CHORDA TYMPANI NERVE RE PAIR WITH A POLYGLYCOLIC ACID-COLLAGEN TUBE IN CHOLESTEATOMA SURGERY
Introduction
During cholesteatoma surgery in the middle ear, the chorda tympani nerve is frequently severed.1 Resection of the chorda tympani nerve causes a defect of gustatory function in the affected side resulting in a taste disturbance. Although some patients experience gradual recovery of the symptoms, alteration or loss of taste forms a real problem for them. Restoration with sufficient functional recovery after nerve injury continues to be a clinical challenge. Various artificial nerve conduits have been tried as alternatives that regenerate severed peripheral nerves to autografts . There is no report of applying the device to the chorda tympani nerve reconstruction. The chorda tympani nerve seems hard to restore because this nerve runs through the aerial space without any floors as a scaffold for grafting. A bio-absorbable polyglycolic acid (PGA) tube filled with collagen sponge (PGA-collagen tube) (Fig. 1) has been developed recently. In experimental and clinical trials, it has proven to be effective for regeneration of peripheral nerve defect. Using a PGA-collagen tube, we attempted to reconstruct the chorda tympani nerve gaps in a patient with cholesteatoma who underwent a tympanoplasty, and examine whether the gustatory dysfunction restored.
Fig. 1. Polyglycolic acid (PGA) tube and its transverse.
A 52-year-old male presented with a three-month history of taste disturbance and a two-month history of hearing loss in the right ear. Physical examination showed a cholesteatoma white mass with formation of inflammatory granulation tissue in the pars flaccida over the manubrium of the malleus. The pure-tone hearing testing revealed the moderate conductive hearing loss of 41.3 dB in the pure tone average (PTA). A CT scan with a bone window demonstrated the presence of soft-tissue mass in the epitympanum and antrum with ossicular erosion.
The patient underwent surgery for removal of cholesteatoma. During surgery, a cholesteatoma sac was found in the attic and antral cavity, that destroyed ossicles such as malleus and incus. It was found that the choles-teatoma sac was attached to the chorda tympani nerve and was likely to invade the nerve fibers on dissection of the sac. Since the chorda tympani nerve attenuated and was adhered to the lateral aspect of the sac, the decision was made to section the nerve in order to achieve the removal of the cholesteatoma sac. The chorda tympani nerve in continuity with the cholesteatoma sac was resected in the healthy portion of both proximal and distal nerve apart from the sac involvement. The resulting seven-mm nerve gap was reconstructed with a PGA-collagen tube (nine mm in length and three mm in diameter). Both the proximal and distal stumps of the severed nerve were inserted into the PGA-C tube to a depth of one mm. The tube was secured to the proximal and distal nerve ends with epineural 10–0 polypropylene monofilament sutures (Prolene, Ethicon, Somerville, NJ, USA) (Fig. 2). The tympanic membrane was reconstructed with the temporalis fascia.
The gustatory function was assessed with electrogustometry (EGM) using an electrogustometer (Rion, TR-06, Rion Co, Tokyo, Japan) which is a more reliable and objective method to evaluate quantitative taste function.1,2 A five-mm probe was touched to the lateral edge of the tongue at two cm from its tip to stimulate the CTN territory. The stimulation range of EGM was -8 to 34 dB (normal range ≤ 8 dB). Scale out, not detected with any EGM stimulation was taken as 36 dB.
Fig. 2. Intraoperative view after bridge of a PGA-C tube. CTN: chorda tympani nerve.
Pre-operative EGM threshold scoring 25 dB showed objective gustatory mild disturbance. The threshold of EGM on the affected side elevated up to 32 dB in one week after the CTN reconstruction. However, the threshold started to decrease within ten days and returned to normal level (≤ 8dB) at two weeks, leading to complete recovery at 56 days, while the EGM threshold on the intact side showed little change all the time through the postoperative course (Fig. 3). Afterwards, the EGM threshold maintained the recovery level for 72 days.
This study was approved by the clinical research ethics board of the Nara Medical University Hospital.
Fig. 3. The clinical course of the EGM threshold after reconstruction of CTN with a PGA-C tube.
Discussion
The artificial nerve conduit used in this study is composed of a biodegradable tube filled with biodegradable filaments. The tube framework is made of cylindrically woven PGA mesh of which outer and inner surfaces are coated with amorphous collagen layers. The inner space of this tube was filled with a 3D circumstance matrix spongiform collagen. Sponge-form collagen, which makes the surface area larger than fiber-form, seems to provide a favorable micro-environment for nerve progression (axonal sprouting cellular proliferation and tissue healing).3,4 Although collagen has a tendency to dissolve easily in the body, it is likely able to remain the shape in the nerve conduit for periods long enough to complete the nerve regeneration in the body, since PGA was used as outer cover of collagen.3,5 The PGA-C tube (30 mm in length, four mm in diameter) was trimmed in nine mm long pieves, in accordance with demand during surgery.
To take an advantage of this feature in the PGA-C tube, some experimental studies and clinical trials was extended to examine on the performance of PGA-C tube for nerve gap reconstruction. Histologic examination (four months) after implantation of the PGA-C tube showed regeneration of nerve tissue structure, including myelinated axons and Schwann’s cells. Electrophysiological analysis demonstrated functional recovery of the regenerated nerves at a growth rate of 0.5–1.0 mm/day.3,5
PGA-C tubes have recently been applied for clinical cases with a defect of the peripheral nerve such as a proper digital nerve and superficial peroneal nerve with successful results regarding symptomatic and functional recovery.6,7
In this study, the nerve reconstruction for the severed chorda tympani nerve in the aerial space using a PGA-C tube, brought successful recovery of the taste function as assessed by EGM. There is little study reporting on the time course in the evaluation of EGM, a quantitative gustatory function test2 used for each patient with a severed nerve. One study reported that the threshold of EGM, which was found to increase considerably two weeks after the section of CTN, did not get back to the baseline level in the follow-up cases. Thirty percent or less of the cases demonstrated partial recovery after two years.8 Another report suggested that one to two years are needed until the EGM threshold is recovered and stabilized.9
According to these reports, the mechanism underlying the recovery of taste after unilateral CTN section seems to be associated with neuronal innervation to the lesioned side from contralateral intact side and /or from ipsilateral glossopharyngeal nerve.10-14
Fig. 4. Possible mechanism underlying a regeneration of severed nerve with a PGA-C tube.
In our study, the gustatory function as measured by EGM started improving at ten days, got back to normal range at 14–21 days and had recovered completely 56–72 days after the reconstruction of the severed chorda tympani nerve with a PGA-C tube. This fast improvement of the gustatory function appears to be caused not by the innervation from the other healthy regions such as contralateral chorda tympani or ipsilateral glos-sopharyngeal nerve, but by the regeneration of the nerve itself through the PGA-C tube.
Tube framework consisting of PGA likely plays a role in preventing nerve fibers from misdirection in a process of regeneration and guiding them correctly to each other nerve cut ends through tube lumen filled with collagen sponge, as nerve fibers extended and regenerated successfully toward a rectified way without any misleading even if it is in the air without any scaffold (Fig. 4).
In conclusion, these results suggest that reconstruction with an artificial nerve conduit, PGA-C tube involves functional and morphological regeneration of the chorda tympani nerve and is possible intervention to facilitate a recovery of the taste function.
References
1.Anson BJ, Donaldson JA, Shilling BB. Surgical anatomy of the chorda tympani. Ann Otol Rhinol Laryngol 81:616–631, 1972
2.Murphy C, Quinonez C, Nordin S. Reliability and validity of electrogustometry and its application to young and elderly persons. Chem Senses 20:499–503, 1995
3.Nakamura T, Inada Y, Fukuda S, et al. Experimental study on the regeneration of peripheral nerve gaps through a polyglycolic acid-collagen (PGA-collagen) tube. Brain Res 1027:18–29, 2004
4.Toba T, Nakamura T, Shimizu Y, et al. Regeneration of canine peroneal nerve with the use of a polyglycolic acid-collagen tube filled with laminin-soaked collagen sponge: a comparative study of collagen sponge and collagen fibers as filling materials for nerve conduits. J Biomed Mater Res 58:622–630, 2001
5.Kiyotani T, Teramachi M, Takimoto Y, Nakamura T, Shimizu Y, Endo K. Nerve regeneration across a 25-mm gap bridged by a polyglycolic acid collagen tube: a histological evaluation of regenerated nerves. Brain Res 740:66–74, 1996
6.Inada Y, Morimoto S, Takakura Y, Nakamura T: Regeneration of peripheral nerve gaps with a polyglycolic acid-collagen tube. Neurosurg 55:640–646, 2004
7.Inada Y, Morimoto S, Moroi K, Endo K, Nakamura T. Surgical relief of causalgia with an artificial nerve guide tube: Successful surgical treatment of causalgia (Complex regional pain syndrome Type II) by in situ tissue engineering with a polyglycolic acid-collagen tube. Pain 117:251–258, 2005
8.Nin T, Sakagami M, Sone-Okunaka M, Muto T, Mishiro Y, Fukazawa K. Taste function after section of chorda tympani nerve in middle ear surgery. Auris Nasus Larynx 33:13–17, 2006
9.Saito T, Manabe Y, Shibamori Y, et al. Long-term follow-up results of electrogustmetry and subjective taste disorder after middle ear surgery. Laryngoscope 111:2064–2070, 2001
10.Mahendran S, Hogg R, Robinson JM. To divide or manipulate the chorda tympani in stapedotomy. Eur Arch Otorhinolaryngol 262:482–487, 2005
11.Kiverniti E, Watters G. Taste disturbance after mastoid surgery: immediate and long-term effects of chorda tympani. J Laryngol Otol 126:34–37, 2012
12.Kveton JF, Bartoshuk LM. The effect of unilateral chorda tympani damage on taste. Laryngoscope 104:25–29, 1994
13.McManus LJ, Stringer MD, Dawes PJ. Iatrogenic injury of the chorda tympani: a systematic review. J Laryngol Otol 126:8–14, 2012
14.Leung R, Ramsden J, Gordon K, Allemang B, Harrison B, Papsin B. Electrogustometric assessment of taste after otologic surgery in children. Laryngoscope 119:2061–2065, 2009
Address for correspondence: Toshiaki Yamanaka, toshya@naramed-u.ac.jp
Cholesteatoma and Ear Surgery – An Update, pp. 477–481
Edited by Haruo Takahashi
2013 © Kugler Publications, Amsterdam, The Netherlands