Ventricular

The percutaneous ventricular tap is almost exclusively performed in infants since it requires an open fontanelle (in adults a transorbital ventricular puncture has been described). The anterior fontanelle does not close completely until the middle of the third year of life. This procedure can only be performed safely if the width of the fontanelle is sufficient to avoid the superior sagittal sinus. Practically, this means a ventricular tap is not a feasible option after about the ninth month of life.

Indications

1. Emergency drainage of CSF from the lateral ventricles.

2. CSF for diagnosis in a patient with spina bifida.

3. An alternative to LP for the drainage of communicating hydrocephalus. This is usually in the setting of posthemorrhage hydrocephalus when lumbar punctures are no longer successful.

Procedure

The intracranial compartment is entered at the junction of the coronal suture and the anterior fontanelle in the lateral corner of the fontanelle. (Fig. 1 shows the entry point using a burr hole, but the lateral corner of the fontanelle is usually immediately posterior to Kocher's point.) This point avoids the superior sagittal sinus and is directly over the lateral ventricle. The right side is preferred unless a hematoma or pathological lesion is located on that side. The scalp is shaved, prepped and draped in a sterile fashion. A 20-gauge, 2-inch angiocatheter is used to pierce the skin and a trajectory perpendicular to the skin is taken. The catheter is passed about 1 to 2 cm until CSF is seen in the hub of the needle. This is then withdrawn leaving the catheter in place in the lateral ventricle. Once again the CSF pressure is measured and fluid is removed for analysis. In a neonate, the ICP may not be sufficient to overcome the resistance through the catheter. Gentle, negative pressure with a syringe or lowering a piece of extension tubing below the level of the head will facilitate drainage.

Complications

1. Hemorrhage. Passing the needle through the brain may cause a subdural, intracerebral, or intraventricular hemorrhage. Usually these are self-limiting. In the event of large a intraventricular hemorrhage, an external drain may be necessary.

2. Infection. Always possible with percutaneous procedures. Increased risk in premature infants or neonates.

3. Porencephaly. Multiple taps may result in an area of brain loss that may communicate with the ventricle.

Figure 1. The entry point for a frontal entry point to the lateral ventricle is demonstrated. (Reprinted by permission, Cheek WR, ed, Pediatric Neurosurgery. 3rd ed. Saunders, 1994).

4. CSF leak. The overlying skin is often thin and if a large needle is used there may be sufficient pressure to force the CSF through the tissues. In order to avoid this one can stagger the puncture points of the skin and dura. This is done by pulling the skin slightly posteriorly when puncturing it and then letting it relax back over the fontanelle to pierce the dura. Sometimes a small diameter (5-O or 6-O) suture is required to close the entry point.

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