Facial nerve paralysis following repair of the external ear canal with ionomeric cement.
A 20-year-old man developed a complete facial nerve paralysis following surgical reconstruction of the posterior ear canal with ionomeric cement. The paralysis developed gradually during the second and third postoperative weeks. Six weeks following the complete removal of the cement, the facial nerve recovered completely. The literature contains reports of diffusion of aluminum ions, which can reach toxic levels in tissue fluid and adjacent bone as the cement hardens. This side effect has been reported to cause an inflammatory response in the dura and brain and has led to fatalities. To our knowledge, there has been no other report of an ionomeric cement having a direct toxic effect on peripheral nerve transmission. Because ionomeric cements are used routinely in otosurgery, especially in canal reconstructions where the proximity to the facial nerve is evident, it is important to use caution when introducing ionomeric cements into near-nerve anatomic locations.
Glass ionomeric cements are hybrid bone substitutes that were developed in 1969 and have since found a place as a filling material in dentistry.  They were specifically designed as a bone replacement material, especially in otosurgical procedures.  As the cement hardens, the reaction between calcium-aluminum fluorosilicate (a basic glass) and polymaleic acid is minimally exothermic.  But as the neutralization reaction proceeds, the cement's initially low pH level of 1.6 rises within 5 minutes and reaches values above 4.0. 
Encapsulation of the glass particles by the polymaleinate is exceedingly stable and produces a composite that fully matures in approximately 15 minutes.  The composite can be shaped easily with diamond burrs and water irrigation. As the cement sets and hardens, it forms a stable and durable bond with the apatite of the adjacent bone without interpository soft tissue. Contact with fluid during the setting process causes the release of aluminum ions, which can reach critical levels as high as 3 mg/L.  Stringent manufacturing guidelines notwithstanding, there are reports in the literature that during the vulnerable setting stage, neurotoxic aluminum ions have been released into the dural space; two patients have died as a result. [6,7] In this article, we report the case of a patient who developed a complete facial nerve paralysis following reconstruction of his ear canal wall with ionomeric cement.
An otherwise healthy 20-year-old man had undergone a right-sided myringoplasty in 1989 to correct a perforation of the tympanic membrane. In 1992, during a physical examination for military service, he was evaluated for a left-sided perforation. Computed tomography revealed a cholesteatoma in the atticus without destruction of the lateral semicircular canal or the facial nerve canal. Surgery to remove the cholesteatoma was performed in 1995. Preoperatively, there was no evidence that the cholesteatoma had damaged the bone covering the facial nerve. The antral defect of the canal wall was repaired with ionomeric cement (Ionocem; Ionos GmbH & Co., KG, Seefeld, Germany). The myringeal perforation was covered with a fascia graft from the temporal muscle, and the skin flaps were closed. The sutures and packing material were removed on postoperative day 8 when the patient reported good hearing in that ear. There was no sign of infection or facial nerve impairment.
Three days later, the patient returned with a partial facial nerve paralysis on the left side. The paresis progressed to a complete paralysis the following day. Clinically, there was no sign of infection, but the patient was prescribed a 10-day course of cephalosporin therapy.
The patient was explored again, and the ionomeric cement was removed, along with the fascia and middle ear mucosa, and the facial nerve was re-evaluated. Preoperatively, there was no sign of surgical damage to the nerve canal, which was still intact and covered with bone. The canal was reconstructed with a piece of bone, and a new myringoplasty was performed.
The ionomeric cement and soft tissue that were removed were fixed in 4% neutral buffered formaline and processed for routine histology. Light microscopy revealed an ordinary middle ear mucosa, bone fragments and inflammatory cells scattered among the mucosal cells, and extensive debris and particles of ionomeric cement (figure).
During the 6 weeks following surgery, the facial nerve regained its normal function, and hearing tests in that ear revealed a 15-dB air-bone gap and no sign of cochlear damage. The patient has been followed for 4 years postoperatively and has not experienced any recurrence of the cholesteatoma or facial nerve paresis.
Preserving the posterior canal wall during surgery to eradicate chronic middle ear disease presents a challenge to the otologic surgeon. [8-10] Because of the large extent of bone damage usually present, the surgeon must often reconstruct the auditory canal with materials other than autologous bone. Tos has published an extensive survey of reconstructive techniques with autologous, allogenic, and alloplastic materials.  Alloplastic materials include Plastipore, glass ceramics, hydroxyapatite, and ionomeric cements. The advantage that ionomeric cements have over other alloplastic materials is that during the hardening process, intimate hydrogen bonding of the cement to the bone is achieved.  The continuous bonding zone between the cement and the bone is virtually impermeable to water.  Unlike ionomeric cements, Plastipore, glass ceramics, and hydroxyapatite ceramics must be individually trimmed to size and forced into position between the floor and the roof of the ear canal. Also, bone has been foun d to grow into hydroxyapatite ceramic, and after some years has been followed by its total resorption. Finally, residual gaps between bone and glass ceramic have allowed the in growth of squamous epithelium, which places the patient at risk for new cholesteatoma development. 
Restoration of the normal anatomy of the posterior wall with ionomeric cement has been described in a number of reports. [2,12-14] In skilled hands, the technique is easy to perform and does not have any evident drawbacks or side effects. 
None of these articles on ionomeric cement restoration has reported the development of facial nerve paralysis in any patient. At our institution, we have used ionomeric cement in 20 other patients, and we have not observed any side effects. In the patient we describe in this case study, there is no reason to believe that surgical trauma might have caused the facial nerve paralysis. If that had been the case, symptoms would have manifested earlier. During the second exploration of our patient, we found no sign of mechanical damage in the nerve canal. It is possible that our patient could have developed an idiopathic facial nerve paralysis (Bell's paresis), but it is improbable that it would have occurred 14 days postoperatively. Such is certainly not a common event in routine ear surgery.
The more likely explanation is that the paralysis was caused by toxic levels of aluminum released by the cement. Once the implant was removed, aluminum levels declined and nerve function returned. We encourage surgeons to be vigilant to the possibility that ionomeric cements might be toxic to nerves, and we request that surgeons report any similar findings.
From the Department of Otolaryngology--Head and Neck Surgery, Goteborg University, Gothenburg, Sweden.
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|Publication:||Ear, Nose and Throat Journal|
|Date:||Jul 1, 2000|
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