DISCUSSION There are several issues to be considered with cochlear implan- tations after transverse temporal bone fractures. First, the num- ber of surviving ganglion cells would seem to be a very impor- tant factor in determining the success of electrical stimulation (4). Nadol et al. (4) reported an average survival of only a third of the ganglion cell population after temporal bone fractures. Second, the patency of the cochlea after a fracture is another important factor for a successful insertion of electrodes. Tran- sverse fractures may cause direct trauma to the otic capsule resulting in destruction of the organ of Corti and stria vascu- laris, hemorrhage into the inner ear and subsequent labyrinthi- tis ossificans (5). Displaced fracture lines and labyrinthitis ossifi- cans associated with temporal bone fractures may complicate the insertion of the electrode array. The most frequent site of an ossification is the basal turn of the cochlea (5). Third, patients with structural abnormalities may have a higher predisposition toward developing meningitis (3). Meningitis is not only a seri- ous disease, but also accelerates the process of labyrinthitis ossi- ficans. Fourth, there is a significant risk of facial nerve stimula- tion. It is assumed that current leaks from the electrode through the low resistance of the fracture line to stimulate the facial nerve in the region of the geniculate ganglion or in the horizontal por- tion may occur (2). That may be overcome by programming out the responsible channels. When there is a significant time delay between the initial CT scan after temporal bone trauma and the cochlear implantation, repeated imaging studies are beneficial to rule out labyrinthitis ossificans or other structural abnormalities such as granulation tissue in the middle ear (6). However, there are no available reports on the prevalence of labyrinthitis ossificans after a tem- poral bone fracture and the safe time period for no new bone formation. It seems that the sooner a cochlear implant is per- formed after the time of the temporal bone fracture, the less time is available for labyrinthitis ossificans to occur, and there- fore the greater probability for successful electrodes insertion (3). Seidman et al. (7) reported that in up to 22% of cases high resolution CT failed to show a luminal obstruction subsequent- ly found at surgery. T2 weighted MR imaging may be a more sensitive method for determining the patency of the cochlea. Fig. 2 showed similar findings in the present case. And fracture line on the left side extended to the internal audi- Shin J-H et al.: CI after Bilateral Temporal Bone Fractures 173 tory canal. It may have disrupted the eighth cranial nerve, incur- ring a postganglionic injury and rendering the cochlear implan- tation useless. Through the careful evaluation of the imaging studies, left side was not recommended for performing the cochlea implantation due to the possibility of direct damage to the eighth cranial nerve and the uncertainty of the patent cochlea. Cochlear implantations following temporal bone fractures have been proven to have good audiometric and psychoacoustic results, comparable with other etiologies. However, several issues must be considered before performing cochlear implants in patients with profound sensorineural hearing losses caused by bilateral temporal bone fractures. Preoperative imaging stud- ies with both high resolution CT and MRI are highly recommend- ed in patients with temporal bone fractures. This case demon- strated that cochlear implantation with careful planning in such patients can be a very effective method for aural rehabilitation. ACKNOWLEDGEMENT The authors thank the patient and his family for their cooper- ation. And we are very grateful at the thorough review and valu- able comments by the anonymous reviewers. REFERENCES 1. Morgan WE, Coker NJ, Jenkins HA. Histopathology of temporal bone fractures: implications for cochlear implantation. Laryngoscope. 1994 Apr;104(4):426-32. 2. Camilleri AE, Toner JG, Howarth KL, Hampton S, Ramsden RT. Cochlear implantation following temporal bone fracture. J Laryngol Otol. 1999 May;113(5):454-7. 3. Simons JP, Whitaker ME, Hirsch BE. Cochlear implantation in a patient with bilateral temporal bone fractures. Otolaryngol Head Neck Surg. 2005 May;132(5):809-11. 4. Nadol JB Jr, Young YS, Glynn RJ. Survival of spiral ganglion cells in profound sensorineural hearing loss: implications for cochlear implan- tation. Ann Otol Rhinol Laryngol. 1989 Jun;98(6):411-6. 5. Fredrickson JM, Griffith AW, Lindsay JR. Transverse fracture of the temporal bone. A clinical and histopathologic study. Arch Otolaryngol. 1963 Dec;78:770-84. 6. Levine SC. A complex case of cochlear implant electrode placement. Am J Otol. 1989 Nov;10(6):477-80. 7. Seidman DA, Chute PM, Parisier S. Temporal bone imaging for co- chlear implantation. Laryngoscope. 1994 May;104(5 Pt 1):562-5.