Abstract
Since their introduction by Prof. Ya,sargil in the 1960s, Microneurosurgical techniques have been the essentials of neurosurgical practice. Principles of Microneurosurgery are mainly based upon handling the lesions of different characteristics that can be localized in any part of the nervous system. Whereas the aim is to treat these lesions with efficacy and precision, the performance should be non-traumatic and minimally invasive. Delicate movements of instruments under the magnification of an operating microscope require a good knowledge of Microneurosurgical anatomy and experience. Professional teamwork is the essential part of Microneurosurgical operations. Fascinating approaches are not practical unless combined with appropriate positioning and optimal conduction of Neuroanesthesia. Although the neurosurgical operations are highly dependent on technological advancements, their use should be adjusted according to personal preferences and financial resources. To keep the operations simple and fast, and appreciate normal anatomy, only a limited array of instruments is preferable for use. The basic principles of Microneurosurgery discussed in this chapter are based on the Helsinki and Kuopio Neurosurgery practices in Finland, as well as the Senior Author's (J.H.) experience in approximately 10,000 microsurgery operations. The question to be addressed is: How does one perform operations safer and faster while preserving the normal anatomy?

Abstract
This chapter assesses the safety of freehand placement of an infusion catheter (outer diameter, 0.3 mm) in brainstems of cynomolgus monkeys (Macaca fascicularis) for local infusion therapy. A posterior midline approach through the cerebellum and roof of the fourth ventricle was used to implant catheters into a pontine target area. Computer tomography (CT), magnetic resonance imaging (MRI), and histology were used to examine the position of the implants. The freehand placement of a catheter resulted in approximately 5-mm variations in anterior-posterior and dorsal-ventral locations of the targeted implantation site. No evidence of morbidity from the surgery, or from the infusion process was present. In conclusion, small-diameter catheters for chronic drug infusions can be implanted safely into the brainstem, an eloquent region that has been considered surgically inoperable. Infusion systems may offer a minimally invasive, generally applicable tool to provide chronic therapy for central nervous system (CNS) lesions.