(a) Temporo-sphenoidal abscess. The abscess occupies one of the so-called ‘silent’ areas of the brain, an area merely exercising a word-hearing faculty (see [p. 163]). Insomuch, however, as auditory power is already impaired or lost from the disease existent in the middle ear, it follows that a temporo-sphenoidal abscess may not give rise to any localizing symptoms whatever. Definite motor symptoms will only be observed when an abscess of considerable size exercises an upward pressure on the lower motor areas, or an inward pressure on the internal capsule. Thus, (1) when the pressure effects are exercised in the upward direction the lower motor areas will suffer with resultant paresis or paralysis of the muscles of the contra-lateral face and upper extremity, and, if the abscess be situated on the left side, aphasia may also be present. And (2) when the pressure is exerted mainly in the inward direction so as to interfere with the internal capsule the motor areas are affected in the reverse order, lower extremity first and face last.
Fig. 76. To illustrate the Pressure Effects of a Temporo-sphenoidal Abscess:—(1) upward pressure on the lower cortical motor area, and (2) inward pressure on the internal capsule. T.S., Temporo-sphenoidal abscess; a., Cortical area for lower extremity; b., Cortical area for upper extremity; c., Cortical area for face; C.N., Caudate nucleus; L.N., Lenticular nucleus; I.C., Internal capsule; O.T., Optic thalamus.
Aphasia will partake of the motor or sensory type according to the situation of the abscess. Thus, motor aphasia indicates pressure on Broca’s area, sensory points to the involvement of the region of the angular gyrus (see [p. 163]). According to Schmiegelow, some type of aphasia was present in 23 out of 54 cases of otitic temporo-sphenoidal abscess.
Facial paralysis, whether due to inward or upward pressure, is of the incomplete or cortical type, the upper face-muscles escaping or being but slightly affected. No difficulty need be experienced in differentiating between the ipso-lateral paralysis which results from destruction of the facial nerve in the aqueductus Fallopii and the contra-lateral palsy dependent on the cortical lesion.
Pressure may also be exercised on the post-Rolandic sensory areas and on the tracts that evolve therefrom, but the general condition of the patient seldom allows of any accurate diagnosis with respect to sensory involvement in general.
When the abscess is of considerable size, both third and sixth nerves may be involved. For instance, the third nerve, emerging from the brain at the anterior border of the pons, and passing along the inner border of the temporo-sphenoidal lobe, is liable to irritation or pressure paralysis. In the former case, the pupil on the affected side will be contracted, in the latter instance dilated. When ipso-lateral third nerve paralysis coexists with paralysis of the opposite face and upper extremity, a condition of crossed paralysis results.
When the sixth nerve is involved the external rectus on the side of the lesion is paralyzed with resultant internal squint. Conjugate deviation of the eyes towards the side opposite to the lesion and secondary lateral nystagmus have both been observed.
Further assistance in the localization may be obtained by careful observation as to the position of the headache, by palpation and percussion of the skull, and by a comparison of the intensity of optic neuritis in the two disks.
(b) Cerebellar abscess. Many of the symptoms previously described when dealing with brain abscess in general are intensified when the focus of suppuration is situated in the confined space beneath the tentorium cerebelli. Thus, headache is exceptionally severe and more or less localized to the occipital and cerebellar regions. Again, optic neuritis may develop rapidly and reach a high grade of intensity, vomiting is early in onset and of frequent occurrence, whilst certain other symptoms dependent on the increased intracranial pressure—slowing of the pulse, alterations in respiratory rhythm—are correspondingly accentuated.