Neuropsychological Characteristics of Idiopathic Normal Pressure Hydrocephalus

The neuropsychological presentation in INPH manifests as a pattern of prominent frontal subcortical dysfunction. Deficits are observed in memory, executive functions, attention and concentration, and processing speed. The extent and severity of cognitive impairments can range from mild, largely undetectable changes to more widespread impairments or advanced dementia. Early cognitive symptoms in INPH typically present as mild frontal systems dysfunction but can progress to a severe frontal dysexecutive syndrome when left untreated. Advanced cases without intervention may become indistinguishable from other forms of dementia, making differential diagnosis a challenge. The presence of cortical deficits such as aphasia, agnosia, and alexia is not uncommon in advanced INPH, but when these features are observed early on or as one of the primary features, this would be a strong indicator of an alternate diagnosis or significant comorbid disease. The onset, duration, and pattern of progression of cognitive symptoms are critical factors that neuropsychologists consider in the differential diagnosis. Below is a detailed description of the neuropsychological sequelae associated with symptomatic INPH broken down by specific cognitive domain:

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  Attention/Executive/Psychomotor: Deficiencies in attention, working memory, set-shifting, response inhibition, and other aspects of executive functioning are commonly observed in INPH and can be seen early in the disease course. In a large European trial, impairment at baseline compared with controls was observed on the Stroop Color Word Test, a test of complex attention and response inhibition. Others have demonstrated impairments in complex attention and set-shifting on Trailmaking A and B, ^, Symbol Digit Modalities, as well as measures of executive skills such as verbal fluency and recitation of digits backward.

  
  
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  Memory: Memory deficits observed in the early stages of INPH are characterized predominantly by difficulty acquiring new information and retrieval as opposed to rapid forgetting of information. This is typically secondary to deficits in the organization and efficient processing of information. Learning of new information can also be impaired in INPH, but performance typically improves with repeated trials and when organizational strategies are provided. ^{, ,} Delayed recall is typically facilitated by cueing, and performance on recognition memory paradigms (forced choice) is usually spared, suggesting preserved memory storage. Comparison of INPH patients and controls on word list learning tasks revealed decrements in learning and delayed recall. ^, Memory for verbal contextual material, such as story recall, has also been shown to be compromised. Visual memory skills have not been widely studied, but some investigations including nonverbal memory paradigms have demonstrated impaired learning and recall of visual stimuli, ^, whereas others have shown that visual memory is less likely to be impacted than verbal memory.

  
  
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  Language: Basic language skills such as naming are relatively preserved in patients with INPH; however, deficits are observed in more complex language tasks that rely heavily on executive functions or processing speed. When compared with patients with Alzheimer’s disease (AD) and normal controls on letter fluency tests, patients with INPH perform more poorly than both groups. On measures of semantic fluency, however, patients with INPH perform worse than healthy controls but comparable to patients with AD or Parkinson’s disease. ^,

  
  
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  Visuospatial: Impairments have also been observed in visuospatial and visuocontructive skills. INPH patients had greater difficulty than both normal controls and AD patients on tasks of visual counting and visual discrimination, suggesting impairment in visual form perception or constructive function. Ogino and colleagues showed INPH patients had poorer performance compared with patients with AD on block design, a visuocontructional task. It is important to note, however, that this task is timed and the speeded motor requirement may partially explain the decrement observed in INPH patients. Impairments have also been found in INPH patients when asked to draw a clock, demonstrating visuospatial disturbances as well as frontal dysfunction as the task requires planning, fund of knowledge, and self-monitoring. An interesting case reported by Otani and colleagues described deficits in higher-order visual functions such as facial recognition, spatial orientation, and object recognition which reversed after shunt placement. More work is needed to determine whether visuospatial deficits in INPH reflect a true underlying impairment in the processing of visual information or may be secondary to motor and executive impairment.

  
  
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  Motor skills: Given that motor impairment is a cardinal feature of INPH, it is not surprising that these patients exhibit deficits in motor speed, fine motor coordination, and motor precision. Deficits in fine motor coordination on measures such as the Grooved Pegboard and Perdue Pegboard tests have been widely documented. Impairments have also been demonstrated in simple motor speed on standardized tests of tapping ability. In addition, deficits were observed in motor precision on Serial Dotting and Line Tracing, 2 nonstandardized tests of motor speed and precision. ^,

  
  
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  Psychiatric Presentations and Mood Factors: Psychiatric disturbances in association with INPH have been reported mostly in case studies but may exist in as many of 71% of patients. A study of 64 INPH patients found apathy was the most frequently observed neuropsychiatric symptom, followed by anxiety and aggression. While atypical, psychiatric symptoms can emerge as a presenting feature complicating the differential diagnosis. There have been case reports of INPH presenting with depression, ^, anxiety, bipolar mania, psychosis, ^, aggressivity, ^, and obsessive-compulsive disorder. It is important to recognize the behavioral disturbances associated with INPH, since they may be refractory to conventional pharmacologic treatment and may, in some cases, be responsive to shunt placement, although this has not been systematically studied. ^,

Neuropsychological Characteristics of Secondary Hydrocephalus

SH can result from a wide range of conditions that disrupt the normal flow or absorption of cerebrospinal fluid (CSF), leading to increased intracranial pressure and ventriculomegaly. Common etiologies include neoplastic causes (eg, benign and malignant brain tumors, and other masses), vascular issues (nontraumatic subarachnoid hemorrhage, intraventricular adhesion, cerebellar hemorrhage or infarction, and cerebral ischemia), infectious or inflammatory conditions (meningitis/ventriculitis, brain abscess, encephalitis, central nervous system [CNS] vasculitis), trauma-related origins (head trauma, craniotomy not associated with traumatic brain injury [TBI]), and other neurologic disorders (chronic subdural hematoma, neurodegeneration such as possible Alzheimer’s dementia, aqueductal stenosis, acquired obstructive hydrocephalus, and postirradiation atrophy). ^, Each of these causes can lead to significant damage to the brain, which is compounded by the presence of hydrocephalus. The origin and underlying cause of hydrocephalus play a critical role in determining both the prognosis and the cognitive outcomes of patients. For instance, an individual with hydrocephalus secondary to an infection like meningitis may experience more severe global brain damage compared with someone whose hydrocephalus is caused by a slowly growing CNS tumor. This pre-existing damage, coupled with the effects of hydrocephalus itself, heavily influences developmental and cognitive outcomes, making it a key consideration in clinical management.

The cognitive and developmental outcomes of patients with SH are highly variable due to the diverse nature of its causes and the complex interplay between brain injury and raised intracranial pressure. While some research suggests that the patients with SH may present with mild impairments in executive functioning, visuospatial skills, and memory, these deficits are not universal and often depend on the extent of damage caused by the initial injury. For example, intraventricular hemorrhage may result in more localized brain damage, while TBI may cause diffuse axonal injury, both of which have different neuropsychological consequences. Additionally, the presence of other comorbid conditions such as hypoxia, recurrent infections, or additional episodes of trauma can further complicate the clinical presentation. As a result, there is no single cognitive profile for patients with acquired hydrocephalus. Instead, each case must be considered individually, carefully considering the underlying pathology, the location and severity of brain injury, and any concurrent neurologic issues. This variability underscores the importance of comprehensive, individualized neuropsychological assessments to guide treatment and long-term care strategies.

Neuropsychological Characteristics of Unrecognized Congenital Hydrocephalus

Unrecognized congenital hydrocephalus (UCH), sometimes known as long-standing overt ventriculomegaly in adults is typically characterized by enlarged head circumference and/or ventriculomegaly of the third and lateral ventricles. UCH is believed to originate in infancy and present asymptomatically or very mildly, often going undetected until early or late adulthood. Its etiology remains unclear, in many cases unknown, but more recent evidence from registry data from the Adult Hydrocephalus Clinical Research Network found 2/3 of UCH patients had aqueduct stenosis. Like normal pressure hydrocephalus (NPH), clinical features of UCH can include abnormalities in gait, urinary incontinence, and cognitive decline; however, there is a significant variability in severity as many patients with UCH are unaware of their ventriculomegaly until incidentally discovered after a head CT for other causes (eg, concussion), so initially are asymptomatic. In fact, in the largest registry to date for UCH patients, it was found that 63% of these patients were untreated at enrollment. From a neurosurgical standpoint, the challenge with UCH patients with minimal to no symptoms is whether treatment is warranted.

Much of our current understanding of the relationship between hydrocephalus and cognition is that it is associated with a “subcortical” or frontostriatal pattern of deficits, such as slowed processing speed, inefficient encoding or learning of new information, and executive dysfunction, but with relatively spared retention, language, and visuospatial abilities. ^, This conceptualization is derived predominantly from research on survivors of pediatric-onset populations, such as spina bifida, or on older adults with INPH. Unfortunately, neuropsychological research on adults with UCH has yielded more variable results and is significantly confounded by methodological issues. For instance, much of the earliest research is difficult to generalize as it was limited to case studies and samples of only a handful of participants, which also revealed highly variable baseline neuropsychological deficits ranging from mild, isolated memory deficits to broader impairments in learning efficiency, attention, visuospatial skills, and executive dysfunction. ^, Relatively larger samples have been incorporated in more recent research, which revealed baseline deficits more predominantly in attention and memory; however, these results were yielded from a minimal neurocognitive battery that lacked the variance and sensitivity to best encapsulate comprehensive cognitive abilities. Furthermore, while a distinct neuropsychological profile for UCH remains allusive, there is some evidence to suggest that asymptomatic UCH may make the brain more vulnerable to age-related cognitive decline over time, ^, and the development of symptomatic NPH. ^, As such, longitudinal, comprehensive neuropsychological studies are needed to understand the unique cognitive impact of untreated UCH in adulthood as well as its effects on aging and cognition.

Neuropsychological Characteristics of Transitional Hydrocephalus

Patients defined with TH include those with identified pediatric-onset hydrocephalus that survived into adulthood. This category includes patients with a wide range of outcomes, from significant impairment and comorbidities to normal functioning. This variability reflects common patterns in pediatric hydrocephalus, where the underlying cause of the condition can directly lead to neurologic impairment. However, while largely based on patients with spina bifida (SB) with and without hydrocephalus (which confounds generalizability to other etiologies), specific cognitive challenges in fluid intelligence, visuospatial skills, executive functioning, and nonverbal reasoning abilities, but with relatively spared verbal abilities are not uncommon in this population. ^, Individuals with TH may also show impairments in assembled processing, which involves integrating information across domains for tasks like mental rotation, but still retain relative strengths in “associative processing,” such as categorizing information. Educational attainment in this group also tends to be significantly lower than adults with other forms of hydrocephalus, which is likely due to intellectual developmental delays caused by the hydrocephalus, or its treatment, at an early age. Therefore, while the SB literature offers insights into potentially common cognitive deficits in children with congenital hydrocephalus that may persist into adulthood and TH, no specific neuropsychological pattern has been identified due to the variability in etiology, treatment rates, and comorbidities affecting cognitive development.

Neuropsychological Treatment Outcomes of Idiopathic Normal Pressure Hydrocephalus

Research into the effects of shunting on patients with INPH shows variable cognitive outcomes, ranging from significant improvements to more modest changes. Studies such as those by Poca and colleagues and Raftopoulos and colleagues indicate that a considerable proportion of patients experience cognitive gains postshunting, with Hellstrom and colleagues reporting over 80% of patients exhibiting improvements. However, Thomsen and colleagues and Katzen and colleagues found a lower improvement rate of around 40%, suggesting a broad range of responses to the treatment. This variability may be linked to the severity of symptoms before treatment, where those with milder symptoms often show greater improvements, potentially due to less extensive neural damage. ^,

Some evidence exists to suggest that specific cognitive domains, such as verbal memory and psychomotor speed, are more responsive to shunting. Duinkerke and colleagues and Chaudhry and colleagues documented notable improvements in these areas, including immediate and delayed verbal learning and visuospatial performance. Conversely, improvements in executive functions appear inconsistent across different studies. For example, Mataro and colleagues observed significant enhancements in verbal memory and visuoconstructive skills, yet some memory measures and attention did not show significant change after intervention. Even among INPH patients with overlapping AD, cognitive improvements have been observed postshunting, suggesting some recovery of function in these patients as noted by Golomb and colleagues.

Despite these advancements, predicting which patients will benefit most from shunting remains challenging. Savolainen and colleagues highlighted that while physical symptoms like gait and urinary control consistently improve, only specific neuropsychological tests, such as word recognition, effectively differentiate patients who will show cognitive improvements postshunt. Beyond cognitive aspects, shunt surgery significantly enhances the quality of life with a large percentage of patients reporting marked improvements in life quality and independence. However, the correlation between improved mobility and self-reported quality of life is stronger than that with cognitive improvements, which tend to recover more slowly and variably postoperatively. This underscores that while patients readily acknowledge physical improvements, the impact of cognitive gains may not be as immediately perceptible or impactful to their overall well-being, especially in the first year following surgery.

Overall, while shunting is effective for many patients in improving cognitive function, the degree of improvement can vary based on the severity of the symptoms, duration of disease before treatment, degree of cerebrovascular burden and other comorbidities, and the number of cognitive domains affected. Further studies, including randomized control trials, are needed to optimize patient selection and predict treatment outcomes.

Neuropsychological Treatment Outcomes in Other Adult Hydrocephalus Subtypes

Neuropsychological outcomes following the treatment for other forms of hydrocephalus vary significantly given the range of etiologies, medical complications, and treatments, both for hydrocephalus and other comorbidities (eg, chemoradiation for tumor). As such, given the limited scope of this article, outcomes reviewed are limited to the most common, broader etiologies including post-traumatic hydrocephalus (PTH) and brain tumor, which represent the most common forms of SH in adults.

PTH is a treatable complication of TBI, resulting from impaired CSF flow, causing ventricular enlargement. PTH occurs in up to 45% of cases involving subarachnoid hemorrhage, intraventricular hemorrhage, diffuse axonal injury, or cortical contusions during inpatient rehabilitation. Cognitive impairments in PTH are diverse, reflecting the variability of affected brain regions from initial injury and secondary complications. ^, While no uniform neuropsychological profile exists, early identification and treatment, particularly with ventricular shunting, are crucial for improving recovery outcomes. Timely intervention during inpatient rehabilitation can enhance cognitive functions and recovery metrics, underscoring the need for vigilant monitoring and early diagnostic assessments to ensure interventions provide maximum benefit.

Tumoral hydrocephalus, prevalent in posterior fossa brain tumors, occurs in 10% to 70% of surgically resected cases due to obstruction of CSF pathways. Cognitive outcomes vary based on tumor type, location, and treatment approach, with posterior fossa tumors affecting regions critical for cognitive processing and motor control. While shunting or endoscopic third ventriculostomy can relieve intracranial pressure, these treatments do not address underlying brain damage caused by tumor growth. High-grade gliomas and metastatic diseases, though less frequently associated with hydrocephalus (5%–10%), can also impair cognition through direct brain invasion or SH effects. ^, Although cognitive improvements are common post-treatment, challenges in motor coordination, emotional regulation, and cognitive flexibility may persist, particularly if hydrocephalus is untreated for a prolonged period.

Neuropsychological Evaluation as a Diagnostic Tool

As part of a standard diagnostic work-up of INPH, a comprehensive neuropsychological evaluation should be performed to fully characterize the cognitive presentation and provide key information for differential diagnosis and to inform treatment decisions ( Table 1 ). This is especially important for cases where there may be a concern about comorbid disease but is also invaluable for any patient being referred for treatment. A detailed neuropsychological assessment will document the baseline cognitive profile so that follow-up assessments can be conducted to monitor treatment response. In cases where significant comorbid disease is suspected to be underlying the cognitive dysfunction, expectations for cognition improvement following treatment will be measured; however, comorbidities are not a contraindication for intervention. In fact, improvements in gait alone can lead to substantial benefits in patient independence and quality of life, as well as reducing caregiver burden, even when cognitive gains are minimal.

Table 1

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