The subject of local diagnosis can be approached in several ways, according to the method of subdividing the brain into regions. Thus, Rosenthal discusses, in the first place, tumors of the convexity of the brain, but as this is a very general term, covering portions of several lobes, we can see no advantage in making such a subdivision.
A few general remarks might be made in the first place, however, with regard to the general symptoms presented by surface or cortical growths as compared with those which are produced by deep-seated neoplasms. The direct or indirect involvement of the membranes in nearly all cortical tumors makes the symptoms of irritation referable to these envelopes very numerous and important.
The various centres so called, motor, sensory, and of the special senses, which have their highest differentiation in the cerebral cortex, are each and all represented by well-defined tracts of white matter in the centrum ovale and capsules which connect these centres with the lower brain, the spinal cord, and the periphery of the organism. It therefore follows that symptoms produced by localized lesions of the cortex will be reproduced in other cases by those of the tracts which go to or come from these centres. We may thus have a monoplegia or a hemiplegia, a partial anæsthesia or a hemianæsthesia, a hemianopsia, a word-blindness or word-deafness, a loss of power to perceive odors or to appreciate gustatory sensations, from a peculiarly limited tumor or other lesions of either the gray centres of the cortex or of the white matter of the central area of the brain; but these specialized symptoms are more likely to arise from cortical lesions in the case of intracranial neoplasms, because of the much greater frequency with which these adventitious products arise from membranes and therefore involve the cortex.
Peculiar symptoms arise in the case of lesions of the centrum ovale from the fact that it contains not only projection-fibres which more or less directly connect cerebral centres with the outer world; but also a system of commissural fibres which unite corresponding regions of the two cerebral hemispheres by way of the corpus callosum and commissures, and a system of association-fibres which connect different convolutions together, in special cases even those which are situated remotely from each other, but are associated in function.
It is evident, therefore, as asserted by Starr,39 that a peculiar set of additional symptoms will be referable to the destruction or irritation of these commissural and association fibres. For example, failure to perform easily corresponding bilateral motions in face, hands, or feet would indicate some obstruction to conduction in the commissural fibres joining the motor convolutions. “Integrity of both occipital lobes, and simultaneous, connected, and harmonious action in both, are necessary to the perfect perception of the whole of any object when the eyes are fixed upon one point of that object.” Starr gives the following examples of the methods of detecting a lesion of such fibres: “In the case of the fibres associating the auditory with the motor speech-area the symptoms to be elicited seem to be very simple. Can the patient talk correctly? Can he repeat at once a word spoken to him? These are the questions which any one will ask who examines a case of aphasia. But this is not all. The patient must be further questioned. Can he read understandingly to himself, and tell what he has read? This will test the occipito-temporal tract. Can he read aloud? This will test the occipito-temporo-frontal tract. Can he write what he sees? This will test his occipito-central tract. Can he write what he hears? This will test the temporo-central tract. Can he write what he says, speaking to himself in a whisper? This will test his fronto-central tract. Can he name an odor or a color? Brill has recorded40 a case of lesion of the cuneus associated with color-blindness to green, and he states that the patient had difficulty in naming various colors on account of the presence of a slight degree of amnesic aphasia.... Can the patient write the name of an odor? Can he tell how a surface feels—smooth, or warm, or heavy? Such questions as these will suggest themselves at once to any one who studies the association of ideas subjectively.
“Take as an example a lesion in the centrum ovale of the occipito-temporal region. Such a lesion will produce hemianopsia, because it involves the visual tract of the projection system. It may also produce a peculiar mental condition known as word-blindness, in which the patient is no longer able to associate a word or letter seen with its corresponding sound or with the motion necessary to write it. Charcot has reported a case of this kind.... The man, who was a very intelligent merchant, was suddenly seized with right hemianopsia while playing billiards, and was surprised to find that he saw but one-half of the ball and of the table. Soon after he had occasion to write a letter, and after writing it was surprised to find that he could not read what he had just written. He found, however, that on tracing individual letters with the pen or fingers he became conscious of the letters—a few letters (r, s, t, x, y, z), however, being an exception to this rule. When a book was given him to read he would trace out the forms of the letters with some rapidity, and thus manage to make out the words. If his hands were put behind him and he was asked to read, he would still be observed to put his fingers in motion and trace the letters in the air. Speech was in no way interfered with, but reading aloud was only accomplished, like reading to himself, by the aid of muscular sense. Here, then, was an example of a lesion which had separated entirely the tract associating sight with speech—viz. the occipito-temporal tract—but had left intact the tract associating sight with muscular sense—viz. the occipito-central tract.”
39 Med. Record, vol. xxix. No. 7, Feb. 13, 1886.
40 Amer. Journ. of Neurology, Feb., 1883.
Our tabulated cases, although collected for the purpose of studying inductively the phenomena of intracranial tumors from all points of view, have been arranged to indicate, so far as is possible, the special symptoms which are produced by growths in special localities. Thus we have made thirteen subdivisions:
I. Superior antero-frontal region (5 cases).—The lateral and median aspects of the hemisphere from the anterior tip backward to the posterior thirds of the first three frontal convolutions, the region roughly bounded by the coronal suture.