Mediastinal NeoplasmsMediastinal DiseasesMediastinumThymus HyperplasiaAzygos VeinMediastinal CystThymus NeoplasmsThymomaSuperior Vena Cava SyndromeTomography, X-Ray ComputedBronchogenic CystSyphilis, CardiovascularRadiography, ThoracicThoracoscopesTomography Scanners, X-Ray ComputedHodgkin DiseaseBiopsy, NeedleProcarbazineMechlorethamineIncidental FindingsPleural EffusionLymphatic DiseasesVincristineAsparaginasePrednisoneThoracotomyLeukemia, LymphoidMass SpectrometryThoracic Surgery, Video-AssistedCranial Fossa, Posterior