Stereotactic Bipsy Friday, May 06, 2022

Stereo - 3 dimensional, Taxis - to move toward 

Frame-Based Stereotaxis 4 system has been used: 

1. Polar coordinate 
• Guidance of the probe be described with regard to the angle in relation to a skull entry point 
2.  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 
3. Focal point
4. Phantom target  

Frameless Stereotaxis

• 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 

Indication for Stereotactic Biopsy

• 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

Contraindication 

• 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 

Sampling Error

• Particularly in non-enhancing lesion eg LGG
• To improve accuracy: use PET scan, MR Perfusion, MRS

Complications

• Hemorrhage 
• Damage to friable vessels within targeted neoplastic lesion 
• Vessels along trajectory
• Neurological deficits
• Direct brain damage
• Edema 

Stereotactic Biopsy of Brainstem Lesions 

Approaches:

• Transtentorial approach
• Ipsilateral transfrontal trajectory
• Suboccipital transcerebellar route
• Contralateral, extraventricular, transfrontal approach 

Trajectory Planning

• Area of thickest enhancement 
• Slightly deeper or shallower samples could be obtained along the same trajectory 

Entry point

• 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