In civil matters "sentenza" is "judgement" and this is what is meant here. An alternative term is decision. Ruling is OK too but in many cases this term is used to refer to part of a judgement, so you are still better off using judgement. As for the Court's name in English, the numerous legal texts I have in English on Italian law refer to it as the Supreme Court of Cassation, the Court of Casation or the Supreme Court. I myself tend to use them all indifferently - depending on who the reader of the translation will be and instructions/ reference material given by the client.