Abstract
This report details an unusual case of a human sternal developmental abnormality of an anatomical specimen part of the skeletal collection curated by University College London, Anthropology Department skeletal collection. This rarely reported developmental abnormality is caused by the non-fusion of lateral ossification centres in the sternebrae, resulting in the mesosternum having a honeycomb-like appearance. Sternal defects are typically underreported in the clinical literature as many cases being asymptomatic that they are typically diagnosed incidentally, as such there is a dearth in our current understanding of the development and anatomical variants of the sternum. Although in recent years, large-scale CT studies have investigated the prevalence of sternal developmental abnormalities, these studies have not reported sternal defects similar to the individual presented in this report. While most sternal defects are clinically uneventful, the lack of awareness of these variants can result in misinterpretation of radiological and pathological findings as such an understanding of anatomical variants even when asymptomatic is vital.
Highlights
The adult sternum is comprised of three sections connected by secondary cartilaginous joints: the manubrium located superiorly, the mesosternum in the centre, and the xiphoid process inferior to these other elements [7,8,9, 14, 17]
While the manubrium and the first sternebra of the mesosternum were single fused sternebrae, the third and fourth were comprised of two unfused ossification centres, and the fifth sternebra appears to have originally had three ossification centres which had almost completely fused into a single section
Yekeler et al [18] reviewed the morphology and frequency of sternal variation and abnormalities in 1000 patients (582 men and 418 women; 20–92 years with a mean age of 54 years) who underwent thoracic multidetector CT examinations. Their results revealed the frequency of a number of previously documented sternal abnormalities such as sternal clefts, fissures, tubercles and fusion patterns, as well as CT examination of developing sterna in clinical contexts has found that accessory ossification centres are frequent in the manubrium and mesosternum [1, 7]
Summary
The adult sternum is comprised of three sections connected by secondary cartilaginous joints: the manubrium (the first sternebrae) located superiorly, the mesosternum (or body, comprised of the second to fifth sternebrae) in the centre, and the xiphoid process (the sixth sternebrae) inferior to these other elements [7,8,9, 14, 17]. Development of the sternum begins during the sixth week of intrauterine life, originating from a pair of longitudinal mesenchymal bands on either side of the anterior chest wall, which migrate medially to form the cartilaginous sternum [9, 14] Fusion of these two halves—known as the sternal bars—progresses from the cranial end to the caudal end of the sternum in a process which normally completes by the tenth week [2, 5, 10]. When bifurcated (or multiple) ossification centres are present, the sternebrae initially exhibit osseous discontinuity, altered morphology of the adjacent margins, and/or asymmetrical forms. These ossification patterns are visible from the last month in utero until around 4 years of age when the separate sections of the sternum start to fuse [7]. These segments fuse during growth and it is often not possible to identify ossification patterns in adult individuals [1, 7]
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