- Department of Neurosurgery, Sir Charles Gairdner Hospital and Royal Perth Hospital, Western Australia
Department of Neurosurgery, Sir Charles Gairdner Hospital and Royal Perth Hospital, Western Australia
DOI:10.4103/2152-7806.133886Copyright: © 2014 Honeybul S. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
How to cite this article: Honeybul S. Neurological susceptibility to a skull defect. Surg Neurol Int 04-Jun-2014;5:83
How to cite this URL: Honeybul S. Neurological susceptibility to a skull defect. Surg Neurol Int 04-Jun-2014;5:83. Available from: http://sni.wpengine.com/surgicalint_articles/neurological-susceptibility-to-a-skull-defect/
Background:There continues to be considerable interest in the use of decompressive craniectomy in the management of neurological emergencies. The procedure is technically straightforward; however, it is becoming increasingly apparent that it is associated with significant complications. One complication that has received relatively little attention is the neurological dysfunction that can occur due to the absence of the bone flap and the subsequent distortion of the brain under the scalp as cerebral swelling subsides. The aim of this narrative review was to examine the literature available regarding the clinical features described, outline the proposed pathophysiology for these clinical manifestations and highlight the implications that this may have for rehabilitation of patients with a large skull defect.
Methods:A literature search was performed in the MEDLINE database (1966 to June 2012). The following keywords were used: Hemicraniectomy, decompressive craniectomy, complications, syndrome of the trephined, syndrome of the sinking scalp flap, motor trephined syndrome. The bibliographies of retrieved reports were searched for additional references.
Results:Various terms have been used to describe the different neurological signs and symptoms with which patients with a skull defect can present. These include; syndrome of the trephined, posttraumatic syndrome, syndrome of the sinking scalp flap, and motor trephined syndrome. There is, however, considerable overlap between the conditions described and a patient's individual clinical presentation.
Conclusion:It is becoming increasingly apparent that certain patients are particularly susceptible to the presence of a large skull defect. The term “Neurological Susceptibility to a Skull Defect” (NSSD) is therefore suggested as a blanket term to describe any neurological change attributable to the absence of cranial coverage.
Keywords: Complications, decompressive craniectomy, syndrome of the trephined
Over the past two decades, there has been a resurgence of interest in the use of decompressive craniectomy in the management of neurological emergencies.[
Numerous studies have demonstrated that the procedure can reduce mortality and this was most clearly demonstrated by the pooled analysis of the three European stroke trials that compared decompressive hemicraniectomy with standard medical management in patients who clinically deteriorated following cerebral swelling secondary to ischemic stroke. The results of this analysis confirmed a dramatic reduction in mortality in those patients treated surgically and this provides unequivocal support for the use of the procedure as a lifesaving intervention.[
Notwithstanding a number of criticisms,[
One complication that has received relatively little attention is the neurological dysfunction that can occur due to the absence of the bone flap and the subsequent distortion of the brain under the scalp as cerebral swelling subsides.
In 1939, Grant and Norcross coined the term “syndrome of the trephine” to describe the symptoms of headache, vertigo, tinnitus, fatigue, insomnia, memory disturbance, seizures, mood swings, and behavioral disturbance that was observed in some individuals with a large skull defect.[
Until recently, these conditions have been described as being either rare or uncommon; however, it is becoming evident that certain patients are particularly susceptible to neurological signs and symptoms relating to the presence of a large skull defect. Clinical presentation can range from the classical description of a reversal of neurological deficits,[
In view of this variation it may be simpler to use a blanket term that applies to all clinical manifestations attributable to the absence of a bone flap such as “Neurological Susceptibility to a Skull Defect” (NSSD)
The underlying pathophysiology responsible for the various neurological manifestations has yet to be established, however, a number of theories have been proposed including direct effects of atmospheric air on the brain,[
Direct effects of atmospheric air on the brain
One of the most easily observed consequences of a decompressive craniectomy is the development of a sunken concave deformity that occurs once the original brain swelling subsides. Because the “closed box” or skull has become open the principles of the Monroe–Kellie doctrine no longer apply and the brain cannot “float” in supportive CSF.[
Disturbance of CSF hydrodynamics following decompressive craniectomy
In normal circumstance when there is complete cranial coverage, the ICP will often be negative in the upright position. However, in the presence of a large skull defect, the ICP will tend to equalize with that of the atmospheric pressure. In these circumstances, the ICP may actually be higher than normal when patients are in the upright position. These changes were demonstrated in studies that used CSF infusion tests before and after cranioplasty and demonstrated that hydrodynamic abnormalities present before cranioplasty were reversed after the bone flap was replaced.[
Another manifestation of the hydrodynamic disturbances that can occur is the development of subdural effusions and hydrocephalus. This is most commonly seen in the context of trauma, however, it has been reported in other pathological conditions.[
Disturbance in cerebral blood flow and metabolism
A number of studies have used either dynamic computed tomography (CT) scanning,[
The pathophysiology underlying this vascular response is unknown. It may merely be a reflection of the transmission of atmospheric pressure on to the cerebral vasculature or impairment of venous return as a result of direct cerebral compression by the inwardly distorted scalp.[
These changes in cerebral blood flow may also relate to changes observed in cerebral metabolism following cranioplasty. Fludeoxyglucose (18F) (18FDG) Positron emission tomography (PET) scanning has demonstrated depressed cerebral metabolism in the underlying hemisphere in patients who have had a unilateral hemicraniectomy.[
Overall the effect that the skull defect has on neurological function may not be due to a single pathophysiological mechanism rather it may in fact be multifactorial. Indeed support for this hypothesis would come from the wide variety of clinical manifestations reported.
The number of patients who exhibit some degree of neurological dysfunction due to the absence of cranial coverage remains unknown. Most publications have been a combination of case reports and retrospective cohort studies and although they detail some impressive neurological recoveries, there is rarely a baseline denominator that records the number of patient in which the cranioplasty has no clinical impact. Most reports have described the various neurological manifestations as rare or uncommon, however, it is becoming increasingly apparent that some form of neurological improvement is more common than previously appreciated.
More recently, a prospective cohort study found a slightly lower incidence of clinical recovery, however, there was a measureable improvement in some aspect of neurological function in 4 (16%) out of 25 patients who were assessed a few days before and after cranioplasty.[
Overall it would appear unequivocal that some patients are particularly susceptible to having a large skull defect and further studies will be required in order to determine not only the true incidence but also what factors predispose patients to this susceptibility. These issues may be important when considering the impact that this condition can have on rehabilitation and also on the timing of the cranioplasty procedure.
Rehabilitation facilities are a valuable resource that have been shown to improve neurological outcome by improving motor and cognitive function and by re-engaging individuals into meaningful activities of daily living and enhancing social integration.[
The conventional role of cranioplasty has been to reconstruct the cranial vault in order to provide protection[
The optimal timing of cranioplasty has not been clearly established, however, for many years it was suggested that the procedure should be delayed in order to reduce the risk of infection.[
In view of these findings it would seem logical to replace the bone flap as soon as clinically possible not only to provide protection and restore cosmesis but also to provide therapeutic benefit to some patients. This would also avoid the need for prolonged use of protective head-gear, which is often uncomfortable and not particularly dignified.
Patients who have had a decompressive craniectomy face a particularly challenging recovery and all efforts should be made to maximize the potential for neurological recovery. It would appear that certain individuals are particularly susceptible to having a skull defect and although the precise pathophysiology remains to be established it would appear to be multifactorial. The term NSSD is a reflection of the wide variety of clinical manifestations with which this susceptibility can present.
Recognition of this susceptibility is important in order to expedite earlier treatment in some cases and prevent scarce rehabilitation resources being unnecessarily apportioned to patients who cannot derive maximal benefit.
A final consideration is perhaps not why patients improve following restoration of cranial coverage, but why most patients seem to tolerate considerable sinking of the scalp with obvious distortion of the cortical surface. This would be an interesting focus of future research.
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