Lumbar Puncture

At 2 months postfertilization the spinal cord and canal are approximately the same length. Between 9 and 18 weeks, the canal grows rapidly longitudinally and by midgestation, the conus medullaris is at the level of the L4 vertebral body. Growth then slows so that by birth the tip of the conus is at the L3 vertebral body level. Over the next 2 months the spinal cord comes to rest at its adult level, which ranges from the T12-L1 disc space to the L1-2 disc space.

Indications

1. Chemical and/or bacteriological analysis of CSF.

2. Evaluation and treatment of increased intracranial pressure (ICP) in communicating hydrocephalus.

3. Diagnosis and treatment of pseudotumor cerebri.

Contraindications

1. Intracranial mass lesion.

2. Suspected noncommunicating hydrocephalus.

3. Recently ruptured aneurysm. Care must be taken to prevent a large drop in ICP, as this increases the transmural pressure across the aneurysm increasing the risk of rupture.

4. Complete spinal CSF block. There have been reports of patient deterioration following a lumbar puncture (LP).

Pediatric Neurosurgery, edited by David Frim and Nalin Gupta. ©2006 Landes Bioscience.

Procedure

In the neonate, the interspace between the L4-5 spinous processes is used as the entry point for the puncture. In older children the L3-4 space can also be used. The rostral/caudal extent of the L4-5 interspace can be approximated by using a transverse plane intersecting the superior edge of the iliac crests. The patient is positioned in either the lateral position, with the hips and knees flexed, or in the upright position; the latter is often preferred in neonates. In both cases the lower back is maintained in a position of flexion in order to maximally spread the posterior elements of the vertebral column.

After a thorough antiseptic prep, local anesthetic is infiltrated at the point of entry both superficially and in the deeper tissues. A 22 gauge spinal needle is then advanced slowly through the skin in a slightly rostral direction between the two spinous processes. The stylet is always left in place while advancing the needle to prevent carrying epidermal components into the deeper tissue. If bony structures are encountered, the needle should be withdrawn and redirected. It is often possible to feel the passage of the needle through the different tissue planes. Once a trajectory is chosen, it should not be modified en route. The needle should be withdrawn into the subcutaneous tissues and then redirected.

Once the dura is punctured and spinal fluid seen, it is crucial to measure the opening pressure with a manometer prior to decompressing the spinal subarachnoid space. If the patient is upright or the head elevated they must be placed horizontal for an accurate reading. Children are usually minimally sedated and if agitated, a falsely high pressure reading will be obtained. Often it may be necessary to wait with the needle in place until the patient is quiet. It is convention to send four tubes of CSF are for analysis. The first and fourth tubes are used for cell count and the second and third tubes for culture, protein and glucose.

In patients with communicating hydrocephalus or pseudotumor cerebri who require high volume taps, the ICP can be measured intermittently and enough fluid removed to normalize the pressure.

Complications

1. Failure to obtain CSF. Usually this is due to an improper trajectory. The most common problem is directing the needle too far laterally so that the needle either strikes the facet joints or tangentially passes next to the the-cal sac. It is crucial to ensure that the needle is directed perfectly towards the midline. If the patient is on his or her side, use an assistant to tell you from the foot of the bed that the needle is perpendicular to the spine.

2. Low pressure headache. This is a common complication following LP. This is much less common in children under 13 years old.

3. Cerebral herniation in the presence of a cerebral mass. The presence of normal optic discs does not ensure that LP can be performed without risk. Herniation has also been reported in children with meningitis who undergo LP with normal computed tomography (CT) scans.

4. Infection. Bacterial meningitis can occur if adequate sterile technique is not used, if there is a persistent CSF leak or if the tap is performed through an area of cellulitis.

5. Nerve root irritation. The passage of the needle into a nerve root can cause a transient shock-like pain; it has been reported in about 13% of adults undergoing the procedure.

6. Subdural hemorrhage. Rare in children unless there is significant cerebral atrophy.

7. Spinal hemorrhage. These include epidural hematomas and subarachnoid hemorrhages. These are usually associated with coagulation disorders.

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