AJR 2000; 174:223-228
© American Roentgen Ray Society
Sonographic Appearance of Cricoid Cartilage Calcification in Healthy Children
Simon Strauss1
1
Department of Radiology, Assaf Harofeh Medical Center, Zerifin 70300 Israel;
and Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv Israel
Received May 10, 1999;
accepted after revision June 29, 1999.
Address correspondence to S. Strauss.
Abstract
OBJECTIVE. The purpose of this study was to determine the
distribution pattern of calcification in cricoid cartilage of healthy
children.
SUBJECTS AND METHODS. Sonography of the neck was performed with a
high-resolution linear array transducer to show the sides of the cricoid
cartilage ring in both the sagittal and transverse planes. Twenty-three boys
and 33 girls, who ranged in age from 6 to 17 years, were examined.
Calcifications in the cartilage were characterized by number and size,
distribution pattern, and side-to-side symmetry.
RESULTS. Calcifications were seen either as small echogenic,
nonshadowing foci or as larger irregular, echogenic areas with acoustic
shadowing. Calcifications were found in 19 of the 23 boys and 26 of the 33
girls. The earliest cases were in three 7-year-old children. The incidence and
number of echogenic foci generally increased with age. Most calcifications
were in the center of the cartilage or distributed diffusely throughout.
Side-to-side comparison of the number, size, and distribution pattern of the
calcifications showed considerable variation.
CONCLUSION. The sides of the cricoid cartilage ring could be seen on
sonography in both the sagittal and transverse planes. Calcifications within
the cartilage were readily shown and were found in children at an earlier age
than previously reported.
Introduction
The cricoid cartilage is shaped like a signet ring, with a narrow
anterior arch widening posteriorly to the quadrate lamina. The upper poles of
the thyroid gland are in direct contact medially with the sides of the cricoid
ring, except in the superior and posterior aspects in which the cricothyroid
muscle and superior constrictor muscles of the pharynx intervene between the
gland and the cartilage [1].
The posterior lamina of the cricoid is obscured on sonography by air in the
trachea, but the sides of the ring are easily visualized in both the sagittal
and transverse planes. These sides of the ring are seen as relatively
hypoechoic structures with a homogenous texture, except when calcification is
present.
As part of the aging process, ossification and calcification take place in
the various cartilages of the laryngeal skeleton. Current anatomy and
radiology literature suggest that this process begins during the third decade
of life 2,
3,
4] but, to our knowledge,
calcification in cricoid cartilage has not been evaluated previously using
sonography. The purpose of this study was to determine the pattern of
calcification in cricoid cartilage in healthy children on sonography.
Subjects and Methods
The cricoid cartilage of 56 healthy children who ranged in age from 6 to 17
years was examined using sonography in the sagittal and transverse planes.
None of the children had clinical manifestations of syndromes associated with
premature laryngeal calcification, such as chondrodysplasia punctata; none
were receiving warfarin sodium therapy; and none of the mothers had been
treated with warfarin during pregnancy. Parental consent was obtained for all
patients. Twenty-three boys and 33 girls comprised the study population and
results were analyzed according to the age of the patient (age groups: 6-9
years, 10-13 years, and 14-17 years). Sonography was performed on a
commercially available unit (HDI 3000; Advanced Technology Laboratories,
Bothell, WA) using a broadband 5-10-MHz linear array transducer. The
examinations were performed with patients lying supine in a position routinely
used for scanning the thyroid gland—that is, with the neck
hyperextended. A standoff pad was not used.
Sagittal images of the cartilage on both sides of the neck were obtained
with the transducer inclined medially to approximately 30°. The cricoid
cartilage was identified as a round or oval structure adjacent to the upper
part of the lobe of the thyroid gland. The cartilage was uniformly hypoechoic
relative to the adjacent thyroid gland, except for a thin anechoic peripheral
layer. In this projection, the cartilage was 1-2 cm in diameter, depending on
the age of the child. In the transverse view, with the transducer placed in
the midline of the neck, both sides of the cricoid cartilage were seen as thin
(2-4 mm) echogenic layers draped over the sides of the infraglottic air column
(Fig. 1A,
Fig. 1B).
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Fig. 1. —Healthy 17-year-old boy.
B, Transverse sonogram of left side of neck shows relationship
between cricoid cartilage (arrows), cricothyroid muscle and inferior
constrictor muscles of pharynx (M), thyroid gland (T), and carotid artery
(A).
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Calcifications were seen as bright echogenic foci within the cartilage and
were easily located on the two orthogonal views. The calcifications were
characterized by number and size of foci, position within the cartilage, and
side-to-side symmetry. For the purpose of comparison, the cricoid cartilage in
five volunteers who were more than 50 years old was examined.
Results
The incidence of cricoid cartilage calcification related to sex and age is
reported in Table 1.
Calcifications were found in 19 of 23 boys and 26 of 33 girls. All children in
the 14- to 17-year-old group had calcifications in one or both sides of the
cricoid ring. The earliest cases of calcification were in a 7-year-old girl
and two 7-year-old boys. The oldest child without evidence of calcification in
either side was a 13-year-old boy.
Calcifications were usually uniform in size in each patient. In 39 of the
45 children with calcifications, these calcifications were characterized as
bright, echogenic, nonshadowing foci of 1 mm in diameter
(Fig. 2A,
Fig. 2B). In the six other
children, the calcifications were larger, measuring up to 10 mm in diameter,
and cast acoustic shadows (Fig.
3). All cases of the larger calcifications were found in the 14-
to 17-year-old group.
The number of calcifications on each side was semiquantitatively estimated
as more or less than three echogenic foci in a single plane. This analysis
showed that the number of foci in each cartilage generally increased with age
(Fig. 4A,
Fig. 4B). Only two of the 12
children in the 6- to 9-year-old group had more than three echogenic foci
counted on a single image. Children with larger calcifications tended to have
fewer echogenic foci, which possibly resulted from coalescence of the foci
into a larger unit.
In all the children except five, the echogenic foci were either distributed
in a diffuse pattern throughout the cartilage or localized to the center.
Calcification confined to the periphery, which was seen generally in older
children, tended to be larger and either irregular or curvilinear in shape
(Fig. 5A,
Fig. 5B). Side-to-side
comparison of the number, size, and distribution pattern of the echogenic foci
showed considerable variation (Fig.
6A, Fig. 6B). Of
all the children with cartilage calcification, the echogenic foci were found
bilaterally in 27 and unilaterally in 18. Unilateral calcification was
confined to the right side in 16 of the 18 children. No relationship between
the age of the child and the symmetry of the calcifications was seen.
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Fig. 5. —Healthy 15-year-old girl.
A, Sagittal sonogram of cricoid cartilage shows a large curvilinear
calcification in periphery of cartilage (large arrow). Acoustic
shadow is cast behind calcification. Small echogenic focus is seen in center
of cartilage (small arrow). T = thyroid gland.
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In the five volunteers who were more than 50 years old, the cricoid
cartilage was found to be heavily calcified and the outline of the cartilage
was poorly visualized because of acoustic shadowing
(Fig. 7).
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Fig. 7. —Healthy 62-year-old man. Sagittal Sonogram of neck reveals heavy
calcification in periphery of cartilage (arrows). Outline of
cartilage is obscured by acoustic shadow. T = thyroid gland.
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Discussion
Ossification and calcification of the laryngeal cartilages have been the
subject of investigation since the anatomic studies by Chievitz in 1882
[5]. He concluded that
ossification begins normally when skeletal growth is otherwise
complete—that is, in males at age of 20 years and females at age 22
years. Since then, researchers using unenhanced radiography
[6], low-voltage radiography
[7], CT
[8], and MR imaging
[4,
9] have reported that
ossification of the thyroid cartilage commences at the beginning of the third
decade and that ossification of the cricoid cartilage begins several years
later. The earliest cases of ossification of the cricoid in healthy subjects
were in two 17-year-old girls
[6] and an 18-year-old man
[10]. To the best of our
knowledge, sonography has not been used previously to evaluate cricoid
cartilage calcification.
The thyroid, cricoid cartilage, and greater part of the arytenoid cartilage
consist of hyaline cartilage that undergoes calcification and ossification as
part of the aging process. The terms "ossified" and
"calcified" are often used synonymously, although calcification
always precedes ossification when cartilage becomes transformed into bone
[10]. In this study, the term
"calcification" is used, although no histologic proof is available
to decide whether the bright foci seen in the cricoid cartilage are the result
of ossification or calcification.
There are scant reports in the literature concerning the use of sonography
for examination of the larynx. Garel et al.
[10] assessed the anatomy of
the larynx in healthy infants and children up to the age of 15 years on
sonography. These researchers reported that the cricoid cartilage appears as a
round hypoechoic structure in the transverse plane. Raghavendra et al.
[11] studied the sonographic
anatomy of the larynx in adult volunteers. Their study, however, focused on
the vocal cords, and images were obtained only in the transverse plane. In
these reports, calcification in the laryngeal cartilages is not mentioned.
We are not aware of any report of the use of sonography to visualize the
cricoid cartilage in the longitudinal view. This view is easily obtained using
the upper pole of the thyroid gland as an acoustic window and scanning in a
medially angled sagittal plane. Because of the homogeneously hypoechoic nature
of the cricoid cartilage and the superior spatial resolution of high-frequency
transducers, echogenic foci as small as 1 mm in diameter are readily
displayed. These echogenic foci do not cast acoustic shadows, presumably
because of their small size.
Based on radiographic and dissection findings, Keen and Wainright
[12] reported that
ossification on the right and left sides of the cricoid was equal and
symmetric in extent. Jurik [7]
used low-voltage radiography and found not only symmetric ossification of the
cricoid, but also an unequal configuration of calcification on both sides.
With only 48% of our cases showing calcifications in both the right and left
sides, our findings agree with the CT findings of Yaeger et al.
[8] that the process is
asymmetric. We also found that the distribution and size of echogenic foci
frequently differed between the two sides. The discrepancy in the literature,
however, may be explained by the synonymous use of the terms calcification and
ossification.
Comparing the sexes, Jurik
[7] found calcification of the
cricoid cartilage to be more marked and more frequent in females but the
degree and frequency of ossification to be lower in females. Hately et al.
[6] reported that the cricoid
ossified similarly in both male and female patients. No significant sex
differences emerged from our study.
We found that calcification of the cricoid cartilage increased with age but
that there was no strict correlation between the two. The earliest cases of
calcification were in two 7-year-old boys and one 7-year-old girl, but 21
(48%) of the 44 children in the 10- to 13-year-old and 14- to 17-year-old
groups had no evidence of calcification in one side or both sides of the
cricoid ring. This finding is in accordance with previous reports that
differences between individuals belonging to the same age group may be
considerable [6,
7,
12,
13]. A genetic factor to
account for individual differences has been proposed by Vastine and Vastine
[14]. They found the same
pattern of calcification in the laryngeal cartilages in five pairs of
identical twins.
There are two limitations of our study. First, the results account for
calcifications only along the sides of the cricoid cartilage ring. Previous
studies have shown that the calcification process usually starts in the
posterior lamina and later spreads anteriorly along the arch
[6,
7,
12]. It is therefore possible
that if all parts of the cricoid cartilage could be visualized
sonographically, calcification would be seen in the lamina in most, if not
all, patients in whom it was seen along the sides of the ring. Second,
histologic proof that the echogenic foci are indeed calcifications was not
obtained. We are not aware, however, of any process other than calcification
that could account for the echogenic foci, which were found in increasing
numbers and size with advancing age. Histologic findings in a study of the
ossification of the larynx were reported by Keen and Wainright
[12]. They found that
calcified foci that are unaccompanied by ossification may appear as early as
the second decade. These foci of calcification may become confluent, forming
plaques of calcium that can be regarded as precursors of ossification because
the foci invariably disappear with the spread of ossification.
Congenital conditions causing premature calcification and acquired forms of
premature calcification of the larynx are rare and present as stridor in
infants and young children. Premature calcification is usually associated with
tracheal or tracheobronchial calcification, and its cause is unknown
[15,
16]. Although in this study we
examined only healthy children, our method could potentially be used to assess
the occurrence of laryngeal calcification in children with congenital
conditions such as a chondrodysplasia punctata and Keutel syndrome; in
children with acquired forms of premature cartilage calcification, such as
warfarin embryopathy after long periods of warfarin therapy; and in children
with idiopathic infantile hypercalcemia
[17,
18].
The results of our study are important in cases in which children undergo
radiographic examination for a foreign body embedded in the hypopharynx. Our
findings show that cricoid cartilage calcification occurs earlier than
previously reported; therefore, the possibility that it may masquerade as a
foreign body should not be discounted in children
[19].
In summary, the sides of the cricoid cartilage ring are easily visualized
on sonography in both the sagittal and transverse planes. The cartilage has a
homogeneous hypoechoic texture relative to the adjacent thyroid gland.
Calcifications are readily displayed as bright, nonshadowing, small echogenic
foci or as larger irregular echogenic areas that may cast acoustic shadows.
Calcifications were found at an earlier age than previously reported.
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Abstract
Introduction
