The lucid interval is pathognomonic of EDH — arterial bleeding accumulates rapidly, compressing the brain after an initial lucid period. EDH does not cross suture lines (dura is tightly attached at sutures). SDH is crescent-shaped and crosses sutures freely. Pterion — thinnest part of the skull, overlies the middle meningeal artery groove; fractures here cause EDH.
OPSI (Overwhelming Post-Splenectomy Infection) — fulminant bacteraemia with encapsulated organisms. Lifetime risk ~5%; highest in first 2 years. Encapsulated organisms (SHiN mnemonic: Streptococcus pneumoniae [MC], Haemophilus influenzae, Neisseria meningitidis) escape opsonisation without splenic macrophages. Patient must carry an emergency antibiotic card and take prophylaxis lifelong.
Antibiotic prophylaxis is given for Class II and above; for Class I, only if implant is used. Prophylaxis is given 30–60 minutes before skin incision (not on call to theatre, not post-op). Cefazolin is first-line for most clean and clean-contaminated surgery. SSI timing: superficial incisional (<30 days); deep incisional or organ/space (<30 days, or <1 year if implant).