Objective:To explore the detection rate, missed diagnosis rate, and clinical significance of incidental extra-hip findings (IEHFs) in hip joint MRI.Methods:The data of 1 734 cases who underwent MRI examination of hip joint from September 2014 to September 2018 at the First Central Hospital of Baoding City were retrospectively analyzed. According to the revised CT colonography reporting and data system (C-RADS), the IEHFs were divided into 4 types using structural imaging reading method. E1 type was anatomical variation; E2 type was sign without clinical significance; E3 type was sign with little clinical significance; E4 type was sign with important clinical significance. The types and distributions of IEHFs were analyzed, and the results of structural imaging reading were compared with those of the initial MRI reports. The missed diagnosis rate was calculated in this group.Results:Among the 1 734 patients, 1 651 of IEHFs were found in 1 064 patients. There were 1 080 E2 type IEHFs (65.4%, 1 080/1 651), with cervical cysts (26.0%, 281/1 080) accounting for the largest number. There were 354 IEHFs of E3 type (21.4%, 354/1 651), with most cases were prostatic hyperplasia (47.2%, 167/354). There were 217 IEHFs of E4 type (13.1%, 217/1 651), most of which were the enlarged lymph nodes in the inguinal region (30.9%, 67/217). E2 and E3 IEHFs accounted for a great proportion in male patients. The proportion of E2 IEHFs was the largest in female patients. There was significant difference in IEHFs composition between male and female patients (χ2=294.080, P<0.001). The IEHFs of patients under 60 years old were mainly E2 type, while those of over 60 years old patients were mainly E3 type. There was significant difference in IEHFs composition among different age groups (χ2=206.702, P<0.001). The overall missed diagnosis rate of IEHFs was 85.2% (1 406/1 651). The missed diagnosis rate of E2 was the highest (91.1%, 984/1 080), and that of E4 was the lowest (63.1%, 137/217). Conclusion:The incidence of IEHFs in patients undergoing hip joint MRI are prevalent. The structural imaging reading method can increase the detection of IEHFs. Therefore, it is suggested that revised C-RADS be used to grade IEHFs to reduce the rate of missed diagnosis.