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Clinical Observations |
1 All authors: Department of Radiology, Istanbul University, Istanbul Faculty of Medicine, Millet Cad. Capa, Istanbul 90, Turkey 34390.
Received November 17, 2004;
accepted after revision February 9, 2005.
Address correspondence to E. Yekeler
(yekelerensar{at}yahoo.com).
Abstract
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SUBJECTS AND METHODS. One thousand consecutive patients who underwent thoracic MDCT examination were enrolled in the study. All MDCT data, including multiplanar and curved-planar reconstructed images, were evaluated for detection of sternal variations and anomalies. Various kinds of sternal variations and anomalies, such as suprasternal bones and tubercles, manubriosternal and sternoxiphoidal fusions, sternal clefts and foramina, and sternal sclerotic bands were documented.
RESULTS. In 1,000 subjects, the frequencies of main sternal variations and anomalies were as follows: suprasternal bone in 4.1%, suprasternal tubercle in 4%, complete manubriosternal fusion in 19.6%, complete sternoxiphoidal fusion in 30.3%, sternal foramen in 4.5%, and sternal sclerotic band in 37.1%. Xiphoidal foramen was seen in 27.4%, and the most common type was single foramen. Xiphoid process mostly ended as a single process (71%). Double-ended xiphoid process was also frequent (27.2%). Pseudocleft and pseudoforamen at the sternoxiphoidal junction were detected in 3.3% and in 3.6% of subjects, respectively.
CONCLUSION. MDCT exhibited various sternal variations and anomalies. Sternal foramen is a frequent minor anomaly and generally associated with sternal sclerotic bands. Early manubriosternal and sternoxiphoidal fusions can be seen in early adulthood without osteodegeneration. Double-ended xiphoid process and single xiphoidal foramen are frequent sternal variations. Awareness of MDCT appearances of sternal variations and anomalies provides a better differential diagnosis with pathologic conditions.
Keywords: anomalies • developmental • MDCT • musculoskeletal imaging
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The largest series evaluating sternal variations and anomalies were based on macroscopic [2] and radiographic [3] appearances of the sternum in autopsy populations. The frequencies of sternal anomalies in living subjects have been described based on their radiograph [4, 5], helical CT [6, 7], or MRI [8] appearances. In those studies, the number of subjects and the kinds of investigated variations and anomalies are limited. Three-dimensional imaging by helical CT was used in the evaluation of anterior chest wall deformities during childhood without focusing on the sternum by 3D or multiplanar imaging [9]. Three-dimensional CT images of the sternum were obtained in a few cases with sternal anomalies, such as complete sternal cleft [10].
Multiplanar and 3D reconstructed CT images are useful in the evaluation of the human skeleton, especially in complex parts such as the skull base, shoulder, and sternum. To our knowledge, the sternum has not been studied by MDCT for variations and anomalies. The purpose of this investigation was to reveal the frequency and MDCT appearances of sternal variations and anomalies in an adult population with no obvious sternal deformities.
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MDCT Protocol
MDCT imaging was performed with a four-detector row CT scanner (Somatom
Sensation 4, Siemens Medical Solutions). Common scanning parameters for all
patients were as follows: 120 kVp, 90 mAs, 0.5-sec gantry rotation, 4 x
2.5-mm collimation, pitch of 6 (4 x 1.5), 30-mm/sec table feed, and 2-mm
axial and 3-mm multiplanar reconstruction image thicknesses. For CT
angiographic and bronchoscopic evaluations, thinner collimation and slice
thickness values were selected. All patients underwent imaging from the
thoracic inlet superiorly to the level of the adrenal glands inferiorly,
including the sternum within the imaging area.
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Suprasternal Bone and Suprasternal Tubercle
Suprasternal bones were found in 41 (4.1%) subjects (22 bilateral, 18
unilateral, one midline). Suprasternal bones fused with each other in the
midline were seen in only one subject (Fig.
1). Suprasternal tubercle was detected in 40 (4%) subjects (27
bilateral and 13 unilateral) (Fig.
2).
Manubriosternal and Sternoxiphoidal Fusions
Manubriosternal and sternoxiphoidal fusions were determined as partial or
complete. Manubriosternal fusion was partial in 100 (10%) subjects and
complete in 196 (19.6%) subjects (Fig.
2). Incomplete and complete sternoxiphoidal fusions were found in
324 (32.4%) and 303 (30.3%) subjects, respectively. Complete fusion at both
manubriosternal and sternoxiphoidal junctions was encountered in a patient as
young as 20 years, without findings of osteodegeneration; 20% of the subjects
with partial or complete manubriosternal and sternoxiphoidal fusion were
younger than 45 years (Fig.
2).
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Focal Defect of Sternal Cortex and Sternal Notch
Focal defect or notch of the sternal cortex was found in 77 (7.7%)
subjects. The majority (68.8%) of those were seen in the posterior cortex of
the inferior sternal body. In one subject with a sternal notch in the inferior
portion of the sternal body, the appearance was similar to a recently closed
sternal foramen (Fig. 6).
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Xiphoidal Ending and Ossification
Xiphoid was absent in 11 subjects (1.1%; age range, 20–53 years; mean
age, 27 years). Xiphoidal endings were three types: a single- (71%), double-
(27.2%), or triple-ended (0.7%) xiphoid process
(Fig. 7). In five subjects with
a single-ended xiphoid process, the xiphoid was longer than usual
(Fig. 8). Xiphoidal
ossification was not depicted in 23 subjects (2.3%; age range, 20–86
years; mean age, 39 years). The majority of the subjects without xiphoidal
ossification (61%) were under 30 years. Xiphoidal ossification was total in
70.3%, superior in 23.9%, superior and inferior but partial in 4.8%, and
middle in 1%.
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Serious complications after sternal puncture for bone morrow biopsy [13, 14] or acupuncture [14] have been reported in the literature. Fatal cardiac tamponade resulting from a congenital sternal foramen located in the inferior part of the sternum [13, 15] and thin sternal body [14] was seen during the sternal puncture. Therefore, the awareness of the presence of sternal variations and anomalies is important to prevent these fatal complications by avoiding the inferior part of the sternal body during bone marrow aspiration.
To be familiar with the imaging appearances of the sternal variation and anomalies, it is necessary to differentiate those from pathologic conditions, such as traumatic fissure or fracture and lytic lesions. Absence of cortical irregularity, expansion, and soft-tissue mass can be taken into consideration in the differentiation.
It is difficult to visualize sternal variations and anomalies by radiography. Therefore, cross-sectional imaging such as CT and MRI is generally required to describe the findings detected on radiography and to reveal the additional minor changes. CT with multiplanar reconstruction may show relevant anatomic detail of sternal variations and anomalies. The largest series describing sternal anomalies examined 2,016 plastron radiographs in an autopsy population [3] and 562 radiographs in living subjects [4]. In the largest living subject series using CT as a cross-sectional imaging method, 140 subjects were evaluated to determine the incidence of sternal foramen [6]. The superiorities of the current study to previous studies are as follows: describing multiplanar MDCT appearances of sternal variations and anomalies, studying the largest living subject population (1,000 living subjects), and comprehensively evaluating sternal variations and anomalies.
Multiplanar reconstructed MDCT images were helpful in wholly revealing sternal anatomy. Curved-planar coronal multiplanar reconstruction images nicely showed manubriosternal and sternoxyphoidal fusions, sternal bands and clefts, sternal and xiphoidal foramina, the types of xiphoidal ending, and xiphoidal ossification.
Suprasternal bone is an unfamiliar normal variation in the vicinity of the sternoclavicular joint. It may occur singly or paired at the superior margin of the manubrium. Suprasternal tubercle is considered to be the osseously fused type of suprasternal bone [4]. In a study by Ogawa et al. [4], eight (10.8%) suprasternal bones and 14 (18.9%) suprasternal tubercles were found in 74 cadavers. Among them, three had suprasternal bone and tubercle on each side. In the same study including 562 living subjects, 39 cases (6.9%) had suprasternal bones and eight cases (1.4%) had suprasternal tubercles. Among them, three had both on each side. The incidence of suprasternal bones was lower in our study than their study result (4.1% vs 6.9%). The frequency of suprasternal tubercles in our subjects was lower than in their cadaver population (4% vs 18.9%) but markedly higher than their living subject population (4% vs 1.4%). We did not detect suprasternal bone and tubercle on each side. However, suprasternal bones fused with each other are described to our knowledge for the first time in our study (Fig. 1).
In the present study, 20% of the subjects with complete manubriosternal and sternoxiphoidal fusion were younger than 45 years, and complete fusion in both locations was detected in patients as young as 20 years without osteodegeneration at the junction. These findings suggest that the complete fusion without osteodegeneration could be due to the developmental fusion of manubriosternal and sternoxiphoidal junctions similar to those of vertical sternal pairs.
Sternal cleft is a rare congenital defect of the anterior chest wall and is the result of a failed midline fusion of the sternum. There are complete and incomplete forms depending on the degree of separation. The clinical significance is that it leaves the heart and great vessels unprotected [1]. In the present study, complete sternal cleft was not observed. All incomplete sternal clefts were located in the inferior part of the sternal body as the sternal foramina.
Sternal foramen is a round defect at the lower third of the sternum and the result of incomplete fusion of multiple ossification centers. It is usually asymptomatic and could be detected by CT incidentally [7]. Cooper et al. [2] found sternal foramina in 6.7% of a large contemporary autopsy population. These sternal foramina were usually solitary and located in the body of the sternum. They also detected a foramen in the manubrium. Similar results were found by Moore et al. [3]. They detected 135 (6.6%) sternal foramina on plastron radiographs from 2,016 radiographs in an autopsy population. Stark [6] detected six (4.3%) cases of a midline sternal foramen on the chest CT of 140 cases. The percentage of sternal foramina detected in our subjects was slightly higher than in Stark's study result (4.5% vs 4.3%).
Triple-ended xiphoid process (Fig. 7) and three xiphoidal foramina (Fig. 9) were first described in the present study. Sternal sclerotic bands at the fusion site of sternal pairs were highly frequent in those subjects with a sternal foramen (Fig. 4). Pseudocleft and pseudoforamen terms for the sternum were first used in our study because these clefts or foramina depicted on reconstructed MDCT images were observed at the incomplete fused manubriosternal or sternoxiphoidal junctions.
In conclusion, the sternum has various variations and anomalies. The sternal foramen is a frequent minor anomaly and generally associated with sternal sclerotic bands. Early manubriosternal and sternoxiphoidal fusions can be seen in early adulthood without osteodegeneration. A double-ended xiphoid process is a frequent variation and a triple-ended xiphoid process has been described for the first time to our knowledge in the present study. A xiphoidal foramen is a highly frequent variation and a single foramen is the most common type. Multiplanar and curved-planar reconstructed MDCT images are useful in revealing sternal anatomy and describing sternal variations and anomalies. Awareness of MDCT appearances of sternal variations and anomalies provides a better differential diagnosis with pathologic conditions.
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