From the Guidelines
To ensure it's safe to proceed with a Lumbar Puncture (LP), a CT head scan should be examined for signs of increased intracranial pressure (ICP), including midline shift, mass effect, ventricular compression or effacement, cerebral edema, loss of sulci and gyri differentiation, compression of basal cisterns, and hydrocephalus, as these findings suggest elevated ICP and increase the risk of brain herniation during LP 1. When evaluating a CT head scan for increased ICP, it's crucial to look for specific signs that may indicate a risk for brain herniation. These signs include:
- Midline shift
- Mass effect
- Ventricular compression or effacement
- Cerebral edema
- Loss of sulci and gyri differentiation
- Compression of basal cisterns
- Hydrocephalus Other concerning findings on a CT head scan include space-occupying lesions such as tumors, abscesses, or large hemorrhages, as well as evidence of obstructive hydrocephalus 1. The presence of any of these findings on a CT head scan suggests elevated ICP and increases the risk of brain herniation during lumbar puncture. In such cases, the lumbar puncture should be postponed until ICP is managed or alternative diagnostic approaches should be considered 1. Even with a normal CT, clinical signs of increased ICP, such as severe headache, altered mental status, papilledema, and focal neurological deficits, should prompt caution, as CT may occasionally miss early signs of increased pressure 1. It's also important to note that a CT scan should only be performed if there are clinical signs suggestive of a shift of brain compartments, such as focal neurological signs and a reduced Glasgow Coma Scale (GCS) score 1. In general, a lumbar puncture can be performed without prior neuroimaging if the GCS is >12, but those with a GCS ≤12 will require a brain scan before LP 1.
From the Research
Signs of Increased Intracranial Pressure (ICP) on CT Head Scan
To ensure it's safe to proceed with a Lumbar Puncture (LP), the following signs of increased ICP should be looked for on a Computed Tomography (CT) head scan:
- Lateral shift of midline structures 2
- Loss of the suprachiasmatic and basilar cisterns 2
- Obliteration of the fourth ventricle 2
- Obliteration of the superior cerebellar and quadrigeminal plate cisterns with sparing of the ambient cisterns 2
- Sulcal obliteration 3
- Lateral ventricle compression 3
- Third ventricle compression 3
- Midline shift 3
- Herniation 3
Clinical Predictors of Increased ICP
The following clinical predictors can be used to identify patients with increased ICP:
Importance of CT Scan Before LP
A CT scan before LP can help identify patients with increased ICP and prevent potential complications such as herniation 5, 2, 6. However, the decision to perform a CT scan before LP should be based on individual patient risk factors and clinical judgment 5, 4.