Normal pressure hydrocephalus (NPH) is a condition that can cause dementia-like symptoms, and it is characterized by an abnormal buildup of cerebrospinal fluid (CSF) in the brain’s ventricles, leading to their enlargement without a significant increase in pressure. Detecting NPH as a cause of dementia involves a combination of clinical evaluation and brain imaging, with CT scans playing an important role in the diagnostic process.
CT scans can detect the characteristic enlargement of the brain’s ventricles seen in NPH. This ventricular enlargement is a key radiological sign, but it must be carefully distinguished from ventricular enlargement caused by brain atrophy, which is common in other types of dementia. In NPH, the ventricles are enlarged due to impaired CSF flow dynamics rather than loss of brain tissue. On CT images, radiologists look for specific features such as an increased size of the lateral ventricles, especially the frontal horns, and the temporal horns of the lateral ventricles being dilated beyond a certain threshold. The bicaudate index, which measures the width of the lateral ventricles relative to the brain width, is often used as a quantitative marker. A bicaudate index larger than the 95th percentile for a person’s age suggests ventricular enlargement consistent with hydrocephalus.
Other subtle signs on CT that support the diagnosis of NPH include the “disproportionate enlargement” of the ventricles compared to the sulci on the brain surface. In NPH, the sulci over the vertex (top of the brain) may appear compressed or effaced, while the Sylvian fissures (deep grooves on the brain surface) are often dilated. This pattern, sometimes called the “disproportionate sulcal enlargement” or “dish sign,” helps differentiate NPH from cortical atrophy where sulci are typically enlarged. Additionally, the shape and angle of the corpus callosum (the band of nerve fibers connecting the brain’s hemispheres) can be altered in NPH, with a reduced angle indicating ventricular stretching.
While CT scans provide valuable structural information and are widely available, they have limitations compared to MRI. MRI offers better soft tissue contrast and can more clearly show the brain structures and CSF spaces, helping to exclude other causes of dementia such as tumors or vascular lesions. MRI can also detect subtle changes in white matter and CSF flow dynamics that CT cannot. However, CT remains a practical first-line imaging tool, especially when MRI is contraindicated or unavailable.
Importantly, imaging findings alone are not sufficient to diagnose NPH definitively. Clinical symptoms must be present, typically a triad of gait disturbance, cognitive impairment (dementia), and urinary incontinence. The diagnosis is supported by clinical assessment and may be confirmed by CSF testing, such as a lumbar puncture to measure CSF pressure and observe symptom improvement after CSF removal.
In summary, CT scans can detect the ventricular enlargement and other radiological signs suggestive of normal pressure hydrocephalus, making them a useful tool in identifying NPH as a potential cause of dementia. However, CT findings must be interpreted alongside clinical symptoms and further testing to establish the diagnosis and guide treatment decisions.
