Post-craniotomy pain is a common occurrence which is associated with poor outcomes. Pre-emptive scalp infiltration with dexamethasone and ropivacaine has been proven effective in previous studies but with limited clinical significance. Dexamethasone palmitate emulsion (D-PAL) is a pro-drug incorporating dexamethasone into lipid microspheres with greater anti-inflammatory activity and fewer side effects than free dexamethasone. However, its effects in post-craniotomy pain management remain unknown. This study hypothesizes that pre-emptive scalp infiltration with ropivacaine plus D-PAL emulsion can achieve superior analgesic effects to ropivacaine alone in adult patients undergoing craniotomy.