RESUMEN
<p><b>OBJECTIVE</b>To study causes of ineffectiveness of microvascular decompression (MVD) in treatment of hemifacial spasm (HFS).</p><p><b>METHODS</b>Reoperative MVD was performed in 23 HFS patients with previous ineffective MVD. In the patients, the main causes of ineffectiveness included misjudgment of compressing vessels (7 patients), improper insertion of decompressing grafts (9), improper selection of grafts (5) and small grafts (2).</p><p><b>RESULTS</b>Symptoms of HFS disappeared immediately after the second MVD in 21 patients and delayed in 2 patients (after 2 weeks, 6 weeks). No recurrence of HFS was noted during the follow-up period of 1.0 - 6.0 years (mean 3.4 years).</p><p><b>CONCLUSIONS</b>MVD is an effective microsurgical method for treating HFS. Accurate judgement of compressing vessels and proper decompression are the key to surgical effectiveness.</p>