Discussion

Mastoid air cells are important in middle-ear physiology because they act as an air reservoir and regulator for middle-ear pressure.^{Reference Tumarkin10,Reference Holmquist11} Their volume ranges between 5.8 and 12.2 ml as measured by computed tomography scan on healthy ears.^{Reference Colhoun, O'Neill, Francis and Hayward12} Mastoid air cell pneumatisation is associated with various factors involving overall growth of the skull, height of the individual, genetic factors and Eustachian tube function.^{Reference Graham and Brackmen13} There are many studies on the association of otological disorders such as congenital cholesteatoma and Ménière's disease with the degree of mastoid pneumatisation.^{Reference Iino, Imamura and Hiraishi14,Reference Schneider-Arnold15} However, a limited number of studies were available for the relationship between mastoid pneumatisation and the success rate of tympanoplasty.

Factors associated with the success of tympanoplasty are a matter of debate and controversy. Mastoid pneumatisation is one of these factors.^{Reference Lee, Jun and Kim16} To date, our study is the first meta-analysis study to look at this important issue in the literature.

Our study showed no significance difference between the two groups (well pneumatised group vs sclerotic mastoid group) in the graft uptake rate in tympanoplasty, although the well pneumatised group had a higher success rate. Our result agreed with Amer et al. ^{Reference Amer, El-Anwar, Abdelhady, Abdulmonaem and Elgerby5} (2017), Metin et al. ^{Reference Metin, Kaptan, Dogan, Yazici, Bayraktar and Gocmen6} (2014), Sethi et al. ^{Reference Sethi, Singh, Agarwal and Sareen8} (2005), Toros et al. ^{Reference Toros, Habesoglu, Habesoglu, Bolukbasi, Naiboglu and Karaca9} (2010) and Yegin et al. ^{Reference Yegin, Çelik, Şimşek, Olgun, Karahasanoğlu and Çolak24} (2016). However, Mohan et al. ^{Reference Mohan, Sharma and Srivastava7} (2015) found that graft uptake rate in cases of tubotympanic chronic suppurative otitis media was better and statistically significant in well pneumatised mastoids when compared with sclerotic mastoids.

In terms of ABG change, there was no significant difference between the well pneumatised group and the sclerotic mastoid group concerning ABG improvement in studies performed by Metin et al., Sethi et al. and Toros et al.^{Reference Metin, Kaptan, Dogan, Yazici, Bayraktar and Gocmen6,Reference Sethi, Singh, Agarwal and Sareen8,Reference Toros, Habesoglu, Habesoglu, Bolukbasi, Naiboglu and Karaca9}

Holmquist and Bergström preferred not to intervene with well pneumatised mastoid during surgery.^{Reference Holmquist and Bergström17} Bonding advocated that problems with the mastoid cell system might be the cause of unsuccessful tympanomastoidectomy in children.^{Reference Bonding18} However, Palva and Virtanen, Siedentop et al. and Gimenez et al. did not agree with that in their studies.^{Reference Palva and Virtanen19–Reference Gimenez, Marco-Algarra, Carbonell, Morant and Cano21} Holmquist reported a success rate of 70 per cent with well pneumatised mastoid air cells as compared with a 57 per cent success rate with poorly pneumatised mastoid air cells.^{Reference Holmquist22} McGrew et al. supported performing mastoidectomy with tympanoplasty over performing tympanoplasty alone to decrease the progression of disease and the need for surgical revision.^{Reference McGrew, Ackson and Glasscock4} Jackler and Schindler strongly supported mastoidectomy with myringoplasty in sclerosed mastoids.^{Reference Jackler and Schindler23}

Metin et al. observed that graft success in tympanoplasty was greater with diploic mastoiditis than pneumatic mastoids, so they suggested that there was no relationship between tympanoplasty success and the degree of mastoid pneumatisation.^{Reference Metin, Kaptan, Dogan, Yazici, Bayraktar and Gocmen6} Balyan et al. concluded that mastoidectomy was not necessary for treatment of patients with non-cholesteatomatous chronic otitis media and that it added extra effort and risk, without giving better chance for graft success or functional hearing results.^{Reference Balyan, Celikkanat, Aslan, Taibah, Russo and Sanna25} Gimenez et al. ^{Reference Gimenez, Marco-Algarra, Carbonell, Morant and Cano21} found no relationship between myringoplasty results and the degree of mastoid pneumatisation. Recent data showed that a cavity would be of no benefit at all as it does not form a reliable pressure buffer.^{Reference Doyle26,Reference Miura, Takahashi, Honjo, Hasebe and Tanabe27} Yegin et al. concluded that the degree of mastoid pneumatisation did not affect the success rate of type 1 tympanoplasty.^{Reference Yegin, Çelik, Şimşek, Olgun, Karahasanoğlu and Çolak24}