Practical pathology

by Aldred Scott Warthin

The left hemisphere is now turned still more to the left, and with the brain-knife a broad, smooth cut is made through it downward and outward at an angle of 45°, reaching nearly to the cortical surface, in a line connecting the cut through the frontal lobe with that through the occipital and passing along the outer borders of the corpus striatum. The left hemisphere is thus separated in the form of a prism-shaped mass having a convex under surface. (See Fig. [29].) The severed hemisphere falls back by the force of its own weight and the flat cut-surface of the cerebrum is then bisected by a cut made at right angles to it, from before backward, and extending nearly to the cortical surface. (See Fig. [29].) In the case of both of these large incisions of the hemisphere the severed parts are left connected by a small portion of cortical tissue and the pia. The knife should be perfectly dry and clean while making these cuts, and the cut surfaces should not be touched with the fingers or knife-blade, or wet with water, until they have been carefully inspected. Other straight parallel cuts may be made through the brain substance toward the cortex, the severed portions being left connected by the pia so as to permit future orientation.

The right lateral ventricle is now opened. The four fingers of the left hand are placed outside and beneath the right hemisphere with the thumb on the median surface, gently raising the hemisphere toward the left, taking care to see that the corpus callosum is not pulled over to the right of the median line. The knife is held in the right hand beneath the left one. The right ventricle is then opened in the same way as the left, beginning in the middle of the corpus callosum near to the gyrus cinguli, and opening first the anterior horn and then the posterior. The operation is somewhat more difficult on the right side than it is on the left, owing to the lack of tension in the cut corpus callosum, so that greater care must be taken to avoid injuring the floor of the ventricle. After the opening of the ventricle the right hemisphere is cut by long parallel incisions made in the same way as on the left side. (See Fig. [29].)

Some prosectors in opening the right ventricle prefer to turn the board around so that the frontal lobe points to the operator. The right hemisphere is then held in the left hand and the right ventricle opened just as if it were the left ventricle, except that the posterior horn is opened before the anterior. The method given above can be just as easily learned, and time is saved by not turning the board around twice, as is necessary in the latter case.

After the right ventricle has been opened the corpus callosum and fornix are raised by the thumb and index-finger of the left hand, putting the septum pellucidum on the stretch. The narrow brain-knife is then introduced through the interventricular foramen from the right, its blade flat, with cutting edge directed forward and upward, and the fornix and the corpus callosum are cut anteriorly, exposing the cavity of the septum pellucidum. To expose the third ventricle, the corpus callosum, septum pellucidum and fornix are then lifted up and laid back from the velum chorioides. The tela chorioidea is then, with the chorioid plexus of the third ventricle, pulled backward from over the pineal body and the corpora quadrigemina, care being taken not to tear away the pineal body. The veins entering the tela from the great ganglia are cut with the point of the knife. The right descending posterior pillar or crus of the fornix is then lifted with the thumb and index-finger of the left hand, the brain-knife on the flat side with cutting edge to the right is introduced beneath it, and the crus is cut toward the right. The corpus callosum, fornix and tela are then turned over to the left (see Fig. [29]), fully exposing the pineal body and the corpora quadrigemina.

The cerebellum and medulla are now supported by the index-finger of the left hand placed beneath the latter; while the brain-knife is held nearly horizontally in the right, and a deep sagittal cut is made into the vermis exactly in the median line so as to make a small opening into the fourth ventricle. The point of the knife with cutting edge upward is then introduced into this opening and the incision through the vermis increased anteriorly and posteriorly until the two cerebellar hemispheres fall apart and the fourth ventricle is wholly opened. The point of the knife, with cutting edge upward may then be introduced into the posterior opening of the aqueduct and the latter opened to the third ventricle, the pineal body being removed before the cut through the roof of the aqueduct is made. In the Virchow method the corpora quadrigemina and the vermiform portion of the cerebellum are sectioned in the median line by a cut opening up both aqueduct and the fourth ventricle. Other prosectors open the aqueduct from the third ventricle toward the fourth. The left cerebellar hemisphere is now cut through in the line of the middle branch of the arbor vitæ, exposing the dentate nucleus. Each half of the hemisphere is again bisected by a cut made at right angles to the surfaces exposed by the first cut. The right cerebellar hemisphere is then similarly sectioned.

The section of the brain now shows all of the ventricles and their relations, as well as the condition of a large part of cerebral and cerebellar brain-substance. (See Fig. [29].) All cut portions are connected with each other and it is possible to fix the entire brain as it now stands and later find no difficulty in topographic orientation. There still remains, however, the demonstration of the conditions in the basal ganglia, pons, medulla, etc. These structures are best shown by transverse cuts made across the entire brain as it lies after the opening of the ventricles. The hemispheres may be cut singly, but it is better to cut both of them at the same time, using a dry blade and drawing the knife from left to right, making identical cuts on the two sides, that the histologic features may be compared. The transverse cuts may be made in the same region as recommended in the method of Pitres (see below), or they may be made closer together. As the cuts are made the sections are separated from each other by the knife-blade and the cut surfaces examined. After the cerebrum has been cut transversely in this way the peduncles, pons, medulla and cervical cord are elevated on the index-finger of the left hand and also sectioned transversely and the cut surfaces examined. If the index-finger be placed beneath the medulla parallel with its long axis, and medulla and pons raised up the cerebellar lobes fall to the side out of the way. All transverse cuts are made from left to right and so deep that only a small portion of brain-tissue, or the basal meninges hold the parts together for future orientation. The brain is now completely sectioned, with all parts preserved and capable of being restored to their normal relations. The parts may be re-assembled and the entire brain put into the fixing fluid, when it is desirable to save the entire organ for microscopic study.

Fig. 30.—Method of Pitres. 1, Sectio præ-frontalis; 2, Sectio pediculo-frontalis; 3, Sectio frontalis: 4, Sectio parietalis; 5, Sectio pediculo-parietalis: 6, Sectio occipitalis.

Other Methods of Opening Brain. For the demonstration of large localized pathologic conditions the brain may be opened by a very simple method of transverse or sagittal incisions extending entirely through the organ. The broad-bladed brain-knife should be used and the blade should be wet. The cuts should be made symmetrically on the two sides and with due reference to anatomic landmarks. They may be made either from the convexity or from the basal side.

The method of Pitres (see Fig. [30]) is also employed for the same purpose. After the inspection of the meninges and basal vessels and opening of lateral ventricles, the brain is divided into three parts, consisting of the two hemispheres and one part made up of the cerebellum, pons and medulla. The anterior ends of the cerebral peduncles are cut transversely in front of the corpora quadrigemina, and the hemispheres are then separated by a sagittal median incision through the corpus callosum, septum pellucidum, commissure of third ventricle, substantia perforata posterior, tuber cinereum and infundibulum, the optic chiasm and neighboring optic tract having first been removed. The hemispheres are then cut as follows: The hemisphere is laid upon its median surface with the occipital lobe toward the operator. The four fingers of the left hand are then put into the central fissure and six parallel transverse cuts (see Fig. [30]) are made through the hemisphere with a dry brain-knife, as follows: