The surgical detail of PNS has been described previously [13 (link)]. One supine position was used with the head of patient turning slightly to the contralateral side of the surgical region. After local anaesthesia with 1% lidocaine, a 14-G Tuohy needle was introduced into the 2 cm posterolateral junction of the frontal and zygomatic portion of the orbital rim. The cannulation was then penetrated through the subcutaneous tissue and reached the plane of supra-periosteal tissue over the eyebrow in a semilunar path. The tip of cannula was slightly beyond the cranial middle line (Figure 1a). One eight-contact electrode (Model 3873; Medtronic, Minneapolis, MN, USA) was inserted into the Tuohy needle. The distal ending of electrical lead was connected to one extension multi-lead cable (Model: 355531; Medtronic), to adjust the stimulation parameter with one external neurostimulator (Model 37022; Medtronic). The stimulation electrode was programmed with a pulse width of 500 µS at a frequency of 40 Hz, to induce a sensation of paresthaesia covering the painful region. The amplitude of stimulation voltage was set between 0.5 and 3.0 mV according to the pain severity reported by the patient.