Anterior Fontanelle Tap Procedure in Infants
The anterior fontanelle tap is performed by positioning the infant supine with head midline, identifying the anterior fontanelle, preparing the site with sterile technique, inserting a spinal needle perpendicular to the skull surface through the fontanelle, advancing until CSF flows, and collecting the required sample.
Procedural Steps
Pre-Procedure Preparation
- Position the infant supine with the head in midline position, slightly elevated if possible
- Restrain the infant appropriately to prevent movement during the procedure
- Identify the anterior fontanelle by palpation (diamond-shaped soft spot between frontal and parietal bones)
- Gather equipment: spinal needle (typically 22-gauge), sterile gloves, antiseptic solution, sterile drapes, collection tubes
Sterile Technique
- Don sterile gloves and prepare a sterile field
- Cleanse the fontanelle area with antiseptic solution (chlorhexidine or povidone-iodine) using concentric circles from center outward
- Allow antiseptic to dry completely
- Drape the area with sterile towels, leaving only the fontanelle exposed
Needle Insertion
- Insert the spinal needle perpendicular to the skull surface through the center of the anterior fontanelle
- Advance slowly and steadily, aiming slightly toward the inner canthus of the eye
- The needle typically enters 1-2 cm before reaching the ventricle in young infants
- Remove the stylet periodically to check for CSF flow
- Once CSF flows freely, stabilize the needle and collect the required sample
Sample Collection and Completion
- Collect CSF in appropriate tubes for analysis (typically 3-4 tubes for cell count, glucose/protein, culture, and additional studies)
- Replace the stylet before withdrawing the needle
- Apply pressure to the puncture site with sterile gauze
- Apply a sterile dressing
Critical Safety Considerations
Monitor the infant's neurological status closely after the procedure, as rare but serious complications can occur. A case report documented distant epidural hematoma formation after transfontanellar tapping 1, emphasizing the need for post-procedure neurological monitoring to detect deterioration early.
Key Pitfalls to Avoid
- Never perform the tap if the fontanelle is bulging or tense without first addressing increased intracranial pressure
- Avoid angling the needle excessively—maintain perpendicular trajectory to prevent vascular injury
- Do not advance the needle too deeply (risk of penetrating the opposite side of the ventricle)
- Ensure complete antiseptic drying to prevent chemical meningitis
When to Consider Alternative Approaches
While the anterior fontanelle tap is commonly used in resource-limited settings for CSF access in infants with open fontanelles 1, consider alternative routes if:
- The fontanelle is closed or nearly closed
- There is overlying infection or skin breakdown
- Recent neurosurgical procedures contraindicate the approach (consider C1-2 puncture as alternative 2)
The procedure can be performed at bedside without imaging guidance, though ultrasound guidance may improve success rates and safety, particularly in complex cases. Recent evidence supports that children are especially amenable to cranial procedures through open fontanelles 3, making this a practical approach when lumbar puncture is contraindicated or unsuccessful.