CT Measurements of Cranial Growth

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                                                                                     CT Measurements        of Cranial
                                                                                     Growth: Normal Subjects

                                                Francis    J. Hahn1                     Growth     patterns    of the cranium measured     directly as head circumference             have been
                                                  Wei-Korn     Chu1                  well documented.         With the availability of computed tomography    (CT), cranial          dimensions
                                               John Y. Cheung2                       can be obtained      easily. The objective   of this project was to establish              the mean values
                                                                                     and their normal variance of CT cranial area of subjects at different ages. Cranial areas
                                                                                     and its long and short axes were measured on CT scans for 215 neurologic patients of
                                                                                     a wide age range who presented no evidence of abnormal growth of head size. Growth
                                                                                     patterns of the cranial area as well as the numeric product of its linear dimensions        were
                                                                                     determined      via a curve fitting process.  The patterns resemble    that of the head circum-
                                                                                     ference    growth chart, with the most rapid growth observed in the first 12 months of age
                                                                                     and reaching       full size    during   adolescence.       It is believed   that the availability     of such
                                                                                     reference,    in addition      to the head circumference          measurement,      will be valuable    to the
                                                                                     CT reviewer     in determining       the growth    status    of head size.

                                                                                         The growth         pattern   of the cranium        of children,    as measured       by their head
                                                                                     circumferences,         has been extensively        studied and well documented           [i -5]. Before
                                                                                     the availability      of computed      tomographic      (CT) scanners,     the measurement        of head
                                                                                     circumference         was the only feasible        means of estimating         cranial size. With CT
                                                                                     scanners,     area or linear dimensions        of the cranium can be easily obtained.           However,
                                                                                     mean values for the cranial area as determined                      on CT scans are not widely
                                                                                     available. The primary objective           of our study was to establish         a set of mean values
                                                                                     of cranial areas and their normal variances                    for subjects    at different     ages. By
                                                                                     comparing        individual    patient   measurements         with these mean values,           abnormal
                                                                                     growth of the cranium may be detected                  by CT.

                                                                                     Subjects      and Methods
                                                                                         The subjects consisted of 21 5 pediatric neurologic patients who demonstrated no evidence
                                                                                     of any disease that might affect their cranial size. Patients with indications as “rule out
                                                                                     hydrocephalus”   or “rule out microcephalus”       were automatically eliminated. There were 125
                                                                                     boys and 90 girls with ages ranging from birth to 1 8 years of age. The CT scanner used was
                                                                                     a GE 8800 with JC software package. The scan time was 9.6 sec, and the images were
      This article            appears      in the March/April                1984
                                                                                     displayed on a 320 x 320 matrix. All the patients were scanned in the standard supine
issue          of   AJNR      and the June        1984 issue         of AJR.         position with an approximately               tilt from
                                                                                                                        5#{176}-10#{176} the canthomeatal         line. The midventncular
    Received               August 13, 1982; accepted                 after revi-     slice of the CT scan, which shows the most prominent frontal horns of the lateral ventricle,
sion August                22, 1983.                                                 was selected for the estimation of the cranial area since it reflects the maximum size of the
      1   Department            of   Radiology,         University      of    Ne-    cranium. The same window setting (center at 35 with width 100) was used for screen viewing
braska         Center, 42d and Dewey Ave.,
                    Medical                                                          and hard-copy filming. Changing the window level and width to obtain an optimal display did
Omaha, NE 681 05. Address reprint requests to F.                                     not influence the measurement of the cranial area or its linear dimensions. A representative
J. Hahn.
      2   5c            of Electrical     Engineering       and Computer             slice of the CT head scan is shown in figure 1 A. Using a built-in cursor, the outer edge of the
                                                                                     cranial vault was traced and the enclosed cranial area was automatically calculated by the
Sciences,             University     of Oklahoma,          Oklahoma          City,
OK 73104.                                                                            computer. In addition, the maximum anteroposterior          (AP) dimension as well as the maximum
                                                                                     width of the cranium were also estimated            (fig. 1B). Outer diameters     of the skulls were
AJR       142:1253-1255,                June    1984
0361 -803x/84/1426--1 253                                                            assessed as AP and lateral dimensions. Both the head areas and cranial linear dimensions
c American Roentgen Ray Society                                                      were recorded for each subject. More than 90% of the measurements                  were performed by
1254                                                                                           HAHN   ET AL.                                                                                       AJR:142,June              1984

                                                                                                        TABLE          1 : Mean         Cranial          Areas     and Their         Normal              Ranges

                                                                                                                      Age                    No. of Subjects                     Mean Area          in cm         (Ranget)

                                                                                                        Subjects              2 years       old (months):
                                                                                                            1                                        17                             75.5           (63.0-88.0)
                                                                                                            2                                         6                            93.9            (81.4-106.4)
                                                                                                            3                                         4                           104.7            (92.2-117.2)
                                                                                                            4                                         6                           1 1 2.3          (99.8-124.8)
                                                                                                            5                                         8                           1 18.2 (1 05.7-i 30.7)
                                                                                                            6                                         6                           123.0 (1 10.5-1 35.5)
                                                                                                            7                                         3                           127.1        (114.6-139.6)
                                                                                                            8                                         7                           130.7        (1 1 8.2-1 43.2)
                                                                                                            9                                         7                           133.8        (1 21 .3-1 46.3)
                                                                                                           10                                         1                           136.6        (124.1-149.1)
    Fig. 1 -A,    Midventricular     shoe of CT head scan showing        prominent frontal                11                                             3                        139.1        (126.6-151.6)
horns of lateral ventricles      selected for measurement      of cranial area and linear                 12                                             9                        141 .4       (1 28.9-i 53.9)
dimensions.     B, Illustration of measurements      of maximum      AP and lateral (LAD                   13                                            1                        143.5        (131.0-156.0)
dimensions     of outer margin of cranium.                                                                 14                                            1                        145.5        (133.0-158.0)
                                                                                                           15                                            1                        147.3        (134.8-159.8)
                                                                                                          16                                             3                        149.0        (136.5-161.5)
                                                                                  .    *   .
                                                                                                          17                                             3                        150.6        (138.1-163.1)
           220                                                                                            18                                             3                        152.1        (139.6-164.6)
                                                                                                          19                                             1                        153.6        (141.1-166.1)
            200                                                                                           20                                             1                        154.9        (142.4-167.4)
            150                                                                                           21                                 2                                    156.2        (143.7-168.7)
            180                                                                                           22                                 1                                    1 57.5       (145.0-170.0)
 t          170                                                                                           23                                 2                                    1 58.7       (146.2-171.2)
     ,      160                                                                                           24                                14                                    159.8        (147.3-172.3)
     <      150                                                                                         Subjects              3 years old (years):
     t      140
                                                                                                            3                               13                                    1 63.0       (146.4-179.4)
     .-j    130
                                                                                                               4                                     14                           169.4        (152.9-185.9)
                                                                                                               5                                      5                           174.4        (157.9-190.9)
     <      110
                                                                                                               6                                         8                        178.6        (162.1-195.1)
                                                                                                               7                                         7                        182.0        (165.5-198.5)
     0      100
                     XMULTIPLE                                        DATA       SAMPLES                       8                                         8                        1 85.0       (168.5-201.6)
                                                                                                               9                                         6                        187.7        (171.2-204.2)
                                                                                                           10                                            8                        190.1        (173.6-206.6)
             70’                                                                                                                                                                  192.2        (195.7-208.7)
                                                                                                           11                                            7
             60’                                                                                           12                                                                     194.2        (177.7-210.7)
                                                                                                           13                                        11                           196.0        (179.6-212.6)
                                 1012141618202224             4   6   8   1012141618
                                    MONTH                 -               YEAR                  -=
                                                                                                           14                                            5                        197.7        (180.7-213.7)
                                                    AGE                                                    15                                            6                        199.2        (182.7-215.7)
                                                                                                           16                                            6                        200.7        (184.2-217.2)
                                                                                                           17                                            7                        202.1        (185.6-218.6)
    Fig. 2.-Growth  pattern of head sizes as measured  by CT cranial area from
                                                                                                           18                                            3                        204.4        (187.9-220.9)
blrth to 18 years of age. One-month-old group includes   newborn    to 45 days:
24-month-old group includes 24-30 months. Each dot represents one subject.                                 .   Mean    area    is derived   from   the   regression    formula   provided     in   the    text.

                                                                                                           t Range reflects the 90% of the population                  closest   to the mean.

the        primary       author, with less than 10% being measured by CT
technicians.            The interobserver  error was determined by requesting
different          observers (two radiologists     and two CT technicians) to                           base together        with the mean and variance values is shown in
measure            the same CT head scan. The error was less than 3% in                                fig. 2. Analyses        were performed          separately     for data below 2
both the           area and dimensional measurements.        The accuracy of the                        years old and above 2 years old. The mean values as well as
area and            distance measurements      were better than 1 % when meas-                         their normal limits are also shown in table i . The regression
urements            were performed on phantoms with comparable dimensions.                             formula      for cranial area as a function              of age for ages less
                                                                                                       than or equal to 24 months is: area (cm2) = 75.55 + 26.5 x
                                                                                                       logn (age in months);         for this equation,        r = 0.96. The regres-
                                                                                                       sion formula        for cranial area as a function              of age for ages
     The data recorded       for each subject      included    age, cranial                            more than 2 years is: area (cm2) = 1 40.i i + 21 .44 x log,,
area, and AP and lateral cranial dimensions.             Under 2 years of                              (age in years); for this equation,            r    0.86.            =

age, the ages were recorded             in monthly      units, and over 2                                  Although     the head area can be measured              easily when scans
years in yearly units. The 2 year dividing point was arbitrarily                                       are displayed        on a CT display monitor, their values cannot be
chosen because        rapid head growth was observed             during the                            obtained      easily when the scans are presented                   in hard-copy
first 1 2 months,     gradually   slowing   in the second i 2 months;                                  format. To overcome            this difficulty,     linear dimensions       of the
and the patient ages recorded           on the requisition     forms were                              cranium,      which can be easily measured               on films, are thought
monthly below 2 years and yearly beyond that age. A scatter                                            to be useful              in determining              the      growth         status         of the           cranium.
plot showing      all the cranial areas that constitute            the data                             Since         the cranium             is often           elliptical,      both        its long              (AP) and
AJR:142,         June 1984                                                CT       MEASUREMENTS                                  IN        NORMAL       CRANIAL              GROWTH                                                       1255

                                                                                                                                               200   cm2. The same growth          pattern is seen on the standard
                                                                                                                                               Nellhaus   head circumference           charts    used by the bedside
       240’                                                                                                                                    physician   [1]. An identical growth pattern is observed              for the
   E   220.                                                                                                                                    product   of the linear dimensions          measured      from CT scans,
   U   200’                                                                                                                                    which show the mean values to increase from 95 cm2 to 180
  0    180’                                                                                                                                    cm2 during the first i 2 months of age, and then increase                   to
                                    ----         5%                                                                                            200 cm2 at 2 years. When fully grown the mean value of the
  0    140’
                                                                                                                                               product is about 260 cm2. Although             the profiles of both area
                                                                                                                                               and product      curves are similar, the area curves              should be
           80                                                                                                                                  used to obtain the head size. The product                   should only be
           60’                                                                                                                                 used when area values are not available. We also believe that
                    I     I     J                 I      J          I     I    I        ‘   T1                                                 the normal ranges are of more clinical value than the mean
                    2     4     6      8    10    12

                                                         14   16   18    20   22   24   4   6    8    10

                                                                                                            12     14      16

                                                                                                                                               values to determined       abnormal      growth.
   Fig. 3.-Growth                  pattern  of head sizes                      as product        of CT           cranial        linear
dimensions   from             blrth to 1 8 years of age.                                                                                         We thank W. Boyd, M. Ferguson, and D. Plettner for measure-
                                                                                                                                               ments; A. Torkelson and A. Fisher for clinical information; F. Messner,
                                                                                                                                               Sacred Heart Hospital, Yankton, SD, for sending CT measurements
                                                                                                                                               of his patients;     and C. A. Dobry,             Department       of Radiology,     for interest
short lateral axes have to be measured.              To better estimate                                                                        and encouragement              in this project.
its size from the measured          linear dimensions,     numeric    prod-
ucts of these two dimensions           were obtained     and used as the
cranial size estimator.       Figure 3 shows the predicted            mean                                                                     REFERENCES
values and their normal ranges as estimated                by regression                                                                        1.   Nellhaus       G. Head circumference                from birth to eighteen           years.
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cranial product as a function of age when age is less than or                                                                                   2. Pryor HB. Charts                 of normal       body measurements              and revised
equal to 24 months is: product (cm2) = 96.1 8 + 34.5i                x log,,                                                                         width-weight            in graphic form. J Pediatr 1966;68:615-631
(age in months);      for this equation,     r = 0.96. The regression                                                                           3. McCammon            AW. Human growth and development.         Springfield,
formula    for cranial product        as a function     of age for ages                                                                            IL: Thomas,         1970
greater   than 2 years is: product         (cm2) = 1 81 .64 + 28.06 x                                                                           4. Marks HG, Boms P, Stag NL, Stine SB, Stroud HH, Zates TS.
                                                                                                                                                   Catch-up brain growth-demonstrations by CAT scans. J Pediatr
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                                                                                                                                                5. Sher PK, Brown SB. A longitudinal study of head growth in
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                                                                                                                                                   Med Child Neuro! 1975;17:7i        1-718
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cranial size as determined            by the number of pixels has also                                                                          7. Hahn FJY, Aim L. A quantitative analysis of ventricular size on
been investigated          [9]. Sabattin   [1 0] has presented      a critical                                                                     computed tomographic scans. CT 1977;1 :121-125
                                                                                                                                                 8. Hahn FJY, Schapiro   AL. The                        excessively  small ventricle    on
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                                                                                                                                                    computed  axial tomography                          of the brain.    Neuroradiology
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                                                                                                                                                     1976;12:       137-1     39
    The most rapid head growth              is noted during the first i 2
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