Ten Neurosurgical Myths
Gregory Dowd, MD and Deepak Awasthi, MD
Department of Neurosurgery
Louisiana State Universiy Medical Center
New Orleans, Louisiana USA
[Abstract | Introduction
| Myth 1 | Myth 2
| Myth 3 | Myth 4
| Myth 5 | Myth 6
| Myth 7 | Myth 8
| Myth 9 | Myth 10
| Conclusions | References]
There are several techniques and concepts in neurosurgical practice that have been in perpetuated, untested, for decades. Research has shown, however, that many of these sacred beliefs may really be just myths. Ten such "myths" are explored in this short review. Although, one may not agree with the alternative thinking, it is thought provoking and can potentially lead to improvement in patient care.
Many of techniques and concepts used in neurosurgical practice are untested. They are often based on the assumption of what is best. Subsequently, these are handed down from mentor to apprentices in a "here is what you do" format. Although tradition and ritual may be important to put the practitioner at ease, blindly reproducing the errors of a previous generation is not good.(3) Some ancient practices, such as bloodletting, were clearly harmful to the patient. However, in the contemporary practice of that era, this was felt to represent quality medical care. Only by questioning the scientific foundations of our daily practice can we confidently believe in their merit.(6) Several ideas and techniques that follow have been put to the test and found to lack a solid foundation.
Myth 1: Head
elevation is beneficial in the treatment of elevated intracranial pressure.
This is based on the observation that elevation of the patients head may augment the venous drainage from the head and result in reduced intracranial pressure. This is routinely practiced for patients following craniotomy with orders such as "HOB (head of bed) at 30 degrees". However, quantitative investigation has shown that while elevation of the head may result in a decrease in intracranial pressure (ICP), there is a greater fall in the mean arterial pressure (MAP) at the level of the head.(28). This results in an overall decrease inthe cerebral perfusion pressure (CPP=MAP-ICP). For patient's brain, elevation of the head of the ed may mean a decrease in the effective perfusion of the brain. The extreme form of this may result in cerebral ischemia partially resulting from head elevation.
Myth 2: Hyperventilation (induced hypocapnia) is useful to treat elevated intracranial pressure.
This recommendation is based on the physiological knowledge that carbon dioxide acts as a potent vasodilator at the cerebral arteriolar bed. It follows that by reducing the pCO2 (arterial partial pressure of carbon dioxide), constriction of this vascular bed may reduce the intracranial blood volume and lower intracranial pressure. The mechanism of vasoconstriction is based on a differential of the hydrogen ion in the blood to the perivascular CSF spaces.(10) Over time, equilibration will occur and the vascular effect will diminish. Abrupt normalization of the pCO2 will cause a reversal of the blood- CSF hydrogen gradient and can lead to rebound vasodilation in the brain. However, this effect is dependent on an intact autoregulatory bed. In damaged tissue, this control may not be present. Also, in patients with a relative hypovolemia, hyperventilation may lead to a decreased perfusion of the brain.(12) A randomized controlled trial of hyperventilation for severe brain injury found worse outcome with the use of this modality.(20) Its use as a temporizing measure until definitive treatment can be instituted may still be beneficial.
Myth 3: Glucocorticoids
are beneficial in the treatment of brain injury.
Certainly steroids have shown a great benefit in the treatment of vasogenic forms of edema, such as that present in intrinsic brain tumors.(12) By stabilizing cell membranes, scavenging of free radicals and reducing the prostaglandin cascade, edema surrounding these lesions decreases. This can result in improvement both symptomatically and objectively in the patients' condition. It was believed that the use of steroids to combat the cytotoxic damage resulting from brain injury would also prove beneficial.(12) Data from the use of high dose glucocorticoid treatment for spinal cord injury suggest an improvement in outcome.(5) However, similar trials in the brain injury population have failed to show an improved outcome wuth respect to mortality or functional status.(12) In fact, an increase of infectious complications may result form the use of steriods in these patients. As such, the American Association of Neurological Surgeons (AANS) guidelines for the management of head trauma do not support the use of glucocorticoids.(12)
Myth 4: Antihistamines (H2 blockers, eg, cimetidine) should be used to avoid stress gastritis.
Since the early descriptions by Harvey Cushing of the gastro- doudenal ulcers that bear his name, patients with severe neurological injuries and those taking glucocorticoid medications have been known to be at risk for upper gastrointestinal bleeding.(17) In some cases, these ulcers can lead to severe complications requiring surgery or even fatal outcomes. The use of agents that lower gastric acidity were found to decrease both the incidence and severity of the gastric ulcers.(18) However, the neutralization of gastric juice can lead to bacterial overgrowth into this normally sterile environment. These critically ill patients often have bouts of subclinical gastric reflux and pulmonary aspiration of this fluid. Increased rates of pneumonia have been found in patients receiving H2 blockers. This resultant increase in pulmonary complications more than offset the decrease in gastric bleeding. The end result is that these agents do not lead to an actuarial better outcome. Subsequently, studies comparing sucralfate, another gastric protective agent that does not alter the gastric pH, have shown a similar decrease in GI bleeding without an increased rate of pneumonia.(8)
Myth 5: Shaving
the operative site reduces infection.
This seemingly logical concept does not hold true. There is along standing bias across cultures that the absence of hair denotes purity. Monks shave their heads . The profession of hair cutting and surgery were closely related in the past as manifest by the barber- surgeon. It apparently held true that "when you have a hammer, everything looks like a nail". These early surgeons would shave the site to be operated on. This has evolved into a rich tradition practiced for hair removal at some surgical centers, such as shaving the head on the night prior to surgery and the use of straight razors. In fact, the art of shaving was felt to reflect the technical skill of those involved. Any evidence of bleeding suggested that the resident was not yet ready to perform the surgical procedure. However, the length of time from shaving until the operation increases the chance of infection. Also, some reports indicate that not shaving at all can yield low infection rates comparable to the best reported series .(32) This evidence should make the surgeon question the benefit of even this seemingly worthwhile technique.
Myth 6: Following
anterior cervical discectomy (ACD), a fusion procedure is required.
This belief stems from the early use of a fusion in the treatment of cervical discogenic disease (ACDF). (27) Subsequently, practitioners continued to employ a fusion procedure to avoid a postoperative kyphotic deformity at the operated level. However, a minority of neurosurgeons have employed ACD alone and achieved results comparable to ACDF.(7,21) In fact, three randomized, controlled trials comparing ACD and ACDF have shown similar outcomes in both groups .(7) Although there is a higher rate of fusion in the ACDF group, the patient satisfaction amongst both groups is the same. Thus, it appears that fusion is not mandatory for a favorable result following anterior cervical discectomy.
Myth 7: Congenital
disorders such as neural tube defects and hydrocephalus are not preventable.
It has been known for a long time that environmnetal factors played a role in the development of neural tube defects (NTDs), which are more frequent in mothers who are malnourished and come from lower socioeconomic groups. However, when folate administration was found to decrease the incidence of recurrent birth of children with NTDs, a new insight into this problem was found.(26) Folate is a key element in the transfer of one carbon (methyl) groups to amino acids. It is this step which is somehow involved in the development of NTDs. Subsequently, deficiencies of other molecules and enzymes in this pathway have been associated with NTDs.(29) This progress has made neural tube defects a largely preventable condition. Hydrocephalus is a condition that has challenged medicine since antiquity. The treatment has improved vastly in the last century resulting in decreased cosmetic disfigurement and near normal mental function in many patients. However, an understanding of the events leading to failure of CSF circulation have been slower to develop. In the early part of this century, it was found that sequential lumbar puncture could prevent progressive head enlargement in some patients. Cerebral imaging such as ultrasonography has shown that these infants often have intraventricular hemorrhage either related to precipitous delivery or bleeding from the germinal matrix. Improvements in the related fields of obstetrics and neonatology have decreased the incidence of hemorrhage and the incidence of hydrocephalus for relatively healthy babies, but the increasing survival of the early premature and sickest neonates suggest this problem will not disappear in the near future.(9)
Myth 8: Primary brain tumors
do not metastasize.
The observation by oncologists that individuals with primary brain tumors die of local disease without evidence of distal spread supported this concept.(16) This stands out even more prominently when compared with other forms of cancer (e.g., lung, breast) in which death is often a result of the metastatic disease. Studies of lepto- meningeal tissue suggest that this structure acts as a barrier to invasion and therefore to distant spread.(25) However , with longer survival of patients harboring primary brain tumors and new techniques used in their treatment, evidence of distant disease have become more common. Spread through out the subarachnoid space has been well documented for ependymoma and primitive neuroectodermal lesions, but recently meningiomas and gliomas have been found to metastasize by the same route.(1,16) Growth at distant sites may also result from medical treatment. Peritoneal disease has been found following ventriculoperitoneal shunt placement.(23) Subcutaneous glioma formation has been found following local implantation.(25) Additionally, hematogenous spread to bone marrow spaces has been documented.(33) Metastatic spread is possible for several types of primary brain tumors and may travel through many routes. (1,16)
Myth 9: Knowledge
of neuroanatomy will allow the surgeon to avoid iatrogenic neurological
The science of cerebral localization developed in the late 1800's with descriptions of language areas by Broca and Wernicke and motor organization by Jackson.(24) It was felt that the nervous system was relatively "hard wired" and that lesions (e.g, hemorrhage or infarct) could be localized reliably on the basis of the clinical findings. A corollary to this is that predictable deficits will arise with injury to certain brain regions (e.g., contralateral paresis with a pre-central gyrus injury.) These regions are felt to be surrounded by clinically silent areas in which the surgeon may operate with relative safety. However, the advent of sophisticated radiological imaging has shown that often the abnormality is distant from the region predicted on clinical grounds. The cortical mapping work of Penfield and Ojemann demonstrated a wide distribution of important functions, even extending into areas that were previously felt to be "safe".(24) This important field of functional mapping will help provide the surgeon with specific information for the individual patient. Thus, the surgeon cannot confidently localize eloquent cortex on the basis of surface landmarks alone.
A similar situation holds for the peripheral nervous system as well. An example of this is the variability of motor function arising from specific spinal nerves. McCormick has found that section of spinal nerves during the course of para-spinal tumor removal yields a deficit in only 10 to 33% of cases.(19) This is presumably due to the chronic compensation by neighboring nerves that occurs during the slow growth of these tumors. Even in the absence of local pathology, intentional division of spinal nerves may not result in the expected deficit. For example, one technique for the repair of a damaged brachial plexus involves section of the contralateral 7th spinal nerve for a neurotization source.(13) This has been found to be well tolerated and rarely results in motor loss.
Myth 10: The "Brain" is the surgical domain of the neurosurgeon.
This obvious truism is slowly turning into a myth. In the era when angiography or pneumoencephalography were the only effective means of visualizing intracranial pathology, neurosurgeons who performed these tests had "squatter's rights" to the treatment of these patients. This has changed with (1) the improvement in imaging techniques (CT, MRI) which can show intracranial pathology and (2) a third party (e.g; radiologist) who performs these tests. This means that the contents of the skull are no longer a "black box" that only the neurosurgeon can see into and that the workup of the patient is largely done by other specialties. Thus, the treatment of a given pathological entity is open to whichever surgeon is willing to attempt the procedure. Also, development of new and at times superior techniques by related fields has earned them preeminence in certain areas. For example, the innovative techniques of House in the treatment of acoustic neuromas has fostered the involvement on ENT for these lesions.(15) Radiologists have exteneded their experience with angiography to "endovascular surgery" of vascular abnormalities. This trend will continue and highlights the need for neurosurgical involvement with emerging technology.
The above represent just a few (ten) concepts that used to be entrenched traditions, but are now challenged by newer research and innovations. There are several other aspects of neurosurgery that deserve mentioning including spontaneous deep intracerebral hemorrhage should not be operated; lesions in the clivus ("no man's land") and cavernous sinus are not resectable; there is not much one can do for a stroke. All these concepts have been challenged by recent research and innovative techniques. Spontaneous deep intracerebral hemorrhages are now being tackled with sophisticated equipment like endoscopy and frameless stereotactic navigation.(14) The clivus and cavernous sinus regions are now approachable with skull base techniques.(2,4,30,31) Stroke is considered a neurlogical emergency ("Brain Attack") and early (within 6 hours of onset of symptoms) management can involve intravenous or intra-arterial thrombolytic therapy to improve or restore perfusion to the brain and thus reversing ischemia to the brain.(11,22) Thus, controversy leads alternative thinking which leads to research which leads to new and improved management which, ultimately, leads to improved patient outcome. So let us keep thinking and challenging!