hydrocephalus is an entity which embraces a variety of diseases whose final result is the enlarged size of cerebral ventricular system , partially or completely . among usual classifications ,
the most important are those who differ the communicating from non - communicating and congenital from acquired .
its prevalence is near 11.5% among general population and is progressively rising with populational growth , thus representing an impressive healthy concern .
congenital hydrocephalus due to a myriad of causes has a rate of 12/1000 births , being a common finding among pediatric age ( rekate , 2009 ) .
the physiopathology of hydrocephalus lies in the dynamics of circulation of cerebrospinal fluid ( csf ) .
there should be a disturbance either in production , circulation , or in reabsorption , resulting in positive balances and dilation of ventricular system , producing abnormal high pressure on the ventricles walls .
elevated pressure reflects blocked blood flow out of the lateral ventricle . the consequent csf stasis in hydrocephalus interferes with cerebral and ventricular system development ( penn and linninger , 2009 ) .
responses to elevated csf pressure can be marked oxidative changes in hydrocephalus that are reflected in the way that injured neurons metabolize neurotransmitters and myelin .
contrary to the previously held belief that gliosis in the hydrocephalic brain is restricted only to the periventricular white - matter , gliosis extends through all of the cortex and the peri - aqueductal area ( penn and linninger , 2009 ) .
the neighboring neuropil exhibits notable enlargement of extracellular space , synaptic plasticity and degeneration , damage of myelinated axons , and myelination delay .
the role of ischemia , oxidative stress , increased calcium concentration , activation of nmda receptors , and disturbance of ion homeostasis are discussed in relationship with the fine structural alterations of hydrocephalic brain parenchyma ( castejn , 2010 ) .
clinical manifestations depend especially on the time of appearance and form of onset , if acute / subacute or chronic . as a general rule ,
acute hydrocephalus produce pronounced symptoms as headache , vomitus , papilledema , and impaired consciousness , leading patient to coma and death ( drake , 2008 ) .
chronic hydrocephalus , on other hand , produces skull enlargement , spasticity , progressive neurological deficits in children and dementia , urinary incontinence , and gait changes in elderly ( bergsneider et al . , 2008 ;
the treatment , usually represented by some variation of a diversion procedure , consists in deviating csf flux and acts by reducing intracranial pressure , restoring periventricular , and global perfusion ( bergsneider et al . , 2008 ; drake , 2008 ) .
in children , it is generally performed to restore csf dynamics and prevent worsening of symptoms . in chronic cases ,
it controls symptoms of intracranial pressure and interfere in cognitive and motor functions ( ishikawa et al . , 2008 ;
thus , the form of onset is also the great determinant of cerebral tissue response , leading to physical adaptations , changing elastance and complacency , determining chemical and biological changes , including neuronal plasticity ( penn and linninger , 2009 ) . in this context , we will try to settle a link between the notable modifications to neurophysiology secondary to hydrocephalus and the ability of neuronal tissue to reassume and reorganize its functions toward adaptation .
computational models such as the  small - world  and  scale - free  network might explain clinical resilience in various situations ( friston and price , 2003 ; noppeney et al .
, 2004 ; achard and bullmore , 2007 ; van den heuvel et al . , 2008 ) .
small - world networks predicts that neuronal cells are engaged in clustered connectivity with fewer long - range connections ( friston and price , 2003 ; achard et al . , 2006 ) .
thus , there would be a shorter path length between any pair of neurons or brain regions , resulting in higher dynamical complexity , lower wiring costs , and resilience to tissue insults .
a scale - free network is characterized by the existence of a small number of nodes having more connections than the other nodes .
the nodes that have such a high connectivity degree are referred to as hub - nodes and are suggested to play an important role in the overall network organization ( friston and price , 2003 ) .
brain resilience may be also the final result of processes such as redundancy , degeneracy , and pluripotentiality of neural systems ( friston and price , 2003 ; noppeney et al . , 2004 ) .
another possible mechanism would be the local neurogenesis already reported in structures such as the basal ganglia , with preferential distribution in sub - regions of the ventral striatum ( stopczynski et al . , 2008 ) .
neuronal plasticity is a continuous process where the central nervous system learn skills and remember information , structure neuronal networks in response to environment , and recover from brain and spinal cord injuries , being a fundamental tool in brain resilience to lesions ( johnston , 2009 ) .
basic mechanisms that are involved in plasticity include neurogenesis , programmed cell death , and activity - dependent synaptic plasticity ( wojtowicz , 2011 ) .
clinical examples of adaptive neuronal plasticity include reorganization of cortical maps of the fingers in response to practice playing a stringed instrument and constraint - induced movement therapy to improve hemiparesis caused by stroke or cerebral palsy ( ewing - cobbs et al . , 2003 ;
hydrocephalus , congenital or acquired , represents a model of brain resilience too , once transient or permanent perfusional deficits generate structural and/or functional injuries , being partially or completely compensated by remaining cortical areas ( ewing - cobbs et al . , 2003 ) .
much evidence shows that the brain has an astounding ability to modulate cognitive and motor skills after acute insults , during insidious neurodegenerative processes , psychological stress , or even along the aging course ( price and friston , 2002 ; meunier et al .
permanent and transient lesions caused by strokes , tumors , head trauma , and hydrocephalus are good models to understand how the compensation process works , following focal or even broader damage ( price and friston , 2002 ; oliveira et al . , 2011 ) .
john lorber ( 19151996 ) , a british pediatrician recognized by his work with spina bifida and ethic issues in sheffield university , had the opportunity of attending two young children with hydrocephalus presenting with normal mental development for their age . in both children
, there was no evidence of a cerebral cortex , which was filled by csf .
one of the children died at age 3  months , the second at 12  months .
later , a young man with macrocephaly was referred to lorber ( lewin , 1980 ) .
although the boy had an iq of 126 and had a first class honors degree in mathematics , he had  virtually no brain . 
thus , he thought , there should be a tremendous amount of redundancy or spare capacity in the brain .
these ideas were shared with scientifical community in a pediatric conference in 1980 . later in the same year
additionally , norman geschwind ( 19261984 ) , an american neurologist at boston s beth israel hospital known for his works with behavioral neurology , also stated a certainty of capacity for reassigning functions following trauma and injuries in the brain , what should represent a high level of organization of cerebral tissue in order to promote adaptation ( berker et al . , 1992 ) .
other reports even generate a scientifical query in the past , where the main question was the seemingly normal brain function with remarkable images of hydrocephalus and congenital malformations ( lewin , 1980 ) .
for example , scans of a 44-year - old man s brain , showed fluid - filled ventricles , leaving little more than a thin sheet of actual brain tissue . he was married and father of two children , and worked as a civil servant .
the man went to a hospital after he had mild weakness in his left leg .
he used to have a shunt inserted into his head to drain away hydrocephalus as an infant and was removed when he was 14 .
intelligence tests showed the man had an iq of 75 , below the average score of 100 but not considered mentally retarded or disabled , either ( feuillet et al .
, we try to illustrate this scene by presenting the brain parenchyma of a normal subject followed by the brain of a normal subject with impressive hydrocephalus ( oliveira et al . , unpublished data ) and then an equally impressive hydrocephalus of a patient with profound symptoms ( oliveira et al . , unpublished data ) .
the contrast among a normal brain in a normal adult ( left ) , the brain of a normal man with impressive hydrocephalus ( oliveira et al . , unpublished data ; middle ) , and an equally impressive hydrocephalus in a 54-year - old man with deep cognitive and motor impairment since childhood ( right ; oliveira et al . , unpublished data ) .
the surprising question is that patients with very similar neuroradiological aspects may present with different and complex neurological impairments , from motor to cognitive .
some important discussions about symptoms in hydrocephalic and non - hydrocephalic patients were already reported .
previous studies of 10 sets of twins discordant for hydrocephalus in early life displayed differences in quality and quantity of development of verbal versus non - verbal cognitive functions , birth order , and hand and eye preference ( berker et al . , 1992 ) .
the differences between those discordant twins seems to indicate systematic changes in pre- , peri- , and/or early postnatal organization and development of hemispheric function ( berker et al . , 1992 )
. other study considering the development of five language domains ( word finding , fluency and automaticity , immediate sentence memory , understanding of grammar , and metalinguistic awareness ) was held in children and adolescents , 75 with hydrocephalus in the first year of life , and 50 normal controls ( dennis et al . , 1987 ) .
the results revealed a limited resilience of language to the effects of early hydrocephalus ( dennis et al . , 1987 ) .
in adult hydrocephalus , especially idiopathic normal pressure hydrocephalus ( inph ) , it is observed recover after shunting procedures , which represents proof of brain resilience ( bergsneider et al . , 2008 ; ishikawa et al . , 2008 ; ladika and gurevitz , 2011 ) .
a study displayed significant improvements at follow - up demonstrated on tests of verbal memory as well as in one test of psychomotor speed .
eight of 10 patients showed improvement by more than 1 sd on at least one memory test .
six of 10 patients improved significantly on more than 50% of the tests administered ( mcgirt et al . , 2008 ; simon et al . , 2009
patients elected for surgery and with good response after execution of tap test in the pre operatory period , usually present a remarkable recovery in cognitive and especially motor functions gradually ( oliveira et al .
, unpublished data ) . in a report , there was a significant reversal in neuropsychological test scores with increased brain volume and increased regional cerebral glucose utilization in several brain regions after shunting of inph ( simon et al .
rat models of chronic hydrocephalus suggested that disturbance in the postsynaptic integration processes , rather than axonal conduction or synaptic transmission , are more important for the production of the neurological deficits seen in chronic hydrocephalus ( kaye et al .
, it was found impaired hippocampal plasticity ( tsubokawa et al . , 1988 ) .
recent evidences also hypothesize the role played by dopamine d2 receptors in normal pressure hydrocephalus . in nph ,
d2 receptor down regulation was attenuated at 1  month after shunt surgery ( nakayama et al . , 2007 ) .
a pet study showed significant increases of glucose metabolism in the cerebral cortical areas after surgery and a micro dialysis study showed a postoperative reduction in the glutamate content of the cerebral cortex , pointing that shunting and consecutively better regional perfusion reestablish the citoarquitecture and synthesis of dopamine d2 receptors , attenuating motor dysfunctions ( nakayama et al . , 2007 ) .
therefore , several examples can be elicited to assign neural plasticity and resilience applied to hydrocephalic models , reassuming concepts of basic neurophysiology and discussing neural networks and integration , regeneration of neuronal tissue , and resilience to injuries .
degeneracy and resilience are probably continuous and simultaneous events taking part in this complex process .
we should not forget that , as long as there are large hydrocephalic , tumoral , traumatic , and ischemic samples of brain resilience and recovery , there are also cases of specific and punctiform lesions , sometimes only seem in high definition image studies , causing aggressive impairment of neurological function , even compatible with death . clinical experience and experimental models
have already shown the resistance of the brain tissue to injuries , acute or chronic .
until now , what we have summarized are pieces of individual reports and atypical manifestations of neurological diseases . doubtlessly , further multicenter investigations will be needed to clarify the infinite questions asked about neuronal tissue physiology .
the authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest .
 hydrocephalus is an entity which embraces a variety of diseases whose final result is the enlarged size of cerebral ventricular system , partially or completely . 
 the physiopathology of hydrocephalus lies in the dynamics of circulation of cerebrospinal fluid ( csf ) . the consequent csf stasis in hydrocephalus interferes with cerebral and ventricular system development . 
 children and adults who sustain congenital or acquired brain injury typically experience a diffuse insult that impacts many areas of the brain . 
 development and recovery after such injuries reflects both restoration and reorganization of cognitive functions . 
 classic examples were already reported in literature . 
 this suggests the presence of biological mechanisms associated with resilient adaptation of brain networks . we will settle a link between the notable modifications to neurophysiology secondary to hydrocephalus and the ability of neuronal tissue to reassume and reorganize its functions 
 . 
Presentation
Hypothesis
Scientifical Background
Discussion
Outcome
Conclusion
Conflict of Interest Statement