■ BACKGROUNDS: Delayed facial nerve palsy (DFP) is sometimes experienced after temporal bone surgeries without direct touch to the facial nerve during operative procedures and annoys both surgeons and patients until DFP is cured. So far, it has been reported that DFP is occurred after such otologic surgeries as tympanoplasty with mastoidectomy, stapes surgery and cochlear implant. However, DFP after endolymphatic sac surgery has never been reported before. Recently, we experienced a case of DFP after endolymphatic sac surgery and the ratio of its occurrence was 1.0% in our own cases (1 out of 100).

■ CASES: The case is a 44-year-old male, with complaints of repeated right persistent tinnitus and fluctuating hearing loss in spite of various kinds of medication. We performed endolymphatic sac surgery on his right ear. DFP on the right side was occurred 8 days after surgery. A couple of herpes serum tests indicated positive in this case. His DFP was mild and it took 18 days to cure of DFP after corticosteroids administration.

■ CONCLUSIONS: In our own cases of the other otologic surgeries, the ratios of DFP occurrence were as follows: 0.7% (2/305) in tympano-mastoidectomy, 0.8% (3/354) in cochlear implant and 0.4% (1/260) in stapes surgery. All the surgeries except for endolymphatic sac surgery exposed chorda tympani, and all the surgeries except for stapes surgery underwent drilling for mastoidectomy. Furthermore, all these DFPs after otologic surgeries were always observed ipsilaterally to the operated ear and rare in the other types of surgery like head and neck. All these findings suggest that there may be some relationships among DFP, herpes virus infection and surgical procedures.