OBJECTIVE: Understanding the distinct subtypes of adhesive otitis media (AdOM) is crucial for appropriate treatment such as balloon Eustachian tuboplasty (BET), particularly in distinguishing between patulous and obstructive Eustachian tube (ET) function. Nevertheless, AdOM caused by patulous Eustachian tube dysfunction (ETD) remains underexplored. This study aims to describe the detailed characteristics and define the patulous type of AdOM associated with patulous ETD (PET). STUDY DESIGN: A prospective cohort study. SETTING: A total of 62 ears of patients diagnosed with AdOM, PET, and traumatic perforation were included from a tertiary referral center (university hospital). METHODS: Obstructive-AdOM, patulous-AdOM, PET, and a control group with traumatic perforation patients underwent endoscopic examinations, completed symptom questionnaires, and had passive ET opening pressure evaluated using a modified inflation-deflation test following tympanostomy tube insertion. RESULTS: Patulous-AdOM was identified in 43% of the patients and was characterized by significantly lower median opening pressures (222 daPa) than those in patients with obstructive-AdOM (400 daPa) and PET (below 100 daPa). Habitual sniffing was reported in 92.3% of patients with patulous-AdOM, and reduced mastoid pneumatization was observed in both the patulous and obstructive subtypes. CONCLUSION: Accurate differentiation between patulous-AdOM and obstructive-AdOM is essential because BET may exacerbate symptoms in patients with patulous characteristics. A comprehensive evaluation of ET function is critical before initiating treatment, underscoring the need for tailored approaches to manage AdOM.