Subdural Tap
Aaron Mohanty
1. The most common indication for subdural tap is drainage of subdural collection to relieve increased intracranial pressure.
2. Subdural taps also are indicated to sample subdural fluid for cytologic, biochemical, and microbiologic studies.
B. Contraindications
1. Overlying infected scalp.
2. Uncorrected bleeding diathesis or thrombocytopenia.
3. Closed fontanelle with nonseparated sutures.
4. Performing subdural taps in the absence of radiologic imaging like CT, ultrasound, and MRI scans (Fig. 20.1) can no longer be justified unless the investigations cannot be performed due to nonavailability or in a life-threatening situation.
 FIGURE 20.1 Subdural collections can be difficult to detect on ultrasound and are more readily apparent on MRI. LEFT: Conventional transcranial ultrasound on a neonate with seizure, coronal view. RIGHT: MRI brain, T2-weighted sequence coronal view, performed on the same neonate 1 day before the ultrasound. A subdural hemorrhage spans the right frontal convexity, shown as hypointense T2-weighted signal abnormality (arrow). Large scalp hematoma is also present (asterisk), which extends across the coronal suture consistent with subgaleal hematoma. (Images courtesy Dr. Arash Zandieh, MedStar Georgetown University Hospital) |
C. Principles
1. The subdural tap is performed through an open fontanelle (usually anterior fontanelle) or through the open or splayed sutures (Fig. 20.2).
a. In patients with previous bone defects like burr holes, the subdural tap can be performed through the bone defect.
b. Thus, the tap is uncommon after 6 to 9 months of age when the sutures and fontanelles close.
2. It is essential to enter the subdural space without injuring the underlying pia or cortex and to avoid any traversing veins in the subdural space.
a. The tap site should correspond to the thickest location of the subdural collection as demonstrated in the imaging studies.
b. If the collection is noncontiguous and the collection needs to be drained from different sites, the tap sites should be carefully identified depending on the
location of the subdural collection and the suture or bone defect.
location of the subdural collection and the suture or bone defect.
 FIGURE 20.2 Position and restraint for subdural tap. Stippling demonstrates area to be prepared for procedure. An arrow indicates site for needle puncture. |
3. The most ideal location for the subdural tap is the lateral edge of the anterior fontanelle away the midline.
a. The side of the tap depends on the thickness of the subdural collection; the side with thicker collection is preferred.
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