Text and Data Mining valid from 2019-08-28
Received: 28 March 2019
Accepted: 6 August 2019
First Online: 28 August 2019
Ethics approval and consent to participate
: For this type of retrospective study formal consent is not required; any personal data was protected accordingly to the Helsinki Declaration and to the Italian law (Legislative Decree of 30 June 2003, n. 196. Code on the protection of personal data).
: Not applicable.
: All authors have no competing interests to declare.