Blood in the pleural space (hemothorax) can arise by many mechanisms.
Traumatic hemothorax:
(1) blunt or penetrating trauma
(2) iatrogenic during an invasive procedure (surgery, minimally invasive surgery, intravascular line, etc)
(3) iatrogenic by CPR
Drug-related hemothorax:
(1) anticoagulant
(2) thrombolytic therapy
"Spontaneous" hemothorax:
(1) rupture of artery or vein, associated with aneurysm, vasculitis or varicose vein
(2) arteriovenous malformation
(3) primary or metastatic tumor
(4) hemorrhagic snakebite
(5) hemorrhagic fever (dengue, other)
(6) intra-abdominal hemorrhage, including ruptured spleen
(7) associated with endometriosis
(8) perforation esophagus
(9) hydatid disease
(10) severe coagulopathy
(11) fistula from a pancreatic pseudocyst
