In most cases, spinal tap procedures are quick, relatively painless and effective. The test uses a flexible needle that makes it only mildly to moderately uncomfortable. This needle is so flexible that it can be wrapped around a finger without breaking. The spinal cord is not affected, because the needle is usually inserted below the level where the cord ends.

As with any invasive procedure, there is a risk of infection with a spinal tap. In rare cases, children can develop meningitis if a skin infection is located on the area where the needle for the spinal tap is inserted. In this situation, another diagnostic method would be performed instead of a spinal tap. Factors that increase the risk of complications from a spinal tap include a recent or chronic illness, a central nervous system infection or increased intracranial (within the skull) pressure.

Other risks associated with the spinal tap include:

• Damage to the spinal cord, spinal canal or surrounding tissues by the spinal tap. The risk of this complication increases if the patient moves during the spinal tap.
  
  
• An allergic reaction to the anesthetic.
  
  
• Bleeding into the spinal canal.
  
  
• Brain herniation, an extremely rare and potentially fatal condition in which the brain pushes through the opening at the back of the skull where the spinal cord is attached.

When cerebrospinal fluid (CSF) is withdrawn during a cisternal puncture or ventricular puncture, there is the additional risk of damage to the brainstem or brain tissue causing bleeding that could result in brain damage or death. The increased risk associated with these procedures is the major reason why the spinal tap is the preferred method of collecting CSF for laboratory testing.

According to the National Institute of Neurological Disorders and Stroke, about one-quarter of patients experience a post-spinal tap headache within 48 hours of the spinal tap. This usually affects patients 18 to 30 years of age, and is considered rare in children. The causes of a post-spinal tap headache are unknown, but it may be the result of either leakage of the CSF or low CSF pressure in the spinal canal.

Pain is typically centered near the forehead and/or the back of the head and may be accompanied by nausea, dizziness or tinnitus (ringing in the ears). It is usually more severe when sitting or standing than when lying down. The headache usually dissipates with bed rest, but if it persists or becomes more severe, a physician should be notified immediately. This headache can last from a few days to a few weeks. 

The post-spinal-tap headache can usually be avoided by remaining absolutely still during the spinal tap procedure, drinking ample fluid afterward and limiting the movement of both head and neck following the tap. Drinking caffeinated beverages such as tea or coffee after the tap may also help replenish cerebrospinal fluids and relieve the headache. Parents are urged to consult with a child’s physician about whether caffeinated beverages are a good idea for their child. Parents may also wish to consult with their child’s pediatrician about giving a child acetaminophen, ibuprofen or another non-aspirin pain reliever.

Children with certain health conditions may not be good candidates for a spinal tap, including:

• Children who have had back surgery
  
  
• Children with scoliosis (abnormal curvature of the spine)
  



• Children who are obese
  
  
• Pregnant adolescents
  
  
• Children with bleeding disorders who take anticoagulant medication
  
  
• Children with a skin infection on the lower back

In such cases, imaging tests such as an MRI (magnetic resonance imaging) or CAT scan (computed axial tomography scan) may be used instead of the spinal tap.