Dissection Of Brain And Spinal Cord

Brain weight in the fresh and fixed state should be recorded. It is not necessary to use a very large knife to dissect the brain. We prefer a single-blade autopsy knife about 25 cm long and 2 cm wide.

DISSECTION OF FRESH BRAIN IN ADULTS The most exacting examination of brain in terms of recognition of lesions and correlation of their topography with clinical symptoms and images generated by computerized trans-axial tomography (CT) or magnetic resonance imaging (MRI) techniques can be achieved only when the brain is sectioned after adequate fixation (2022). At times, however, the fresh brain must be dissected, particularly when microbiologic and chemical investigations are of prime importance or when an immediate diagnosis is needed (this speed unfailingly leads to distortion of the cut surface during subsequent fixation). As a compromise, we limit fresh dissection to three or four coronal cuts through the cerebral hemispheres, leaving more complicated anatomic structures such as the basal ganglia and upper brain stem (thalamus and midbrain)

as undisturbed as the circumstances permit. This preliminary dissection usually reveals the presence of large lesions, directly or indirectly, by showing distortion of the ventricular system or other anatomic landmarks.

Further judiciously selected sections may be made into the primary slices of the brain tissue to expose the suspected hidden lesions. The central portion of the cerebral hemispheres is left connected with the brain stem, and this block is suspended by a string, as described earlier. It may be necessary to sever the brain stem and cut into the infratentorial structures; one horizontal cut through these structures usually suffices for preliminary examination. Even with several cuts, one should not be satisfied solely with fresh dissection of the brain because many small lesions are easily missed and subtle lesions such as an early infarct, small or large, can be overlooked. Every brain should be reexamined with new dissection after adequate fixation.

Preliminary perfusion or cooling of the brain in a refrigerator for about 30 min, preferably in a contoured support as described earlier, makes the brain firmer and dissection easier. If diffuse, roughly symmetric lesions are expected, as in lipi-doses, "degenerative diseases," "demyelinating" disorders, other inborn or acquired toxic-metabolic diseases, or widespread infectious conditions, the brain may be bisected along the sagittal plane, one half being further sectioned and submitted for chemical or microbiologic investigations while the other half is retained for later sectioning and histologic examination. This latter half must be fixed either by suspension or by letting it lie on its midsagittal plane to avoid undesirable distortions.

Dissection of fresh brain (according to the aforementioned procedure) may be required by brain-banking protocols or specific research protocols (e.g., Alzheimer's disease), in order to provide adequate material for histological, immunocytochemi-cal, biochemical, and molecular biology studies. References (23) and (24) provide a general overview regarding procedures involved in "brain banking."

We find no use for the classical Virchow method of fresh dissection. Any brain subjected to this method would look, after adequate fixation, like a book immersed in water and subsequently dried.

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