As with any procedure, there are times when it is not safe to proceed with lumbar puncture. These contraindications are:

• Skin infection near the site of the lumbar puncture
• Suspicion of increased intracranial pressure due to a cerebral mass
• Uncorrected coagulopathy
• Acute spinal cord trauma

The presence of skin infection near the site of the LP increases the risk of carrying the infection into the CSF with the LP needle. Thus, infection at the potential LP site is a contraindication to performing a lumbar puncture at that area.

Perhaps the more worrisome contraindication to lumbar puncture is the suspicion of increased intracranial pressure (ICP) due to a cerebral mass lesion. In the presence of a potential brain tumor, cerebral hemorrhage, cavernous sinus thrombosis, brain abscesses, epidural or subdural hematomas , patients are at increased risk of deteriorating neurologically with LP. As the space-occupying lesion grows, ICP rises. When lumbar puncture is performed in these patients, a low-pressure shunt is formed at the site of LP where CSF can escape. As the CSF pressure drops in the spinal column, CSF and brain mass may then shift towards the low-pressure outlet (the LP site). This may lead to either trans-tentorial or uncal herniation and acute neurological deterioration. Patients with increased ICP from mass lesions often display decreased levels of consciousness, focal neurological signs or papilledema on physical exam. Any of these findings make lumbar puncture contraindicated until further evaluation can be undertaken. The next section "To CT or Not to CT", addresses the issue of when imaging is required prior to LP.

As with most invasive procedures, uncorrected coagulopathy is a contraindication to LP. This includes those on heparin, coumadin, or with clotting defects such as disseminated intravascular coagulation, hemophilia or thrombocytopenia. Having said that, when these clotting abnormalities are corrected, lumbar puncture is no longer contraindicated. Reversal of coumadin with Vitamin K or fresh frozen plasma, replacement of a hemophiliac's clotting factors or transfusion of platelets to the thrombocytopenic patient would all allow for safe lumbar puncture.

In the presence of acute spinal trauma, LP is understandably contraindicated as both the bony anatomy and spinal structure may be altered and not allow for safe placement of the LP needle.