. 185. Charts showing characteristic temperature and pulse rate in various intracranial complications
of middle ear suppuration.
The level of chlorides in the cerebrospinal fluid is of prognostic significance,
and if it remains normal the case is likely to recover.
An otitic brain abscess is usually found close to the disease which causes it,
and is therefore situated, in the vast majority of cases, in the temporal lobe
(Fig. 186) or in the cerebellum (Fig. 187) of the diseased side. Most autho-
rities believe that the temporal lobe abscess is the more common. An otitic
brain abscess is usually single. It may be acute, i.e. without a definite capsule,
especially in cases in which the abscess results from acute middle ear
suppuration. Chronic abscesses have a more defined capsule.
Meningeal abscess formation may occur—either subdural or between the
pia and arachnoid. Such collections of pus may be regarded as a protective
process which tends to prevent general infection of the meninges. Brain
abscess occurs as a rule between the ages of 10 and 30; it is commoner in
males than females, and is more frequently the result of chronic than of
acute suppuration. In chronic cases cholesteatoma is usually present.
Cerebellar abscess is due to: (1) Extension of infection from the mastoid
process posteriorly and medially, through the triangular area (Trautmann's)
bounded above by the superior petrosal sinus, below and in front by the
facial nerve, and behind by the sigmoid sinus: this is the most frequent route
of infection, and as a rule an extradural abscess precedes the formation of
the cerebellar abscess which is situated in or near the anterior surface of
the cerebellum, (2) Septic thrombosis of the sigmoid sinus which is usually
associated with an extradural perisinus abscess. (3) Labyrinthitis in cases
of chronic middle ear suppuration. As the cerebellar abscess grows it may
produce iofaanal hydrocephalus and "coning' of the brain -stem.
Temporal lobe abscess is caused by the spread of the infection through
the roof of the tympanic cavity or mastoid antrum. Abscess of the brain
is frequently preceded by extradural abscess. The dura mater, pia arachnoid
membrane and brain become adherent, and, an area of encephalitis or red
softening having formed first of all, the abscess develops in close relation