Frame-Based Stereotaxis
4 system has been used:
- Polar coordinate
- Guidance of the probe be described with regard to the angle in relation to a skull entry point
- 2. Arc-radius
- Commonly used
- Basis for Leksell frame
- Probe equivalent to the radius of a semicircular arc will reach the center of the arc when introduced perpendicular to any point along the arc
- Focal point
- Phantom target
- Principles: point-pair registration or surface contour registration can be used to establish the relationship between the preoperative images and those in the surgical field
- Requires a set of at least three non-colinear points to be defined in the coordinates of the images
- Registration
- Marker
- Surface contour
- Goal: to provide a representative sample for pathologic diagnosis to guide subsequent treatment
- Advantages:
- Higher accuracy
- Minimize potential adverse effects
- Lesion that support stereotactic over open biopsy:
- Lesions that do not exert a symptomatic mass effect
- Not treatable by surgical excision eg metastases, malignant intrinsic brain tumor
- Deep seated lesion or occupying space in eloquent area or deep nuclei
- Infiltrative lesion eg gliomatosis cerebri
- Lesion suggest infection or demyelinating rather than tumor
- Vascular tumor eg metastatic renal cell carcinoma, etc
- Location of tumor close to major blood vessel, vessel-rich Sylvian fissure, cavernous sinus
- Patients on anticoagulant
- Particularly in non-enhancing lesion eg LGG
- To improve accuracy: use PET scan, MR Perfusion, MRS
- Hemorrhage
- Damage to friable vessels within targeted neoplastic lesion
- Vessels along trajectory
- Neurological deficits
- Direct brain damage
- Edema
Approaches:
- Transtentorial approach
- Ipsilateral transfrontal trajectory
- Suboccipital transcerebellar route
- Contralateral, extraventricular, transfrontal approach
- Area of thickest enhancement
- Slightly deeper or shallower samples could be obtained along the same trajectory
- Avoid entry into a dural blood vessel, cortical blood vessel, or sulcus
- Entry point could be planned to be incorporated into future craniotomy incision avoid unnecessarily traversing pial or ependymal surfaces