Footnotes

• Contributors MPS conceived the idea, performed the literature search, wrote the manuscript draft, provided the images, performed a critical review, and is the guarantor. HB contributed to the drafting of the manuscript, edited the draft, and performed a critical review of the manuscript. AS critically revised the manuscript.

• 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.

• Patient consent for publication Not required.

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