LONG-TERM EUSTACHIAN TUBE DYSFUNCTION IN POST-RADIOTHERAPY NASOPHARYNGEAL CARCINOMA PATIENTS

Wong Kein Low,1,2 Mahalakshmi Rangabashyam1

1Department of Otolaryngology, Singapore General Hospital, Singapore; 2Duke-NUS Graduate Medical School, Singapore

Introduction

Chronic middle ear effusion (MEE) is a common sequela of nasopharyngeal carcinoma (NPC) patients who have been treated with radical radiotherapy (RT). Although knowledge of how MEE develops in these patients is important in determining appropriate treatment options, its pathogenesis is still not well understood. This study aimed to find out if there was a correlation between obliteration of the Eustachian tube (ET) and the development of MEE in long-term post-irradiated NPC patients.

Methods

NPC patients who have been successfully treated by RT for at least five years were prospectively studied. Flexible nasal endoscopy focusing on visualization of the opening of the Eustachian tubal orifice was carried out, to see if the tubal lumen was obliterated. Microscopic examination of the tympanic membrane was also performed in each patient. Findings of MEE were confirmed by pure-tone audiometry and tympanometry.

Results

Of the 23 patients studied, 45 ears were available for evaluation. One of the patients had undergone surgery with blind-sac closure in one ear for cerebrospinal leak post-RT; hence only 45 ears were assessed for this study. Thirty-four were noted to have obliterated Eustachian tubes, and there was a tendency for effusion to develop in ears with obliteration of the Eustachian tube (Table 1)(p < 0.0001, chi-squared test).

Table 1. The relationship between obliteration of the Eustachian tube and the presence of ipsilateral middle ear effusion.*

Effusion present

Effusion absent

Total

Oblitrated ET

33

1

34

Patent ET

4

7

11

Total

37

8

45

*ET- Eustachian tube; Two-tailed P value < 0.0001.

Discussion

MEE is a common clinical condition and its development has been attributed to various mechanisms. Although physical obstruction of the Eustachian tubal lumen has been the most popular, alternative mechanisms have been proposed. Bluestone suggested altered cartilage compliance could impact tubal function and lead to ef-fusion.1 The same mechanism applies in Down’s syndrome, which has defective cartilage formation.2 In cleft palate, involvement of the muscles relating to the Eustachian tube leads to tubal dysfunction and effusion.2

We studied the existence of MEE in NPC patients who have received radiotherapy for a minimum period of five years. Of the ears studied, 34 out of 45 ears (73.3%) were found to have obliteration of the tubal lumen. Not uncommonly, there was associated distortion or even absence of Eustachian cushion (Fig 1). These observations could be attributed to tumor destruction of tubal cartilage and/or post-irradiation changes. MEE was noted to be present in almost all the ears with associated obliterated Eustachian tubes, suggesting that physical obstruction of the Eustachian tube could be a key mechanism in the development of MEE in long-term post-radiotherapy NPC patients.

image

Fig. 1. Endoscopic image of an obliterated left Eustachian tube with destruction of the cartilaginous cushion.

However, it has been argued that mere anatomical obstruction of the Eustachian tube does not always culminate in effusion.3 In fact, the ‘hydrops-ex-vacuo’ theory of attributing MEE to the highly negative middle-ear pressure formed as a result of continuous gaseous absorption in a closed biological space has largely been discredited.4 In the development of MEE in long-term post-irradiated NPC patients therefore, besides obliteration of the Eustachian tube, other factors may play a role as well. These include the detrimental effects of radiation on mucosal function as radiation could cause irreversible ciliary loss, intra and inter cellular vacuolation and ciliary dysmorphism.5

As long-term post-radiotherapy NPC patients are likely to have chronic MEE because of irreversible Eustachian tube dysfunction from multiple etiologies, one should exercise caution in recommending ventilation tube insertion as this may lead to chronic or recurrent troublesome otorrhea.6 These patients should be appropriately counseled, as hearing amplification devices may be preferred alternative treatment options.7

Conclusion

Eustachian tubal cartilage destruction and obliteration is an important factor in the development of MEE in long-term post-radiotherapy NPC patients. Together with other factors such as radiation-induced impairment of the mucosal function, these patients develop irreversible Eustachian tube dysfunction, which has implications in management of the resulting middle-ear effusion.

References

1.Takahara T, Sando I, Bluestone CD, Myers EN. Lymphoma invading the anterior eustachian tube. Temporal bone histopathology of functional tubal obstruction. Ann Otol Rhinol Laryngol 95(1 Pt 1):101–105, 1986

2.Shibahara Y, Sando I. Congenital anomalies of the Eustachian tube in Down syndrome. Histopathologic case report. Ann Otol Rhinol Laryngol 98(7 Pt 1):543–547, 1989

3.Grøntved A, Møller A, Jørgensen L. Studies on gas tension in the normal middle ear. Gas chromatographic analysis and a new sampling technique. Acta Oto-Laryngol 109(3–4):271–277, 1990

4.Hergils L, Magnuson B. Human middle ear gas composition studied by mass spectrometry. Acta Oto-Laryngol 110(1–2): 92–99, 1990

5.Lou PJ, Chen WP, Tai CC. Delayed irradiation effects on nasal epithelium in patients with nasopharyngeal carcinoma. An ultrastructural study. Ann Otol Rhinol Laryngol 108(5):474–480, 1999

6.Morton RP, Woollons AC, McIvor NP. Nasopharyngeal carcinoma and middle ear effusion: natural history and the effect of ventilation tubes. Clin Otolaryngol Allied Sci 19(6): 529–531, 1994

7.Skinner DW, van Hasselt CA. A study of the complications of grommet insertion for secretory otitis media in the presence of nasopharyngeal carcinoma. Clin Otolaryngol Allied Sci 16(5):480–482, 1991


Address for correspondence: Wong-Kein Christopher Low, MBBS, PhD, FRCS, Adj Associate Professor (Duke-NUS Graduate Medical School), Novena ENT-Head & Neck Surgery Specialist Centre, #04–21/22/34, Mt Elizabeth Novena Hospital, 38 Irrawaddy Road, Singapore 329563. low.wong.kein@gmail.com

Cholesteatoma and Ear Surgery – An Update, pp. 41–43

Edited by Haruo Takahashi

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