Cholesteatomas are benign but expansive aggregations of keratinized squamous debris, which can damage surrounding spaces and eventually reach intracranial space, and usually occurs in the ear and brain (1). Cholesteatoma of the ear is mostly seen in the middle ear, while cholesteatoma of the external auditory canal (EAC) is considered to be rare or uncommon, and accounts for approximately 1/60–30 of all middle ear cholesteatomas (2). Its annual incidence has been reported to be approximately 1.5–3 cases per million individuals in Europe (3–6), and 23.3 cases in Ningde, Fujian Province (7). There are various staging (grading or classification) schemes for EAC cholesteatoma (EACC) (7–13), but none has been widely accepted to date. At the same time, there is no uniform treatment mode for EACC, for the same degree of lesions, the choice of treatment modality greatly varies among doctors (13). The low incidence of EACC has largely limited the clinical summarization of its characteristics. Thus, it is necessary to conduct an in-depth discussion on the clinical staging of this disease and the recommended therapeutic surgical modalities.

When EACC involves the middle ear, it needs to be differentiated from middle ear cholesteatoma involving the EAC (Figures 1D,E), which is more commonly observed in individuals with mastoid pneumatization insufficiency. In middle ear cholesteatoma involving the EAC, the main body of the lesion is located in the mastoid rather than the EAC and may lead to the destruction of bone in the posterior wall of the EAC, further leading to the involvement of the entire EAC. In contrast, in EACC, the involvement of multiple bony walls is common in early lesions; additionally, the disruption of the scutum caused by EACC occurs from the outside in rather than from the inside out. However, it is difficult to identify some extensive lesions.

The male-to-female ratio in this study was 1:1.75, the median age was 34.5 years, and the right-to-left side ratio was 1:1.6, which was similar to previous reports (7, 10, 13, 14). Among the clinical symptoms, complaints of hearing loss (blockage) were the most frequent, but acute otorrhea and otalgia were often the main reasons for patient visits to the clinic. Among the bony wall disruptions of the EAC, the posterior wall was the most involved followed by the inferior wall, which is in line with our previous case reports, and multiple bony wall involvement was also common (37/42). In most cases, the hearing loss caused by the lesion manifested as conductive deafness, and the hearing significantly improved postoperatively (p < 0.05), suggesting that the patients’ mechanical impairment of auditory conduction was alleviated after lesion removal.

There are several staging schemes for EACC (7–13). Holt’s (8) earliest proposed staging scheme was more general: when the lesion invades the tympanic cavity medially, destroying the auditory ossicle chain without invading the mastoid process, it is classified as a stage II lesion, whereas if the lesion progresses posteriorly and invades a small amount of the mastoid air cells, it can be classified as stage III, which may not be clinically recognized as a more serious lesion compared with the stage II lesions; furthermore, there is no separate classification for lesions that extend beyond the temporal bone. The greatest advantage of Naim’s et al. (9) staging scheme is that it combines pathological evidence of the disease and includes early lesions. Thus it is useful for understanding the development of EACC, but the difference in intraoperative sampling may misclassify stage II and III lesions (15), and six patients in this group received only outpatient debridement without pathological examination. Accordingly, these individuals could not be staged using this scheme. Shin’s et al. (10) staging is based primarily on the patient’s pre-treatment CT of the temporal bone, which is simple to use and clinically useful, and its stage II (involvement of the tympanic membrane and middle ear) and stage III (involvement of the mastoid air cells) lesions represent a different direction of focal invasion rather than a difference in the severity of the disease. Stage II and III lesions in Chang’s et al. (11) staging scheme were evaluated regularly only for bony destruction in the inferior wall of the EAC; in three of our cases, the bony destruction of the lesions was not located in the inferior wall of the EAC, and therefore, these individuals could not be staged using this scheme. In Kaneda’s et al. (12) staging scheme, it was difficult to differentiate between “bony erosion” and “bony deficit” in stage I and II lesions, and in the present study, there were five such patients in whom we had difficulty determining whether they were stage I or stage II lesions. Overall, the Hn et al. (13) staging scheme may be a good guide for the development of surgical strategies. A good staging scheme should have the following characteristics: it should incorporate all degrees of lesions; it should be based on basic routine investigations, such as CT, as far as possible; the individual stages should be clearly defined and it should be easy to differentiate between the various levels of lesions, and each stage should be able to reflect the progression or severity of the disease; and ideally it should be able to guide decision-making on treatment options or suggest a prognosis to a certain degree. The He’s et al. (7) staging scheme better meets the abovementioned characteristics and is worthy of reference and application by clinicians.

In our opinion, stage I lesions in He’s et al. (7) staging do not yet have bone destruction and can be treated with a single or consecutive multiple debridement. Stage II lesions have slight bone destruction but the lesion is still confined to the EAC, and during this time, if the transition of the EAC bone wall is gentle (Figures 2A,B), simple TCR is an appropriate choice of treatment (16, 17). If there is a large depression in the EAC, it is recommended to perform canalplasty to abrade the bone around the depression to form a gentle transition; otherwise, there is a risk of recurrence (16) (Figures 2C–E, 3A–C), and debridement can also become difficult after recurrence (Figures 3D,E). Stage III lesions have already exceeded the EAC but are still confined to the temporal bone. The lesions in stage IIIA mainly extend toward the mastoid, which can be resected like malignant tumors, i.e., under the premise of ensuring an appropriate “safety margin” (resection to healthy bone), as many air cells as possible should be resected; it is not necessary to pursue total resection of the mastoid air cells (Figure 4C), but it is necessary to ensure that the transition of the bony wall of the EAC is smooth and gentle. In our clinical observation, we have found that it is not required to strictly pursue the “large mouth and small bottom” EAC. In case of the involvement of a small number of air cells, if the transition of the EAC is smooth, the skin of the EAC can be reconstructed using only cartilage membrane, fascia, and skin fragments without reconstructing the bony wall; in case a large number of air cells are involved, if the wall of the EAC forms a depression or bony defect after resection of the lesion, the EAC wall can be reconstructed using bone fragments, cartilage, muscle, and other soft tissues (18–20) (Figure 4). The extent of lesion involvement should be determined by intraoperative viewing, and preoperative CT should be used as a reference, because sometimes the shadows in the mastoid air cells do not represent lesion involvement, but only infection (7). Stage IIIB lesions mainly extend toward the tympanic cavity, and the surgical approach here needs to be flexible depending on the extent of involvement. For example, the destruction of the tympanic membrane or even the auditory chain will require tympanoplasty to improve hearing. Stage IIIC lesions combine the tympanic cavity and mastoid air cells, and may require simultaneous partial or complete mastoidectomy + tympanoplasty + canalplasty (with or without reconstruction). Stage IV lesions extend beyond the temporal bone, and the choice of surgical procedure depends on the extent of involvement of the lesion.

It is worth noting that in areas of bone destruction, the bone in close contact with the cholesteatoma after resection can be smoothed with an electric drill to ensure “safe margins” in turn minimizing the recurrence risk of the lesion. In the case of EACC, the normal skin of the canal needs to be lifted up and properly protected. Although the patient’s wishes should be taken into consideration when choosing the treatment strategy, special care should be taken when adopting relatively conservative treatment strategies, such as TCR, because sometimes complete resection seen with the naked eye is not very reliable. Therefore, great importance should be given to the postoperative follow-up, and successive debridement should be performed when necessary to remove the residual or recurrent lesions in the EAC (16). For example, three cases in this group were found to have recurrence during follow-up within 1 year after surgery, all of which were treated with outpatient debridement and no recurrence was observed thereafter. Intraoperative perforation of the tympanic membrane may be seen in some patients, which may be caused by the direct destruction of the lesion or ischemia of the tympanic membrane caused by compression of the lesion. Intraoperatively, the diameter of the surgical suction tube tip can be used to estimate the size of the perforation. Our experience suggests that perforations less than 5 mm in diameter can be considered unnecessary to repair because small perforations tend to self-heal with the improvement of tympanic membrane blood supply after lesion resection and compression release. However, perforations larger than 5 mm can be repaired in stage I or II, which can be considered comprehensively in the light of the status of the perforated tympanic membrane, cholesteatoma lesion, and the condition of the patient (17).

In summary, the He’s staging scheme can be used to evaluate the EACC to formulate a treatment plan. After cleaning up the lesion, it is necessary to ensure that the transition of the bony EAC is smooth, and canalplasty can be considered for small depressions, whereas reconstruction of the EAC is required for larger defects. Lesions involving the mastoid air cells need partial or total mastoidectomy to remove the lesion up to healthy bone, and lesions involving the tympanic cavity need tympanoplasty. In clinical practice, treatment should be chosen flexibly according to the patient’s preference and the extent of lesion, and regular follow-up should be conducted.