Background: Eustachian tube function (ETF) plays a crucial role in middle ear ventilation and pressure regulation, potentially influencing outcomes of tympanoplasty. The interlay technique in Type I tympanoplasty has shown promising results in terms of graft uptake and hearing improvement. However, the impact of ETF on surgical success remains debated due to a lack of standardized assessment methods.

Objectives: To evaluate the role of Eustachian tube function in predicting graft uptake and hearing outcomes following interlay Type I tympanoplasty in patients with chronic otitis media (COM) of the tubotympanic type.

Methods: This prospective cohort study included 96 patients aged 18–47 years with inactive mucosal COM and large tympanic membrane perforations. ETF was assessed preoperatively using the Eustachian Tube Dysfunction Questionnaire-7 (ETDQ-7) and a tympanometric inflation-deflation test. All patients underwent interlay Type I tympanoplasty, and outcomes were assessed at 12 weeks postoperatively, focusing on graft uptake and hearing improvement (air-bone gap closure).

Results: ETF was normal in 33.3%, moderately impaired in 33.3%, and severely impaired in 33.3% of patients based on ETDQ-7. A significant correlation was observed between ETDQ-7 and tympanometric results (p = 0.000225). Graft uptake was high across all groups: 100% in normal and moderate ETF, and 96.9% in severe ETF (p > 0.05). Hearing improvement occurred in all groups, with mean air-bone gap closure ranging from 15.88 ± 2.71 dB to 17.34 ± 3.90 dB. Patients with normal ETF achieved better postoperative air-bone gaps (<10 dB) compared to those with impaired function (p < 0.05). Middle ear mucosal edema was significantly more common in patients with severe ETD (p < 0.0001).

Conclusion: While interlay tympanoplasty achieves high graft uptake irrespective of ETF, better hearing outcomes and healthier middle ear mucosa are associated with normal Eustachian tube function. ETF assessment using combined subjective and objective methods can aid in surgical planning and patient counselling.