Patient population
At this retrospective study, 1150 patients who underwent MDCT scan of the chest, were evaluated. Medical records of the patients were available at the time the MDCT examination was performed. The study protocol was approved by the Institutional Review Board.
Patients with gross sternal deformities, sternal fractures, sternal surgery and sternal masses or infections were excluded from the study. Therefore, MDCT images of 950 patients (573 men, 377 women; age range 18-95 years; mean age 63 years) were evaluated for detection of sternal variations and anomalies.
MDCT Protocol
All CT scans were performed using a 128-row MDCT system (Philips Ingenuity CT 128). MDCT of the chest was performed with the patient at supine position and after the intravenous injection of contrast medium, at arterial phase (25 sec), covering the area from the thoracic inlet to the level of the adrenal glands, including the sternum and the xiphoid. The following imaging parameters were applied: detector collimation 16x1.0 mm; tube voltage 120 kVP; tube current 200-400 mA; pitch 1; slice thickness 1 mm; matrix 512x512. Contrast medium (iomeprol [Iomeron, Bracco Imaging], iopromide [Ultravist, Bayer]) was administered through an antecubital vein by a power injector at a rate of 3 ml/sec followed by saline injection of 10 ml. The injected contrast medium volume was 70 ml.
Image Analysis
All images were post-processed and analyzed in a dedicated workstation, IntelliSpace Portal (version 7.0.1.20482, Philips Medical Systems, Best, The Netherlands). In all subjects, after the standard approach of studying axial images of 1 mm thickness, sagittal and coronal multiplanar reconstruction (MPR) was performed, using bone algorithm and 3D reformation was obtained, using maximum intensity projection (MIP) and Volume Rendering Technique (VRT), in order to succeed better identification of sternal variations.
All images were evaluated by two radiologists (with 4 and 25 years of experience, respectively), independently.
Findings
The following sternal variations and anomalies were observed (Table 1).
Suprasternal Bone and Suprasternal Tubercle
Suprasternal bones are small accessory ossicles at the superior margin of manubrium due to supernumerary ossification centres [4]. In our study, they were found in 5 patients (0.53%), 3/5 being bilateral and 2/5 being unilateral on the right side. Oblique coronal or sagittal planes were better in depicting this variation (Fig. 1).
Suprasternal tubercle results from the fusion of a suprasternal ossicle with manubrium [4]. A bilateral suprasternal tubercle was detected in only 1 patient, and it was better depicted in oblique coronal and axial planes (Fig. 2).
Manubriosternal and Sternoxiphoidal Fusion
At 25 patients (2.63%) both manubrio-sternal and sterno-xiphoidal fusions were detected. At 39 patients (4.1%) manubrio-sternal fusion only was detected, whereas at 38 patients (4%) sterno-xiphoidal fusion only was detected (Fig. 3, 4, 5).
All fusions were complete and no partial fusion was observed. They were best seen in sagittal and oblique coronal planes.
Sternal Sclerotic Band and Cleft
Sternal sclerotic bands were observed in 122 patients (12.8%). Most of them (98/122) were located at the sternal body (81%), and 24/122 were located at the manubrium (19%) (Fig. 6).
Sternal clefts are midline congenital defects at the junction of the sternal bars, due to failure or incomplete fusion of sternal segments and can be associated with other anomalies [4]. They were seen in 11 patients (1.2%), all of them located at the sternal body (Fig. 7 & 8).
They were better seen in oblique coronal and axial planes.
Sternal Foramen
Sternal foramina result from incomplete fusion of a pair of sternebrae [4]. They were found in 48 patients (5%) located at the inferior part of the sternal body. Only one foramen was found at the manubrium. Sternal foramina were directly adjacent to the pericardium in 37.14%, to mediastinal fat in 17.1% and to the lung parenchyma in 8.5% of patients. They were better detected in coronal and axial planes (Fig. 9 & 10).
Cortical sternal defect or notch
Focal defect or notch of the sternal cortex was found in 96 patients (10%). The majority were located posteriorly and were better seen in the axial plane (Fig. 11).
Xiphoidal Ending
The xiphoid process was absent in 2 female patients (0.2%), 19 and 25 years old, respectively.
The xiphoidal ending was classified into three groups:
- single-ended, detected in 562 patients (59.2%).
- double-ended, detected in 351 patients (36.9%) (Fig. 12)
- triple-ended, detected in 35 patients (3.7%) (Fig. 13)
According to the literature [12], the length of xiphoid process is about 2 - 5 cm and is triangular. In 91 patients (9.6%) with single-ended xiphoid process, the xiphoid was longer than usual with mean length 6.02 cm (Fig.14 & 15). In 9 patients (0.9%) with single-ended xiphoid process, this was smaller than usual with mean length 2.23 cm (Fig. 16).
Xiphoidal Foramen
Xiphoidal foramina were more frequent than sternal foramina [4]. They were observed in 245 patients (25.8%) and were better detected in oblique plane (Fig. 17). Multiple foramina were seen in 10/245 patients.
Xiphoidal Ligament Calcification
Xiphoid ligament calcification was detected in 79 patients (8.3%), it was either bilateral or unilateral and was better seen in oblique coronal plane (Fig. 18).
Sternal Pseudoclefts and Pseudoforamina
These variations were seen due to partial fusion at manubriosternal and sternoxiphoidal junction [4]. In our study, pseudoforamina were found in 6 patients (0.6%) and pseudoclefts in 5 patients (0.5%). All of them were located at the sternoxiphoidal junction and were better detected in oblique coronal plane (Fig. 19).