Stereotaxic Technique

a method that utilizes extracranial or intracerebral landmarks in order to insert accurately a small instrument, such as a cannula or electrode, into the deep structures of the brain or spinal cord. The stereotaxic technique is used for scientific, therapeutic, or prophylactic purposes. Operations on the brain are performed using special apparatus that guide the surgical instrument to a predetermined location in the depths of the brain. The first stereotaxic apparatus was developed in 1889 by Professor D. N. Zernov of Moscow University. Modern stereotaxic apparatus differ in complexity of design, methods of attachment to the cranial bones, and systems of coordinates. They do, however, all adhere to the basic principle of the stereotaxic technique, whereby the conventional coordinate system of the brain is juxtaposed with the coordinate system of the stereotaxic apparatus.

Points near the ventricles of the brain serve as intracranial landmarks for determining the location of a deep structure of the brain. The introduction of air or a contrast medium makes the structure visible on a roentgenogram of the head and permits the calculation of the coordinates of the desired structure. Information for use in calculations may be found in special stereotaxic atlases, which are anatomical atlases of the human brain that reflect the topographic relationships between subcortical structures and the skull. The atlases contain photographs of sections of a typical brain taken in three planes. The corresponding angles of correction of the direction of the cannula are transferred to the protractors of the sterotaxis apparatus, and the cannula is inserted into the predetermined point in the brain. An image tube is used to control the insertion of the instrument. All the stages of the operation are recorded on the screen of the image tube.

Various methods are used to destroy subcortical structures during operations performed employing the stereotaxic technique. These methods include anodic electrolysis (action with direct current), high-frequency electrocoagulation, the introduction of radioactive isotopes into the brain, and local freezing with liquid nitrogen. A special apparatus is available for the local freezing of subcortical structures.

The stereotaxic technique is widely used in modern neurophysiology in neurophysiological experiments on animals in order to study the functions of the deep structures of the brain. The highly selective destruction or electrostimulation of cerebral structures, as well as the removal of bioelectric potentials, contributes to the elucidation of the functional significance of the structures under study and substantially increases our knowledge concerning the complex mechanics that govern the activity of various parts of the brain. The stereotaxic technique has been used more and more frequently in neurosurgery to treat such severe diseases of the human central nervous system as parkinsonism, muscular dystonia, athetosis, choreoathetosis, Huntington’s chorea, spasmodic torticollis, multiple sclerosis, severe algetic syndromes, epilepsy, and several kinds of brain tumors, including hypophyseal tumors. Other therapeutic methods are often ineffectual with these diseases. Besides their practical therapeutic value, operations utilizing the stereotaxic technique provide a unique opportunity for studying the physiology of subcortical and truncal structures and brain function in general.