AJR 2001; 177:441-445
© American Roentgen Ray Society
Use of Three-Dimensional Reconstructed Helical CT Images in Recognition and Communication of Chest Wall Anomalies in Children
Lane F. Donnelly1
1
Department of Radiology, Children's Hospital Medical Center, 3333 Burnet Ave.,
Cincinnati, OH 45229-3039.
Received December 22, 2000;
accepted after revision January 29, 2001.
Address correspondence to L. F. Donnelly.
Introduction
Because of the potential for malignancy, children who have lumps palpated
in the chest wall at physical examination are often referred for
cross-sectional imaging. It has been shown that in most of these children, the
cause of the lump is a benign variation in the anatomy of the anterior chest
wall
[1,2,3].
Many of these variations can be difficult to identify on axial images. When
performing CT to evaluate these patients, we have found that three-dimensional
(3D) reconstructions are often helpful in identifying a benign anatomic
variation as the cause of the palpable lump and in communicating the nature of
such a lesion to both the referring physician and the child's family. These
images also aid us in understanding the sometimes complex anatomy that leads
to these palpable protrusions. This pictorial essay reviews the use of 3D
reconstructed images from helical CT in the evaluation of benign entities of
the anterior chest wall. The use of 3D CT imaging in the evaluation of
children with pectus excavatum is also illustrated.
The Palpable Lump
A number of aggressive lesions can involve the chest wall in children. The
most common malignant primary bone tumors in the chest wall are Ewing's
sarcoma and Askin's tumor (primitive neuroectodermal tumor of the chest wall)
[3,
4]. Metastases by
neuroblastoma, lymphoma, or leukemia can also occur and are more common than
primary bone malignancies [3,
4]. In addition, aggressive
nonmalignant conditions such as osteomyelitis and Langerhans cell
histiocytosis can involve the chest wall
[3]. Because of the potential
for these aggressive lesions, the discovery of a palpable lump in the chest
wall of a child can be alarming. Such children are often referred for imaging
to exclude malignancy.
In most children, the cause of this palpable area is a benign variation in
the configuration of the anterior ribs or costal cartilages
[1,2,3].
These variations include asymmetric findings such as tilted sternum, prominent
convexity of anterior rib or costal cartilage, prominent asymmetric costal
cartilage, parachondral nodules, mild degrees of pectus excavatum or
carinatum, and other anterior rib anomalies
[1,2,3].
In a review of all cases of palpable chest lesions referred for
cross-sectional imaging, investigators found that all patients whose lesions
were asymptomatic (no history of pain, not tender on examination) had benign
anatomic variations as the underlying cause of the lump
[1]. Another study showed that
such variations are common [2].
A review of CT scans of the chest performed in children not suspected of
having chest wall anomalies showed that such variations are present in
approximately one third of children
[2].
When parents palpate a chest wall lump, they often believe that it is new
(if it had been there previously, they would have noticed it). Even after a
lesion is discovered, there is often a reported history of interval growth. An
earlier study showed that a history of progressive or rapid growth was
unreliable in predicting whether a lesion was caused by an anatomic variation
or true abnormality [1]. In
fact, most lesions reported to be growing are caused by static anatomic
variations [1]. Although the
primary goal of CT in these patients is to exclude malignancy, the
identification of a benign cause of the lump is important in easing the
parents' and referring physician's anxieties. When a palpable lesion is
present on physical examination and the only findings of an imaging study are
no evidence of a mass, the underlying concern for a missed lesion, in our
experience, often persists.
Three-dimensional helical techniques have been described as useful in the
evaluation of vascular lesions in the pediatric chest such as congenital heart
disease or vascular rings [5,
6] but have not been described
as helpful in the evaluation of the pediatric chest wall. In a child with an
asymptomatic palpable lump who is referred for cross-sectional imaging, we
perform unenhanced helical CT. Typical parameters include 5-mm detector
configuration, high-quality mode, and weight-based low-tube current technique
[7] (LightSpeed multislice
helical CT scanner; General Electric Medical Systems, Milwaukee, WI). Images
are then evaluated on an independent work station (Advanced Windows
Workstation; General Electric Medical Systems), and surface-rendered or
maximum-intensity-projection images are created as needed.
Often, the presence of an anatomic variation will be subtle on standard
axial CT images alone. This finding is particularly true of prominent
convexity of the anterior rib or costal cartilage (Figs.
1A,1B,1C
and
2A,2B),
prominent asymmetric costal cartilage, tilted sternum and its associated
findings (Figs.
3A,3B,3C
and
4A,4B),
and other rib anomalies (Figs.
5A,5B,5C
and
6A,6B).
It may be difficult on axial images alone to show that the anomaly at the
level of the palpable lump is more anterior than the ribs and costal
cartilages superior and inferior to that level. We have found that 3D
reconstructions of the helical CT images are helpful in identifying and
defining such lesions. Surface-rendered images showing the patient's skin
surface can be used to identify the protrusion palpated on physical
examination. Three-dimensional surface-rendered images showing the underlying
bone and cartilage can be used to correlate the anatomic variation with the
exact site of the palpate lump. In some cases, a combination of several
anatomic anomalies leads to the finding of a palpable protrusion. For example,
a tilted sternum may be associated with a subluxed clavicular head or convex
costal cartilage (Fig.
3A,3B,3C
and
4A,4B),
or a rib anomaly can be associated with the adjacent rib protruding anteriorly
(Fig.
5A,5B,5C
and
6A,6B)
and cause a palpable lesion. These combined anomalies may involve several
levels of ribs or costal cartilage and are often more easily seen on 3D
images. Three-dimensional images are also helpful if the palpated lesion is
caused by a disease process. The relationship between the mass and the
adjacent ribs can be further depicted (Fig.
7A,7B,7C).
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Fig. 1B. —Anterior convex costal cartilage presenting as palpable lump
in 6-year-old boy. Three-dimensional reconstruction depicting skin surface
reveals lump (arrows) palpated on physical examination.
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Fig. 1C. —Anterior convex costal cartilage presenting as palpable lump
in 6-year-old boy. Three-dimensional reconstruction depicting bone and soft
tissue reveals asymmetric anterior convexity of costal cartilage
(arrows), correlating with lump palpated on physical examination.
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Fig. 2B. —Anterior convex costal cartilage presenting as palpable lump
in 4-year-old boy. Three-dimensional reconstruction depicting skin surface
reveals lump (arrow) palpated on physical examination, which
correlates with area of convex costal cartilage.
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Fig. 3A. —Tilted sternum with associated asymmetric anterior convexity
of right costal cartilage presenting as palpable lump in 15-year-old boy.
Axial CT image shows tilted sternum (arrow) with right margin being
more anteriorly positioned than left margin. Note associated anterior
convexity of right costal cartilage (arrowhead).
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Fig. 3B. —Tilted sternum with associated asymmetric anterior convexity
of right costal cartilage presenting as palpable lump in 15-year-old boy.
Three-dimensional reconstruction depicting bone in inferior projection reveals
tilted sternum (arrow).
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Fig. 3C. —Tilted sternum with associated asymmetric anterior convexity
of right costal cartilage presenting as palpable lump in 15-year-old boy.
Three-dimensional reconstruction depicting soft tissue and bone in inferior
projection depicts prominent anterior convexity (arrows) of right
costal cartilage that was palpated on physical examination.
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Fig. 4A. —Tilted sternum with associated subluxation of calvicular head
in 12-year-old girl. Axial CT image shows tilted sternum (arrow) with
left margin being more anteriorly positioned than right margin.
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Fig. 4B. —Tilted sternum with associated subluxation of clavicular head
in 12-year-old girl. Three-dimensional reconstruction depicting bone in
superior projection reveals tilted sternum (arrow). Note anterior
subluxation of left clavicular head (arrowhead) at sternoclavicular
joint. Subluxed clavicle protrudes anteriorly.
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Fig. 5A. —Anterior convex clavicle associated with fused ribs
presenting as palpable lump in 10-year-old girl. Axial CT scan shows vitamin E
capsule (arrow) marking site of lump palpated on physical
examination. Clavicle, which has asymmetric prominent convexity, underlies
capsule. Note fusion of right first and second ribs (arrowheads).
Initial report and axial images were shown to referring pediatric surgeon and
patient's family. Both reported suspicion that convex clavicle was not cause
of palpated mass because both had reported recent rapid growth of lesion.
Three-dimensional (3D) reconstructed images were then created.
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Fig. 5B. —Anterior convex clavicle associated with fused ribs
presenting as palpable lump in 10-year-old girl. Three-dimensional
reconstruction depicting bone in superior projection reveals relationship
between fusion of right first and second ribs and right clavicle. Abnormal
configuration of fused ribs (arrowheads) has resulted in remodeling
of right clavicle, causing anterior convexity (arrow).
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Fig. 5C. —Anterior convex clavicle associated with fused ribs
presenting as palpable lump in 10-year-old girl. Three-dimensional
reconstruction shown to depict bone in inferior projection reveals
relationship between fusion of right first and second ribs
(arrowheads) and right clavicle. After viewing 3D images, pediatric
surgeon and family were convinced that anomaly was cause of palpable lump.
Arrow indicates anterior convexity.
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Fig. 6A. —Bifid left sixth rib with associated anterior protrusion of
anterior left fifth rib, presenting as palpable lump in 4-year-old boy. Axial
CT image shows subtle anterior protrusion (arrow) in region of left
fifth costal cartilage.
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Fig. 6B. —Bifid left sixth rib with associated anterior protrusion of
anterior left fifth rib, presenting as palpable lump in 4-year-old boy.
Three-dimensional reconstruction depicting bone in left lateral projection
reveals anterior left sixth rib (6) to be bifid. In association with bifid
rib, anterior portion of left fifth rib (5) protrudes more anteriorly
(arrow) than adjacent ribs. Anterior protrusion of fifth rib caused
palpated lump.
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Pectus Excavatum
Although most problems due to pectus excavatum are cosmetic, pectus
excavatum can be associated with chest pain, fatigue, dyspnea on exertion,
palpitations, and restrictive lung disease
[3]. When the deformities are
severe, surgical repair is often performed. Although the diagnosis is made
visually and does not involve imaging, cross-sectional imaging with CT has
been useful in showing the anatomy of severe deformities. CT is often used to
evaluate children with pectus excavatum who are being considered for surgery
and in the evaluation of postoperative complications after pectus repair
[8]. In the child who is being
considered for potential repair of pectus excavatum, CT can define the
severity of the deformity and identify any anomalously positioned
cardiovascular structures that may complicate deployment of a pectus repair
device. Three-dimensional reconstructions can provide further information
concerning the relationship of the thoracic deformity on physical examination
compared with the cartilaginous and bony abnormalities depicted on CT (Figs.
8A,8B,8C
and
9A,9B,9C,9D).
The severity and level of the deformity of the bony sternum can be shown (Fig.
9A,9B,9C,9D).
Three-dimensional reformatted images have also been helpful in the evaluation
of growth arrest after surgical repair of pectus excavatum
[8].
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Fig. 9B. —Pectus excavatum in 11-year-old boy. Three-dimensional (3D)
reconstructions in oblique (B) and lateral (C) projections
reveal extent of depression of bony sternum (arrow) in relationship
to thorax.
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Fig. 9C. —Pectus excavatum in 11-year-old boy. Three-dimensional (3D)
reconstructions in oblique (B) and lateral (C) projections
reveal extent of depression of bony sternum (arrow) in relationship
to thorax.
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Summary
In conclusion, 3D reconstructed helical CT images assist in the evaluation
of children with potential chest wall abnormalities or anatomic variations.
Because of the orientation of many of these variations, the information
displayed on 3D images may be helpful in identification of the anatomic
variations, in communication of the presence of these benign anomalies to
referring physicians, and in the development of understanding of these
anomalies. Likewise, 3D reconstructed images also enhance CT of children being
imaged because of pectus excavatum.
References
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Donnelly LF, Frush DP, Foss JN, O'Hara SM, Bisset GS III. Anterior
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Radiology
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Donnelly LF, Frush DP. Abnormalities of the chest wall in pediatric
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Faro SH, Mahroubi S, Ortega W. CT diagnosis of rib anomalies,
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Introduction
The Palpable Lump
