STUDIES IN A-SCAN ECHOENCEPHALOGRAPHY. EVALUATION OF A
PROPOSED T W O PHASE SHIFT
HELIO LEMMI; A M I N A . FARIS; JOSEPH BELLUOMINI
The use of ultrasound for diagnosis of intracranial pathology was
introduced by Ballantine and associates
1. Leksell
1 0>
1 1and Lithander
1 2further confirmed its value in clinical practice. These authors also
con-tributed to the theoretical and practical applications of the A-scan
Echoen-cephalograph. These reports were followed by those of Jeppson
8, Ambrose ~
L,
and Ford and Ambrose
5, the latter report analyzing the findings in 1,000
cases and confirming the value of echoencephalography in demonstrating
shifts of the midline intracranial structures in pathologic states. Similar
conclusions were reached by Jefferson
6, Dreese and Netsky
4, White and
associates
1 4, and Lapayowker and Christen
9, and many others.
To date, 3 mm shift of the midline intracranial structures has been
considered normal. In our experience much significant pathology is found
in individuals demonstrating midline shifts within the border zones of 3 mm.
Establishment of an intermediary zone of midline shift around 3 mm between
normal and abnormal seemed desirable and would be significant in alerting
the physician to seek pathology by additional available means of diagnosis.
The purpose of this study is to present data in support of this hypothesis.
We will not concern ourselves with the type and precise location of
the neoplastic and other pathology encountered. Such discussions have
been presented by several previous workers.
M A T E R I A L A N D M E T H O D S
Echoencephalography w a s performed on 4 4 0 consecutive cases. A n Ekoline 2 0 D i a g n o s t i c U l t r a s o n o s c o p e w a s used. This w a s equipped w i t h a Polaroid L a n d -C a m e r a for p e r m a n e n t recording. T h e transducer probe w a s a barium t i t a n a t e crystal with a diameter of 1 7 . 5 m m operating a t 2 . 2 5 m e g a c y c l e s with approxi-m a t e l y 200 pulses per second and a pulse l e n g t h of 1 approxi-microsecond. T h e recordings w e r e performed by placing the transducer a t the s q u a m o u s portions of the temporal
bone 2 c m a b o v e t h e m a n d i b u l a r j o i n t . T h e records were produced both the left a n d right side of the head a n d t h e t w o midline echos were compared. T h e final m e a s u r e m e n t w a s obtained f r o m t h e a v e r a g e of several readings.
T h e patients were referred for this study w i t h suspected intracranial p a t h o l o g y . T h e g r o u p was an a d u l t one, the ages r a n g i n g f r o m 1 7 to 7 4 years. T h e 4 4 0 cases were divided into three g r o u p s : Group I, n o r m a l midline m e a s u r e m e n t - t h a t showed less than 2.5 m m shift ( T a b l e 1 ) ; Group II, borderline midline m e a s u r e m e n t - t h a t showed 2 . 5 to 3 . 5 m m shift ( T a b l e 2 ) ; Group III, a b n o r m a l midline m e a s u r e m e n t -demonstrated m o r e t h a n 3.5 m m shift f r o m midline ( T a b l e 3 ) .
T h e diagnosis w a s m o s t often verified by a n g i o g r a p h y , p a r t i c u l a r l y in those patients suspected of h a v i n g a space o c c u p y i n g lesion; p n e u m o e n c e p h a l o g r a p h y w a s performed infrequently. Verification w a s also obtained by surgical exploration a n d / o r autopsy. A s indicated by the t a b u l a t i o n s some patients were n o t subjected to a n y of these m o r e elaborate diagnostic studies. A clinical f o l l o w - u p of not less t h a n six m o n t h s w a s regarded as reliable evidence of absence of surgical and non-surgical progressive lesions in these patients.
A l l the analyses were m a d e without f o r e k n o w l e d g e of the reason for which t h e study w a s performed. T h e results were t a b u l a t e d and correlated with the clinical and other laboratory studies a t a l a t e r date. T h e time interval between p e r f o r m a n c e of the e c h o e n c e p h a l o g r a m and the contrast study, surgery a n d / o r a u t o p s y did not e x c e e d in m o s t instances a period of one week.
Mention of the pineal g l a n d on plain skull x-rays will be omitted f r o m the analysis; it w a s found to be visibly calcified in less than 1 0 % of these cases studied.
R E S U L T S
Group I totaled 3 4 7 cases interpreted as "normal" by echoencephalography because there was less than 2 . 5 m m shift of midline. T h e results of diagnostic studies of this group are s h o w n in T a b l e 1. In this group there w e r e 5 cases of intracranial neoplasm. One w a s a k n o w n a s t r o c y t o m a of the right hemisphere that w a s re-operated without further contrast studies. One case was an a s t r o c y t o m a of the cerebellum. T h r e e additional cases showed shifts of the anterior cerebral artery exceeding 2 m m by arteriography: one a craniopharyngeoma, one a m e t a s t a t i c c a r c i n o m a and one a g l i o m a . Cerebellar and midline cerebral t u m o r s obviously are not expected to s h o w a midline deviation. There were 7 subdural and 4 epidural h e m a t o m a s . T h e epidural h e m a t o m a s were diagnosed upon surgical e x ploration w i t h n o contrast studies h a v i n g been performed. F o u r subdural h e m a -t o m a s were diagnosed by ar-teriography, bu-t none showed any r e m a r k a b l e shif-t of midline structures. Of 2 9 cases of cerebral infarction, cerebral arteriography w a s done in 1 1 cases. N i n e demonstrated m o r e t h a n 2 m m shift of the anterior cerebral artery; t w o d e m o n s t r a t e d occlusive disease of the middle cerebral artery. T h e two cases of intracerebral h e m a t o m a diagnosed by arteriography showed shifts of the midline structures t h a t w e r e not d e m o n s t r a t e d by echoencephalography. In the category of contusion, 1 0 of 38 cases were studied by cerebral a n g i o g r a p h y and seven showed b o w i n g of the anterior cerebral arteries. Of these, four showed recognizable shift of the anterior cerebral arteries t o one side or the other. I n the m i s c e l l a n e o u s group that has been t a b u l a t e d separately in T a b l e 4, eight cases of subarachnoid h e m o r r h a g e d e m o n s t r a t e d t h e presence of berry a n e u r y s m s by arteriography but no shift of the midline structures.
I n s u m m a r y , in this g r o u p of 347 cases s h o w i n g less t h a n 2.5 m m shift, there w e r e 3 3 cases t h a t d e m o n s t r a t e d significant intracranial p a t h o l o g y by other procedures, b u t t h a t were missed by echoencephalography for a "miss rate" of roughly 1 0 % .
T h e results in Group I I — 37 cases — a r e s u m m a r i z e d in T a b l e 2. T h e r e were six cases of t u m o r . By a r t e r i o g r a p h y f o u r d e m o n s t r a t e d definite shifts and t w o showed questionable shifts. T h e r e were five cases of subdural and epidural h e m a t o m a , f o u r or which on contrast studies d e m o n s t r a t e d midline shifts of over 2 m m . There w e r e also t w o cerebral h e m a t o m a s , and t w o cases of contusion for a total of 1 7 cases ( 4 6 % ) with significant intracranial p a t h o l o g y causing shift of the midline structures. T h e miscellaneous portion of t h e group is s h o w in T a b l e 4.
D I S C U S S I O N
Previous workers studying the midline structures by
echoencephalo-graphy have regarded a 3 mm shift as the upper limit of normal in adults.
DeVlieger and Ridder
3studied 47 cases by this criterion, with confirmation
of the midline by other studies in 45. Jefferson
7in a series of 50 cases
found. 85% accuracy in the echoencephalographic as confirmed by other
parameters. Lithander
1 2studied 373 patients, of which 229 were also
examined by cerebral contrast studies. In this study, of the 83 patients
with echoencephalographic displacement of the midline beyond 3 mm, 82
were verified by radiography. Eight of 14 cases demonstrating lesser shifts
were found to have significant shifts on a radiologic examination, but of
147 cases demonstrating midline echoencephalograms only eight were found
to have significant midline shifts by intracranial contrast studies. Taylor
et a l .
1 3confirmed the midline measurement by contrast studies in 87%
of 248 patients. Jeppson
8studied 579 cases, using the criteria of 3 mm
shift as upper limit of normal, and divided his patients into groups of tumor,
trauma and vascular disorders. In 12 cases the echoencephalogram was
incorrect in the prediction of the midline position. Jefferson
7concluded
that echoencephalography was unreliable in 10% of 229 neurosurgical cases.
In the study of Ford and Ambrose
5a series of 1,000 patients was reported of
which 857 were subject to radiologic investigation. In this study the
correlation rate was 95% in cases that had no significant intracranial
pathology — showing no midline shifts — and 91% correlation with
pathology in those cases showing displacement of midline structures.
In our experience there seemed to be unreliability of interpretation
primarily in those echograms where the apparent shift fell within the
range of 2.5 — 3 . 5 mm. In order to test this impression, we elected to
set arbitrarily the upper limits of normal deviation of the midline echo
at 2.5 mm; 2.5 to 3 . 5 was designated as borderline; above 3.5 mm was to
be regarded as abnormal. Use of these criteria afforded a practical and
reliable basis for judgment within the results obtained in our study. Thus,
of the 347 cases in Group I demonstrating less than 2 . 5 mm shift, the
"miss" rate was an overall 10%, correlating favorably with previous authors.
In Group II, the overall rate of significant intracranial pathology was 46%.
In these cases the midline measurement fell almost equally on either side
of the 3 mm point, indicating that a shift within this narrow range would
have almost a 50% chance of demonstrating significant intracranial
pa-thology.
Group III cases demonstrated 100% correlation with significant
in-tracranial pathology, almost exclusively space occupying lesions as indicated
in Table 3.
From the reported material in the literature and our present material
it is clear that midline shifts of up to 2.5 mm seldom relate to intracranial
pathology. Those cases demonstrating midline echo shift of 2.5 to 3.5 mm
should have further clinical evaluation. A shift of 3.5 mm or more is very
reliable evidence of a space occupying lesion.
S U M M A R Y
A series of 440 patients studied by echoencephalography is reported. Rather
than dividing the patients in the classic two groups of less than 3 mm and
more than 3 m m deviation of the midline, the patients in this study were
divided into three groups, correlating the degree of midline shift to the
presence of intracranial pathology. Group I, showing 0 to 2.5 m m shift
proves to be normal with a "miss" rate of only 10%. Group II, showing
2.5 to 3.5 m m shift is regarded as a borderline group with an incidence
of significant intracranial pathology of 46%, clearly indicating the need for
further evaluation. Group III, demonstrating greater than 3.5 mm shift
from the midline, is designated with confidence as abnormal, with a yield
of significant intracranial pathology of 100% in this study.
R E S U M O
com menos de 3 m m e mais de 3 m m de desvio). Subseqüentemente cada um
dos três grupos foi analisado com relação ao diagnóstico final de cada
paciente. Os pacientes do grupo I, com desvio máximo de 2,5 m m e
con-siderados normais c o m relação ao ecoencefalograma, apresentaram
aproxi-madamente 10% de patologia intracraniana que não foi denunciada pelo
eco. O grupo II, considerado questionável e com desvio de 2,5 até 3,5 mm,
mostrou uma incidência de patologia intracraniana de 46% e, porisso
mes-mo, claramente necessita outros meios diagnósticos. N o grupo III, c o m
mais de 3,5 m m de desvio e considerado anormal, quase todos os doentes
apre-sentaram patologia intracraniana séria, principalmente de ordem tumoral.
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