<prompt> Secondary retrosternal goitre derives its blood supply from :Mediastinal vesselsThyroid vesselsArch of aortaBronchial vessels  <response>: Secondary retrrosternal goitre : Is the extension of thyroid tissue to mediastinum from thyroid in the neck. and it derives blood supply from thyroid vessels.Primary retrrosternal goitre : Is the ectopic thyroid tissue in the mediastinum and it derives blood supply from mediastinal vessels. 