings with minimal brain exposure and confident instrument passage were the key elements to the reduction in complication rates for brain biopsy. The most significant complications of diagnostic stereotacticbiopsy are hemorrhage, neurologic deficits from injury to critical structures, seizures, and infection. Complication rates for the major published series of stereotacticbrain biopsy are listed in Table 1.2,4,10,17,18,20 Although the overall complication rate is low, varying from 0 to 7%, a definite mortality rate exists for these procedures. When complicated by a hemorrhage, insertion of the biopsy needle into critical areas of the brain can cause fatal injury. Seizures, although rare, can occur after a diagnostic biopsy. The direct relationship of the biopsy procedure itself to the onset of seizures as well as the risk of development of chronic epilepsy is not well understood. Infection is remarkably uncommon, even when no hair is shaved. New or worsened neurologic deficits secondary to tissue trauma or edema are also uncommon and are usually transient phenomena. Failure to obtain diagnostic tissue during biopsy varies among reported series, but in experienced centers nondiagnostic biopsy occurs in fewer than 10%of cases and can be related to the size and location of the lesion, the technique of surgery, and the nature of the lesion itself. Successful stereotactic biopsy depends on appropriate patient selection, correct interpretation of imaging studies, proper selection of biopsy instruments and trajectory, judicious tissue sampling, and expert neuropathologic evaluation. Complications are predictable when any of the aforementioned steps are not taken. Each of these factors, addressed in order subsequently, represents general principles for complication avoidance in all aspects of stereotactic brain surgery but are discussed within the context of diagnostic biopsy, the most common procedure. Selection of Patients for Brain Biopsy
Although lesions in nearly any brain location can be biopsied, the proper selectionof appropriate patients for biopsy must be analyzed. Patients undergoing stereotactic biopsy should have lesions for which one or more plausible diagnoses are suspected but not confirmable by any other simpler means (i.e., an enhancing
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY
37
Figure 1. A, The Leksell stereotactic arc and instrument carrier. B, The Leksell model G stereotactic system consists of a base ring, four posts for rigid pin fixation, and the stereotactic arc and probe carrier. (Courtesy of Elekta Instruments, Inc., Atlanta, GA.)
mass that could represent neoplasm, infarction, or infection). Furthermore, knowledge of the correct diagnosis should in some way alter the management of the patient, at least for appropriate counseling. Tumors, therefore, are among the most common lesions selected for stereotactic biopsy. Choices of surgical resection, radiation, and chemotherapy are influenced by the histologic diagnosis of specific brain tumors. In contrast, for example, a patient with recently diagnosed metastatic bronchogenic adenocarcinoma who presents with multiple cerebral enhanc-
302 102 500 547 338 300 367
No. Cases
Data from references 2, 4, 10-14, 17, 18, and 20.
1990-1 996”-14
Ostertag, 1 98018 Lunsford, 1984” Apuzzo, 1 9872 Kelly, 1991lo Voges, 1993’0 Bernstein, 19944 Kondziolka and Lunsford
Series
1 0 0.2 0.9 0.3 0 0.3
0.3
Nonhemorrhage Deficit (%)
2.9 2 0.4 0.9 2.4 4.7
(”/.I
Hemorrhage
Table 1. COMPLICATIONS OF DIAGNOSTIC STEREOTACTIC BIOPSY
1 0.2
0
0 0
NA
NA
1 0.2 1.1 0.6 0 0
(”/.I
Infection
NA
Seizures (”/.)
2.3 0 1 0.3 0.6 1.7 0
(”/I
Death
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY
39
ing lesions (and no evidence of systemic infection) almost certainly has metastatic brain involvement of the underlying primary cancer. A stereotactic biopsy is not likely to alter the treatment plan. Some issues, however, are more controversial. Patients with rapidly progressive dementing or neurodegenerative illnesses, for example, sometimes present to neurosurgeons for brain biopsy, but only infrequently does obtaining brain tissue alter the management and prognosis of these patients. Stereotactic biopsy, however, remains important in the setting to rule out treatable disorders (i.e., vasculitis). Furthermore, if no discrete imaging abnormalities exist, and a diagnosis might be achieved via meningeal or blood vessel biopsy, open brain sampling is preferred over stereotacticbrain biopsy. Patients with acquired immunodeficiency syndrome (AIDS)-related brain lesions present similar challenges because treatment of AIDS-related brain disease is not always possible or beneficial. In addition to identifying patients who are likely to benefit from brain biopsy, an assessment of whether brain biopsy might be dangerous at the desired time of surgery should also be made. Patients with coagulopathies or thrombocytopenia must have these parameters corrected before planning a stereotactic brain biopsy. Patients with known liver disease are highly suspect. Normal coagulation function and a platelet count above l U O , O O O / ~ L are required. Aspirin, warfarin, ticlodipine, and nonsteroidal anti-inflammatory drugs must be discontinued 5 to 7 days before stereotactic brain biopsy. Patients who require warfarin for cardiac valve prophylaxis may be converted to heparin-induced anticoagulation and the biopsy performed within a short 24-hour window of normalized coagulation function. Patients whose lesions on CT or MR imaging appear to be highly vascular should undergo appropriate imaging to rule out the possibility that the lesion is a vascular malformation or aneurysm. A lesion that appears to be a small hemorrhagic tumor on a CT scan, for example, may have the characteristicappearance of a cavernous malformation on MR imaging. Diagnostic cerebral angiography may be necessary in rare cases to distinguish between a neoplasm and an arteriovenous malformation. It should be noted, however, that even tumors that have a propensity toward hemorrhage, such as glioblastoma multiforme or renal cell metastasis, can be safely biopsied with proper technique. Lesions adjacent to vascular structures, such as pineal region tumors, can be biopsied with low surgical risk with proper attention to the regional anatomy. Lesions in the sylvian fissure, posterior fossa, or third ventricular region may present a higher surgical risk from stereotactic biopsy. Such lesions are associated with higher risk of hemorrhage because of their contiguity to pial or ependymal surfaces wherein lie important arterial or venous structures. Such cases often benThe type of imaging (CT versus efit from an experienced surgeon (Fig. 2).1,3,6,12,14 MR imaging) should be chosen for clarity of lesion definition (Figs. 3, 4). Smaller slice thicknesses and intervals provide greater accuracy for target selection. Judicious Brain Tissue Sampling
What portion of a brain lesion should be biopsied? Many brain lesions are inhomogeneous. Ring-enhancinglesions frequently require sampling of a portion of the enhancing rim to establish a diagnosis because the nonenhancing core may contain only necrotic debris with disrupted cytoarchitecture. Some cystic lesions, such as craniopharyngiomas, can be diagnosed simply by obtaining cyst fluid, but most often a sample of tissue from a solid portion of the lesion must be obtained. So as not to miss anaplastic regions of an otherwise benign tumor, Kelly'O has described taking a series of biopsy specimens from one end of the tumor to the other. Although this has proved helpful in defining the nature of a general neo-
40
KONDZIOLKA et a1
Figure 2. CT scan showing a post-biopsy hematoma following a trans-Sylvian approach (arrows). (Case referred from another institution.)
Figure 3. The intraoperative CT scanner at the University of Pittsburgh for stereotactic surgery. Note stereotactic frame placement before imaging.
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY
41
Figure 4. CT scan (left)of a young woman with a thalamic mass for biopsy. The tumor is obscured by artifact from the posts of the stereotactic frame. With stereotactic MRI (right),no artifact is seen and the tumor can be targeted appropriately. The tumor proved to be an astrocytoma.
plasm, bleeding complications can be avoided by obtaining only as much tissue as necessary to make a diagnosis. As a general maxim, a negative biopsy specimen is preferred to a patient with a negative outcome. Depending on the lesion diameter, a single 10-mm long core biopsy specimen contains both solid and necrotic tumor, useful in both diagnosis and grading of glial neoplasms. If bleeding is encountered after a biopsy specimen is obtained, it is crucial to allow the blood to drain spontaneously out the needle rather than to attempt to tamponade the bleeding in any way. This approach limits the volume of hematoma that otherwise would form in the brain. When this maneuver is used, hemorrhages are usually small and self-limited.Rarely, severe or persistent bleeding requires craniotomy to control. Chimowitz and colleagues5reported that three patients with intractable hemorrhage after stereotactic procedures had control of bleeding achieved by instilling thrombin into the target site. Injection of peroxide through the needle must be avoided because a catastrophic bubbling mass could result. Hemorrhage during stereotactic surgery is easier to prevent than to treat. In addition to strategic planning to avoid major vessels, a normotensive (<150 mm Hg systolic) blood pressure must be maintained throughout surgery. A frequent cause of intraoperative episodic hypertension is bladder distention often brought about by the contrast-enhanced scan. Sedation should be provided to patients who are anxious or restless. Children under 13 years of age undergo surgery under general anesthesia.
Selection of Biopsy Instrumentation and Trajectory
For virtually all stereotactic approaches, the authors use twist-drill craniostomy for cerebral access (Fig. 5). The dura is punctured with a blunt-tip 1.9-mm diameter probe; the dura can be coagulated with monopolar cautery touched to
42
KONDZIOLKA et a1
Figure 5. Twist-drill craniostomy set for the Leksell stereotactic system. The authors use a 4 mm drill bit to facilitate instrument passage into the brain. (Courtesy of Elekta Instruments, Inc., Atlanta, GA.)
the probe. The side-cuttingaspiration needle is preferred for biopsy. Other options include biopsy cup forceps (bronchoscopy type) and spiral needle devices (Fig.6). The authors prefer the Sedan-type aspiration cannulas of 2.1- to 2.5-mm outer diameter, which safely provide adequate brain samples for histologic analysis. Although Apuzzo and colleagues2prefer cup forceps biopsy technique, the authors are hesitant to use it because of poor tactile feedback between tissue and blood vessels. Selection of the type of biopsy instrument is less important than its proper use. The biopsy trajectory is chosen such that important gyri, white matter tracts, and blood vessels are avoided whenever possible. A general principle in choosing a safe trajectory is to traverse as few pial and ependymal surfaces as possible en route to the target. Pial and ependymal surfaces harbor the blood vessels that lead to intraoperative hemorrhages. It is surprising that for the most part the blood vessels within a tumor are unusual sources of hemorrhage. The biopsy needle should enter the brain via a gyrus, rather than a sulcus. This is easy to plan using current imaging techniques. Passage of the needle into a gyrus to obtain a specimen from an underlying white matter abnormality requires traversing only a single pial surface, whereas a pathway through a sulcus may enter and exit the pia several times where two pial surfaces are closely apposed. One advance in the planning of stereotactic biopsy trajectories is the use of Surgiplan (Elekta Instruments, Atlanta GA), a computer program that enables the surgeon to view coronal, sagittal, and probe-view image reconstructions that show the exact location of the biopsy device at each level through the brain. This program allows the surgeon to refine the trajectory planning such that important structures can be avoided. Careful attention to imaging information all the way from the skull to the target is important in reducing the risks of stereotacticbiopsy.
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY
43
Figure 6. The selection of stereotactic instruments includes needles for dural entry or aspiration, a spiral biopsy needle (bottom), a 0.9 mm fine needle aspirate or injection instrument, and the side-coring Sedan cannulas with 3 or 10 mm openings. (Courtesy of Elekta Instruments, Inc., Atlanta, GA.)
Using the techniques described previously, the authors have observed only one postbiopsy hemorrhage that required craniotomy in 367 cases (0.3%) since 1990.
Proper NeuropathologicEvaluation Expert neuropathologic evaluation begins with careful handling and preparation of tissue in the operating room. Because of the necessarily small tissue volumes obtained at stereotactic biopsy, each piece is important. Samples should not be wiped off the biopsy instrument by hand with a cloth or gauze because this traumatizes and disrupts the tissue. Small volumes of tissue deposited into large volumes of saline for transportation may also damage the cytoarchitecture of the tissue or make it difficult to retrieve. The preferred technique for biopsy specimen handling is to remove the tissue from the biopsy instrument with a 22gauge needle and to place it into an empty petri dish. Here the specimen can be clearly seen and separated from any associated blood clot. The neurosurgeon should take an active role in presenting the tissues to the neuropathologist (who should come to the operating room). At that time, the clinical question is reviewed as well as the patient history and imaging findings. The authors demonstrate on the scans the exact location from which each specimen was obtained. The neuropathologist provides input as to whether samples should be sent for culture, placed in formalin before paraffin embedding, or placed in glutaraldehyde for electron microscopic analysis. At times, all of these tests may be important to yield the final diagnosis. On average, two to three specimens are obtained. At the au-
44
KONDZIOLKA et a1
thors’ center, which contains a dedicated intraoperative CT scanner, a postoperative CT scan confirms the diagnostic site and absence of bleeding after biopsy (Fig. 7). The authors’ ability to reach a diagnosis from small samples is related to the skills of a neuropathologist who is familiar with evaluating and interpreting small biopsy specimens. The main goal of the intraoperative neuropathology consultation is to determine whether or not potentially diagnostic tissue is present. The
Figure 7. A, Axial and sagittal MR showing a mass in the pons of a 65 year-old man with no prior history of malignancy.A systemicevaluation was negative. 6,Following a transcerebellar biopsy that disclosed metastatic adenocarcinoma, air is identified both at the biopsy site and along the trajectory (arrows).
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY
45
final diagnosis is frequently suggested during this initial phase of tissue evaluation, but it is reserved for the permanent sections. Making use of a touch preparation allows the neuropathologist to determine whether abnormal or diagnostic tissue is present intraoperatively and conserves the tissue for permanent sections. Pollack and c o - w o r k e r ~have ~ ~ refined the technique of diagnosis from touch preparations and in many cases prefer them to frozen sections, which are more timeconsuming and tissue-consuming. FLUID CAVITY ASPIRATION
Neurosurgeons occasionally are requested to drain cystic lesions within the brain. Cerebral abscesses and tumor or developmental cysts may be drained for either diagnostic or therapeutic purposes. Similar to diagnostic stereotactic biopsy, these procedures also are rarely associated with the risk of hemorrhage, neurologic deficit, seizures, or diagnostic failure. The principles of patient selection, target selection, and complication avoidance are the same as those for diagnostic stereotactic biopsy with some specific considerations. Brain abscesses (>3 cm in average diameter), in addition to being aspirated, should also be drained. In most instances, about one half to two thirds of the calculated volume of purulent material should be allowed to drain spontaneously from the abscess (Fig. 8). Gentle aspiration may be required if the fluid is tenacious. Overzealous aspiration of pus can lead to hemorrhage from a friable and vascular abscess cavity wall. The remainder of the pus should be allowed to drain through a closed system external catheter, which drains the abscess cavity over the next 1 to 3 postoperative days. This may prevent reaccumulation of pus and abscess recurrence. The catheter should be placed so that the drainage bag remains in a dependent portion. The catheter length should be chosen so that it does not extend into a critical location when the abscess volume has diminished. Great care should be taken not to communicate an abscess cavity with the ventricular system; this should be carefully thought out in the trajectory planning stage of the operation. Nonpurulent cystic fluid collections in the brain may be drained to make a diagnosis or to relieve mass effect. Craniopharyngioma cysts can be diagnosed and often definitively treated in one setting by sampling the fluid (to identify cholesterol crystals) and instilling a radioactive isotope (P32) to destroy the epithelial lining. The soft tissue penetrance of the isotope is limited and associated with minimal morbidity even when the injection dose is 200 to 250 Gy. Glial tumor cysts are sometimes treated by aspiration, but they frequently require repeated aspirations or placement of an indwelling catheter for periodic drainage. Stereotactic intracavitary radiation may also be beneficial. Colloid cysts of the third ventricle, when filled with a low-density, low-viscosity fluid, can often be definitively treated by a single a~pirati0n.l~ The complications of cyst aspiration and drainage are similar to those of diagnostic stereotactic biopsy. MOVEMENT DISORDER SURGERY
Thalamotomy and pallidotomy are the two most common stereotactic procedures designed to treat the symptoms of Parkinson's disease. Although thalamotomy is selected primarily to affect the tremor component of Parkinson's disease, pallidotomy has emerged as a procedure that addresses not only tremor, but also rigidity, bradykinesia, and dopamine-induced dyskinesias. Leksell first evaluated stereotactic lesions in the pallidum in the late 1950s.After the introduction of levodopa in the late 1960s, progress with his concepts largely subsided until
46
KONDZIOLKA et a1
Figure 8. Stereotactic management of a brain abscess in a young man with a congenital ventricular septa1 defect. A, Abscess before biopsy. B, After stereotactic aspiration of pus, air is seen within the abscess (arrow). The organism was Hemophilus paraphrophilus. C,One month after antiobiotic therapy, the abscess had regressed. 0,Gentle aspiration of abscess for approximatelytwohhirds the calculated volume.
the early 1990s. Laitinen and colleagues16reevaluated pallidotomy in a modern series of patients. He emphasized the ability of pallidotomy to complement levodopa therapy by ameliorating the drug-induced movements (dyskinesia). Complications of pallidotomy and thalamotomy are u n ~ o m m o n . ~Both ,~,~~,~~ procedures are designed to create defined lesions in deeply seated and critically located brain nuclei. Hemorrhage is the primary concern in both procedures. Because the electrode is small and no tissue is removed during such procedures, the hemorrhage rate is low (Table 2). Neurologic deficits may be produced by the lesion itself. The most common neurologic deficits after pallidotomy include visual field deficit, hemiparesis, and dysarthria. Such symptoms are usually temporary. The close approximation of the globus pallidus interna to the internal capsule and optic tract are the basis for these deficits. Radiofrequency lesion generation causes focal tissue necrosis surrounded by a zone of edema. This peripheral edema may cause transient deficits. Whenever a probe is inserted into the brain, abscess formation is possible; this was reported in a single patient in Iacono and colleagues’ series9Seizures resulting from pallidotomy have yet to be reported. The mainstays of complication avoidance for pallidotomy surgery are appro-
U
rp
42 194 18 40
No. Cases
0
3.2 0
0
(”/.I
~
~
~
~
16.7 2.1 6 8
Nonhemorrhage Deficit (%)
0
0
0
0
0 0
(“w
Death
0 0.5
(”/.I
(“4 0 0 0 0
Infection
Seizures
Data from Dogali M, Fazzine E, Kolodry E, et al: Stereotatic ventral pallidotomyfor Parkinson’s disease. Neurology 45753-761, 1995; lacono RP, Shima F, Lonser RR, et al: The results, indications, and physiology of posteroventral pallidotomy for patients with Parkinson’s disease. Neurosurgery 36:1118-1127, 1995; Kondziolka D, BonarotiEA, Lunsford LD: Pallidotomy for Parkinson’s disease. Contemp Neurosurg 18:l-7, 1996; and Laitenen LV, Bergenheim AT, Hariz MI: Leksell’s posteroventral pallidotomy in the treatment of Parkinson’s disease. J Neurosurg 76:53-61, 1992
Laitinen, 199216 lacono, 19959 Dogali, 19957 Kondziolka. 1996”
Series
~
Hemorrhage
~~
Table 2. SYMPTOMATIC COMPLICATIONS OF STEREOTACTIC PALLIDOTOMY
48
KONDZIOLKA et a1
priate patient selection and target planning, the use of test lesions and visual evoked potential monitoring, physiologic evaluation, careful intraoperative neurologic examinations, and judicious lesion generation. Attention to each of these steps reduces complications of pallidotomy procedures; each is addressed subsequently. Selection of Patients for Pallidotomy The appropriate candidate for pallidotomy is a patient with Parkinson's disease who has exhausted maximal medical therapy but nevertheless remains symptomatic with tremor, rigidity, bradykinesias, and dopamine-induced dyskinesias. Patients with tremor only may be best treated by thalamotomy. Patients with parkinsonism secondary to other Parkinson's plus syndromes, because of the underlying differences in pathophysiology, are not thought to be appropriate candidates for pallidotomy. Signs of autonomic, cerebellar, and extraocular movement dysfunction may signal that potential patients have some other disease process, such as Shy-Drager syndrome, olivopontocerebellar atrophy, or progressive supranuclear palsy, each of which would make the patient less likely to respond to surgery. Patients undergoing pallidotomy should have the capacity for rehabilitation, either in a formal program or at home, because this affords them the best opportunity to benefit from their procedure. Patients who necessarily return to a sedentary environment after surgery may have symptomatic improvement but may not make functional gains after surgery. Severe dementia is a contraindication for surgery. Patients with bleeding diatheses, major intercurrent medical problems, and severe structural brain abnormalities (with distorted anatomy) are not acceptable candidates for pallidotomy. Poorly controlled hypertension is thought to increase the risk of hemorrhage during pallidotomy. Patients with preexisting ipsilateral hemianopsia have a relative contraindication to pallidotomy because the complication of contralateral hemianopsia would be unacceptable to them. Target Planning for Pallidotomy Most centers use stereotactic MR imaging to guide electrode placement in pallidotomy. Other surgeons have used CT or contrast-enhanced ventriculography. At present, neither the risk nor accuracy of ventriculography argues for its use. The resolution and and accuracy provided by high-quality volume acquisition MR imaging has been d o c ~ m e n t e d . ~For , ~ 'pallidotomy, attention to identification of the anterior and posterior commissures, the midcommissural line, and the basal ganglia is important. The authors select a target 2 to 3 mm anterior to the midcommissural point, 19 to 22 mm lateral, and 3 to 6 mm inferior, which places the target just above the optic tract (Fig. 9). To limit complications even further, the authors use a computerized surgical planning system (Surgiplan, Elekta Instruments, Atlanta, GA), which facilitates trajectory planning through cieated coronal and sagittal reformatted images. In this fashion, the electrode is introduced through a gyrus (not a sulcus), and a safe trajectory is identified before instrument passage. To avoid injury to the optic tract during surgery, the authors use visual evoked potential monitoring.'' Visual evoked potential monitoring is helpful to identify physiologic changes through the optic tract during pallidal stimulation and during success in lesion generation. Although the onset of visual complica-
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY
49
Figure 9. Stereotactic pallidotomy with MR targeting. A, Coronal sequencefor trajectory planning with entry of the electrode within a gyrus. 6,The electrode tract is identified on MR 24
hours after surgery.
tions has been rare (1.4% for a quadrant field deficit in the authors’ experience), the authors continue to use visual evoked potential monitoring as an adjunct to pallidal testing. Physiologic Testing
Some surgeons use microelectrode recording to identify pallidal neurons, pallidal borders, and regional structures. Others use macroelectrode-based stimulation. With stimulation, parameters include 1 msec pulse wave, 50 to 100 Hz, and use of 0 to 3 volts. If stimulation causes a capsular response with marked increased tone and dysarthria at less than 1.5volts, most surgeons move the electrode further away from the internal capsule (either lateral or more anterior). If a capsular response is achieved at or above 2 volts, this threshold usually is safe for pallidotomy. Identification of visual phosphenes during stimulation is an indication that the electrode should be moved away from the optic tract. Lesioning During Pallidotomy
Before formal pallidotomy, the authors create a test lesion using a 1 X 3 mm electrode (45°C is delivered for 30 seconds). This lesion usually is temporary and reversible. If no deficits are identified on clinical examination and with visual evoked potential .monitoring, a permanent lesion is created at 70 to 80°C for 60 seconds, usually at two or three locations in the globus pallidus interna. Each lesion created by the 3-mm electrode is spaced at 2-mm increments in the superoinferior axis. The patient is monitored clinically during each lesion for strength, speech, and the appropriate clinical response off medications. If any adverse reaction is identified, lesion generation is stopped. If the level of consciousness of the patient changes, an immediate CT scan is performed. In the authors’ first 120 pallidotomies, no patient has developed a surgical brain hemorrhage or other
50
KONDZIOLKA et a1
major neurologic morbidity using this technique. Five percent of patients have had transient dysarthria lasting 1 to 3 weeks. This may be related to perilesional edema in the early period after surgery (Fig. 10). STEREOTACTIC RADIOSURGERY
Radiosurgery is an increasingly used technique for the management of selected patients with vascular malformations, brain tumors, and functional disor-
Figure 10. A, The pallidotomy lesion on long TR MRI 24 hours after surgery shows perilesional signal change (arrows). 6,Seven months after surgery,a smaller and permanent pallidotomy is identified.
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY
51
ders. Single-session radiation delivery with stereotactic guidance provides precise irradiation of a defined intracranial target. Stereotactic radiosurgery is performed with the Leksell Gamma Knife (Elekta Instruments, Atlanta, GA) at the University of Pittsburgh (Fig. 11). The desired antitumor biologic effect is cessation of tumor cell division and delayed blood vessel occlusion.Radiosurgery has been evaluated extensively in terms of clinical results, complications, and cost-effecti~eness.'~ The complicationsof stereotacticradiosurgery are based on the radiation dose delivered, the brain region targeted, and prior patient history (such as receipt of prior radiation therapy). Radiation-related complications can be either early or delayed. The early complications of radiosurgery are rare and consist only of mild headache or occasional nausea lasting several hours after the procedure. Delayed complications occur 3 months to 3 years after radiosurgery and include both cranial nerve deficits and deficits associated with brain injury. In the radiosurgery of acoustic neuromas, currently the authors have seen a 5% to 7% incidence of delayed facial or trigeminal neuropathy (usually mild) that occurs a mean 6 to 9 months after radiosurgery. The dose tolerance of the optic nerve and chiasm has been investigated and is considered by many to be at 8 to 9 Gy. Thus, for tumors of the parasellar region, the authors limit the dose received by the chiasm. Using this approach, the authors have not detected visual complications in any patient treated during the last 7 years. Special techniques of beam blocking or beam shaping are effective in reducing the dose received by normal structures surrounding the brain target. Delayed vascular effects can include thrombosis and ischemia.These are most prominent in the management of patients with vascular malformations of the brain in which regional brain edema can occur before vascular malformation obliteration (Fig. 12). It is not known whether obliteration of the malformation itself causes this response or if it is a direct response of radiation. Up to 3% of patients in the authors' series of vascular malformations developed permanent morbidity after r a d i ~ s u r g e r yThe . ~ ~occurrence of radiation necrosis is rare. The authors usually select a radiation dose associated with a less than 3% chance for permanent necrosis based on lesion volume.8In evaluation of the first 1600 patients with at least 3-year follow-up, the rate of symptomatic significant morbidity (temporary or permanent) was 1.9% (permanent morbidity = 0.9%).
Figure 11. The Leksell model U Gamma Knife for stereotactic radiosurgery.
52
KONDZIOLKA et a1
Figure 12. A, angiogram in a young woman with a seizure disorder and a parietal AVM. 13, Serial contrast-enhancedMR scans after radiosurgeryshow enhancement at the AVM target that resolves over time a, 5 months; b, 9 months; c, 15 months. C,Long TR imaging shows parenchymal edema that resolves over time. At 5 months she experienced increased headache that resolved a, 5 months; b, 9 months; c, 15 months. Illustration continued on opposite page
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY
53
Figure 12 (Continued). D, 22 months after treatment, her AVM was completely obliterated with no permanent neurologic sequelae.
Although some physicians have suggested that radiosurgery might be associated with the later development of radiation-induced malignancy, this has not yet been reported. With more than 60,000 radiosurgical procedures performed since the early 1960s, no increased rate of subsequent tumor development has been noted. This reduced risk of delayed oncogenesis may be one advantage of stereotactic radiosurgery as an alternative to conventional fractionated radiation therapy. Complication avoidance in radiosurgery depends on proper patient selection; the use of high-resolution neuroimaging for dose planning; the creation of a conformal dose plan that fits the lesion margin precisely; the selection of a safe, yet effective radiation dose; and proper education of the patient and family as to the realistic expectations of radiosurgery. SUMMARY
Stereotactic neurosurgery is a minimally invasive management strategy for patients with brain tumors, vascular malformations, and functional disorders. With proper attention to the guidance provided by high-resolution neuroimaging, the use of advanced computer workstations, and proper use of surgical tools, surgical morbidity should be low. Patients and referring physicians must be informed as to the results and expectations of stereotactic surgery. As these techniques become more common in the neurosurgical armamentarium, proper attention to the details of these approaches must be maintained. References 1. Abernathy CD, Camacho A, Kelly PJ: Stereotaxic suboccipital transcerebellar biopsy of pontine mass lesions. J Neurosurg 70:195-200, 1989 2. Apuzzo MLJ, Chandrasoma PT, Cohen D, et al: Computed imaging stereotaxy: Experi-
54
KONDZlOLKA et a1
ence and perspective related to 500 procedures applied to brain masses. Neurosurgery 20:930-937, 1987 3. Apuzzo MLJ, Chandrasoma PT, Zelman V, et al: Computed tomographic guidance stereotaxis in the management of lesions of the third ventricular region. Neurosurgery 15:502-508,1984 4. Bernstein M, Parrent AG: Complications of CT-guided stereotactic biopsy of intra-axial brain lesions. J Neurosurg 81:165-168,1994 5. Chimowitz MI, Barnett GH, Palmer J: Treatment of intractable arterial hemorrhage during stereotactic brain biopsy with thrombin. J Neurosurg 74301-303,1991 6. Coffey RJ, Lunsford LD: Stereotactic surgery for mass lesions of the midbrain and pons. Neurosurgery 1712-18,1985 7. Dogali M, Fazzine E, Kolodny E, et al: Stereotactic ventral pallidotomy for Parkinson’s disease. Neurology 45:753-761,1995 8. Flickinger JC: An integrated logistic formula for predictions of complications after radiosurgery. Int J Radiat Oncol Biol Phys 172379-885, 1989 9. Iacono RP, Shima F, Lonser RR, et al: The results, indications, and physiology of posteroventral pallidotomy for patients with Parkinson’s disease. Neurosurgery 36~1181127,1995 10. Kelly PJ: Tumor Stereotaxis. Philadelphia, WB Saunders, 1991 11. Kondziolka D, Bonaroti EA, Lunsford L D Pallidotomy for Parkinson’s disease. Contemp Neurosurg 18:l-7,1996 12. Kondziolka D, Lunsford LD: Results and expectations of image-guided brainstem biopsy. Surg Neurol43:558-562,1995 13. Kondziolka D, Lunsford LD: Stereotacticmanagement of colloid cysts: Factors predicting success. J Neurosurg 75:45-51, 1991 14. Kondziolka D, Lunsford LD: Stereotactic biopsy for intrinsic lesions of the medulla through the long-axis of the brainstem: Technical considerations. Acta Neurochir 128:8991,1994 15. Kondziolka D, Lunsford LD, Flickinger JC: Stereotactic radiosurgery using the Gamma knife: Indications and results. Neurologist 3:45-52, 1997 16. Laitinen LV, Bergenheim AT, Hariz M I Leksell’s posteroventral pallidotomy in the treatment of Parkinson’s disease. J Neurosurg 76:5341,1992 17. Lunsford LD, Martinez AJ: Stereotactic exploration of the brain in the era of computed tomography. Surg Neurol22:222-230,1984 18. Ostertag CB, Mennel HD, Kiessling M Stereotactic biopsy of brain tumors. Surg Neurol 14:275-283,1980 19. Pollack IF, Martinez A, Hall W, et al: Touch preparations in the rapid intraoperative analysis of central nervous system lesions: A comparison with frozen sections and paraffin embedded sections. Mod Pathol 1:378-384, 1988 20. Voges J, Schroder R, Treuer H, et al: CT-guided and computer assisted stereotactic biopsy: Technique, results, indications. Acta Neurochir 125:142-149, 1993
Address reprint requests to Douglas Kondziolka, MD Department of Neurological Surgery Suite B-400, Presbyterian University Hospital 200 Lothrop Street Pittsburgh, PA 15213-2582
IATROGENIC DISORDERS
+ .OO
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY Douglas Kondziolka, MD, FRCS (C), FACS, Andrew D. Firlik, MD, and L. Dade Lunsford, MD, FACS
Stereotactic surgery refers to an image-guided neurosurgical procedure in which a three-dimensional guidance stereotactic system is used to facilitate a diagnostic or therapeutic goal in the brain. A surgical complication is defined as an adverse event that occurs either during surgery or within a 30-day postoperative interval. Such a complication must arise as a direct consequence of the surgery or its associated administration of anesthesia. Traditionally, stereotactic surgery uses a stereotactic head frame to register accurately high-resolution neurodiagnostic brain images for use in neurosurgery. Most frame-based stereotactic procedures involve accessing brain targets using probes, electrodes, or catheters through small cranial openings. The use of closed-skull, single treatment session radiation to treat brain disease (stereotactic radiosurgery) is an important and increasingly used treatment. Invisible radiation beams replace rigid surgical instruments. More recently, both frame-based and frameless stereotactic systems have proven helpful during conventional craniotomy procedures. These techniques use external cutaneous fiducial markers to correlate preoperative brain imaging with the surgical approach. Image-guided craniotomies are stereotactic procedures because of their use of a three-dimensional localizing system, but postoperative complications are mainly those associated with the craniotomy itself, rather than with the stereotactic technology. This article discusses only complications associated with stereotactic frame-based procedures that involve minimal or no opening of the cranial vault, including diagnostic brain biopsy, cyst or abscess management, ablative movement disorder surgery, and stereotactic radiosurgery. DIAGNOSTIC STEREOTACTIC BIOPSY
Before 1980, stereotactic brain biopsy was usually performed using either freehand brain needle aspiration techniques or less sophisticated stereotactic devices. From the Department of Neurological Surgery, University of Pittsburgh, and Center for Image-guided Neurosurgery, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania. NEUROLOGIC CLINICS OF NORTH AMERICA VOLUME 16 *NUMBER 1 * FEBRUARY 1998
35
36
KONDZIOLKA et a1
The target was localized by cerebral angiography, radioisotope scintigraphy, ventriculography, or early generation computed tomography (CT), none of which provided high-resolution brain mapping. The field of stereotactic surgery was considered complex, risky, and backroom (i.e., not in the forefront). Most patients who underwent these procedures were either considered too old or too medically ill to undergo the preferred craniotomy for resection of their brain lesion. A biopsy was frequently requested so that palliative chemotherapy or radiation could be offered. Stereotactic technology did maintain a dominant role in functional neurosurgery with a history dating back to the 1940s. With the advent of high-resolutionCT and magnetic resonance (MR),imaging over the past two decades, new stereotactic frame systems were introduced. The two most popular stereotactic devices in North America are the Leksell (Elekta Instruments, Atlanta, GA) and the Brown-Roberts-Wells (BRW) (Radionics, Burlington, MA) systems (Fig. l). With the availability of spatially accurate brain parenchymal imaging (as CT quality improved), the role of stereotactic biopsy entered a renaissance. For the first time, brain lesions could be imaged and specific targets selected for sampling. The surgeon could choose a safe trajectory from the skull to the lesion that avoided critical brain regions, blood vessels, or the ventricular system. Most surgeons recognized that the bony opening need only be slightly larger than the diameter of the inserted probe. The opportunity to sample defined brain lesions through minute cranial openings with minimal brain exposure and confident instrument passage were the key elements to the reduction in complication rates for brain biopsy. The most significant complications of diagnostic stereotacticbiopsy are hemorrhage, neurologic deficits from injury to critical structures, seizures, and infection. Complication rates for the major published series of stereotacticbrain biopsy are listed in Table 1.2,4,10,17,18,20 Although the overall complication rate is low, varying from 0 to 7%, a definite mortality rate exists for these procedures. When complicated by a hemorrhage, insertion of the biopsy needle into critical areas of the brain can cause fatal injury. Seizures, although rare, can occur after a diagnostic biopsy. The direct relationship of the biopsy procedure itself to the onset of seizures as well as the risk of development of chronic epilepsy is not well understood. Infection is remarkably uncommon, even when no hair is shaved. New or worsened neurologic deficits secondary to tissue trauma or edema are also uncommon and are usually transient phenomena. Failure to obtain diagnostic tissue during biopsy varies among reported series, but in experienced centers nondiagnostic biopsy occurs in fewer than 10%of cases and can be related to the size and location of the lesion, the technique of surgery, and the nature of the lesion itself. Successful stereotactic biopsy depends on appropriate patient selection, correct interpretation of imaging studies, proper selection of biopsy instruments and trajectory, judicious tissue sampling, and expert neuropathologic evaluation. Complications are predictable when any of the aforementioned steps are not taken. Each of these factors, addressed in order subsequently, represents general principles for complication avoidance in all aspects of stereotactic brain surgery but are discussed within the context of diagnostic biopsy, the most common procedure. Selection of Patients for Brain Biopsy
Although lesions in nearly any brain location can be biopsied, the proper selectionof appropriate patients for biopsy must be analyzed. Patients undergoing stereotactic biopsy should have lesions for which one or more plausible diagnoses are suspected but not confirmable by any other simpler means (i.e., an enhancing
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY
37
Figure 1. A, The Leksell stereotactic arc and instrument carrier. B, The Leksell model G stereotactic system consists of a base ring, four posts for rigid pin fixation, and the stereotactic arc and probe carrier. (Courtesy of Elekta Instruments, Inc., Atlanta, GA.)
mass that could represent neoplasm, infarction, or infection). Furthermore, knowledge of the correct diagnosis should in some way alter the management of the patient, at least for appropriate counseling. Tumors, therefore, are among the most common lesions selected for stereotactic biopsy. Choices of surgical resection, radiation, and chemotherapy are influenced by the histologic diagnosis of specific brain tumors. In contrast, for example, a patient with recently diagnosed metastatic bronchogenic adenocarcinoma who presents with multiple cerebral enhanc-
302 102 500 547 338 300 367
No. Cases
Data from references 2, 4, 10-14, 17, 18, and 20.
1990-1 996”-14
Ostertag, 1 98018 Lunsford, 1984” Apuzzo, 1 9872 Kelly, 1991lo Voges, 1993’0 Bernstein, 19944 Kondziolka and Lunsford
Series
1 0 0.2 0.9 0.3 0 0.3
0.3
Nonhemorrhage Deficit (%)
2.9 2 0.4 0.9 2.4 4.7
(”/.I
Hemorrhage
Table 1. COMPLICATIONS OF DIAGNOSTIC STEREOTACTIC BIOPSY
1 0.2
0
0 0
NA
NA
1 0.2 1.1 0.6 0 0
(”/.I
Infection
NA
Seizures (”/.)
2.3 0 1 0.3 0.6 1.7 0
(”/I
Death
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY
39
ing lesions (and no evidence of systemic infection) almost certainly has metastatic brain involvement of the underlying primary cancer. A stereotactic biopsy is not likely to alter the treatment plan. Some issues, however, are more controversial. Patients with rapidly progressive dementing or neurodegenerative illnesses, for example, sometimes present to neurosurgeons for brain biopsy, but only infrequently does obtaining brain tissue alter the management and prognosis of these patients. Stereotactic biopsy, however, remains important in the setting to rule out treatable disorders (i.e., vasculitis). Furthermore, if no discrete imaging abnormalities exist, and a diagnosis might be achieved via meningeal or blood vessel biopsy, open brain sampling is preferred over stereotacticbrain biopsy. Patients with acquired immunodeficiency syndrome (AIDS)-related brain lesions present similar challenges because treatment of AIDS-related brain disease is not always possible or beneficial. In addition to identifying patients who are likely to benefit from brain biopsy, an assessment of whether brain biopsy might be dangerous at the desired time of surgery should also be made. Patients with coagulopathies or thrombocytopenia must have these parameters corrected before planning a stereotactic brain biopsy. Patients with known liver disease are highly suspect. Normal coagulation function and a platelet count above l U O , O O O / ~ L are required. Aspirin, warfarin, ticlodipine, and nonsteroidal anti-inflammatory drugs must be discontinued 5 to 7 days before stereotactic brain biopsy. Patients who require warfarin for cardiac valve prophylaxis may be converted to heparin-induced anticoagulation and the biopsy performed within a short 24-hour window of normalized coagulation function. Patients whose lesions on CT or MR imaging appear to be highly vascular should undergo appropriate imaging to rule out the possibility that the lesion is a vascular malformation or aneurysm. A lesion that appears to be a small hemorrhagic tumor on a CT scan, for example, may have the characteristicappearance of a cavernous malformation on MR imaging. Diagnostic cerebral angiography may be necessary in rare cases to distinguish between a neoplasm and an arteriovenous malformation. It should be noted, however, that even tumors that have a propensity toward hemorrhage, such as glioblastoma multiforme or renal cell metastasis, can be safely biopsied with proper technique. Lesions adjacent to vascular structures, such as pineal region tumors, can be biopsied with low surgical risk with proper attention to the regional anatomy. Lesions in the sylvian fissure, posterior fossa, or third ventricular region may present a higher surgical risk from stereotactic biopsy. Such lesions are associated with higher risk of hemorrhage because of their contiguity to pial or ependymal surfaces wherein lie important arterial or venous structures. Such cases often benThe type of imaging (CT versus efit from an experienced surgeon (Fig. 2).1,3,6,12,14 MR imaging) should be chosen for clarity of lesion definition (Figs. 3, 4). Smaller slice thicknesses and intervals provide greater accuracy for target selection. Judicious Brain Tissue Sampling
What portion of a brain lesion should be biopsied? Many brain lesions are inhomogeneous. Ring-enhancinglesions frequently require sampling of a portion of the enhancing rim to establish a diagnosis because the nonenhancing core may contain only necrotic debris with disrupted cytoarchitecture. Some cystic lesions, such as craniopharyngiomas, can be diagnosed simply by obtaining cyst fluid, but most often a sample of tissue from a solid portion of the lesion must be obtained. So as not to miss anaplastic regions of an otherwise benign tumor, Kelly'O has described taking a series of biopsy specimens from one end of the tumor to the other. Although this has proved helpful in defining the nature of a general neo-
40
KONDZIOLKA et a1
Figure 2. CT scan showing a post-biopsy hematoma following a trans-Sylvian approach (arrows). (Case referred from another institution.)
Figure 3. The intraoperative CT scanner at the University of Pittsburgh for stereotactic surgery. Note stereotactic frame placement before imaging.
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY
41
Figure 4. CT scan (left)of a young woman with a thalamic mass for biopsy. The tumor is obscured by artifact from the posts of the stereotactic frame. With stereotactic MRI (right),no artifact is seen and the tumor can be targeted appropriately. The tumor proved to be an astrocytoma.
plasm, bleeding complications can be avoided by obtaining only as much tissue as necessary to make a diagnosis. As a general maxim, a negative biopsy specimen is preferred to a patient with a negative outcome. Depending on the lesion diameter, a single 10-mm long core biopsy specimen contains both solid and necrotic tumor, useful in both diagnosis and grading of glial neoplasms. If bleeding is encountered after a biopsy specimen is obtained, it is crucial to allow the blood to drain spontaneously out the needle rather than to attempt to tamponade the bleeding in any way. This approach limits the volume of hematoma that otherwise would form in the brain. When this maneuver is used, hemorrhages are usually small and self-limited.Rarely, severe or persistent bleeding requires craniotomy to control. Chimowitz and colleagues5reported that three patients with intractable hemorrhage after stereotactic procedures had control of bleeding achieved by instilling thrombin into the target site. Injection of peroxide through the needle must be avoided because a catastrophic bubbling mass could result. Hemorrhage during stereotactic surgery is easier to prevent than to treat. In addition to strategic planning to avoid major vessels, a normotensive (<150 mm Hg systolic) blood pressure must be maintained throughout surgery. A frequent cause of intraoperative episodic hypertension is bladder distention often brought about by the contrast-enhanced scan. Sedation should be provided to patients who are anxious or restless. Children under 13 years of age undergo surgery under general anesthesia.
Selection of Biopsy Instrumentation and Trajectory
For virtually all stereotactic approaches, the authors use twist-drill craniostomy for cerebral access (Fig. 5). The dura is punctured with a blunt-tip 1.9-mm diameter probe; the dura can be coagulated with monopolar cautery touched to
42
KONDZIOLKA et a1
Figure 5. Twist-drill craniostomy set for the Leksell stereotactic system. The authors use a 4 mm drill bit to facilitate instrument passage into the brain. (Courtesy of Elekta Instruments, Inc., Atlanta, GA.)
the probe. The side-cuttingaspiration needle is preferred for biopsy. Other options include biopsy cup forceps (bronchoscopy type) and spiral needle devices (Fig.6). The authors prefer the Sedan-type aspiration cannulas of 2.1- to 2.5-mm outer diameter, which safely provide adequate brain samples for histologic analysis. Although Apuzzo and colleagues2prefer cup forceps biopsy technique, the authors are hesitant to use it because of poor tactile feedback between tissue and blood vessels. Selection of the type of biopsy instrument is less important than its proper use. The biopsy trajectory is chosen such that important gyri, white matter tracts, and blood vessels are avoided whenever possible. A general principle in choosing a safe trajectory is to traverse as few pial and ependymal surfaces as possible en route to the target. Pial and ependymal surfaces harbor the blood vessels that lead to intraoperative hemorrhages. It is surprising that for the most part the blood vessels within a tumor are unusual sources of hemorrhage. The biopsy needle should enter the brain via a gyrus, rather than a sulcus. This is easy to plan using current imaging techniques. Passage of the needle into a gyrus to obtain a specimen from an underlying white matter abnormality requires traversing only a single pial surface, whereas a pathway through a sulcus may enter and exit the pia several times where two pial surfaces are closely apposed. One advance in the planning of stereotactic biopsy trajectories is the use of Surgiplan (Elekta Instruments, Atlanta GA), a computer program that enables the surgeon to view coronal, sagittal, and probe-view image reconstructions that show the exact location of the biopsy device at each level through the brain. This program allows the surgeon to refine the trajectory planning such that important structures can be avoided. Careful attention to imaging information all the way from the skull to the target is important in reducing the risks of stereotacticbiopsy.
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY
43
Figure 6. The selection of stereotactic instruments includes needles for dural entry or aspiration, a spiral biopsy needle (bottom), a 0.9 mm fine needle aspirate or injection instrument, and the side-coring Sedan cannulas with 3 or 10 mm openings. (Courtesy of Elekta Instruments, Inc., Atlanta, GA.)
Using the techniques described previously, the authors have observed only one postbiopsy hemorrhage that required craniotomy in 367 cases (0.3%) since 1990.
Proper NeuropathologicEvaluation Expert neuropathologic evaluation begins with careful handling and preparation of tissue in the operating room. Because of the necessarily small tissue volumes obtained at stereotactic biopsy, each piece is important. Samples should not be wiped off the biopsy instrument by hand with a cloth or gauze because this traumatizes and disrupts the tissue. Small volumes of tissue deposited into large volumes of saline for transportation may also damage the cytoarchitecture of the tissue or make it difficult to retrieve. The preferred technique for biopsy specimen handling is to remove the tissue from the biopsy instrument with a 22gauge needle and to place it into an empty petri dish. Here the specimen can be clearly seen and separated from any associated blood clot. The neurosurgeon should take an active role in presenting the tissues to the neuropathologist (who should come to the operating room). At that time, the clinical question is reviewed as well as the patient history and imaging findings. The authors demonstrate on the scans the exact location from which each specimen was obtained. The neuropathologist provides input as to whether samples should be sent for culture, placed in formalin before paraffin embedding, or placed in glutaraldehyde for electron microscopic analysis. At times, all of these tests may be important to yield the final diagnosis. On average, two to three specimens are obtained. At the au-
44
KONDZIOLKA et a1
thors’ center, which contains a dedicated intraoperative CT scanner, a postoperative CT scan confirms the diagnostic site and absence of bleeding after biopsy (Fig. 7). The authors’ ability to reach a diagnosis from small samples is related to the skills of a neuropathologist who is familiar with evaluating and interpreting small biopsy specimens. The main goal of the intraoperative neuropathology consultation is to determine whether or not potentially diagnostic tissue is present. The
Figure 7. A, Axial and sagittal MR showing a mass in the pons of a 65 year-old man with no prior history of malignancy.A systemicevaluation was negative. 6,Following a transcerebellar biopsy that disclosed metastatic adenocarcinoma, air is identified both at the biopsy site and along the trajectory (arrows).
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY
45
final diagnosis is frequently suggested during this initial phase of tissue evaluation, but it is reserved for the permanent sections. Making use of a touch preparation allows the neuropathologist to determine whether abnormal or diagnostic tissue is present intraoperatively and conserves the tissue for permanent sections. Pollack and c o - w o r k e r ~have ~ ~ refined the technique of diagnosis from touch preparations and in many cases prefer them to frozen sections, which are more timeconsuming and tissue-consuming. FLUID CAVITY ASPIRATION
Neurosurgeons occasionally are requested to drain cystic lesions within the brain. Cerebral abscesses and tumor or developmental cysts may be drained for either diagnostic or therapeutic purposes. Similar to diagnostic stereotactic biopsy, these procedures also are rarely associated with the risk of hemorrhage, neurologic deficit, seizures, or diagnostic failure. The principles of patient selection, target selection, and complication avoidance are the same as those for diagnostic stereotactic biopsy with some specific considerations. Brain abscesses (>3 cm in average diameter), in addition to being aspirated, should also be drained. In most instances, about one half to two thirds of the calculated volume of purulent material should be allowed to drain spontaneously from the abscess (Fig. 8). Gentle aspiration may be required if the fluid is tenacious. Overzealous aspiration of pus can lead to hemorrhage from a friable and vascular abscess cavity wall. The remainder of the pus should be allowed to drain through a closed system external catheter, which drains the abscess cavity over the next 1 to 3 postoperative days. This may prevent reaccumulation of pus and abscess recurrence. The catheter should be placed so that the drainage bag remains in a dependent portion. The catheter length should be chosen so that it does not extend into a critical location when the abscess volume has diminished. Great care should be taken not to communicate an abscess cavity with the ventricular system; this should be carefully thought out in the trajectory planning stage of the operation. Nonpurulent cystic fluid collections in the brain may be drained to make a diagnosis or to relieve mass effect. Craniopharyngioma cysts can be diagnosed and often definitively treated in one setting by sampling the fluid (to identify cholesterol crystals) and instilling a radioactive isotope (P32) to destroy the epithelial lining. The soft tissue penetrance of the isotope is limited and associated with minimal morbidity even when the injection dose is 200 to 250 Gy. Glial tumor cysts are sometimes treated by aspiration, but they frequently require repeated aspirations or placement of an indwelling catheter for periodic drainage. Stereotactic intracavitary radiation may also be beneficial. Colloid cysts of the third ventricle, when filled with a low-density, low-viscosity fluid, can often be definitively treated by a single a~pirati0n.l~ The complications of cyst aspiration and drainage are similar to those of diagnostic stereotactic biopsy. MOVEMENT DISORDER SURGERY
Thalamotomy and pallidotomy are the two most common stereotactic procedures designed to treat the symptoms of Parkinson's disease. Although thalamotomy is selected primarily to affect the tremor component of Parkinson's disease, pallidotomy has emerged as a procedure that addresses not only tremor, but also rigidity, bradykinesia, and dopamine-induced dyskinesias. Leksell first evaluated stereotactic lesions in the pallidum in the late 1950s.After the introduction of levodopa in the late 1960s, progress with his concepts largely subsided until
46
KONDZIOLKA et a1
Figure 8. Stereotactic management of a brain abscess in a young man with a congenital ventricular septa1 defect. A, Abscess before biopsy. B, After stereotactic aspiration of pus, air is seen within the abscess (arrow). The organism was Hemophilus paraphrophilus. C,One month after antiobiotic therapy, the abscess had regressed. 0,Gentle aspiration of abscess for approximatelytwohhirds the calculated volume.
the early 1990s. Laitinen and colleagues16reevaluated pallidotomy in a modern series of patients. He emphasized the ability of pallidotomy to complement levodopa therapy by ameliorating the drug-induced movements (dyskinesia). Complications of pallidotomy and thalamotomy are u n ~ o m m o n . ~Both ,~,~~,~~ procedures are designed to create defined lesions in deeply seated and critically located brain nuclei. Hemorrhage is the primary concern in both procedures. Because the electrode is small and no tissue is removed during such procedures, the hemorrhage rate is low (Table 2). Neurologic deficits may be produced by the lesion itself. The most common neurologic deficits after pallidotomy include visual field deficit, hemiparesis, and dysarthria. Such symptoms are usually temporary. The close approximation of the globus pallidus interna to the internal capsule and optic tract are the basis for these deficits. Radiofrequency lesion generation causes focal tissue necrosis surrounded by a zone of edema. This peripheral edema may cause transient deficits. Whenever a probe is inserted into the brain, abscess formation is possible; this was reported in a single patient in Iacono and colleagues’ series9Seizures resulting from pallidotomy have yet to be reported. The mainstays of complication avoidance for pallidotomy surgery are appro-
U
rp
42 194 18 40
No. Cases
0
3.2 0
0
(”/.I
~
~
~
~
16.7 2.1 6 8
Nonhemorrhage Deficit (%)
0
0
0
0
0 0
(“w
Death
0 0.5
(”/.I
(“4 0 0 0 0
Infection
Seizures
Data from Dogali M, Fazzine E, Kolodry E, et al: Stereotatic ventral pallidotomyfor Parkinson’s disease. Neurology 45753-761, 1995; lacono RP, Shima F, Lonser RR, et al: The results, indications, and physiology of posteroventral pallidotomy for patients with Parkinson’s disease. Neurosurgery 36:1118-1127, 1995; Kondziolka D, BonarotiEA, Lunsford LD: Pallidotomy for Parkinson’s disease. Contemp Neurosurg 18:l-7, 1996; and Laitenen LV, Bergenheim AT, Hariz MI: Leksell’s posteroventral pallidotomy in the treatment of Parkinson’s disease. J Neurosurg 76:53-61, 1992
Laitinen, 199216 lacono, 19959 Dogali, 19957 Kondziolka. 1996”
Series
~
Hemorrhage
~~
Table 2. SYMPTOMATIC COMPLICATIONS OF STEREOTACTIC PALLIDOTOMY
48
KONDZIOLKA et a1
priate patient selection and target planning, the use of test lesions and visual evoked potential monitoring, physiologic evaluation, careful intraoperative neurologic examinations, and judicious lesion generation. Attention to each of these steps reduces complications of pallidotomy procedures; each is addressed subsequently. Selection of Patients for Pallidotomy The appropriate candidate for pallidotomy is a patient with Parkinson's disease who has exhausted maximal medical therapy but nevertheless remains symptomatic with tremor, rigidity, bradykinesias, and dopamine-induced dyskinesias. Patients with tremor only may be best treated by thalamotomy. Patients with parkinsonism secondary to other Parkinson's plus syndromes, because of the underlying differences in pathophysiology, are not thought to be appropriate candidates for pallidotomy. Signs of autonomic, cerebellar, and extraocular movement dysfunction may signal that potential patients have some other disease process, such as Shy-Drager syndrome, olivopontocerebellar atrophy, or progressive supranuclear palsy, each of which would make the patient less likely to respond to surgery. Patients undergoing pallidotomy should have the capacity for rehabilitation, either in a formal program or at home, because this affords them the best opportunity to benefit from their procedure. Patients who necessarily return to a sedentary environment after surgery may have symptomatic improvement but may not make functional gains after surgery. Severe dementia is a contraindication for surgery. Patients with bleeding diatheses, major intercurrent medical problems, and severe structural brain abnormalities (with distorted anatomy) are not acceptable candidates for pallidotomy. Poorly controlled hypertension is thought to increase the risk of hemorrhage during pallidotomy. Patients with preexisting ipsilateral hemianopsia have a relative contraindication to pallidotomy because the complication of contralateral hemianopsia would be unacceptable to them. Target Planning for Pallidotomy Most centers use stereotactic MR imaging to guide electrode placement in pallidotomy. Other surgeons have used CT or contrast-enhanced ventriculography. At present, neither the risk nor accuracy of ventriculography argues for its use. The resolution and and accuracy provided by high-quality volume acquisition MR imaging has been d o c ~ m e n t e d . ~For , ~ 'pallidotomy, attention to identification of the anterior and posterior commissures, the midcommissural line, and the basal ganglia is important. The authors select a target 2 to 3 mm anterior to the midcommissural point, 19 to 22 mm lateral, and 3 to 6 mm inferior, which places the target just above the optic tract (Fig. 9). To limit complications even further, the authors use a computerized surgical planning system (Surgiplan, Elekta Instruments, Atlanta, GA), which facilitates trajectory planning through cieated coronal and sagittal reformatted images. In this fashion, the electrode is introduced through a gyrus (not a sulcus), and a safe trajectory is identified before instrument passage. To avoid injury to the optic tract during surgery, the authors use visual evoked potential monitoring.'' Visual evoked potential monitoring is helpful to identify physiologic changes through the optic tract during pallidal stimulation and during success in lesion generation. Although the onset of visual complica-
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY
49
Figure 9. Stereotactic pallidotomy with MR targeting. A, Coronal sequencefor trajectory planning with entry of the electrode within a gyrus. 6,The electrode tract is identified on MR 24
hours after surgery.
tions has been rare (1.4% for a quadrant field deficit in the authors’ experience), the authors continue to use visual evoked potential monitoring as an adjunct to pallidal testing. Physiologic Testing
Some surgeons use microelectrode recording to identify pallidal neurons, pallidal borders, and regional structures. Others use macroelectrode-based stimulation. With stimulation, parameters include 1 msec pulse wave, 50 to 100 Hz, and use of 0 to 3 volts. If stimulation causes a capsular response with marked increased tone and dysarthria at less than 1.5volts, most surgeons move the electrode further away from the internal capsule (either lateral or more anterior). If a capsular response is achieved at or above 2 volts, this threshold usually is safe for pallidotomy. Identification of visual phosphenes during stimulation is an indication that the electrode should be moved away from the optic tract. Lesioning During Pallidotomy
Before formal pallidotomy, the authors create a test lesion using a 1 X 3 mm electrode (45°C is delivered for 30 seconds). This lesion usually is temporary and reversible. If no deficits are identified on clinical examination and with visual evoked potential .monitoring, a permanent lesion is created at 70 to 80°C for 60 seconds, usually at two or three locations in the globus pallidus interna. Each lesion created by the 3-mm electrode is spaced at 2-mm increments in the superoinferior axis. The patient is monitored clinically during each lesion for strength, speech, and the appropriate clinical response off medications. If any adverse reaction is identified, lesion generation is stopped. If the level of consciousness of the patient changes, an immediate CT scan is performed. In the authors’ first 120 pallidotomies, no patient has developed a surgical brain hemorrhage or other
50
KONDZIOLKA et a1
major neurologic morbidity using this technique. Five percent of patients have had transient dysarthria lasting 1 to 3 weeks. This may be related to perilesional edema in the early period after surgery (Fig. 10). STEREOTACTIC RADIOSURGERY
Radiosurgery is an increasingly used technique for the management of selected patients with vascular malformations, brain tumors, and functional disor-
Figure 10. A, The pallidotomy lesion on long TR MRI 24 hours after surgery shows perilesional signal change (arrows). 6,Seven months after surgery,a smaller and permanent pallidotomy is identified.
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY
51
ders. Single-session radiation delivery with stereotactic guidance provides precise irradiation of a defined intracranial target. Stereotactic radiosurgery is performed with the Leksell Gamma Knife (Elekta Instruments, Atlanta, GA) at the University of Pittsburgh (Fig. 11). The desired antitumor biologic effect is cessation of tumor cell division and delayed blood vessel occlusion.Radiosurgery has been evaluated extensively in terms of clinical results, complications, and cost-effecti~eness.'~ The complicationsof stereotacticradiosurgery are based on the radiation dose delivered, the brain region targeted, and prior patient history (such as receipt of prior radiation therapy). Radiation-related complications can be either early or delayed. The early complications of radiosurgery are rare and consist only of mild headache or occasional nausea lasting several hours after the procedure. Delayed complications occur 3 months to 3 years after radiosurgery and include both cranial nerve deficits and deficits associated with brain injury. In the radiosurgery of acoustic neuromas, currently the authors have seen a 5% to 7% incidence of delayed facial or trigeminal neuropathy (usually mild) that occurs a mean 6 to 9 months after radiosurgery. The dose tolerance of the optic nerve and chiasm has been investigated and is considered by many to be at 8 to 9 Gy. Thus, for tumors of the parasellar region, the authors limit the dose received by the chiasm. Using this approach, the authors have not detected visual complications in any patient treated during the last 7 years. Special techniques of beam blocking or beam shaping are effective in reducing the dose received by normal structures surrounding the brain target. Delayed vascular effects can include thrombosis and ischemia.These are most prominent in the management of patients with vascular malformations of the brain in which regional brain edema can occur before vascular malformation obliteration (Fig. 12). It is not known whether obliteration of the malformation itself causes this response or if it is a direct response of radiation. Up to 3% of patients in the authors' series of vascular malformations developed permanent morbidity after r a d i ~ s u r g e r yThe . ~ ~occurrence of radiation necrosis is rare. The authors usually select a radiation dose associated with a less than 3% chance for permanent necrosis based on lesion volume.8In evaluation of the first 1600 patients with at least 3-year follow-up, the rate of symptomatic significant morbidity (temporary or permanent) was 1.9% (permanent morbidity = 0.9%).
Figure 11. The Leksell model U Gamma Knife for stereotactic radiosurgery.
52
KONDZIOLKA et a1
Figure 12. A, angiogram in a young woman with a seizure disorder and a parietal AVM. 13, Serial contrast-enhancedMR scans after radiosurgeryshow enhancement at the AVM target that resolves over time a, 5 months; b, 9 months; c, 15 months. C,Long TR imaging shows parenchymal edema that resolves over time. At 5 months she experienced increased headache that resolved a, 5 months; b, 9 months; c, 15 months. Illustration continued on opposite page
COMPLICATIONS OF STEREOTACTIC BRAIN SURGERY
53
Figure 12 (Continued). D, 22 months after treatment, her AVM was completely obliterated with no permanent neurologic sequelae.
Although some physicians have suggested that radiosurgery might be associated with the later development of radiation-induced malignancy, this has not yet been reported. With more than 60,000 radiosurgical procedures performed since the early 1960s, no increased rate of subsequent tumor development has been noted. This reduced risk of delayed oncogenesis may be one advantage of stereotactic radiosurgery as an alternative to conventional fractionated radiation therapy. Complication avoidance in radiosurgery depends on proper patient selection; the use of high-resolution neuroimaging for dose planning; the creation of a conformal dose plan that fits the lesion margin precisely; the selection of a safe, yet effective radiation dose; and proper education of the patient and family as to the realistic expectations of radiosurgery. SUMMARY
Stereotactic neurosurgery is a minimally invasive management strategy for patients with brain tumors, vascular malformations, and functional disorders. With proper attention to the guidance provided by high-resolution neuroimaging, the use of advanced computer workstations, and proper use of surgical tools, surgical morbidity should be low. Patients and referring physicians must be informed as to the results and expectations of stereotactic surgery. As these techniques become more common in the neurosurgical armamentarium, proper attention to the details of these approaches must be maintained. References 1. Abernathy CD, Camacho A, Kelly PJ: Stereotaxic suboccipital transcerebellar biopsy of pontine mass lesions. J Neurosurg 70:195-200, 1989 2. Apuzzo MLJ, Chandrasoma PT, Cohen D, et al: Computed imaging stereotaxy: Experi-
54
KONDZlOLKA et a1
ence and perspective related to 500 procedures applied to brain masses. Neurosurgery 20:930-937, 1987 3. Apuzzo MLJ, Chandrasoma PT, Zelman V, et al: Computed tomographic guidance stereotaxis in the management of lesions of the third ventricular region. Neurosurgery 15:502-508,1984 4. Bernstein M, Parrent AG: Complications of CT-guided stereotactic biopsy of intra-axial brain lesions. J Neurosurg 81:165-168,1994 5. Chimowitz MI, Barnett GH, Palmer J: Treatment of intractable arterial hemorrhage during stereotactic brain biopsy with thrombin. J Neurosurg 74301-303,1991 6. Coffey RJ, Lunsford LD: Stereotactic surgery for mass lesions of the midbrain and pons. Neurosurgery 1712-18,1985 7. Dogali M, Fazzine E, Kolodny E, et al: Stereotactic ventral pallidotomy for Parkinson’s disease. Neurology 45:753-761,1995 8. Flickinger JC: An integrated logistic formula for predictions of complications after radiosurgery. Int J Radiat Oncol Biol Phys 172379-885, 1989 9. Iacono RP, Shima F, Lonser RR, et al: The results, indications, and physiology of posteroventral pallidotomy for patients with Parkinson’s disease. Neurosurgery 36~1181127,1995 10. Kelly PJ: Tumor Stereotaxis. Philadelphia, WB Saunders, 1991 11. Kondziolka D, Bonaroti EA, Lunsford L D Pallidotomy for Parkinson’s disease. Contemp Neurosurg 18:l-7,1996 12. Kondziolka D, Lunsford LD: Results and expectations of image-guided brainstem biopsy. Surg Neurol43:558-562,1995 13. Kondziolka D, Lunsford LD: Stereotacticmanagement of colloid cysts: Factors predicting success. J Neurosurg 75:45-51, 1991 14. Kondziolka D, Lunsford LD: Stereotactic biopsy for intrinsic lesions of the medulla through the long-axis of the brainstem: Technical considerations. Acta Neurochir 128:8991,1994 15. Kondziolka D, Lunsford LD, Flickinger JC: Stereotactic radiosurgery using the Gamma knife: Indications and results. Neurologist 3:45-52, 1997 16. Laitinen LV, Bergenheim AT, Hariz M I Leksell’s posteroventral pallidotomy in the treatment of Parkinson’s disease. J Neurosurg 76:5341,1992 17. Lunsford LD, Martinez AJ: Stereotactic exploration of the brain in the era of computed tomography. Surg Neurol22:222-230,1984 18. Ostertag CB, Mennel HD, Kiessling M Stereotactic biopsy of brain tumors. Surg Neurol 14:275-283,1980 19. Pollack IF, Martinez A, Hall W, et al: Touch preparations in the rapid intraoperative analysis of central nervous system lesions: A comparison with frozen sections and paraffin embedded sections. Mod Pathol 1:378-384, 1988 20. Voges J, Schroder R, Treuer H, et al: CT-guided and computer assisted stereotactic biopsy: Technique, results, indications. Acta Neurochir 125:142-149, 1993
Address reprint requests to Douglas Kondziolka, MD Department of Neurological Surgery Suite B-400, Presbyterian University Hospital 200 Lothrop Street Pittsburgh, PA 15213-2582