Expansion
Epidural is a lens, subdural is a banana
Mnemonic
“Extradural is lens shaped and lentil lasts; subdural is crescent and crosses”:
- Extradural - biconvex (lentiform), does not cross suture lines because the dura is attached there, but does cross the falx and tentorium. Arterial, usually the middle meningeal artery at the pterion
- Subdural - crescent shaped, crosses suture lines freely but not the midline, since the falx blocks it. Venous, from torn bridging veins
“Extradural stops at sutures, subdural stops at the midline.”
Extradural is typically the young patient after temporal trauma with a lucid interval; subdural is the elderly, the alcohol dependent and the anticoagulated after minor trauma, with cerebral atrophy stretching the bridging veins.
Expansion
- Epidural - biconvex, lens shaped, limited by sutures
- Subdural - crescent, banana shaped, can cross sutures