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256 WJM, March 1995-Vol 162, No. 3 Epitomes-Neurosurgery
tactic technique, neuroimaging, and our understanding of Because hypothermic cardiac standstill represents
the pathophysiologic processes of Parkinson's disease are additional risks not normally associated with microsurgical
likely to lead to improved efficacy and lessened risk in the clipping of an aneurysm, the selection of appropriate pa-
surgical management of intractable movement disorders. tients is critical. Only patients with complex aneurysms in
COLE A. GILLER, PhD, MD locations that are difficult to reach are considered candi-
RICHARD B. DEWEY Jr, MD dates for hypothermic cardiac bypass with standstill.
Dallas, Texas
Throughout the past 30 years, the definitions of complex
REFERENCES and inaccessible aneurysms have changed dramatically as
Diederich N, Goetz CG, Stebbins GT, et al: Blinded evaluation confirms long- a result of the introduction of the operating microscope and
term asymmetric effect of unilateral thalamotomy or subthalamotomy on tremor a host of new surgical techniques and approaches.
in Parkinson's disease. Neurology 1992; 42:1311-1314 Aneurysms of the anterior communicating artery complex,
Hariz MI, Bergenheim AT, Fodstad H: Air-ventriculography provokes an ante-
rior displacement of the third ventricle during functional stereotactic procedures. once thought inaccessible, are now routinely clipped using
Acta Neurochir 1993; 123:147-152 these techniques, with a low incidence of morbidity and in-
Laitinen LV, Bergenheim AT, Hariz MI: Leksell's posteroventral pallidotomy frequent fatalities. Many surgeons reserve the hypothermic
in the treatnent of Parkinson's disease. J Neurosurg 1992; 76:53-61
Pollak P, Benabid AL, Gervason CL, Hoffmann D, Seigneuret E, Perret J: bypass procedure for giant aneurysms or other complex
Long-term effects of chronic stimulation of the ventral intermediate thalamic nu-
cleus in different types of tremor. Adv Neurol 1993; 60:408-413
aneurysms with wide or ill-defined necks in the posterior
circulation. These aneurysms, despite the use of micro-
surgery and modem exposure techniques, remain daunting
Cardiac Bypass and Hypothermia in the surgical challenges. The principal advantage of hypother-
Treatment of Complex Aneurysms mic arrest is to convert an otherwise inoperable aneurysm
ALTHOUGH EARLY CLINICAL experience with closed-chest into one that has a reasonable chance of being clipped,
bypass using hypothermia demonstrated its technical fea- while minimizing the risk of intraoperative catastrophe.
sibility in the 1960s, this combination of techniques added JOHN R. ROBINSON, MD
ROBERT F. SPETZLER, MD
considerably to the morbidity and mortality associated Phoenix, Arizona
with the repair of cerebral aneurysms. In particular, post-
operative intracranial hemorrhages accounted for a sub- REFERENCES
stantial portion of the morbidity and mortality. Ausman JI, McCormick PW, Stewart M, et al: Cerebral oxygen metabolism
The procedure was used sporadically over the next ten during hypothermic circulatory arrest in humans. J Neurosurg 1993; 79:810-815
years with intermittent success. During that time, dra- Pacult A, Gratzick G, Voegele D, Worthington C, Quinn G, Utsey T: Surgical
clipping of difficult intracranial aneurysms using deep hypothermia and total cir-
matic improvements in bypass pump-oxygenator technol- culatory arrest. South Med J 1993; 86:898-902
ogy, as well as advances in anesthetic techniques, helped Williams MD, Ranier WG, Fieger HG Jr, Murray IP, Sanchez ML:
to reduce the incidence of complications noted by earlier Cardiopulmonary bypass, profound hypothermia, and circulatory arrest for neuro-
surgery. AnnThorac Surg 1991; 52:1069-1074
studies. These changes, a better understanding of physiol-
ogy, and more experience with correcting the coagulopa- Functional Mapping for Surgically
thy after the procedure led to the increased use of this Removing Brain Tumors
treatment for complex intracranial aneurysms. During the
1980s, studies using hypothermic bypass with cardiac SURGICALLY REMOVING intrinsic brain tumors can reduce
standstill documented distinct advantages for the manage- elevated intracranial pressure, improve neurologic func-
ment of giant aneurysms in previously inaccessible loca- tion, stop recurrent seizures, and prolong quality survival.
tions. These advantages included eliminating the risk of The goal of surgical intervention for intrinsic brain tumors
rupture during final dissection and enhancement of the should be maximal resection of tumor without producing
ability to manipulate the aneurysmal sac during circula- new neurologic deficits. Despite advances such as the use
tory suspension. Using circulatory arrest improves visual- of perioperative glucocorticoids and the operating micro-
ization by collapsing the aneurysmal sac. This enhanced scope, there is still a substantial incidence of increased
visualization allows for more accurate clip placement on neurologic deficit-as high as 11% in some series-
many aneurysms with difficult necks. Furthermore, the following attempted tumor resection. Intraoperative func-
technique allows surgeons to do an endarterectomy of the tional mapping of the cortex can increase the safety of the
aneurysm when necessary for better clip closure. surgical removal of brain tumors and has become an
In addition to these advantages, studies have shown accepted adjuvant to it.
this method to be practical for treating complex The essential site for a given function is usually local-
aneurysms, with a 93% rate of aneurysm occlusion, a per- ized, but the location may vary among persons, especially
manent morbidity rate of 13.3%, and a 6.7% mortality. for language. In some patients, vital functions have been
Several studies of this combination of techniques have found within the tumor. Operations based on standard
shown good or excellent results in 73% of patients anatomic landmarks do not take this variability into
treated. This compares favorably with the best results consideration.
without hypothermic cardiac standstill, a 39% occlusion Despite the myriad of simple and complex functions
rate for giant basilar aneurysms, with a 23% permanent accomplished by the brain, only a few tests are required
morbidity rate and a 25% mortality. to increase the margin of safety when operating in
WJM, March 1995-Vol 162, No. 3 Epitomes-Neurosurgery 257
important cortical regions. The most commonly mapped Percutaneous Discectomy-Update
functions include motor and sensory (simple functions)
and language and memory (higher cortical functions). PERCUTANEOUS TECHNIQUES for treating radiculopathy due
Preoperative studies are done to help predict func- to herniated lumbar discs have stimulated keen interest. This
tional anatomy. Neuropsychometric studies can predict interest is prompted by a need for less invasive techniques,
hemispheric dominance and document subtle preexisting experience with percutaneous approaches in other surgical
cognitive deficits in areas such as verbal and visuospatial specialties, and rapidly advancing technology.
memory. The Wada test (intracarotid amobarbital admin- The first procedures for percutaneous discectomy
istration during cerebral angiography) transiently disrupts used fluoroscopically guided manual instruments that
function in one hemisphere, allowing the confirmation of were designed to remove nucleus pulposus (nucleotomy)
hemispheric dominance. Newer modalities such as mag- and possibly contiguous herniated fragments through an
netic source imaging and functional magnetic resonance intradiscal approach. An automated disc aspirator and
imaging promise to augment the armamentarium of non- laser have recently been used to remove larger amounts of
invasive mapping, but have yet to replace conventional nuclear material in a shorter time. These procedures are
computed tomography or magnetic resonance imaging as purported to decrease irritation of the nerve root and other
standard preoperative studies. innervated structures by either eliminating inflammatory
During the surgical procedure, electrical stimulation mediators (disc material) or reducing intradiscal pressure.
mapping identifies functional cortex. When an electrical Automated disc extraction has recently been found to
remove minimal amounts of disc in a sheep model, lead-
current is applied to the surface of the brain, a reversible ing investigators to hypothesize that perforation of the an-
localized depolarization elicits or blocks the function of nulus alone may be responsible for the observed clinical
that portion of the brain until the current is removed. results. Reported outcomes for both manual and auto-
Motor movements can be seen, sensory phenomena can mated nucleotomy range from 44% to 85%, with results
be reported, and language can be interrupted during lasting as long as two years, compared with 75% to 90%
language tasks. Craniotomies while patients are awake with routine microdiscectomy. Complications have been
are possible because the brain does not feel pain or touch. rare, but include infection, hemorrhage, damage to the
With a regional local anesthetic block and propofol, an lumbar nerve roots, penetration of instruments into the
ultrashort-acting intravenous anesthetic agent, patients thecal sac, and injury to the cauda equina.
are put to sleep for the opening without requiring intuba- Newer technologies are making simple nucleotomy
tion, awakened for the functional mapping, and put back obsolete as surgeons now can remove disc fragments that
to sleep for the remainder of the operation and the are impinging on nerve roots and percutaneously fuse de-
closure. Once awake, low currents and 60-Hz biphasic generated disc spaces. Stereotactic localization of
square wave pulses of 1-millisecond duration are used to intradiscal targets and disc fragments to avoid entry into
map the motor and sensory cortices of the face and hand. the thecal sac or damage to extraspinal nerve roots and
In dominant-hemisphere operations, the patient is asked vessels is being investigated. Stereotactic localization
to count aloud, and stimulation mapping then identifies may eventually be used to guide instruments directly to an
counting arrest sites. These sites are usually associated offending disc fragment within the neural foramina,
with face motor function. Language sites are mapped by allowing its removal.
applying the current to the brain surface while the patient With an intradiscal approach, angled instruments and
names slides of simple objects every four to five seconds. aspiration probes guided by both rigid and flexible endo-
Other modalities such as vision, the ability to read music, scopes are being used in an attempt to remove the nuclear
to generate verbs from nouns, to speak a second language, material in disc bulges and to snare free fragments. This
to perform sign language, and to do mathematical calcu- technology is also being used to remove fragments through
lations can also be mapped if necessary. Once important foraminal approaches because the endoscope allows the
functions are identified, the operation continues with the exiting nerve root, vessels, and herniated fragments in the
avoidance of functional areas. With these techniques, per- foramina to be easily identified. With these technologies,
manent neurologic morbidity from tumor resection oper- the concept of removing large amounts of nucleus and con-
ations can be kept below 5%. comitantly reducing intradiscal pressure may be moot as
Brain mapping techniques increase the safety of brain the offending herniation is able to be removed.
tumor operations and allow for tumor resection with less Along with newer instruments, various multiportal
risk of postoperative deficit. approaches are being attempted with endoscopes and spe-
PETER B. WEBER, MD cialized tools to better remove nuclear material and view
JOHN H. NEAL, MD and remove fragments accurately from an intradiscal
Orange, Califomia
approach. Disc spaces are also being fused using these
REFERENCES approaches and a transabdominal approach. Whether
Berger MS. Ojemann GA: Intraoperative brain mapping techniques in neuro- these approaches are superior to a single-tract approach
oncology. Stereotact Funct Neurosurg 1992; 58:153-161 has yet to be determined.
Ojemann GA, Sutherling WW, Lesser RP, Dinner DS, Jayakar P, Saint-Hilaire The growing excitement for percutaneous techniques
JM: Cortical stimulation, In Engel J (Ed): Surgical Treatment of the Epilepsies,
2nd edition. New York, NY. Raven Press, 1993, pp 399-414 should be tempered by an honest assessment of the
