CNS Tissue Processing
After the brain is removed, the autopsy technician and/or pathologist will visually inspect this tissue for obvious abnormalities. In some cases, a pre-mortem MRI or CT may indicate unilateral brain pathology. In either case, visible lesions are sampled, fixed in formalin, and made into slides for diagnostic studies. If known unilateral pathology is present, that hemisphere is usually reserved for formalin fixation and the opposite hemisphere is selected for freezing. Otherwise the entire brain is hemi-sected; one hemisphere is immersed in formalin and the other is flash frozen. If there is a prolonged PMI and/or the tissue is highly friable, the entire brain will be placed in formalin and no frozen tissue will be available. The hemi-brain that is selected for freezing is chilled briefly, then sectioned in 1.0 to 0.5 cm sections which are sequentially numbered, placed in labeled plastic bags, and frozen. The spinal cord is divided into cervical, thoracic, and lumbosacral segments of approximately 1 cm each and alternately fixed or frozen. As requests are approved, brain sections are removed from the freezer, placed in a laminar flow hood, and tissue samples are dissected out by the neuropathologist, using either a scalpel or a Dremel tool (analogous to a dental drill).
