Footnotes

• Contributors RC drafted the letter, created the figure with included annotations and alterations of ultrasound images and performed the ultrasound imaging included in the letter. AG conceived of the letter based on review of the original repository of ultrasound images, selected the images to be used for the figure and edited the letter for both content and style.

• Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests None declared.

• Provenance and peer review Not commissioned; internally peer reviewed.