'presternal' originates from Latin elements: the prefix 'pre-' from Latin 'prae' meaning 'before' combined with 'sternal' from Latin 'sternum' (itself from Greek 'sternon') referring to the breastbone.

'presternal' was formed in New Latin/medical Latin as 'presternalis' (or by combination of 'pre-' + 'sternal') and entered English usage in medical/anatomical contexts as 'presternal'.

Initially it literally meant 'before the sternum' and this anatomical meaning has been retained in modern usage.