Stereotactic surgery is a minimally invasive form of surgical intervention that makes use of a three-dimensional coordinate system to locate small targets inside the body and to perform on them some action such as ablation, biopsy, lesion, injection, stimulation, implantation, radiosurgery (SRS), etc. In theory, any organ system inside the body can be subjected to stereotactic surgery. However, difficulties in setting up a reliable frame of reference (such as bone landmarks, which bear a constant spatial relation to soft tissues) mean that its applications have been, traditionally and until recently, limited to brain surgery. Besides the brain, biopsy and surgery of the breast are done routinely to locate, sample (biopsy), and remove tissue. Plain X-ray images (radiographic mammography), computed tomography, and magnetic resonance imaging (MRI) can be used to guide the procedure. Another accepted form of "stereotactic" is "stereotaxic". The word roots are stereo-, a prefix derived from the Greek word στερεός (stereos, "solid"), and -taxis (a suffix of Neo-Latin and ISV, derived from Greek taxis, "arrangement", "order", from tassein, "to arrange").
Uses Stereotactic surgery is used to treat various brain cancers, benign, and functional disorders of the brain. This surgery is sometimes combined with whole brain radiotherapy for brain metastasis. A 2021 systematic review from the Agency for Healthcare Research and Quality found no statistically significant difference in overall survival for stereotactic radiosurgery in combination with whole brain radiotherapy compared to either treatment alone. Amongst the malignant brain disorders are: brain metastasis and glioblastoma. The benign brain disorders are: meningioma, cerebral arteriovenous malformation, vestibular schwannoma, and pituitary adenoma. Functional disorders are: trigeminal neuralgia, Parkinson's disease, and epilepsy.
Procedure Stereotactic surgery works on the basis of three main components:
A stereotactic planning system, including atlas, multimodality image matching tools, coordinates calculator, etc. A stereotactic device or apparatus A stereotactic localization and placement procedure Modern stereotactic planning systems are computer based. The stereotactic atlas is a series of cross sections of anatomical structure (for example, a human brain), depicted in reference to a two-coordinate frame. Thus, each brain structure can be easily assigned a range of three coordinate numbers, which will be used for positioning the stereotactic device. In most atlases, the three dimensions are: latero-lateral (x), dorso-ventral (y) and rostro-caudal (z). The stereotactic apparatus uses a set of three coordinates (x, y and z) in an orthogonal frame of reference (cartesian coordinates), or, alternatively, a cylindrical coordinates system, also with three coordinates: angle, depth and antero-posterior (or axial) location. The mechanical device has head-holding clamps and bars which puts the head in a fixed position in reference to the coordinate system (the so-called zero or origin). In small laboratory animals, these are usually bone landmarks which are known to bear a constant spatial relation to soft tissue. For example, brain atlases often use the external auditory meatus, the inferior orbital ridges, the median point of the maxilla between the incisive teeth. or the bregma (confluence of sutures of frontal and parietal bones), as such landmarks. In humans, the reference points, as described above, are intracerebral structures which are clearly discernible in a radiograph or tomograph. In newborn human babies, the "soft spot" where the coronal suture and sagittal suture meet (known as the anterior fontanelle) becomes the bregma when this gap closes(usually between 7-18 months). Guide bars in the x, y and z directions (or alternatively, in the polar coordinate holder), fitted with high precision vernier scales allow the neurosurgeon to position the point of a probe (an electrode, a cannula, etc.) inside the brain, at the calculated coordinates for the desired structure, through a small trephined hole in the skull. Currently, a number of manufacturers produce stereotactic devices fitted for neurosurgery in humans, for both brain and spine procedures, as well as for animal experimentation.
Types frame systems Simple orthogonal system: The probe is directed perpendicular to a square base unit fixed to the skull. These provide three degrees of freedom by means of a carriage that moved orthogonally along the base plate or along a bar attached parallel to the base plate of the instrument. Attached to the carriage was a second track that extended across the head frame perpendicularly. Burr hole mounted system: This provides a limited range of possible intracranial target points with a fixed entry point. They provided two angular degrees of freedom and a depth adjustment. The surgeon could place the burr hole over nonessential brain tissue and utilize the instrument to direct the probe to the target point from the fixed entry point at the burr hole. Arc-quadrant systems: Probes are directed perpendicular to the tangent of an arc (which rotates about the vertical axis) and a quadrant (which rotates about the horizontal axis). The probe, directed to a depth equal to the radius of the sphere defined by the arc-quadrant, will always arrive at the center or focal point of that sphere. Arc-phantom systems: An aiming bow attaches to the head ring, which is fixed to the patient's skull, and can be transferred to a similar ring that contains a simulated target. In this system, the phantom target is moved on the simulator to 3D coordinates. After adjusting the probe holder on the aiming bow so that the probe touches the desired target on the phantom, the transferable aiming bow is moved from the phantom base ring to the base ring on the patient. The probe is then lowered to the determined depth in order to reach the target point deep in the patient's brain.
Treatment
Stereotactic radiosurgery
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