A CT scan plays a crucial role in identifying hydrocephalus that mimics dementia by revealing characteristic changes in the brain’s ventricular system and cerebrospinal fluid (CSF) spaces, which can be difficult to distinguish from other causes of cognitive decline such as neurodegenerative dementias. Hydrocephalus, particularly normal pressure hydrocephalus (NPH), often presents with symptoms similar to dementia—memory problems, difficulty walking, and urinary incontinence—making imaging essential for accurate diagnosis.
Hydrocephalus involves an abnormal accumulation of cerebrospinal fluid within the brain’s ventricles, leading to their enlargement. On a CT scan, this enlargement is visible as dilated lateral and third ventricles that are disproportionately large compared to the surrounding brain tissue and cortical sulci. This disproportion helps differentiate hydrocephalus from brain atrophy, where ventricles may appear enlarged but in proportion to widened sulci due to loss of brain tissue. In hydrocephalus, the ventricles expand because of excess fluid, not because of tissue loss, which is a key distinction when interpreting CT images.
Several specific CT features help identify hydrocephalus mimicking dementia:
– **Ventriculomegaly**: The lateral and third ventricles appear enlarged beyond what is expected for the patient’s age. This can be quantified using measurements like the Evans index, which compares the width of the frontal horns of the lateral ventricles to the widest diameter of the skull. An Evans index greater than 0.3 suggests hydrocephalus.
– **Disproportionate enlargement of ventricles relative to sulci**: Unlike in typical brain atrophy, the cortical sulci, especially at the vertex (top of the brain), may appear compressed or effaced, indicating that the brain tissue is being pushed outward by increased CSF volume rather than lost.
– **Widening of specific CSF spaces**: The Sylvian fissures and insular cisterns may appear abnormally widened, a pattern sometimes called disproportionately enlarged subarachnoid space hydrocephalus (DESH). This pattern is characteristic of normal pressure hydrocephalus and helps distinguish it from other dementias.
– **Morphological changes in brain structures**: The corpus callosum, a thick band of nerve fibers connecting the brain’s hemispheres, may be bowed upward or stretched due to ventricular enlargement. The third ventricular floor may bulge downward, and the temporal horns of the lateral ventricles may be dilated and rounded.
– **Effacement of subarachnoid spaces**: The spaces around the brain, particularly at the convexities, may appear shrunken or obliterated, which contrasts with the widened sulci seen in brain atrophy.
These CT findings are important because hydrocephalus, especially normal pressure hydrocephalus, is potentially reversible with appropriate treatment such as CSF shunting. This contrasts with most dementias, which are progressive and currently irreversible. Therefore, identifying hydrocephalus on CT can lead to interventions that improve symptoms and quality of life.
CT scans are often the first imaging modality used because they are widely available, quick, and effective at showing ventricular size and gross anatomical changes. However, CT is less sensitive than MRI for subtle changes and for assessing CSF flow dynamics, but it remains invaluable for initial evaluation and in emergency settings.
In some cases, hydrocephalus can present with low intracranial pressure despite enlarged ventricles, known as low-pressure hydrocephalus. CT imaging in these cases shows markedly enlarged ventricles with signs of brain tissue compression, but standard shunt treatments may be ineffective unless carefully managed with specialized drainage techniques.
In summary, a CT scan helps identify hydrocephalus mimicking dementia by revealing enlarged ventricles disproportionate to cortical atrophy, characteristic patterns of CSF space changes, and morphological alterations of brain structures. These imaging features guide clinicians towar
