Parent article.

OriginalResearch n MusculoskeletalImaging
172 radiology.rsna.org n Radiology: Volume 271: Number 1—April 2014
Normative MR Cervical Spinal
Canal Dimensions1
Erika J. Ulbrich, MD
Christian Schraner, MD
Chris Boesch, MD, PhD
Juerg Hodler, MD,
André Busato, PhD, DVM, MS
Suzanne E. Anderson, MD2
Sandra Eigenheer, MD
Heinz Zimmermann, MD
Matthias Sturzenegger, MD
Purpose: To provide normal values of the cervical spinal canal and
spinal cord dimensions in several planes with respect to
spinal level, age, sex, and body height.
Materials and
Methods:
This study was approved by the institutional review board;
all individuals provided signed informed consent. In a pro-
spective multicenter study, two blinded raters indepen-
dently examined cervical spine magnetic resonance (MR)
images of 140 healthy volunteers who were white. The
midsagittal diameters and areas of spinal canal and spi-
nal cord, respectively, were measured at the midvertebral
levels of C1, C3, and C6. A multivariate general linear
model described the influence of sex, body height, age,
and spinal level on the measured values.
Results: There were differences for sex, spinal level, interaction
between sex and level, and body height, while age had
significant yet limited influence. Normative ranges for the
sagittal diameters and areas of spinal canal and spinal
cord were defined at C1, C3, and C6 levels for men and
women. In addition to a calculation of normative ranges
for a specific sex, spinal level, age, and body height data,
data for three different height subgroups at 45 years of
age were extracted. These results show a range of the
spinal canal dimensions at C1 (from 10.7 to 19.7 mm),
C3 (from 9.4 to 17.2 mm), and C6 (from 9.2 to 16.8 mm)
levels.
Conclusion: The dimensions of the cervical spinal canal and cord in
healthy individuals are associated with spinal level, sex,
age, and height.
q
RSNA, 2013
Online supplemental material is available for this article.
1
From the Department of Diagnostic, Interventional and
Pediatric Radiology (E.J.U., C.S., S.E.A., S.E.), Depart-
ment of Emergency Medicine (H.Z.), and Department of
Neurology (M.S.), University Hospital and University of Bern,
Inselspital, Bern, Switzerland; Department of Radiology,
University Hospital Zurich, Rämistrasse 100, 8091 Zurich,
Switzerland (E.J.U., J.H.); and Departments of Clinical
Research and Radiology (C.B.) and Institute of Social
and Preventive Medicine (A.B.), University of Bern, Bern,
Switzerland. Received March 23, 2012; revision requested
May 3; revision received December 27; accepted January
1, 2013; final version accepted September 26. Supported
by the National Research Programme NRP 53 “Muscu-
loskeletal Health–Chronic Pain” of the Swiss National
Science Foundation (Project Number 405340-104531), Von
Hevesy Foundation, and Inselspital Research Foundation.
Address correspondence to E.J.U. (e-mail: erikajulbrich@
googlemail.com).
2
Current address: School of Medicine, Department of
Medical Imaging, The University of Notre Dame Australia,
Sydney, Australia.
q
RSNA, 2013
Note: This copy is for your personal non-commercial use only.To order presentation-ready
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Radiology: Volume 271: Number 1—April 2014 n radiology.rsna.org 173
MUSCULOSKELETAL IMAGING: Normative MR Cervical Spinal Canal Dimensions Ulbrich et al
field of view, 260 3 183 mm; section
thickness, 3 mm; 19 sections; distance
factor, 25%; total acquisition time,
5.9 minutes. Parameters for the sag-
ittal VIBE sequence were as follows:
6.86/3.34; 176 3 256 matrix; field of
view, 180 3 124 mm; voxel size, 0.7 3
0.7 3 1 mm3
; section thickness, 1 mm;
72 sections; distance factor, 20; flip
angle, 12°; total acquisition time, 10.8
minutes. A dedicated neck coil and a
spine array coil were used with the pa-
tient in the supine position. Saturation
pulses placed over the upper airway re-
gion were used for reduction of breath
and vessel-related artifacts.
The 19 sagittal images were cen-
tered on the spinal cord at the C4 level
and were obtained from the midpoint of
the cerebellum to the second thoracic
vertebral level, and they included the
entire cervical spine.
Image Analysis
The images were analyzed by using a
picture archiving and communication
system (PACS) (Philips Easy Vision
PACS Viewing and Reporting Worksta-
tion; Philips Healthcare, Best, the Neth-
erlands) with core software (Easy Vi-
sion IDSS; Sectra, Linkoping, Sweden).
Blinded review was performed inde-
pendently by two raters (C.S., medical
student, and S.E., 3rd-year radiologist
in training) with the same viewing
Patients
We recruited 140 consecutive healthy
asymptomatic volunteers by adver-
tisement at involved local university
fraternities, nursing staff, and family
members as control subjects for a mul-
ticenter study aimed to determine the
diagnostic validity of MR imaging in
whiplash injuries, from 2006 to 2008
(12).
Definition of Healthy
The inclusion criteria were as follows:
patient was healthy according to the
EuroQol-5D questionnaire (13,14), es-
pecially without any neck symptoms
actually or in the prior history; age
older than 18 years; and signed letter
of informed consent. Exclusion cri-
teria were any of the following: pre-
vious trauma, fracture, or surgery of
the head or spine; previous history of
whiplash injury; history of any kind
of neurologic symptoms or sensory or
motor deficits of the arms; inflamma-
tory disorders; any other severe illness
(with continuous pain or reduction of
working ability); preexisting head and
neck pain; psychiatric disorders; drug
abuse; tumor or metastases of the head
and neck; claustrophobia; pacemaker;
or pregnancy. All recruited volunteers
had to fill out a questionnaire and were
examined by a physician to check for
exclusion criteria.
MR Protocol
MR images were obtained by using a
1.5-T imager (Sonata; Siemens Medi-
cal Solutions, Erlangen, Germany) and
identical sequences at both centers.
Sagittal T2-weighted and volumetric
interpolated brain examination (VIBE)
sequences were used to measure the
spinal canal and cord dimensions. Pa-
rameters for the sagittal T2-weighted
turbo spin-echo sequence were as fol-
lows: repetition time msec/echo time
msec, 5590/116; 288 3 512 matrix;
V
arious techniques are used to eval-
uate the dimensions of the cervi-
cal spinal canal (1–9). The most
frequently applied radiologic parame-
ters on standard radiographs include
midsagittal diameter and the canal-
to-corpus ratio (ie, the Torg ratio) or
Pavlov ratio measured on a lateral view
(6), interpedicular distance measured
on a frontal view (10), and cross-sec-
tional area measured on a transverse
plane at computed tomography (CT)
(4). Standard radiographs with inher-
ent magnification issues and, in part,
routine CT images primarily allow for
the evaluation of osseous structures;
however, soft-tissue abnormalities may
contribute to cervical spinal canal ste-
nosis. Magnetic resonance (MR) imag-
ing allows for evaluation of both soft tis-
sue and bone structures and accurately
measures functionally relevant spinal
canal and spinal cord dimensions in
various planes (11).
Few studies have been published
regarding potential influences of spinal
level, age, height, and sex on cervical
spinal canal and cord dimensions in
healthy people by using thin-section MR
imaging.
Our study was designed to provide
normal values of the cervical spinal
canal and spinal cord dimensions in
several planes with respect to spinal
level, age, sex, and body height.
Materials and Methods
This prospective study was part of a
larger multicenter study that involved
two university hospital centers (Univer-
sity Hospital of Basel, Basel, Switzer-
land, and University Hospital of Bern,
Bern, Switzerland) and has been ap-
proved by the ethics committees and
institutional review boards.
Implication for Patient Care
nn The reported normal values may
help in the assessment of poten-
tial cervical spinal canal stenosis
for a given clinical situation.
Advance in Knowledge
nn Sex, body height, and the spinal
level have a statistically signifi-
cant influence on spinal canal
and cord dimensions in healthy
people while age affects the
spinal cord only on a significant
level.
Published online before print
10.1148/radiol.13120370 Content code:
Radiology 2014; 271:172–182
Abbreviations:
CSF = cerebrospinal fluid
PACS = picture archiving and communication system
VIBE = volumetric interpolated brain examination
Author contributions:
Guarantors of integrity of entire study, E.J.U., S.E.A., M.S.;
study concepts/study design or data acquisition or data
analysis/interpretation, all authors; manuscript drafting or
manuscript revision for important intellectual content, all
authors; approval of final version of
submitted manuscript,
all authors; literature research, E.J.U., C.S., J.H., S.E.A.,
S.E., H.Z., M.S.; clinical studies, E.J.U., C.B., S.E.A., H.Z.,
M.S.; experimental studies, E.J.U., C.S., C.B.; statistical
analysis, E.J.U., C.S., C.B., A.B., S.E.; and manuscript edit-
ing, E.J.U., C.S., C.B., J.H., A.B., S.E.A., M.S.
Conflicts of interest are listed at the end of this article.

conditions, and one of the raters (C.S.)
performed the measurements twice.
Both were specifically trained in inter-
pretation of cervical spine MR images in
several sessions with a board-certified
radiologist (E.J.U., with 5 years of ex-
perience in spine image interpretation).
The sagittal spinal canal (cerebro-
spinal fluid [CSF] column) diameter at
C1 level was measured on the midsagit-
tal T2-weighted images as the distance
from the tectorial membrane or dura
mater to the most anterior point of the
posterior atlantic arch on a line from
the most anterior point of the anterior
atlantic arch to the most anterior point
of the posterior atlantic arch (Fig 1, A
). At the C3 and C6 levels, the sagit-
tal spinal canal (CSF column) diameter
was measured on a line drawn from the
midpoint between the superior and in-
ferior endplates of the vertebral body
and perpendicular to the anterior sur-
face of the spinal cord (Fig 2, A). The
lines were drawn on the midsagittal
T2-weighted images with magnification
31, and the measurements thereafter
were performed with magnification 33.
The sagittal spinal cord diameters were
measured along the same lines as de-
scribed above (Figs 1, A, and 2, A) at
C1, C3, and C6 levels (Figs 1, B, and
2, B). The midsagittal diameter mea-
surements were also performed on
reformatted transverse 1-mm VIBE im-
ages at the C1, C3, and C6 levels. At
the C1 level, the spinal canal diameter
was measured on a line drawn from the
most concave point of the anterior at-
lantic arch to the most concave point of
the posterior atlantic arch (Fig 3, A).
At the C3 and C6 levels, spinal canal
diameters were measured on a line
drawn from the midpoint of the verte-
bral body to the midpoint of the cor-
responding spinous process (Fig 3, B).
The lines were drawn on reformatted
transverse VIBE images with magnifica-
tion 31, and measurements thereafter
were performed with magnification 32.
The transverse VIBE images were re-
formatted on the workstations based
on sagittal VIBE images. The transverse
images were reformatted parallel to the
lines used for sagittal measurements as
described earlier.
Figure 1
Figure 1: Midsagittal T2-weighted images demonstrate the spinal canal (CSF column) and cord
diameter measured at C1 level. A, The sagittal spinal canal (CSF column) diameter (14.2 mm) at C1
level is measured as the distance from the tectorial membrane or dura mater to the most anterior
point of the posterior atlantic arch (red line) on a line drawn from the most anterior point of the anterior
atlantic arch to the most anterior point of the posterior atlantic arch (white line). B, The sagittal
spinal cord diameter (red line, 8.4 mm) is measured on the same line drawn from the most anterior
point of the anterior atlantic arch to the most anterior point of the posterior atlantic arch (white line).
Figure 2
Figure 2: Midsagittal T2-weighted images demonstrate the spinal canal (CSF column)
and cord diameter measured at C3 and C6 level. A, The sagittal spinal canal (CSF column)
diameters (red lines) are measured at C3 and C6 levels on a line from the midpoint between the
superior and inferior endplates of the vertebral body and drawn perpendicular to the anterior
cord surface (white lines). B, The sagittal spinal cord diameters (red lines) are measured on the
same lines drawn as described in A (white lines).

and level, rater, hospital, age, height),
with interaction between sex and level
encoded by binary indicator variables
L1 (L1 = 1 for C3 and 0 otherwise)
and L2 (L2 = 1 for C6, and 0 other-
wise) (15).
Standard deviations were calcu-
lated for estimated parameters of
the log-transformed data and error
propagation for the back-transformed
values was calculated according to
common procedures (16).
Agreement of measurements be-
tween raters and within one rater
(C.S.) was determined by intraclass
correlation coefficients.
P values less than .05 indicated
statistical significance.
Results
A total of 140 healthy volunteers (76
women and 64 men; all were white)
were recruited. The total age range
was 18.3–78.4 years (mean age, 37.6
years); age range for women was 18.3–
78.4 years (mean age, 37.7 years) and
age range for men was 20.0–67.3 years
(mean age, 37.5 years). The height of
the men ranged from 1.5 to 1.93 m
(mean, 1.8 m), and the height of the
women ranged from 1.52 to 1.80 m
(mean 1.66 m).
Table 1 shows the P values and R2
of the various influences. There are
significant differences for sex, spinal
level, and body height, while the age
has significant but limited influence.
The significant P values for the interac-
tion between sex and level indicators
(L1 and L2) show differences between
spinal levels vary according to sex.
Moreover, it is noteworthy that the
two imagers produced significantly dif-
ferent images (P = .001 for distances
and areas), even if identical products
and sequences were used and the pro-
tocol was carefully followed at both
hospitals.
While the intrarater reliabilities of
our measurements were excellent (R2
= 0.85–0.99) and interrater reliabilities
of our measurements were substantial
to excellent (intraclass correlation coef-
ficient = 0.66–0.92) (Table 2), the two
raters measured distances that were
by subtracting the values for the spi-
nal cord from those of the total spinal
canal.
Statistical Analysis
A multivariate general linear model
(PASW Statistics 18; SPSS, Chicago,
Ill) was first applied with a full facto-
rial analysis for the following factors:
spinal level, sex, rater, hospital, and
the covariate age and body height. Ra-
tional for this selection was that body
height, sex, and spinal level will influ-
ence the geometry of the spinal canal,
while age might at least influence spi-
nal cord diameter. A systematic dif-
ference between the measurements of
the two raters could not be excluded
and, since this study was performed
as part of a multicenter study (12),
an influence of the data acquisition in
two hospitals should be tested even if
identical imagers have been used.
Because the Levene test showed
violations of the equality of error var-
iances, the dependent variables were
log transformed, successfully result-
ing in equal variances. The results of
the multivariate tests resulted in the
following model: dependent variable,
f (sex, level, interaction between sex
The areas of the spinal canal (ie,
CSF) and the spinal cord in the trans-
verse plane at the C1, C3, and C6 levels
were measured with irregular regions
of interest by using the PACS tools
(Fig 4). Difference of areas (ie, space
around the cord) (8) was determined
Figure 3
Figure 3: Transverse reformatted VIBE images
demonstrate the midsagittal spinal canal (CSF
column) and cord diameters measured at C1 and
C3 levels in the transverse plane (reformations
were done on the same reference lines as used
for the measurements of Figs 1 and 2). A, The di-
ameters of the sagittal spinal canal (CSF column)
(black and red line,15.5 mm) and cord (black line,
8.4 mm) are measured at the C1 level by using a
line from the most concave point of the anterior
atlantic arch to the most concave point of the
posterior atlantic arch (white line). B, The sagittal
spinal canal (CSF column) (black and red line)
and cord (black line) diameters are measured at
the C3 level by using a line from the midpoint of
the vertebral body to the midpoint of the spinous
process (white lines).
Figure 4
Figure 4: Transverse reformatted VIBE image
demonstrates the areas of the spinal canal (CSF col-
umn, 252.26 mm2
) and the spinal cord (77.93 mm2
)
at C1 level in the transverse plane (reformations use
the same reference lines as the measurements of
Figs 1 and 2). Analysis of the areas is performed by
manually traced regions of interest.

In summary, the diameter and the
area of the spinal canal decrease from
level C1 to C6 in all three height sub-
groups (1.50 m, 1.70 m, and 1.90 m).
The spinal cord shows similar behavior
for the anterior-posterior diameter;
however, the area of the spinal cord re-
mains almost identical from C1 to C6.
This is because the spinal cord area
shape gets broader at the lower levels,
from circular at C1 level and ellipsoid
at C6 level with a broader right-to-left
distance.
and Table in Appendix E1 (online) allow
for an exact calculation of the model.
Table 6 shows a summary of our
MR imaging data compared with recent
studies that reported normal estimates
for cervical spinal canal and cord with
different instrumentations.
Figure 5 shows the spinal dimen-
sions for selected patients who were 45
years of age and were 1.70 m tall. To
increase visibility, standard deviations
are used for illustration instead of 95%
confidence intervals.
significantly different (P , .01 for all
distances and areas) (Table 1).
Tables 3–5 show selected standard
estimates and include 95% confidence
intervals. The estimates are calculated
for an age of 45 years because age has
a statistically significant but minor influ-
ence on the estimates. Therefore, these
Tables can be used for all ages in adult
patients without a substantial error. If
spinal canal or cord dimensions shall be
calculated for a specific spinal location,
sex, age, and body height, the equations
Table 1
P Values and Adjusted Multivariate Analysis of Log-Transformed Dependent Variables
Parameter Sex L1 L2 Rater MR Imager Age Height
Interaction between
Sex and L1
Interaction between
Sex and L2 Adjusted R 2
Diameter (measured on
sagittal images)
Spinal canal .030 ,.001 ,.001 ,.001 .001 .042 ,.001 ,.001 ,.001 0.444
Spinal cord .004 ,.001 ,.001 .009 ,.001 .003 .141 .942 .426 0.405
Difference canal/cord ,.001 ,.001 ,.001 ,.001 .312 .295 ,.001 ,.001 ,.001 0.293
Diameter (measured on
axial images)
Spinal canal .422 ,.001 ,.001 ,.001 ,.001 .050 ,.001 ,.001 ,.001 0.511
Spinal cord ,.001 ,.001 ,.001 ,.001 ,.001 .004 .071 .373 .771 0.437
Difference canal/cord .004 ,.001 ,.001 .041 .223 .426 ,.001 ,.001 .001 0.314
Area (measured on
axial images)
Spinal canal .240 ,.001 ,.001 ,.001 ,.001 .031 ,.001 .002 .016 0.604
Spinal cord .003 ,.001 .003 ,.001 ,.001 .906 .260 .768 .024 0.221
Difference canal/cord .028 ,.001 ,.001 ,.001 ,.001 .034 ,.001 .003 .092 0.633
Note.—Unless otherwise indicated, data are P values. L1 and L2 are binary indicator variables for spinal levels C3 and C6.
Table 2
Intrarater and Interrater Reliability for All Measured Estimates
Parameter
All levels Level C1 Level C3 Level C6
Interrater
Reliability
Intrarater
Reliability
Interrater
Reliability
Intrarater
Reliability
Interrater
Reliability
Intrarater
Reliability
Interrater
Reliability
Intrarater
Reliability
Diameter(measured on sagittal images)
Spinal canal 0.92 0.98 0.90 0.98 0.82 0.93 0.87 0.97
Spinal cord 0.87 0.93 0.79 0.91 0.83 0.90 0.81 0.85
Diameter (measured on axial images)
Spinal canal 0.90 0.98 0.88 0.98 0.77 0.93 0.77 0.94
Spinal cord 0.81 0.94 0.72 0.91 0.71 0.89 0.72 0.88
Area (measured on axial images)
Spinal canal 0.92 0.99 0.91 0.99 0.66 0.95 0.78 0.96
Spinal cord 0.77 0.90 0.79 0.90 0.82 0.91 0.69 0.89
Note.—Data are intraclass correlation coefficients.

differences between two identical im-
agers. It seems that factors such as
corrections of geometrical distortions
or systematically different placement of
the patient can already introduce such
differences that do not play a role in
individual examinations but can be de-
tected in a large cohort. Both influences
(ie, raters and imagers) were averaged
in this study and thus contributed to
larger confidence intervals; however,
this increase of the confidence intervals
was small compared with the biologic
variations in the cohort. Therefore,
these normative ranges were valid for
different imagers and raters.
The sagittal diameters on plain
radiographs (lateral view) report-
ed in literature varied because of
the technical magnification factors
(1–3,6,9,17,20,22), but were always
larger than values at CT or MR im-
aging. Therefore, the assessment
was later optimized by the Torg ratio
(3,6,9,22), which is independent of
technical magnification factors.
the studies that used different imaging
methods, the influence of age, sex or
other variables on the reported data at
the different spinal levels was not evalu-
ated (1–9,17–22).
Most importantly, our findings
show that at all spinal levels individ-
ual factors such as age, sex, and height
have statistically significant influence
on the measurements. Therefore, to
provide valid normal values for cervi-
cal spinal canal and cord dimensions,
these variables must be taken into
consideration.
Because reliability of our measure-
ments was better for diameters than
it was for areas, diameters should be
used.
We found small but important
differences between readings of two
different raters. Even after thorough
teaching sessions, this can be expected
because raters tend to draw the line
between gray levels of anatomic struc-
tures differently. More surprising are
the small but statistically significant
Within each spinal level, both the
diameter and the area of the spinal
canal increased with body height. How-
ever, area and diameter of the spinal
cord showed a divergent behavior:
While the area of the spinal cord in-
creased with body height, the diameter
decreased. The difference in diameters
and difference in areas increased within
each spinal level with body height.
The sagittal difference in diameter
is largest at C1 level and smallest at C3
level with a slight growth at C6 level.
However, the difference in areas (in
millimeters squared) decreased from
C1 to C6 level.
Discussion
Our MR imaging data confirmed the de-
creased width of the spinal canal from
C1 to C6 that was reported in previ-
ous studies (1–9,17–22), while cord
area increased, which puts lower cer-
vical spinal segments at increased risk
for compressive myelopathy (19). In
Table 3
Selected Estimates of Calculated Spinal Canal and Cord Diameters Measured on Sagittal Images for Three Body Heights
Level
Spinal Canal Diameter Spinal Cord Diameter Difference in Diameters
Height (m) Estimate (mm) 95% Confidence Interval Estimate (mm) 95% Confidence Interval Estimate (mm) 95% Confidence Interval
Women
C1 1.50 13.8 10.3, 18.4 8.1 6.6, 10.1 5.5 2.8, 10.8
C1 1.70 14.6 10.7, 19.7 8.0 6.4, 10.1 6.4 3.1, 13.0
C1 1.90 15.4 11.2, 21.1 7.9 6.2, 10.1 7.4 3.5, 15.6
C3 1.50 12.1 9.1, 16.1 7.6 6.1, 9.4 4.4 2.3, 8.6
C3 1.70 12.7 9.4, 17.2 7.5 6.0, 9.4 5.1 2.5, 10.3
C3 1.90 13.4 9.8, 18.4 7.4 5.8, 9.4 5.9 2.8, 12.4
C6 1.50 11.8 8.9, 15.7 7.1 5.7, 8.8 4.6 2.4, 9.0
C6 1.70 12.5 9.2, 16.8 7.0 5.6, 8.8 5.4 2.7, 10.8
C6 1.90 13.2 9.6, 18.0 6.9 5.5, 8.7 6.2 3.0, 13.0
Men
C1 1.50 14.6 11.0, 19.3 8.4 6.8, 10.4 5.9 3.1, 11.4
C1 1.70 15.4 11.4, 20.7 8.3 6.6, 10.3 6.9 3.5, 13.7
C1 1.90 16.2 11.9, 22.2 8.2 6.5, 10.3 8.0 3.9, 16.5
C3 1.50 11.7 8.9, 15.5 7.8 6.3, 9.6 3.9 2.0, 7.5
C3 1.70 12.4 9.2, 16.6 7.7 6.2, 9.6 4.6 2.3, 9.1
C3 1.90 13.1 9.6, 17.8 7.6 6.0, 9.6 5.3 2.6, 10.9
C6 1.50 11.5 8.7, 15.3 7.2 5.9, 8.9 4.2 2.2, 8.1
C6 1.70 12.2 9.1, 16.4 7.1 5.7, 8.9 4.9 2.5, 9.7
C6 1.90 12.8 9.4, 17.5 7.1 5.6, 8.9 5.7 2.8, 11.7
Note.—Differences in diameters are calculated as differences between the diameters of the spinal canal and the spinal cord, which represents the remaining space. Because the influence of the age
is limited, this table (calculated for 45 years of age) can be used for all adult ages without introducing an age-related error of more than 2%.

and cord. The measurements were ob-
tained at the C3–C7 levels and a 0.5-T
MR magnet was used. Fourteen healthy
young male athletes, aged 22–27 years,
were included (7,8). Prasad et al (7)
measured the sagittal diameter of the
spinal canal and cord with a 1.5-T mag-
net and the cross-sectional areas of the
CSF column and cord on MR images in
87 young patients with neck pain (age
range, 20–40 years) and at the C4–C7
level (8). Okada et al measured values
for transverse areas of the spinal cord,
dural tube, and spinal canal in the cer-
vical spine on T1-weighted axial 0.5-T
MR images of 54 men and 42 women
with neck pain but without neurologic
symptoms. They reported a significant
correlation of these three measure-
ments with body height (5). We also
found a significant association between
body height and spinal canal diameter
and spinal canal area, as well as spi-
nal cord area. Because the difference in
diameters and difference in areas (ie,
space around cord) also increase with
(21) diameters of the cervical spine.
Our study only used patients who were
white. Therefore, use of overall average
sagittal cervical canal diameters (14.1
mm 6 1.6, from cadaver specimens
[18] or 13.28 mm 6 1.47, from MR im-
aging studies [8], both measured from
C3 to C7), without taking into account
factors such as spinal level, age, sex, or
body height, is not sufficient for assess-
ment in an individual clinical setting.
Previously published investigations have
demonstrated that the correlation be-
tween standard radiographic measure-
ments (ie, Pavlov or Torg ratio), MR
imaging findings (sagittal CSF diameter
and space available for the cord), and
CT findings is poor (7,25), and that
they should not be relied upon to esti-
mate cervical canal stenosis (3).
There are few published studies re-
garding MR measurements of the spinal
canal and cord (5,7,8). Tierney et al (8)
measured the space available for the
spinal cord, defined as the difference of
the sagittal diameter of the spinal canal
CT has advantages compared with
standard radiographs because direct di-
mensions can be measured. However,
the distinction between spinal cord,
CSF, and soft tissue within the spinal
canal is unreliable. Spinal canal diam-
eters analyzed with CT vary (4,23,24)
and show poor correlation with clinical
findings (24). Matsuura et al (4), in a
study of CT imaging that compared cer-
vical spine–injured patients with con-
trol subjects, concluded that the shape
of the spinal canal, not the area, put
a person at risk for spinal cord injury.
Measurements of the spinal canal in
control subjects were stratified for cer-
vical spine levels C3–C7. The values in
that CT imaging study (4) were gener-
ally larger than the values in our MR
imaging study.
Two anatomic studies (18,21) per-
formed in 168 white and 153 African-
American cadavers reported significant
differences in cervical canal dimensions
related to sex and ancestry by evalu-
ating sagittal (18,21) and transverse
Table 4
Selected Estimates of Calculated Spinal Canal and Cord Diameters Measured on Axial Images for Three Different Body Heights
Level
Spinal Canal Diameter Spinal Cord Diameter Difference in Diameters
Women
C1 1.50 14.0 10.7, 18.2 8.2 6.6, 10.2 5.6 3.0, 10.4
C1 1.70 14.6 11.0, 19.2 8.1 6.5, 10.1 6.4 3.3, 12.1
C1 1.90 15.2 11.3, 20.3 8.0 6.3, 10.1 7.2 3.6, 14.1
C3 1.50 12.0 9.3, 15.6 7.5 6.1, 9.3 4.5 2.4, 8.2
C3 1.70 12.5 9.5, 16.5 7.4 5.9, 9.2 5.0 2.6, 9.5
C3 1.90 13.1 9.8, 17.4 7.3 5.8, 9.2 5.7 2.9, 11.1
C6 1.50 11.7 9.0, 15.2 7.1 5.8, 8.8 4.6 2.5, 8.4
C6 1.70 12.2 9.3, 16.1 7.0 5.6, 8.7 5.1 2.7, 9.7
C6 1.90 12.7 9.5, 17.0 6.9 5.5, 8.7 5.8 3.0, 11.4
Men
C1 1.50 14.8 11.5, 19.1 8.5 6.9, 10.4 6.1 3.4, 11.2
C1 1.70 15.4 11.8, 20.2 8.3 6.7, 10.4 6.9 3.7, 13.0
C1 1.90 16.1 12.1, 21.3 8.2 6.5, 10.3 7.8 4.0, 15.1
C3 1.50 11.9 9.2, 15.4 7.9 6.4, 9.6 4.1 2.3, 7.4
C3 1.70 12.4 9.5, 16.2 7.7 6.2, 9.6 4.6 2.5, 8.7
C3 1.90 12.9 9.7, 17.2 7.6 6.1, 9.6 5.2 2.7, 10.1
C6 1.50 11.6 9.0, 15.0 7.3 5.9, 9.0 4.3 2.4, 7.8
C6 1.70 12.1 9.3, 15.8 7.2 5.8, 8.9 4.8 2.6, 9.0
C6 1.90 12.6 9.5, 16.7 7.1 5.6, 8.9 5.4 2.8, 10.5
Note.—Differences in diameters are calculated as differences between the diameters of the spinal canal and the spinal cord and represent the remaining space. Because the influence of the age is
limited, this table (calculated for 45 years of age) can be used for all adult ages without introducing an age-related error of more than 2%.

a diagnostic test. The next step would
be to apply this data to a spinal canal
stenosis patient group.
This study had limitations. The
measurements in this study were per-
formed at the midvertebral levels to
avoid introduction of further variables
such as individually different degener-
ative changes. Measurements at these
levels are standardized and more reli-
able (7,8) and still allow for estimation
of the predisposition to cord compres-
sion in the case of (additional) degen-
erative canal stenoses. The numbers of
included patients were still small for
statistical analysis of normative spi-
nal canal dimensions, especially in the
different age subgroups. Our patients’
ethnicities were only white. To com-
pare the dimensions at the C1 level
with other studies, the slightly oblique
plane on which we performed the mea-
surements must be considered.
In conclusion, the dimensions of
the cervical spinal canal and the spi-
nal cord in healthy individuals are
dimensions from C1 to C7 and also
between individuals. In addition, the
cervical spinal cord also varies in di-
ameter, which reduces the value of
measurements that are purely bone.
We defined normative ranges for the
sagittal diameters and areas of spinal
canal and spinal cord at C1, C3, and
C6 level for men and women. In addi-
tion to a calculation of normative rang-
es for a specific sex, spinal level, age,
and body height, we extracted data for
three different height subgroups at an
age of 45 years. These results show
that, for example, for women with a
height of 1.70 m, at C1 level the spinal
canal dimensions ranged from 10.7 to
19.7 mm; at C3 level, from 9.4 to 17.2
mm; and at C6 level, from 9.2 to 16.8
mm. It is, however, important to note,
that our study was aimed at the estab-
lishment of normative estimates for a
healthy population and was not aimed
at measures to detect a disease. This
is not a diagnostic study, and we do
not provide operator characteristics of
height, this probably puts a smaller
person on higher risk of cervical cord
compression. To our knowledge, this
finding has not been found attention in
the literature so far.
A reduced spinal canal width in-
creases the risk of cervical cord com-
pression and myelopathy (26). Because
space around the cord (8) is relatively
decreased in the lower cervical spine
segments, the risk is predominant at
these levels (9,19). This space is of-
ten felt to be a more relevant feature
for determination of the risk of cervi-
cal cord compression than the ratio of
perpendicular diameters. These mea-
surements are important as cord com-
pression contributes to spinal cord dys-
function (27).
Standard radiographs indicate
an increased risk for sagittal spinal
canal diameters below 13 mm (relative
spinal canal stenosis) and more pro-
nounced below 10 mm (absolute spi-
nal canal stenosis). However, there is
a wide variability of the spinal canal
Table 5
Selected Estimates of Calculated Spinal Canal and Cord Areas Measured on Axial Images for Three Different Body Heights
Level
Spinal Canal Area Spinal Cord Area Difference Areas
Women
C1 1.50 231 155, 345 71 53, 95 157 86, 285
C1 1.70 254 166, 386 72 53, 97 181 96, 339
C1 1.90 278 179, 433 73 53, 100 208 107, 403
C3 1.50 173 116, 256 74 55, 98 98 54, 177
C3 1.70 189 125, 287 75 55, 101 113 61, 211
C3 1.90 208 134, 322 76 55, 104 130 68, 251
C6 1.50 161 108, 239 74 56, 99 86 48, 156
C6 1.70 177 117, 268 75 56, 102 100 53, 186
C6 1.90 194 125, 301 76 56, 105 115 60, 221
Men
C1 1.50 243 164, 358 75 57, 100 162 91, 290
C1 1.70 266 177, 401 76 57, 102 187 101, 345
C1 1.90 292 189, 450 77 57, 105 215 113, 410
C3 1.50 168 114, 248 78 59, 103 91 51, 162
C3 1.70 184 122, 277 79 59, 106 105 57, 192
C3 1.90 202 131, 311 80 59, 109 120 63, 229
C6 1.50 159 108, 235 76 57, 100 84 47, 150
C6 1.70 175 116, 263 77 57, 103 97 53, 178
C6 1.90 192 125, 295 78 57, 106 111 59, 212
Note.—Differences in areas are calculated as differences between the spinal canal areas and the spinal cord areas and represent the space around the cord. Because the influence of the age is limited,
this table (calculated for 45 years of age) can be used for all adult ages without introducing an age-related error of more than 2%.

author receives grant money from Swiss Na-
tional Science Foundation. Financial activities
not related to the present article: grant money
paid to author’s institution by Bayer, Guerbet,
Siemens, and GE. Other relationships: none
to disclose. A.B. Financial activities related
to the present article: author receives grant
money from Swiss National Science Founda-
tion, Georg von Hevesy Stiftung, Inselspital
Research Foundation, and Basel Rehabilitation
Center. Financial activities not related to the
present article: none to disclose. Other rela-
tionships: none to disclose. S.E.A. Financial
activities related to the present article: author
receives grant money from Swiss National Sci-
ence Foundation, Georg von Hevesy Stiftung,
Inselspital Research Foundation, and Basel
Rehabilitation Center. Financial activities not
related to the present article: none to disclose.
Other relationships: none to disclose S.E. Fi-
sy Stiftung, Inselspital Research Foundation,
and Basel Rehabilitation Center. Financial
activities not related to the present article:
none to disclose. Other relationships: none
to disclose. C.S. Financial activities related
present article: none to disclose. Other rela-
tionships: none to disclose. C.B. Financial ac-
tivities related to the present article: author
Other relationships: none to disclose. J.H. Fi-
nancial activities related to the present article:
dependent on spinal level, sex, age,
and height. The consideration of these
normal values should help radiologists
and clinicians to interpret MR imaging
data. The next step would be to apply
these data to a spinal canal stenosis
patient group.
Acknowledgments: Many thanks to our study
coordinators, our MR imaging technicians, the
computer technicians of the Department of Ra-
diology, University Hospital, Inselspital, Bern
and the leadership of the department.
Disclosures of Conflicts of Interest: E.J.U.
Financial activities related to the present ar-
ticle: author receives grant money from Swiss
National Science Foundation, Georg von Heve-
Table 6
Recent Studies that Reported Normal Estimates for Cervical Spinal Canal and Cord
Study
Sagittal Spinal Canal
Diameter (mm)*
Instrumentation
Health Status and
Ethnicity, If Known
No. of
Patients
No. of
Women
No. of
Men
Age
Range (y) C3 Level C6 Level
Our data†‡
MR imaging Healthy 140 76 64 18–78 12.7/12.4 12.5/12.2
Hellinger et al 1995 (17)§
Radiography ND No data No data No data No data 15.8 14.5
Lee et al 2007 (18) Anatomic study Skeletons 469 204 265 No data 14.0/14.6 13.6/14.3
Morishita et al 2011 (19) MR imaging Healthy 90 No data No data No data 14.4 14.4
Payne et al 1957 (20)||
Radiography Healthy 30 15 15 No data 17.9/18.8 17.0/17.8
Tatarek 2005 (21) Anatomic study Skeletons, Caucasian 168 88 80 No data 14.4/15.0 13.4/14.3
Tatarek 2005 (21) Anatomic study Skeletons, African-American 153 73 80 No data 13.3/14.4 13.3/14.3
Prasad et al 2003 (7)#
** MR imaging Neck pain 87 No data No data 20–40 No data 10.6
Tierney et al 2002 (8)††
MR imaging Healthy 14 0 14 No data No data No data
Okada et al 1994(5)‡‡
MR imaging Healthy 96 42 54 21–73 No data No data
Matsuura et al 1989 (4)§§
CT Healthy 100 53 47 No data 15.2 14.4
Goto et al 2010 (1)||
Radiography Healthy, Japanese 100 50 50 30–39 15.1/16.0 15.1/16.2
Torg et al 1996 (9) Radiography Neck symptoms 105 0 105 15–38 No data/19 No data/18.7
Herzog et al 1991 (3) Radiography Healthy 80 0 80 No data No data/18.6 No data/18.6
Pavlov et al 1987 (6) Radiography Healthy 74 25 49 15–38 17.2/19.2 17.5/19.0
Torg et al 1986 (22) Radiography Healthy 49 0 49 15–32 No data/19.2 No data/19
Hashimoto and
Tak 1977 (2)||||
Radiography Healthy 92 44 48 19–69 13.6/13.8 13.5/13.9
* Data are number of women/number of men.
†
Spinal cord diameter C6: 7.1 mm; difference (space around cord) C3 and C6: 4.9 mm and 5.2 mm, respectively; area spinal canal C3 and C6: 187 mm2
and 176 mm2
, respectively; area spinal cord
C3 and C6: 77 mm2
and 76 mm2
, respectively.
‡
Sagittal spinal canal diameter C1: women, 14.6 mm and men, 15.4 mm.
§
All reported data are means. Sag spinal canal diameter C1: 20.3 mm.
||
#
Estimates are from the study publication’s tables.
** Spinal cord diameter C6: 6.7 mm; area spinal canal C6: 185 mm2
; area spinal cord C6: 85 mm2
.
††
Difference (space around cord) C3 and C6: 5.6 mm and 5.7 mm, respectively.
‡‡
Area spinal canal C3 and C6: 246.9 mm2
and 248.5 mm2
, respectively; area spinal cord C3 and C6: 80.5 mm2
and 76.1 mm2
, respectively.
§§
Area spinal canal C3 and C6: 320 mm2
and 272 mm2
, respectively.
||||

present article: none to disclose. Other re-
lationships: none to disclose. M.S. Financial
activities related to the present article: author
none to disclose. Other relationships: none
to disclose. H.Z. Financial activities related
nancial activities related to the present article:
author receives grant money from Swiss Na-
tional Science Foundation, Georg von Hevesy
Stiftung, Inselspital Research Foundation,
and Basel Rehabilitation Center. Financial
activities not related to the present article:
Figure 5
Figure 5: Graphs of diameter and area (6 standard deviation [SD]) calculated from the fitted parameters for women
(green) and men (red) on different spinal levels. Covariates of age and body height in the model are fixed to 45 years
and 1.70 m, respectively. Note that the distribution (including error bars) is slightly asymmetric due to the reversed
log-transformation of the data. A, Diameters and differences of spinal canal and cord measured on sagittal images. B,
Diameters and differences of spinal canal and cord measured on axial images. C, Areas and differences of spinal canal
and cord measured on axial images.

Other relationships: none to disclose.
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