Ideal Trajectory Planning for Combined Endoscopic Third Ventriculostomy and Pineal Region Biopsy: A Volumetric Analysis of Brain at Risk

Background Pineal region tumors are intimately associated with the ventricular system, being bounded ventrally by the third ventricle. Patients most commonly present with symptoms secondary to obstructive hydrocephalus making cerebrospinal fluid diversion an essential part of treatment. Alternatively, an endoscopic third ventriculostomy can be performed at the same time as tumor biopsy. This can either be performed through a single burr hole or two separate entry points. Utilizing two entry points would theoretically limit the amount of damage to underlying brain parenchyma by minimizing wanding between the two targets. We investigated the volume of brain undergoing potential injury during ETV and tumor biopsy with one- or two-burr hole utilization.

Methods The authors retrospectively reviewed patients with pineal region masses at Saint Joseph's Hospital between April 2000 and August 2010. Two approaches were simulated with volumetric image-guided system on the stealth brain magnetic resonance imaging (MRI) or head computer tomography (CT) scans. The objective in the present study was to compare the volume of brain parenchyma and fornix that may be damaged with utilization of one- versus two-burr holes.

Results The calculated ideal entry point for ETV in two separate burr hole approach was 25.8 ± 6 mm from the midline and 11.4 ± 9 mm behind the coronal suture. The distance from the outer table of the skull to the target on the tuber cinereum was 90.1 ± 5 mm. The ideal entry point for tumor biopsy in two-burr hole approach was 25.7 ± 8 mm from the midline and 53.7 ± 14 mm in frontal of the coronal suture. With a single-burr hole approach, the volume of brain parenchyma susceptible to damage was 852 ± 440 mm³ (mean ± SD). The volume of brain parenchyma susceptible to damage with two-burr hole approach was 2,159 ± 474 mm³ (p < 0.0001, paired t-test). The single-burr hole approach required fornical shift at a length of 14 ± 3 mm, whereas the shift of the fornix in two-burr hole approach was minimal.

Conclusion Volumetric analysis suggests that utilizing a single-burr hole for both ETV and tumor biopsy is likely to traumatize less brain parenchyma than using two separate burr holes. However, the single-burr hole approach predisposes the fornix to stretch injury, whereas utilizing two separate burr holes minimizes this risk. These results should be considered when selecting approaches for individual patients. The authors recommend tailoring entry points for individual patient anatomy and not subscribing to a one-size-fits-all approach.