Understanding "Ex Vacuo" on Brain CT Reports
"Ex vacuo" on a CT brain report indicates that ventricular enlargement or CSF spaces are passively expanding to fill the void left by lost or atrophied brain tissue, rather than being caused by obstructive hydrocephalus or increased intracranial pressure. 1
What Ex Vacuo Means
The term "ex vacuo" literally means "from a vacuum" and describes abnormal collections of cerebrospinal fluid (CSF) that replace brain tissue which is absent or has disappeared due to various pathological processes. 1 This is fundamentally different from hydrocephalus caused by CSF flow obstruction.
Key Distinguishing Features
Ex vacuo changes represent compensatory expansion of CSF spaces secondary to brain parenchymal loss, not active CSF accumulation under pressure. 1 The clinical significance may be minimal despite impressive radiological findings, as the ventricular enlargement is simply filling space where brain tissue once existed. 1
Common Underlying Causes
Brain tissue loss leading to ex vacuo changes can result from:
- Neurodegenerative diseases causing progressive brain atrophy (Alzheimer's disease, frontotemporal dementia, vascular dementia) 2
- Cerebrovascular events including large territory infarctions with subsequent encephalomalacia 2
- Traumatic brain injury with resultant tissue loss 1
- Infections such as encephalitis causing tissue destruction 2, 1
- Congenital maldevelopment or porencephaly 1
- Chronic ischemic changes with white matter disease and cortical atrophy 2
Radiological Differentiation from True Hydrocephalus
Hydrocephalus Ex Vacuo vs. Hydrostatic Hydrocephalus
The critical distinction is whether ventricular enlargement is due to brain atrophy (ex vacuo) or CSF flow obstruction (hydrostatic). 3 This differentiation has major treatment implications, as only hydrostatic hydrocephalus benefits from CSF shunting.
In hydrostatic (obstructive) hydrocephalus, CT shows: 3
- Temporal horn tips visualized and measuring ≥2 mm width
- Frontal horn ratio ≥0.50 with symmetric enlargement
- Effaced or compressed cortical sulci and fissures (key finding)
- Periventricular edema may be present
In hydrocephalus ex vacuo, CT shows: 3
- Ventricular enlargement proportionate to sulcal prominence
- Visible and often widened cortical sulci and fissures (key distinguishing feature)
- Cortical atrophy with brain volume loss 2
- No periventricular edema
Normal Pressure Hydrocephalus Considerations
When evaluating suspected normal pressure hydrocephalus (NPH), the presence of ex vacuo changes argues against the diagnosis. 2, 4 NPH characteristically shows:
- Ventriculomegaly disproportionate to sulcal enlargement
- Effaced sulci along high convexities with widened Sylvian fissures (DESH pattern) 2, 4
- Narrowed posterior callosal angle 2, 4
If sulci are prominently visible alongside ventricular enlargement, this suggests ex vacuo changes from atrophy rather than NPH. 2, 3
Clinical Implications and Management
When Ex Vacuo Changes Matter
Despite often being radiologically impressive, ex vacuo changes may have minimal clinical significance if the underlying brain injury is stable. 1 However, certain contexts require attention:
In congenital toxoplasmosis, the distinction between reversible obstructive hydrocephalus and hydrocephalus ex vacuo is prognostically important—outcomes are poor when ex vacuo changes are present with elevated CSF protein, indicating irreversible brain damage. 2
Ex vacuo collections can occasionally develop expansive tendencies through mechanisms not fully understood, potentially requiring surgical intervention. 1
What Not to Do
Do not perform CSF shunting for ex vacuo ventricular enlargement, as this represents compensatory expansion for brain tissue loss, not obstructed CSF flow requiring diversion. 1, 3 Shunting will not improve symptoms caused by the underlying brain atrophy.
Do not confuse ex vacuo changes with NPH—the presence of prominent sulci alongside ventricular enlargement indicates atrophy, not the disproportionate ventriculomegaly characteristic of NPH. 2, 4, 3
Practical Diagnostic Approach
When you see "ex vacuo" reported:
Correlate with clinical presentation—look for symptoms of the underlying cause (dementia, prior stroke, infection history) rather than symptoms of increased intracranial pressure 2
Review imaging for sulcal prominence—visible, widened sulci confirm ex vacuo rather than obstructive process 3
Identify the underlying etiology—look for evidence of infarction, white matter disease, cortical atrophy pattern, or other structural brain lesions 2, 1
Assess for complications—rarely, ex vacuo collections can become expansive and symptomatic 1
The key clinical message: ex vacuo ventricular enlargement reflects brain tissue loss and does not require CSF diversion procedures. 1, 3 Treatment should target the underlying cause of brain atrophy or injury, not the compensatory CSF space enlargement.