Download Down Syndrome: MR Quantification of Brain Structures and

1207
Down Syndrome:
MR Quantification of
Brain Structures and Comparison with
Normal Control Subjects
Serge Weis 1
Germain Weber-2·3
Andreas Neuhold 4
Andreas Rett 3
For quantification of brain structures from MR scans, a novel, powerful stereologic
tool known as Cavalieri's principle was applied. This tool enables an objective estimation
of volume. The method was applied to detect differences in various brain structures
between persons with Down syndrome and control subjects. On the basis of absolute
values, smaller volumes for the whole brain, cerebral cortex, white matter, and cerebellum were seen in persons with Down syndrome. Similar results were observed when a
normalization procedure, based on the volume of cranial cavity, was used.
Stereologic determinations of the volumes of brain structures from MR images can
reliably identify volume differences between persons with Down syndrome and control
subjects.
AJNR 12:1207-1211, November/December 1991
Received October 2, 1990; revision requested
January 14, 1991 ; final revision received May 13,
1991; accepted May 31 , 1991 .
This work was supported by the Ludwig Boltzmann Society, Austria.
' Institute of Neuropathology, University of Munich , Thalkirchnerstrasse 36, D-8000 Munich 2,
Germany. Address reprint requests to S. Weis .
2
Institute of Psychology, University of Vienna,
Golsdorfgasse 3/2, A-1 010 Vienna , Austria .
3
Ludwig Boltzmann Institute for Research on
Brain Damaged Children, Neurological HospitaiRosenhugel , Riedelgasse 5, A-1130 Vienna, Austria.
' Department of Radiology, Hospital Rudolfinerhaus, Billrothstrasse 78, A-1190 Vienna , Austria.
0195-6108/91 /1206-1207
©American Society of Neuroradiology
Morphometry gives reliable , objective, and reproducible data that permit easy
comparisons of results derived from brains in different clinical conditions . Stereology, a morphometric discipline, is a body of mathematical methods relating threedimensional parameters defining the structure to two-dimensional measurements
obtainable on sections of the structures [1]. By these means, subtle differences in
the structure of the brain as found in various clinical conditions can be assessed
easily. The ensuing information is clinically valuable for diagnostic decisions and
therapeutic interventions.
Down syndrome (OS) is known to be one of the major conditions related to
mental retardation . DS results from meiotic nondisjunction of chromosome 21 in
95% of cases, from translocation of parts of this chromosome in 3% of cases , and
from mosaicism in 2% of cases [2 , 3]. Neuropathologic features of DS are lower
brain weight; smaller frontal lobes, brainstem, and cerebellum; and reduced frontoorbital diameter [4] . These descriptions are based on findings derived from brain
autopsies; therefore , they are affected by possible postmortem problems like
preterminal events, postmortem delay time , fixation , and weighing . All of the
problems mentioned can be avoided with the use of axial CT or MR scans.
Morphometric data derived from the brains of persons with DS and based on
stereologic methods are thus far lacking . The only attempts to quantify brains of
living persons with DS have been based on CT measurements [5 , 6]. However, as
resolution and delineation of different brain structures on CT scans are limited ,
morphometric evaluations based on CT scans seem to be inadequate. In contrast ,
MR scans give higher resolution and allow proper delineation of gray and white
matter as well as of brain nuclei [7 , 8] .
The present study reports on quantitative data of different structures of brains
obtained from MR scans of persons with DS compared with age-matched control
subjects. Cavalieri 's principle [9], a novel , powerful stereologic tool for estimating
the volumes of brain structures, was applied . Furthermore, problems related to
normalization of brain volume to body height were considered, and a normalization
1208
WEIS ET AL
procedure based on the volume of the cranial cavity was
carried out.
AJNR:12 , November/December 1991
For statistical analysis , the one-way analysis of variance (ANOVA)
was computed with the software package STATGRAPHICS.
Results
Subjects and Methods
In the investigation group of OS subjects, we studied seven adults ,
two women and five men 30-45 years old (mean age, 38 years). OS
subjects were participants in an interdisciplinary investigation that
included medical screening tests as well as psychological assessments (1 0). These seven were recruited from their family homes, and
all of them showed a trisomy 21 karyotype originating from chromosomal nondisjunction.
The control group comprised seven persons, two women and five
men 36-44 years old (mean age, 38 years). Neither neuropathologic
nor other clinical symptoms were seen in the control subjects. None
were on neuropsychopharmacologic treatment.
Imaging was performed on a 0.5-T superconductivity unit (Philips
Gyroscan S5) with a spin-echo (SE) technique and an inversionrecovery (IR) technique. With theSE technique, T2-weighted images,
2000/50,100/2 (TRfTEfexcitations), were obtained in axial planes.
The IR technique provided T1-weighted images, 1800f400f80/2 (TR/
TlfTEjexcitations), in axial planes. The images obtained with the IR
technique had a slice thickness of 8 mm and a slice gap of 1.6 mm.
Thus, the slice thickness plus slice gaps equaled 9.6 mm . The imaging
matrix was 256 x 256 and the field of view was 250 mm.
Volume measurements were based on Cavalieri's principle (9, 11 ,
12]: The volume of any object may be estimated from randomized
and parallel sections separated by a known distance by summing up
the areas of all cross sections of the object and multiplying this sum
by the known distance . The MR scans were randomized, since the
first slice hitting the brain fell randomly ; these were followed by
systematic sections, with the known fixed interval equal to the slice
thickness plus slice gap. The first slice was positioned at a distance
less than 9.6 mm below the upper margin of the cortical surface. The
MR images were fed with a camera into the image analysis system,
IBAS 2000 (Kontron , Eching , Germany). The contours of the different
brain structures were manually traced with a cursor by one of the
authors. Each brain structure was traced three times. A mean value
was calculated and subsequently used for statistical analyses. The
accuracy of the measurement was verified by calculating the coefficient of error. The profile area of the brain structures was then
measured for each slice. The profile areas of each brain structure
were summed up and multiplied by slice thickness.
The volumes of the following brain structures were determined:
cerebral cortex , white matter, ventricles , thalamus. caudate nucleus,
lentiform nucleus , cerebellum , and brainstem. The measurement of
the ventricles included measurements of the lateral, third, and fourth
ventricles. Measurement of the lentiform nucleus included measurement of the putamen and globus pallidus . The volume of the whole
brain resulted in summing up the volumes of the previously defined
structures . In addition, the volume of the intracranial cavity was
determined .
The coefficient of error is an indicator for the precision of measurements of individual brain structures . The coefficient of error was
calculated for each brain structure. Details regarding the coefficient
of error have been published (11 ).
The following normalization procedure was used: The volume of
the different brain structures was related to the volume of cranial
cavity. The volume of the cranial cavity was set at 100% . Values for
the volume of the different brain structures were calculated relative
to the cranial cavity. Furthermore , we related the volumes of different
brain structures to the volume of the whole brain. The volume of the
whole brain was set at 100% . Values for the volumes of the different
brain structures were calculated relative to the whole brain .
On the MR scans of the DS and control groups, no pronounced signs of atrophic changes were seen on the basis
of direct visual examination by an experienced neuroradiologist (Fig. 1). Values for the coefficient of error giving the
precision of the measurement were not tabulated . They were
less than 5% for the following brain structures: cranial cavity,
brain, cerebral cortex, white matter, ventricles, thalamus,
cerebellum, and brainstem. They ranged between 5% and
10% for the caudate and lentiform nuclei. Thus, accuracy and
precision of the measurement were given corresponding to
the rules of the coefficient of error and systematic sampling
[11 ].
The morphometric data of the different brain structures as
measured on T1-weighted MR scans for the investigation and
control groups are shown in Table 1. A significantly smaller
volume of the whole brain was measured in persons with DS
as compared with controls. This difference in volume was
attributable predominantly to a reduced volume of cerebral
cortex and white matter in DS as compared with controls .
The volume of the cerebellum in DS also showed significant
differences in comparison with the control group. The other
brain structures did not show significant differences between
persons with DS and control subjects.
Different results were obtained when ratios relating the
volume of brain structures either to the volume of the cranial
cavity or to the volume of the whole brain were calculated
(Table 2). With the use of the proposed normalization procedure based on the volume of the cranial cavity, the ANOVA
computations gave approximately the same results as obtained with absolute values (see Table 1). However, when
Fig. 1.-Horizontal MR scan of a person with Down syndrome. The
following brain structures dispiayed on the scan were analyzed: cerebral
cortex, white matter, ventricles, caudate nucleus, lentiform nucleus.
AJNR :12, November/December 1991
BRAIN MEASUREMENT ON MR IN DOWN SYNDROME
TABLE 1: Absolute Values for Volumes of Different Brain
Structures Obtained by Morphometry of MR Scans from Persons
with Down Syndrome and Control Subjects
Mean Volume in cm 3 (SD)
Structure
Brain
Cerebral corte x
White matter
Ventricles
Thalamus
Caudate nucleus
Lentiform nucleus
Cerebellum
Brainstem
Cranial cavity
Controls
(n = 7)
Down Syndrome
(n = 7)
1313.1 (146.0)
632.5 (65 .1)
462.4 (56.1)
23 .3
(9.1)
16.7
(4 .9)
8.5
(1.7)
14.0 (1 .5)
149.4 (31 .2)
29 .9
(6.2)
1571 .2 (231.0)
1081 .6 (81 .0)
528 .8 (40 .1)
360.3 (51.1)
29 .1 (13.2)
14.3 (6.5)
8.6 (2.5)
14.5 (3 .6)
121.3 (12.5)
24 .4 (3.4)
1443.2 (99.0)
F
Ratio
Value
13.5
12.8
12.6
0.9
0.6
0.0
0.1
4.7
4.0
1.8
.003
.004
.004
.36
.46
.96
.76
.05
.07
.20
p
TABLE 2: Normalization Procedures of Brain Structures: Ratios
in Down Syndrome and Control Subjects
Brain Structure/Whole
Brain
Brain Structure/Cranial
Cavity
Structure
Controls
Brain
Cerebral cortex
White matter
Ventricles
Thalamus
Caudate nucleus
Lentiform nucleus
Cerebellum
Brainstem
48 .2
35 .2
1.7
1.2
0.6
1.1
11 .3
2.3
Down
Down
p
p
Controls
Syndrome Value
Syndrome Value
48.9
33.3
2.6
1.3
0.8
1.3
11 .2
2.2
.57
.27
.09
.88
.18
.08
.90
.88
83.6
40 .3
29.4
1.5
1.1
0.5
0 .9
9 .5
1.9
75 .0
36 .6
25 .0
2.0
1.0
0.6
1.0
8.4
1.7
.001
.01
.02
.16
.66
.59
.36
.06
.22
relating the volume of brain structures to the volume of the
whole brain by relying on these relative values , we were
unable to observe any difference between the two groups
(Table 2).
Discussion
Measurements on CT scans have been performed by different investigators [13-19] in an attempt to quantify changes
of brain structures occurring with normal and pathologic
aging. In most of these investigations, linear, one-dimensional
measurements were used to determine specific parameters
related to the ventricular system, skull vault, and external
CSF spaces. Since the basic rules of stochastic geometry are
not followed , meaningful results based on one-dimensional
parameters are limited. Priority has to be given to volume
estimation as a three-dimensional parameter rather than to
linear, one-dimensional parameters [20] .
Objective estimations of the total ventricular volume of the
brain in 10 hydrocephalic children and adults have been
determined recently by stereologic assessment of CT scans
[21]. Values of ventricular volume were compared with values
obtained by Evan's ratio. Evan 's ratio is derived from the
widths of the right and left anterior horns divided by maximum
width of the internal skull [13, 22]. The authors of the previous
study [21] showed that Evan's ratio is of dubious value .
CT and MR scans have been analyzed by semiautomated
1209
image analysis [5, 6, 19, 23-27] . The analysis procedures
use the differences in gray level of pixels to differentiate
between and delineate brain structures. With some ease, the
ventricles and CSF spaces can be resolved on CT. However,
the exact boundary of cerebral cortex as well as subcortical
nuclei is very difficult to discern from CT scans. Thus , results
of morphometric analysis based on CT scans only yield a
limited amount of information . MR allows a more exact delineation between gray and white matter, as well as between
subcortical nuclei. Recently, semiautomated image analysis
procedures have been developed for morphometric analysis
of MR brain scans [25-27].
A normalization of brain volume to body height has recently
been proposed [28]. These authors rely on data showing that
brain size is proportional to body height. Since persons with
DS are of smaller stature, the authors performed a normalization of brain volume in the following way: The absolute
volume was divided by the subject's height and then multiplied
by 170 em, the average height of the male coworkers at their
laboratory. However, the relationship between brain size and
body height remains obscure, and thus its relevance is questionable. On the basis of an analysis of 3406 autopsy brains,
no significant correlation was found between brain weight
and body height. The correlation coefficient was given for
males as r = .28 and for females as r = .30 [29].
Some authors express their data in relative values or as
ratios [5, 15, 17, 27]. Such results must be interpreted very
carefully , since it should be kept in mind that, when ratios are
used, no significant differences in the structures of interest
can be detected when the structure of interest as well as the
reference structure show equivalent differences. Both arguments lead to the so-called "reference trap, " which has been
discussed in detail [30]. As shown in Table 2, the ratio of the
volume of the brain structure to the volume of the brain
masked differences that were seen when absolute values
were used. It shows that the variable of brain volume is
correlated to the volumes of the other brain structures, and
hence is not a suitable variable for a normalization procedure
in this context. For the normalization procedure, therefore ,
we introduced a reference variable that is independent. In the
sample, it could be pointed out that the volume of the cranial
cavity showed no significant differences between the DS and
control groups. Thus, when using the volume of cranial cavity
as the normalization variable relative to other volumes of brain
structures, it was demonstrated that the normalized values
showed similar differences between the two groups, as those
inferred from the use of absolute volume values .
It is interesting that the typical brachycephalic skull form of
persons with DS, which was also obvious in our DS subjects,
had no influence on the volume of the cranial cavity in comparison with that of the controls (see Table 1). In this study,
we could show that the volume of the cranial cavity was an
independent variable , as seen in Table 1. However, the volume of the cranial cavity should not be treated as an independent variable per se. Its validity as such a parameter must
be determined separately for each study. In another study,
the volume of the cranial cavity was measured in a postmortem session by occupying the cranial cavity completely with
a lubricated balloon filled with water [31] . It was shown that
1210
WEIS ET AL.
the ratio of brain to cranial cavity volume is constant in
persons 20-55 years old [31].
The question about the influence of cranial cavity to brain
size, and of brain size to cranial cavity, has to be addressed
when analyzing changes during developmental stages. In this
case each component can have an influence on the other. In
the case of hydrocephalus, the overproduction or malabsorption of CSF leads to an accelerated expansion of the brain .
Since ossification in this developmental stage is not complete,
the bony skull expands in the same way as the brain. The
opposite occurs in the case of a premature ossification of the
cranial sutures. The bony skull is no longer expanding. The
underlying brain is growing but is restricted by a rigid skull. In
adults, such cases are not encountered. The sizes of the
cranial cavity as well as of the brain have already been
determined. The brain is, however, able to regressively
change, resulting in brain atrophy. When this occurs, the size
of the cranial cavity is not affected. Intracranial space-occupying lesions like tumors, even when they reach a large size,
have no expanding influence on the cranial cavity. Considering
these points, we are confident that in our study the volume
of the cranial cavity was indeed an independent variable .
Absolute values of different brain regions derived from CT
or MR scans can be compared with those values obtained
from autopsy brains. Thus , the reliability of the measurements
performed on CT and MR scans can be evaluated. Major
discrepancies in volume estimation are found between investigations based on CT techniques [6, 19, 23] and our own
investigation, which was performed on MR scans. Comparing
the results of other MR investigations [25, 26] and our own
investigation, it can be seen that the values derived from MR
scans were very close to those values obtained from analysis
of autopsy brains [32].
Until now, only a few quantitative CT investigations have
been carried out in persons with OS [5, 6, 28, 33]. In these
investigations, it was shown that healthy adults with OS had
smaller brains and smaller intracranial volumes than did control subjects [5 , 6, 28]. Normalized volumes of CSF, ventricles , and brain parenchyma did not differ between OS and
control subjects. Furthermore, both persons with OS and
controls showed similar significant age-related incremental
increases in volumes of CSF and ventricles [5] . Increased
CSF and third ventricular volumes as well as decreased gray
and white matter volumes were found in older persons with
OS (> 45 years), who showed signs of dementia as compared
with younger OS adults [6]. The authors concluded that brain
atrophy must be present to accompany dementia in older
persons with OS, despite the presence of Alzheimer neuropathology in all older subjects with OS. Furthermore, in persons with OS who are over 50 years old, a significant widening
of the temporal horns has been demonstrated recently [33] .
The decrease in intracranial size seen in the previous studies
[5 , 6, 28] occurred mainly because the authors used only
seven CT scans for their measurements. Thus , they were not
able to measure the volume of the whole cranial cavity. This
may also explain the discrepancies between our results and
those reported previously.
In the present investigation, data derived by morphometric
AJNR:12 , November/December 1991
analysis of MR scans showed differences between persons
with OS and control subjects in brain volume, cerebral cortex ,
white matter, and cerebellum. In addition, measurements of
the caudate nucleus, lentiform nucleus, and thalamus are
reported. No differences in the volume of these latter structures were found between OS and control subjects. Furthermore, the volume of the brainstem was reduced in subjects
with OS in comparison with controls, but this difference did
not reach statistical significance. The most striking difference
between both groups was smaller volumes of whole brain,
cerebral cortex , white matter, and cerebellum. However, persons with OS did not show specific atrophic changes in the
brain. It is noteworthy that no differences were found in the
volumes of the cranial cavity between persons with OS and
control subjects.
Despite radiologists' finely developed ability to interpret
morphologic patterns visually and intuitively, there are some
things they cannot assess by these means, mainly quantitative differences. Volume differences must be on the order of
30-50% to be discernible [34]. The differences in brain volume in persons with OS amounted to 18%, and thus are
within a range that can be reliably detected only by morphometry.
Cavalieri 's principle for volume estimation of structures is
a very powerful stereologic tool and, when applied to welldelineated brain structures obtained from MR scans or autopsy slices, provides objective data. The combination of the
techniques of morphometry and MR provides the most suitable method for investigating differences and changes in the
CNS in a living population for cross-sectional as well as
longitudinal studies.
ACKNOWLEDGMENTS
We thank H. OrCin and W. Schliesser for technical assistance and
S. Ettlinger, Institute of Psychology, University of Vienna, for advice
and help with the English-language text.
REFERENCES
1. Weibel ER. Stereological methods, vol. 1. London: Academic Press,
1979:1-415
2. Loesch D, Smith CAB. Discriminant diagnosis of 21-trisomy mosaicism. J
Ment Defic Res 1976;20 :207-219
3. Cooper DN, Hall C. Down 's syndrome and the molecular biology of
chromosome 21. Prog Neurobiol1988;30:507-530
4. Scott BS, Becker LE , Petit TL . Neurobiology of Down 's syndrome. Prog
Neurobiol1983 ;21 : 199-237
5. Schapiro MB, Creasey H, Schwartz M, et al. Quantitative CT analysis of
brain morphometry in adult Down's syndrome at different ages. Neurology
1987;37 : 1424-1427
6. Schapiro MB, Luxenberg JS, Kaye JA, Haxby JV, Friedland RP , Rapoport
Sl. Serial quantitative CT analysis of brain morphometries in adult Down 's
syndrome at different ages. Neurology 1989;39 :1349-1353
7. Drayer BP. Imaging of the brain. Part I. Normal findings. Radiology
1988;166: 785-796
8. Wahlund LO , Agartz I, Almquist 0 , et al. The brain in healthy aged
individuals: MR imaging. Radiology 1990;174 :675-679
9. Cavalieri B. Geometria degli indivisibili (original edition, Bologna: 1635).
Torino: Unione Tipografico-Editrice Torinese, 1966 :1-320
10. WeberG , Rett A. Down Syndrom im Erwa chsenenalter. Bern: Verlag Hans
Huber, 1991 : 1-296
AJNR:12 , November/December 1991
BRAIN MEASUREMENT ON MR IN DOWN SYNDROME
11. Gundersen HJG , Jensen EB. The efficiency of systematic sampling in
stereology and its prediction. J Microsc 1987;147:229-263
12. Cruz-Orive LM . Stereology: recent solutions to old problems and a glimpse
into the future. Acta Stereo/1987;6[suppl3]:3-18
13. Gyldensted C. Measurements of the normal ventricular system and hemispheric sulci of 100 adults with computed tomography. Neuroradiology
1977;14: 183-192
14. Meese W, Kluge W, Grumme T , Hopfenmuller W. CT evaluation of the
CSF spaces of healthy persons. Neuroradiology 1980;19 :131-136
15. Yamaura H, Ito M, Kubota K, Matsuzawa T. Brain atrophy during aging: a
quantitative study with computed tomography. J. Gerontal 1980;35 :
492-498
16. Takeda S, Matsuzawa T. Age-related brain atrophy: a study with computed
tomography. J Geronto/1985;40 : 159-163
17. Yerby MS , Sundsten JW, Larson EB, Wu SA, Sumi SM. A new method of
measuring brain atrophy? The effect of aging in its application for diagnosing dementia. Neurology 1985;35 :1316-1320
18. Massman PJ , Bigler ED, Cullum CM , Naugle Rl. The relationship between
cortical atrophy and ventricular volume./nt J Neurosci 1986;30 :87-99
19. Schwartz M, Creasey H, Grady CL, et al. Computed tomographic analysis
of brain morphometries in 30 healthy men, aged 21 to 81 years. Ann
Neuro/1985;17:146-157
20. Weis S, Haug H, Holoubek B, brun H. The cerebral dominances: quantitative morphology of the human cerebral cortex. lnt J Neurosci
1989;47 :165-168
21 . Pakkenberg B, Boesen J, Albeck M, Gjerris F. Unbiased and efficient
estimation of total ventricular volume of the brain obtained from CT-scans
by stereological method . Neuroradiology 1989;31 :413-417
22 . Evans WA. An encephalometric ratio for estimating ventricular enlargement
and cerebral atrophy. Arch Neurol Psychiatry 1942;47:931-937
23. Creasey H, Schwartz M, Frederickson H, Haxby JV, Rapoport Sl. Quantitative computed tomography in dementia of the Alzheimer type. Neurology
1986;36 : 1563-1568
24. Deleo JM , Schwartz M, Creasey H, Cutler N, Rapoport Sl. Computed-
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
1211
assisted categorization of brain computerized tomography pixels into
cerebrospinal fluid , white matter, and gray matter. Comput Biomed Res
1985;18:79-88
Filipek PA, Kennedy DN, Caviness VS , Rossnick SL, Spraggins TA,
Starewicz PM . Magnetic resonance imaging-based brain morphometry:
development and application to normal subjects. Ann Neurol 1989;25 :
61-67
Caviness VS , Filipek PA, Kennedy DN . Magnetic resonance technology in
human brain science: blueprint for a program based upon morphometry.
Brain Dev 1989;11: 1-13
Jernigan TL, Press GA, Hesselink JR. Methods for measuring brain morphologic features on magnetic resonance images: validation and normal
aging. Arch Neuro/1990;47:27-32
Schapiro MB , Haxby JV, Grady CL, Rapoport Sl. Cerebral glucose utilization, quantitative tomography , and cognitive function in adult Down
syndrome. In: Epstein CJ , ed . The neurobiology of Down syndrome. New
York: Raven, 1986:89-108
Rbthig W, Schaarschmidt W. Lineare Zusammenhange zwischen Kbrperlange und Hirnmasse. Gegenbaurs Morpho/ Jahrb 1977;123 :208- 213
Braendgaard H, Gundersen HJG. The impact of recent stereological advances on quantitative studies of the nervous system. J Neurosci Methods
1986;18 :39-78
Davis PJM , Wright EA. A new method for measuring cranial cavity volume
and its application to the assessment of cerebral atrophy at autopsy.
Neuropathol Applied Neurobiol 1977 ;3 : 341-358
Eggers R, Haug H, Fischer D. Preliminary report on macroscopic age
changes in the human prosencephalon. A stereologic investigation . J
Hirnforsc h 1984;25: 129- 139
LeMay M, Alvarez N. The relationship between enlargement of the temporal
horns of the lateral ventricles and the dementia in aging patients with
Down syndrome. Neuroradiology 1990;32 :104-107
Reith A, Mayhew TM . Stereo/ogy and morphometry in electron microscopy.
New York: Hemisphere, 1988 :1-2 15