Abscess due to Middle Ear Disease.—The most common cause of abscess in the brain is chronic middle ear disease, and the majority of cerebral abscesses are therefore situated in the temporal lobe. Some are due to direct spread from a collection of pus in relation to an erosion of the tegmen tympani, either inside or outside the dura, others to infection carried by the veins, and in this way the infective material reaches the white matter; less frequently infection from the middle ear takes place along the peri-vascular lymph spaces. Macewen has pointed out that cerebral abscess never occurs from pyogenic organisms passing from the middle ear by way of the internal auditory meatus, although lepto-meningitis may do so. Cerebral abscess is much more frequently met with in the white matter of the centrum ovale than in the cortex, and in the majority of cases the abscess is single.
The pus is often of a greenish-yellow colour, or it may be dark brown from admixture with broken-down blood-clot; in some cases it is thin and serous and contains sloughs of brain matter, and it frequently has a fœtid odour. In quantity it varies from a few drops to several ounces.
The arachno-pia over an abscess usually has a turbid and milky appearance.
In an acute abscess the surrounding brain tissue is engorged and infiltrated with pus; in a chronic abscess it is condensed, and the pus may be encapsulated by the formation of a zone of young fibrous tissue round its periphery. In this condition the abscess may remain “latent,” giving rise to no symptoms for many weeks or even months.
Clinical features.—The initial formation of pus in the cerebral tissue is associated with the sudden onset of severe pain in the head, shivering and well-marked cutis anserina, and vomiting of the cerebral type. The discharge from the ear usually diminishes or may even cease.
As a localised abscess develops the patient gradually passes, into a stuporous condition; he does not lose consciousness, but, his cerebration is slow, he seems unable to sustain his attention, for any length of time, and he answers questions “slowly, briefly, but, as a rule, correctly” (Macewen). The pain in the region of the ear becomes less intense, but the mastoid and temporal areas on the affected side are tender on percussion. The temperature falls, and, as a rule, remains subnormal. Rigors are unusual: their occurrence usually indicating the development of some complication such as sinus phlebitis. The pulse is full, regular, and slow (40 to 60). Vomiting frequently occurs, and the bowels are often obstinately constipated.
There is no actual paresis, but there is a “gradual diminution of the ability to apply his strength.” The superficial reflexes are late of disappearing and the disturbance is unilateral. The optic discs are moderately swollen. “The face is expressionless, passive, and cloudy. It may assume a meaningless smile, with which the features are not lit; it is too mechanical” (Macewen).
Differential Diagnosis.—In the early stages it is often difficult to distinguish between meningitis and cerebral abscess. The chief points on which reliance is to be placed are that in meningitis the pulse shows an irregularity, both in rate and force, which is wanting in cases of uncomplicated abscess. In meningitis the temperature is raised, while in abscess it is persistently subnormal. The superficial reflexes, particularly the abdominal reflexes, disappear early in meningitis and the disturbance is bilateral; in abscess they are slower to disappear, and one side only is affected. Retraction of the neck, when present, is a characteristic sign of meningitis. In meningitis the optic discs are highly œdematous and are more swollen than in abscess, and the condition is equally marked on the two sides.
Localisation of Cerebral Abscess—Temporal Abscess.—The existence of middle ear disease is always presumptive evidence that the abscess is in the temporal lobe on the same side. A small abscess in this lobe may produce no localising symptoms; one of large size may press indirectly on the motor cortex, on the fibres passing through the internal capsule, or on individual cranial nerves.
It is important to observe the order in which paralysis of the opposite side of the body comes on. When it begins in the face and passes successively to the arm and leg, the pressure is on the cortical centres. When the paralysis progresses in the opposite direction—leg, arm, face—the pressure is on the nerve fibres passing through the internal capsule ([Fig. 195]). The paralysis may be spastic in lesions of the cortex or internal capsule; if it is flaccid the lesion is almost certainly cortical.