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CEREBRAL TOPOGRAPHY AT THE SECTION TABLE.

BY CLARENCE B. FARRAR, M. D.,

Assistant Physician and Director of the Laboratory, Sheppard and Enoch Pratt Hospital; Assistant in Psychiatry, Johns Hopkins University.

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Since the accumulation during the past thirty years of the facts of histologic localisation in the cortex cerebri, it has become necessary for the brain pathologist to be familiar not only with the general structural relations of the cortical grey as a whole, but also with the specific architectonique of the several " organs of the cortex, to revert to a phrenologic term. Not only do the distant areas representing special and determinate function, such as the precentral gyrus, the calcarine region, and the mid-first temporal convolution possess constant individual structural peculiarities, but the fields more closely related to each other both in location and function show likewise distinct differences in formation, less marked to be sure, as a rule in proportion to their proximity in space, but none the less constant. Such are the differences which exist for example between the cortex of the motor area for the face and of the motor area for the trunk, or between the cortex of the frontal pole, and that of the more proximal portions of the frontal lobe.

The regional differences in structure include variations in the thickness of the cortex itself and in its relations to the underlying white; peculiarities in columnar and lamellar arrangement; variations in the number of contained elements, nervous and nonnervous, their morphology and mutual relations, and in the proportions of the intercellular substance.

Obviously two cortices can only be satisfactorily compared, either from the anatomic or pathologic view-point, by comparing approximately similar areas, while in routine pathologic examination, it is essential, not only that representative areas be chosen for making sections, but also that in each case, as nearly as possible, the same representative areas be selected. This rule applies to the usual psychiatric material with assumably diffuse cortical processes. Cases with definite localising symptoms furnish of course individual indications for section. In the regular postmortem work in the psychoses, therefore, certain definite regions

should always be made the subject of study, whatever other areas in addition, special indications or inclination may suggest.

The accompanying brain maps have been found useful in our laboratory in helping to insure the necessary uniformity of operation in removing cortical tissue for examination. At the same time they furnish a simplified topographic nomenclature by means of which, practically the exact site of a section can be indicated at once and in very brief terms.

As will be seen, only the more important fissures have been indicated, and the long convolutions are subdivided by dotted lines, usually into three approximately equal parts, which are numbered from the central regions toward the poles, or, in the case of the Rolandic gyri from above downward. A line joining the distal end of the Sylvian fissure with the proximal end of the lateral occipital fissure, separates the parietal from the temporal convolutions, while a second line dropped vertically from the distal end of the intraparietal sulcus, completes the separation of the parietal and temporal lobes from the occipital.

The indexing is self-explanatory. For example:

F2L1

PCL

TL

IPL2 =

OL1

T'L3 CML

Frontal lobe, second convolution, left hemisphere, first or proximal block.

Postcentral, left, upper third.

First temporal, left, third block.

Infraparietal, left, middle third (gyrus angularis). Occipital, left, upper block (above the lateral occipital sulcus).

Fourth temporal, left, distal block (gyrus fusiformis). Callosomarginal, left (gyrus fornicatus), posterior block (adjoining gyrus Hippocampi, HCL).

The shaded portions in the diagrams represent the five blocks which are taken out at necropsy for histologic examination as a routine procedure. These blocks which should be at least 25 mm. on a side, are taken as follows:

(1) APCL Para C.

Motor region including roughly the upper third of both preand post-central convolutions and the paracentral lobule. It represents the trunk and leg areas and contains the largest Betz cells.

The pia is not removed before making the sections, and should

any difficulty be experienced in locating the fissure of Rolando in the pia-covered hemisphere, its upper extremity is readily found in the following manner. Separate the hemispheres sufficiently to expose the paracentral lobule. The ascending ramus of the callosomarginal sulcus will easily be seen, bounding the paracentral posteriorly. The first fissure in front of the upper end of this ramus, just reaching over on to the mesial surface of the hemisphere, and as a rule pointing backward, is the fissure of Rolando.

(2) Cun Lī T3.

This block representing the visual cortex should be taken so as to include the mid-portion of the calcarine fissure, with a generous margin above and below; the lower portion particularly should be ample, as the visual formation (stripe of Vic d'Azyr) regularly extends a greater distance below than above the calcarine fissure.

(3) T1-2L2.

The block lies just below the post-central gyrus and includes the middle third of the first and second temporal convolutions, containing the specific acoustic cortex.

(4) HCL Unc. & T1L1.

This block representing the olfactory cortex is taken through the Hippocampus to include the uncus, and part of the adjoining fourth temporal convolution.

(5) F1-2L2.

This block, like the first, extends over both external and mesial surfaces of the hemisphere, and contains both first and second frontal convolutions.

In these five blocks we thus have represented the various areas of special sensation, as well as a typical sensori-motor cortex and the association field of the frontal lobe. The examination of these fields in a given case affords a general idea of the extent and distribution of the morbid process. If, however, a more detailed topographic examination is desired, a number of additional blocks, for example, the following five, are also taken:

(6) FL2 (Broca's convolution).

(7) IPL2 (Angular gyrus).
(8) FIL3 (Frontal pole).
(9) CML Precuneus.
(10) APCL (Facial area).

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