Dexmedetomidine Use for Greater Occipital Nerve Block in Pediatric Posterior Fossa Tumor Surgery.

The goal of this clinical trial is to evaluate the effects of ultrasound-guided versus blind greater occipital nerve block (GONB), with or without Dexmedetomidine as an adjuvant, in pediatric patients undergoing posterior fossa tumor excision under general anesthesia. The main questions it aims to answer are: * Does ultrasound-guided GONB improve hemodynamic stability compared with the blind technique? * Does adding dexmedetomidine to GONB affect intraoperative and postoperative opioid consumption, postoperative pain control, and the time to first rescue analgesia? Researchers will compare four groups to evaluate the effects of the nerve block technique and the addition of dexmedetomidine: Group A: Blind GONB using 0.25% bupivacaine. Group B: Blind GONB using 0.25% bupivacaine with dexmedetomidine (1 μg/kg). Group C: Ultrasound-guided GONB using 0.25% bupivacaine. Group D: Ultrasound-guided GONB using 0.25% bupivacaine with dexmedetomidine (1 μg/kg). Participants will be pediatric patients scheduled for elective posterior fossa tumor excision at Children's Cancer Hospital Egypt (CCHE 57357). They will be randomly assigned to one of the four groups and will receive standardized general anesthesia and bilateral GONB according to their assigned group. Intraoperative heart rate and blood pressure, intraoperative and postoperative opioid consumption, and time to first postoperative rescue analgesia will be assessed.