What Is Intracranial Hypertension?

Intracranial hypertension refers to a sustained elevation of the pressure inside the cranial cavity, where the brain, cerebrospinal fluid (CSF), and blood vessels are enclosed within the rigid skull. Because the skull has a fixed volume, any increase in the volume of brain tissue, blood, or CSF can raise the pressure, potentially impairing blood flow, damaging the optic nerves, and causing neurological dysfunction. Raised intracranial pressure can arise from a mass lesion, infection, trauma, or blocked CSF pathways, but two prominent clinical entities are frequently discussed under this umbrella: idiopathic intracranial hypertension and normal pressure hydrocephalus.

IIH and Pseudotumor Cerebri

The condition historically called benign intracranial hypertension (BIH) is now more accurately termed idiopathic intracranial hypertension (IIH), though the name pseudotumor cerebri still appears in practice because the clinical presentation can mimic a brain tumour. The term "benign" was abandoned because the disorder is by no means harmless: raised pressure can cause progressive and sometimes permanent visual loss. IIH predominantly affects young, obese women, but it can also occur in men and children. The pressure elevation occurs in the absence of a tumour, infection, or hydrocephalus, and the cause remains poorly understood despite numerous theories involving impaired CSF absorption and elevated venous sinus pressure.

Symptoms of IIH

• Headache that is often diffuse, throbbing, and worse on waking or with changes in posture
• Papilloedema, or swelling of the optic disc, detected on eye examination
• Transient visual obscurations, sometimes triggered by bending over or coughing
• Pulsatile tinnitus, commonly described as a whooshing sound in time with the heartbeat
• Diplopia due to sixth nerve palsy
• Nausea and dizziness

Because many symptoms overlap with those of more common neurological disorders, the diagnosis of pseudotumor cerebri requires a careful exclusion of alternative causes. Neuroimaging, especially magnetic resonance imaging of the brain, is performed to rule out a mass lesion or venous sinus thrombosis. A lumbar puncture revealing an elevated opening pressure with normal CSF composition strongly supports the diagnosis. Some patients also exhibit empty sella syndrome or flattened posterior sclera as indirect radiological markers of chronic raised pressure.

Treatment of IIH

Management of IIH aims to protect vision and relieve symptoms. Weight loss is a cornerstone of therapy, and even modest reduction in body mass has been shown to lower CSF pressure. The carbonic anhydrase inhibitor acetazolamide reduces CSF production and is frequently the first-line medication. When medical therapy fails, or when visual loss is rapid and severe, surgical intervention may be needed. Optic nerve sheath fenestration can preserve vision, while a CSF diversion procedure, such as a lumboperitoneal or ventriculoperitoneal shunt, provides a direct pathway for excess fluid to drain. The insertion of a shunt can be highly effective, but it also carries risks of infection, obstruction, overdrainage, and the need for repeated revision surgery.

Normal Pressure Hydrocephalus

Normal pressure hydrocephalus (NPH) presents a striking contrast to IIH in its pressure profile, yet it is still a disorder of CSF dynamics and is often considered within the differential diagnosis of intracranial hypertension. In NPH, the cerebral ventricles are enlarged and CSF pressure measured by lumbar puncture may be within the normal range, but the fluid nevertheless fails to circulate and be absorbed properly. This leads to a characteristic clinical syndrome that is frequently mistaken for more common neurodegenerative diseases or for other causes of gait disturbance.

The Classic Triad

NPH classically presents with a triad of ataxia, incontinence, and dementia. The gait disturbance is the most prominent and often the earliest feature, with patients displaying an apraxic gait. This is not a simple imbalance due to cerebellar degeneration; rather, the patient appears to have forgotten how to initiate walking. The feet seem glued to the floor, with short, shuffling steps, difficulty lifting the toes, and a wide base of support. Turning may be particularly difficult, and the patient may freeze when attempting to start walking. Unlike a typical cerebellar ataxia, the apraxic gait of NPH improves when the patient is asked to perform the movement while sitting or cycling the legs in the air, because the motor planning pathways are partially preserved.

Urinary urgency and frequency typically precede true incontinence, which eventually develops as the ventriculomegaly distorts the frontal lobe pathways controlling micturition. The cognitive component, often described as a subcortical or frontal dementia, includes psychomotor slowing, apathy, impaired attention, and executive dysfunction rather than prominent memory loss. Depression is also common. The severity of each component varies considerably from person to person, and imaging frequently reveals periventricular white matter changes alongside the enlarged ventricles.

Diagnostic Evaluation

Recognising NPH is essential because, unlike Alzheimer disease or Parkinson disease, it is a potentially treatable cause of dementia and gait impairment. Brain imaging demonstrates ventricular enlargement out of proportion to cortical atrophy. A lumbar puncture with measurement of opening pressure is important to distinguish NPH from high-pressure hydrocephalus, and many clinicians perform a "tap test" in which a large volume of CSF is removed and the patient is observed for improvement in walking speed, stride length, and cognitive function. A positive response to the tap test increases the likelihood that a shunt will bring lasting benefit, although a negative test does not entirely exclude the diagnosis.

Treatment of NPH

The definitive treatment for normal pressure hydrocephalus is surgical placement of a shunt system that diverts CSF from the ventricles to the peritoneal cavity, and occasionally to the atrium or pleural space. A programmable shunt valve allows the neurosurgeon to adjust the drainage pressure non-invasively in response to clinical symptoms or signs of overdrainage. In carefully selected patients, shunt surgery can produce dramatic improvement, particularly in the apraxic gait, which often recovers within days or weeks. Incontinence and dementia also improve, although they may do so more slowly and incompletely. The decision to operate requires balancing potential benefit against the risk of subdural haematoma, infection, and shunt malfunction, especially in elderly patients who are the typical candidates for this procedure.

Distinguishing the Conditions

Although NPH and IIH both involve disordered CSF physiology, they differ in epidemiology, pressure measurements, and clinical presentation. IIH occurs most often in young obese women and produces headache, papilloedema, and visual disturbance, whereas NPH affects older adults and is characterised by the triad of ataxia, incontinence, and dementia without headache or papilloedema. The two conditions can occasionally coexist or mimic one another, and a careful history, ophthalmological assessment, and pressure measurement are indispensable. The historical label BIH should be abandoned because it minimises the visual risk faced by patients with pseudotumor cerebri, and the term NPH itself is something of a misnomer because the pressure is not always normal at the moment of measurement and is far from physiologically normal in its effects on brain tissue.

Shared Management Themes

In both IIH and NPH, the shunt has transformed outcomes for many patients who would otherwise experience irreversible disability. However, a shunt is not a universal answer, and its long-term performance depends upon careful patient selection, surgical expertise, and vigilant follow-up for complications. For the patient presenting with an apraxic gait, cognitive slowing, and urinary symptoms, the possibility of NPH must be actively explored rather than dismissed as inevitable ageing. Likewise, the young patient with persistent headache and visual complaints deserves a prompt ophthalmological examination for papilloedema so that IIH can be diagnosed before the optic nerves suffer permanent injury.

Conclusion

Intracranial hypertension embodies a spectrum of CSF pressure disorders, from the frankly elevated pressure of idiopathic intracranial hypertension and pseudotumor cerebri to the normal static pressure but abnormal pulsatile dynamics of normal pressure hydrocephalus. While their clinical pictures differ greatly, they share a unifying principle: disturbances in the production, circulation, or absorption of cerebrospinal fluid can exert profound effects on the brain and spinal cord. Awareness of the distinguishing features, including the apraxic gait of NPH and the headache and visual symptoms of IIH, allows earlier diagnosis and more effective intervention. With appropriate treatment, often involving CSF diversion through a shunt, many patients experience meaningful recovery of mobility, continence, cognition, and comfort.