CHAPTER III. EEG FINDINGS IN BRAIN TUMORS
The arrangemet of material complies with basic principles of neuorology:
location, depth, and the character of the pathology.
a. Focal brain lesions
1) Extracerebral (superficial) tumors
(of
frontal, temporal, and parietal, and occipital localization)
Figure
8, figure
8a, figure
13.
In
the majority of cases, meningiomas are characterized by focal, irregular
delta waves of high amplitude, sharply expressed in the region of
tumor localization; they have a frequency of 1-3 cps, with the preservation
of alpha waves if the tumor is not occipital. These tumors are characterized
by less variety, thus easier to diagnose, than intracerebral ones.
It is usually easier to diagnose extracerebral frontal tumors-in
50% of cases, they produce an EEG indicating local abnormal activity
whereas it reaches 75-80% in temporal tumors. In some cases, alpha
rhythm is observed in the damaged hemisphere (Shmelkin, D. 1957).
In meningial tumors of frontal and temporal localization, polymorphic
slow waves (of constantly changing configuration and form) are expressed
in the temporal and frontal regions not as clearly as in other tumors.
More often, in these cases, the increasing amount of alpha rhythm
and waves of the theta range in combination with sharp waves are
noticeable in the damaged hemisphere (in the posterior region of
the temporal lobe).
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In
tumors of the occipital region, only the reduction of alpha rhythm
with polymorphic slow wave activity may occur in the EEG.
2) Intracerebral tumors
Figure
18
The
EEG findings in deep intracerebral tumors differ from extracerebral
ones. They are produced by deeper, severe general changes in the
brain and, consequently, by more severe EEG findings. Typical polymorphic
delta waves (with different, irregular configuration) appear in
the region of the lesion; the presence of these waves are noticeably
weaker in the contralateral hemisphere. Their frequencies occur
through the spectrum of delta range, and their amplitude can reach
up to 200 MKV, and more--the highest amplitude being in the area
of the tumor. These waves may be constant or sporadic and episodic.
At times, delta activity is combined with the slowing down of alpha
rhythm and the presence of sharp waves.
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CHAPTER IV
HEMATOMAS
Figs. 56-59
Hematomas
almost always can be detected in focal EEG changes. The clinical
physician must resolve the question. Which kind of hematoma is it:
subdural or epidural?
In
epidural hematomas (Figs. 57, 58) as a rule, the EEG disturbance
has asymmetrical features (in cases of damage in one hemisphere)
and is more localized and focused in the lesion. Well-expressed
pathological activity is registered as polymorphic delta waves of
high amplitude, often with the preservation of alpha rhythm on the
damaged side and always with positive developed alpha rhythm on
the "healthy" side.
In
subdural hemotomas, and especially intracerebral ones, significant
severe changes are seen (Figs. 59, 60). They appear as polymorphic
activity and also in the hemisphere contrary to the lesion. The
basic EEG rhythm will be significantly reduced in this case.
It
is necessary to notice that in the majority of cases of chronic
subdural and epidural hematomas, essential EEG changes are not noticed
(Zenkov, 1991) and in only 7.5% of all cases non-severe focal changes,
such as theta or delta-waves, are seen in the EEG. In favorable
cases in the time period after trauma, the EEG becomes normal. In
the case of development of traumatic epilepsy, the epileptical activity
appears.
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