Clinical Evaluation of Hydrocephalus in Adults

Key Concepts

The Adult Hydrocephalus Clinical Research Network (AHCRN), an international registry and clinical trial network supported by the Hydrocephalus Association, adopted a pragmatic classification scheme with four categories based on distinct clinical features: transition, unrecognized congenital, acquired, and suspected iNPH. Testing of patients with suspected iNPH will lead to the identification and treatment of patients with iNPH.
iNPH is a disorder of older adults (≥60 years of age). Symptoms usually have an insidious onset, with months to years of progressive worsening of gait and balance, cognition, and urinary control (urgency, frequency, and incontinence). The clinical triad of gait disturbance, dementia, and urinary incontinence, however, is not specific to iNPH.
Gait disturbance is the most common and usually the earliest symptom in over 90% of iNPH patients. The gait and balance disorder of iNPH is characterized by difficulty getting in or out of a seat; difficulty with gait initiation, sometimes described as a magnetic gait; wide base; shuffling steps caused by reduced step height and poor foot clearance that can result in tripping, falling, or festination; slow gait velocity; and multistep turns with postural instability. Note that in Alzheimer dementia, gait impairment does not appear until the late stages. Pitfalls in evaluation of gait and balance include failure to obtain a detailed description of the nature of the gait and balance impairment from both the patient and family, failure to evaluate gait and balance during the physical examination, and failure to consider the differential diagnoses carefully in the context of the other symptoms and examination findings.
Approximately 80% of iNPH patients have cognitive impairment. Complaints range from forgetfulness to severe impairment. The Montreal Cognitive Assessment (MoCA) is an excellent screening examination when properly administered and interpreted. The previously widely used Mini-Mental State Examination is inadequate because it does not evaluate many of the executive functions that are impaired in iNPH. Pitfalls in evaluation of cognitive impairment include failure to obtain a detailed description of the nature and extent of the impairment from both the patient and family, failure to evaluate cognition during the physical examination, and failure to consider the differential diagnoses carefully in the context of the other symptoms and examination findings.
A three-stage approach can be employed when reviewing the neuroimaging for patients with suspected iNPH. The first step is to establish the presence of ventriculomegaly from hydrocephalus and differentiate it from cerebral atrophy (ex vacuo). The second step is to assess for sites of CSF flow obstruction, such as aqueductal stenosis or other obstructive lesions. The third step is to identify imaging features that suggest comorbidities, such as significant T2 or FLAIR white matter abnormalities seen with vascular dementia, cortical atrophy patterns seen with neurodegenerative dementia, or the presence of tumors, old strokes, or microhemorrhages.
Assessment and management of patients with suspected iNPH should employ the currently available guidelines utilizing objective measures of gait and cognition with CSF-based predictive tests whenever possible and CSF shunt surgery for those with positive tests demonstrating gait or cognitive improvement. Careful preoperative optimization of patients for surgery requires a multidisciplinary effort to reduce perioperative complications.

Hydrocephalus is an abnormal dilation of the cerebral ventricles caused by CSF accumulation that results from a mismatch between CSF production and resorption. Symptomatic, hydrocephalus is surgically treated either with insertion of a shunt system or performance of an endoscopic third ventriculostomy (ETV) for obstructive hydrocephalus. Hydrocephalus should be distinguished from ventriculomegaly that is secondary to loss of brain tissue from atrophy or other causes, such as encephalomalacia following traumatic brain injury or stroke.

The mean prevalence of hydrocephalus is 85/100,000 for all ages, 88/100,000 for children, 11/100,000 for adults 19 to 64 years of age, and 175/100,000 for older adults (≥65 years of age). The low reported prevalence in adults most likely reflects the limited literature for the population from young adulthood (≥19 years) through 60 years of age, apart from research specific to particular etiologies (e.g., hydrocephalus secondary to aneurysmal subarachnoid hemorrhage). The prevalence of hydrocephalus increases significantly in older adults and reaches approximately 400/100,000 in those older than 80 years of age, with some estimates as high as 5,900/100,000. Hydrocephalus is more common in older adults than in children, and although it is frequently thought to be uncommon, hydrocephalus in older adults is at least as common as primary brain tumors (209/100,000) or multiple sclerosis (302/100,000).

The approach for assessment of patients referred for possible hydrocephalus starts with a detailed clinical history and a comprehensive neurological examination. Neuroimaging is required to establish the extent of ventricular enlargement, to determine the site of obstruction of CSF circulation (if any), and to rule out other diagnoses that could contribute to the patient’s symptoms. The clinical presentation of hydrocephalus ranges from acute and life-threatening onset to subacute or chronic onset with insidious development of neurologic impairment.

Classification of category or etiology of hydrocephalus is necessary to guide further investigations required for proper patient management. During an acute clinical presentation with suspected high intracranial pressure (ICP), immediate surgical treatment of the hydrocephalus may be required; however, when the onset of symptoms is subacute or chronic, predictive testing may be performed to determine if a patient would have a favorable response to surgical treatment (i.e., a reversible neurological disorder). The objective of this chapter is to outline an approach to the clinical evaluation and treatment of adults with possible hydrocephalus.

Classification of the Adult Hydrocephalus Continuum

Adult hydrocephalus encompasses all patients older than 18 years of age who are diagnosed with the condition. However, to deal with the heterogeneity that exists within the adult hydrocephalus patient population, classification systems have evolved over the past century to encompass etiology, physiology, or anatomic and clinical presentation patterns. One of the simplest classification systems defines adult hydrocephalus as either congenital (primary), acquired (secondary), or idiopathic. Congenital hydrocephalus encompasses those causes that are present at the time birth, such as genetic defects or primary aqueductal stenosis. Secondary hydrocephalus occurs as a consequence of an identifiable antecedent event, such as infection, hemorrhage, trauma, or an obstructive mass lesion, or from iatrogenic causes (particularly after procedures at the skull base, posterior fossa, and within the ventricles). Idiopathic, as the name suggests, is used when a primary or secondary cause is unknown or not suspected.

Another commonly used classification scheme for hydrocephalus is based on the neuroimaging anatomic pattern that establishes whether the hydrocephalus is noncommunicating (obstructive, e.g., aqueductal stenosis) or communicating (nonobstructive), as determined by whether an anatomic or structural obstruction is present in the CSF pathways.

Normal pressure hydrocephalus (NPH) may be idiopathic or may be secondary to known risk factors for developing NPH. The 2005 International iNPH Guidelines define hydrocephalus from an identifiable cause (e.g., subarachnoid hemorrhage, brain trauma, aqueductal stenosis, all with a chromic presentation) as secondary NPH (sNPH). However, confusion often occurs when the term NPH is used to refer to either iNPH or sNPH, and it is therefore recommended that the term secondary NPH (sNPH) be abandoned.

Another classification scheme incorporates measured or suspected ICP: low, normal, or high. It also has some overlap with the sometimes used clinical classification that describes hydrocephalus as acute, subacute, and chronic. For example, although identification of high-pressure hydrocephalus is usually straightforward when patients have classic symptoms and signs including headache, nausea, vomiting, papilledema, abducens nerve palsy, and depressed level of consciousness, a variant referred to as acute low-pressure hydrocephalus (aLPH) on the other hand is a nuanced paradoxical phenomenon in which patients present with the same signs and symptoms of high ICP, but the measured ICP is very low or even negative.

The Adult Hydrocephalus Clinical Research Network (AHCRN), an international registry and clinical trial network supported by the Hydrocephalus Association, adopted a pragmatic classification scheme with four categories of adult hydrocephalus based on distinct clinical features: transition, unrecognized congenital, acquired, and suspected iNPH ( Fig. 43.1 ). Testing of patients with suspected iNPH will lead to the identification and treatment of patients with iNPH ^, ( Table 43.1 ).

Figure 43.1, Representative axial MR images of hydrocephalic patients with transition (A), acquired (B), unrecognized congenital (C), and suspected idiopathic normal pressure (D) forms of hydrocephalus.

TABLE 43.1

Classification of Adult Hydrocephalus

From Williams MA, Nagel SJ, Luciano MG, et al. The clinical spectrum of hydrocephalus in adults: report of the first 517 patients of the Adult Hydrocephalus Clinical Research Network registry. J Neurosurg. 2019;132(6):1773–1784.

Type of Hydrocephalus	Description
Transition	Patients treated for hydrocephalus of any etiology before the age of 18 years
Acquired	Patients with hydrocephalus secondary to known risk factors (e.g., subarachnoid hemorrhage, traumatic brain injury, brain tumor), whether treated or untreated
Unrecognized congenital	Patients with either or both imaging features and large head circumference consistent with congenital hydrocephalus, but not recognized or treated before age 18 years
Suspected idiopathic normal-pressure	Patients age ≥60 years referred for evaluation of iNPH who had not previously received surgical treatment

iNPH , Idiopathic normal pressure hydrocephalus.

Transition Hydrocephalus

Patients with transition hydrocephalus ^, ^, are adults who were treated for hydrocephalus of any cause before 18 years of age. This group includes patients with significant impairment and comorbidities as well as patients who are neurologically intact. Their function tends to be worse if they have significant comorbidities based on the etiology of their hydrocephalus (e.g., myelomeningocele, intraventricular hemorrhage) or complications of treatment that have injured the brain (e.g., shunt infection or obstruction). The prevailing pediatric neurosurgical practice for these patients involves longitudinal care with periodic clinical and intermittent imaging assessments. A similar model of longitudinal care for the adult transition population was recommended by the 2017 Hydrocephalus Association Transition Summit. Lifelong care for this population may require involvement of other adult specialists, including rehabilitation medicine, neurology, ophthalmology, pulmonology, urology, and psychiatry. An important surgical consideration is that patients in the transition category with obstructive hydrocephalus who develop shunt malfunction should be evaluated to determine if ETV is a suitable treatment option, as opposed to shunt revision. The transition of young adults with hydrocephalus from their pediatric care to the adult health care system tends to be ad hoc and haphazard. However, efforts to improve this transition process are under way.

Acquired Hydrocephalus

Patients with acquired hydrocephalus develop hydrocephalus as a consequence of known risk factors, such as subarachnoid hemorrhage (SAH), meningitis, brain tumor, trauma, or colloid cyst. These patients may or may not be treated for their hydrocephalus when first encountered in a hospital or clinic setting. Because the underlying cause of hydrocephalus in many instances can cause direct neurologic injury and impairment as well as ventriculomegaly, a major clinical challenge is to determine whether the patient indeed has hydrocephalus and should be treated surgically. Careful review of the evolution of ventricular size and morphology as well as the progression of possible hydrocephalus symptoms is recommended. Diagnostic ICP monitoring or an assessment of response to temporary CSF removal may be helpful to determine whether a shunt is indicated. For some patients, insertion of a shunt for treatment purposes may be indicated as long as the potential benefits, risks, and goals of care have been explored with the patient and family and the option of disabling the shunt is available if needed.

Unrecognized Congenital Hydrocephalus

Patients with unrecognized congenital hydrocephalus present with imaging features, large head circumference, or both that is consistent with congenital hydrocephalus that was not recognized or treated before 18 years of age. This group has previously been described with various terms including but not limited to arrested hydrocephalus, chronic hydrocephalus, syndrome of hydrocephalus in young and middle-aged adults (SHYMA), long-standing overt ventriculomegaly in adults (LOVA), and adult previously unrecognized congenital hydrocephalus (APUCH). Many patients are first identified when brain or head imaging obtained for other purposes reveals enlargement of the ventricles. When first encountered in a hospital or clinic setting, these patients may or may not have been treated. Some may appear to be asymptomatic and neurologically intact, whereas others may have a subacute or chronic clinical presentation with cognitive complaints often more prominent than gait, balance, or urinary control issues, which may be subtle rather than overt. No consensus exists with respect to treating asymptomatic or minimally symptomatic patients. Formal neuropsychological testing can be helpful to identify whether a pattern of strengths and weaknesses consistent with hydrocephalus exists and, more importantly, to demonstrate whether clinical worsening has occurred in reference to prior testing. When found, such worsening may be an indication for treatment. Asymptomatic or minimally symptomatic patients require longitudinal surveillance to assess for clinical worsening by history and by examination. Patients who are employed should be asked about their job performance reviews, as cognitive worsening may impair their ability to perform job-related tasks that they have performed for years. ^, Evidence of significant cognitive or gait impairment attributed to hydrocephalus at the initial evaluation or evidence of worsening function over time should lead to consideration of surgical treatment. A significant proportion of these patients have obstructive hydrocephalus from uncomplicated causes, such as aqueductal stenosis from a web or a tectal glioma, which when identified makes ETV a reasonable treatment option in addition to shunt surgery.

Suspected Idiopathic Normal Pressure Hydrocephalus

Suspected idiopathic normal pressure hydrocephalus is a disorder in patients older than 60 years of age with signs and symptoms of iNPH, asymptomatic patients, and patients whose symptoms are caused by other disorders. The clinical challenge is to identify those with iNPH who should be treated with shunt surgery and distinguish them from patients whose symptoms are caused by other disorders and those who should be monitored for later development of iNPH symptoms. iNPH is the most common form of adult hydrocephalus. By definition, no known underlying etiology should be present. The remainder of the chapter will focus on the evaluation and treatment of iNPH.

Idiopathic Normal Pressure Hydrocephalus

Idiopathic normal pressure hydrocephalus (iNPH) is a disorder of older adults (>60 years of age). ^, ^, The symptoms usually have an insidious onset, with months to years of progressive worsening of gait and balance, cognition, and urinary control (urgency, frequency, and incontinence). ^, The clinical triad of gait disturbance, dementia, and urinary incontinence, however, is not specific to iNPH. In fact, overreliance on the clinical triad can result in misdiagnosis as each of the primary symptoms has an extensive differential diagnosis in older adults that must be carefully evaluated ( Table 43.2 ). The first step in the diagnosis of iNPH is to exclude or treat other diagnoses that significantly contribute to the patient’s symptoms. On the other hand, patients should not be excluded from consideration of iNPH because they do not have all three symptoms of the clinical triad. Neuroimaging demonstration of ventriculomegaly is required for the diagnosis of iNPH; however, in the older adult population, ventriculomegaly associated with atrophy related to neurodegenerative disorders with similar symptoms may also be present. The international iNPH guidelines additionally recommend assessing the patient’s response to CSF removal or measurement of CSF circulatory physiology, such as CSF outflow resistance. ^, The basic injury and recovery mechanisms of neuronal and glial dysfunction associated with iNPH remain poorly understood.

TABLE 43.2

Differential Diagnosis of Suspected Idiopathic Normal Pressure Hydrocephalus

From Williams MA, Relkin NR. Diagnosis and management of idiopathic normal-pressure hydrocephalus. Neurol Clin Pract. 2013;3(5):375–385.

	Gait	Dementia	Incontinence
Disorders That may Have all Three Symptoms
iNPH, with or without comorbidities	X	X	X
Parkinsonism	X	X	X
Lewy body dementia	X	X	X
Corticobasal degeneration	X	X	X
Progressive supranuclear palsy	X	X	X
Multiple system atrophy	X	X	X
Vascular dementia	X	X	X
Neurosyphilis	X	X	X
Medication side effects	X	X	X
Multifactorial—any combination of diagnoses, with or without iNPH	X	X	X
Disorders That may Have two Symptoms
Multifactorial—any combination of diagnoses, with or without iNPH	X	X	X
iNPH, with or without comorbidities	X	X	X
Vitamin B ₁₂ deficiency	X	X
Cervical stenosis and myelopathy	X		X
Lumbosacral stenosis	X		X
Peripheral neuropathy	X		X
Disorders That may Have Only one Symptom
iNPH	X
Degenerative arthritis of the hips, knees, ankles	X
Spinocerebellar degeneration	X
Peripheral vascular disease (claudication)	X
Alzheimer dementia		X
Frontotemporal dementia		X
Depression		X
Hypothyroidism		X
Sleep apnea		X
Prostatic hypertrophy/obstructive uropathy			X
Pelvic floor abnormalities			X
Interstitial cystitis			X
Disorders That can Aggravate Other Symptoms
Visual impairment	X	X
Hearing impairment		X
Obesity	X
Cardiovascular disease	X
Pulmonary disease	X
Chronic lower-back pain	X
Vestibular disorders	X

iNPH , Idiopathic normal pressure hydrocephalus.

History and Physical Examination

Elements of the history that are particularly relevant include characterization of gait and balance, cognition, and bladder control. Gait and balance impairment usually develops before or over the same period as cognitive and urinary symptoms. Patients who do not have gait or balance impairment are highly unlikely to have iNPH, and in most instances, diagnoses other than iNPH should be evaluated first, especially if dementia is present. Each of the main symptoms of iNPH has an extensive differential diagnosis, as outlined in Table 43.2 .

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