Endoscopic tympanoplasty type I using interlay technique

In a previous review of myringoplasty or endoscopic tympanoplasty type I [7], the perforation closure rate was 69–100% (mean, 88%), the mean postoperative AB gap was 4.0–18.1 dB (mean, 10.8 dB), and 77–100% (average, 90.8%) of the cases with a postoperative AB gap, were within 20 dB. That review was conducted with the underlay technique and had mostly limited target cases due to the sizes of the perforations and anatomical features. Therefore, we believe that our study, which did not limit the target cases, is a significant report, and the surgical success rate for TM closure and the postoperative hearing were good in patients who underwent the described surgical procedure. Comparing the two groups, the TEES with interlay group tended to have a higher perforation closure rate (92.3% vs. 98.0%) than the MS with underlay group, although there was no significant difference. The postoperative AB gap was significantly smaller (10.1 ± 6.6 vs. 6.8 ± 5.8 dB) in the TEES with interlay group. The significant difference in BC threshold (Table) may have resulted from the difference in the average patient age (43.3 vs. 49.0 years).

The interlay technique, in which the graft is placed between the epithelial and fibrous layers, is effective for graft stability [16, 17], but it has been rarely reported in TEES. This could be because most surgeons find detaching the epithelial layer of the TM using only one hand difficult. The epithelial layer can be easily detached from the inferior part of the TM, where the tympanic annulus is more closely attached. After confirming the layer to be detached, the epithelium should be detached parallel to the tympanic annulus using a round knife with no angulation. If the epithelium is detached perpendicular to it, the tympanic annulus is detached from the bone, making it difficult to detach without countertraction. Additionally, the ear canal skin near the anterior wall tympanic annulus should not be detached so as to prevent anterior blunting.

Another key point is to actively improve anteroinferior visibility. The edge of anterior perforation is often visible in TEES without drilling overhang due to a wide field of view (Fig. 3a), even if the EAC is curved and the perforation is not fully visible in MS. However, the visual field for visual recognition and that for operation are different. The available field of view for visual recognition may be inadequate for a successful surgery. This is important because the epithelial layer is detached from the inferior part of the TM; additionally, most perforations and postoperative reperforations are found in the anteroinferior quadrant of the TM [23], and anterior perforation is also considered as a poor prognostic factor for graft uptake because of difficulty in access and graft instability [13, 14]. In other words, the cause of the high rate of anterior reperforation is presumably a technical problem. This is supported by the fact that the localization of stem cells is not different between the anterior and posterior quadrants [24]. Another reason for better anteroinferior visibility is that iatrogenic mechanical damage to the anterior wall may further worsen the surgical field (Fig. 3b), potentially resulting in an incomplete surgery. Moreover, a scab can develop on the ear canal postoperatively and hinder wound healing.

Fig. 3figure 3

Endoscopic image; a case with slight overhanging of the anterior wall. a 30° endoscopic image before surgery. The field of view allows visualization of the entire perforation but does not facilitate ease of instrumentation. b 0° endoscopic image after myringoplasty without shaving the anterior wall. Note the damage to the anterior wall and poor visibility

Other studies using cartilage on type-I endoscopic tympanoplasty reported a closure rate of 91.3–94.4% [11, 13, 15]. These findings indicate that the use of cartilage is a good choice in terms of graft stability. However, the perforation closure rate is still not 100%, and the TM becomes thicker when cartilage is used, making it difficult to determine if there is effusion. Therefore, we believe that it is preferable to use retroauricular fascia or tragus perichondrium. Moreover, these previous reports [11, 13,14,15] did not mention drilling of the anterior wall for good visualization. Although these reports stated that the field of view could be obtained by endoscopic surgery, we believe that in many cases, this is not sufficient. Concerning drilling EAC, we, alongside other institutions, have reported atticotomy or antrotomy in TEES using curved bur [25,26,27], and a similar technique can be performed for drilling anterior overhang.

Furthermore, several studies have recently reported on the effectiveness of Endoscopic Inlay Butterfly Cartilage Tympanoplasty [28,29,30], which does not require detachment of the TM and has a high perforation closure rate. However, indications for this procedure, with regard to the perforation size, are controversial [28, 29], and the procedure is not appropriate for the repair of intratympanic lesions. Interlay technique using an endoscope can be confirmed by analyzing the tympanic cavity, such as the ossicular chain, by temporarily peeling off a small part of the posterior TM in all layers or using a 30° endoscope through the perforation, which is difficult to achieve using the interlay technique in MS.

The limitations of our study are its retrospective nature and the relatively small sample size. In addition, a comparison of the underlay and interlay techniques in endoscopic surgery was not performed, and limited surgeons performed the surgery. Therefore, treatment efficacy could not be determined. A randomized controlled trial with four groups (microscopic interlay technique, microscopic underlay technique, endoscopic interlay technique, and endoscopic underlay technique groups) is required.

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