In purulent meningitis there may be inflammation and thickening of the dura mater (pachymeningitis), and this membrane may be separated from the petrous bone. Often suppuration takes place between it and the bone ; the membrane is perforated, and pus is effused into the cavity of the arachnoid. If disease of the petrous bone is one of the consequences of the otitis, thrombosis of the cerebral sinuses may occur, and pyremia may be produced. In all cases where the dura meter is inflamed, phlebi tis and thrombosis of the cranial sinuses are frequent consequences. The coagulation of the blood and arrest of the circulation in the venous chan nels is due to narrowing of the calibre of the sinus either by pressure upon it of inflammatory products or by thickening of its walls owing to inflammatory infiltrations and abscesses. As a rule the lining membrane of the sinus is smooth, but it sometimes becomes roughened and dull looking. The clot which forms the thrombus is fibrinous, and contains but few red blood corpuscles. It is therefore whitish-yellow in colour, or slightly gelatinous-looking, from the number of white corpuscles. It may lie free in the sinus or form loose adhesions to the walls. These decolourised clots are sometimes very extensive, and may reach from the lateral sinus downwards to the vena cava. If the child live long enough, the thrombus may soften in the centre, and the disintegrated fibrine may present a pus like appearance to the eye.
The pia mater is almost always affected. Its vessels become dilated and filled with blood ; small patches of ecchymosis are scattered about ; and a yellowish or greenish exudation is poured into the subarachnoid tis sue. This exudation may be solid like an ordinary false membrane, but is often distinctly purulent. It varies greatly in amount. The cortex of the brain, as might be expected from the intimate connection which exists between its vessels and those of the investing pia realer, usually shares in the inflammatory condition, and becomes injected and softened.
Encephalitis usually occurs in patches. The vessels are dilated and congested ; there is effusion into the tissue around them which becomes swollen, red, and soft (acute red softening), and can be washed away by a stream of water. Surrounding the inflamed patch the cerebral tissue is congested and oedematous, and of a yellowish colour. As the process goes on the colour of the diseased spot changes from red to greenish ; its substance gets softer and softer, and the central part breaks down into a yellow or green purulent matter. The wall of the abscess thus formed consists of brain-substance more or less softened. The seat of the abscess in cases of otitis is in the adjacent part of the middle or posterior lobe of the cerebrum, or in the cerebellum. As a consequence of the abscess and
inflammation of the brain-substance at the spot, there is enlargement of the affected part of the brain, its convolutions are flattened, and its sulci partly obliterated.
To produce these secondary results in the skull cavity it is not neces sary that caries of the petrous bone should occur. In many cases the bone itself is found intact, the Jura matey even may have the appearance of health, and a layer of healthy-looking cerebral substance may separate the abscess from the surface of the brain.
Symptoms.—Acute otitis may be present without any symptoms indi cating the existence of the inflammation. Usually, however, as the puru lent secretion accumulates in the cavity of the tympanum, especially if the tympanic membrane shares in the inflammation, there is severe pain in the ear and side of the head, and pressure on or around the ear increases the suffering. In babies earache is a common affliction, and may even be a cause of convulsions. The child cries incessantly with a peculiar shrill scream, and refuses to be comforted. He burrows his head in his pillow, or rests it against his mother's shoulder, often lifts his hand to his head, and refuses the bottle or the breast. If the pain cease or subside for a time, he falls asleep, but usually wakes up again after a short interval screaming loudly, and continues to cry again incessantly as before. After some hours of this agony the tympanic membrane gives way, a discharge of pus issues from the meatus, and the cry at once ceases. Examination of the ear in these cases seldom affords much information, althongh the passage sometimes looks red and inflamed.
When a chronic otitis exists, there is a more or less copious purulent discharge from the ear; the tympanic membrane is destroyed, and the sense of hearing is blunted. So long as no more pus is formed than can pass readily away, no other ill effects are observed, and the absence of the tympanic membrane usually allows of free escape of the matter exuded. Sometimes, however, an accumulation of pus takes place in the mastoid cells, and ill consequences follow. The chief danger in these cases is the occurrence of a fresh acute attack. The otorrhma then ceases at once, there is an intense pain in the ear and side of the head, and often menin gitis with all its serious consequences ensues. It must be remembered, however, that as otitis may exist without giving rise to symptoms, menin gitis occurring as a result of inflammation of the tympanum is not always preceded by otorrhma. Sometimes the symptoms of meningitis precede the otorrhcea, and sometimes the otitis is latent throughout.