We searched the PubMed database for all English-language articles related to S-T conization published by July 10, 2022 using the following key words and combinations of key words: “Shimodaira-Taniguchi” and “conization”. Only five articles regarding S-T conization for HSIL have been previously reported [3–7] (Table 6). The overall recurrence rate was reported to be 1.3–5.8% and a positive surgical margin was observed in 13.4–39.1% of patients, which was consistent with the present study. However, postoperative complications and obstetric outcomes after S-T conization were not fully described in the previous literature.
The incidence of cervical stenosis after conization in previous studies varies, and is up to 29% [9], depending on the definition employed. Various factors, including age, deep incision, and time within one year of delivery are associated with cervical stenosis [3, 10]. In the current study, the cervical stenosis was more likely to occur in individuals older than 45 years of age. These findings might be due to the migration of the transformation zone to the cervical canal with increased age and after menopause [11]. In contrast to younger patients, the SCJ of older patients is usually located in the endocervix. Deep conization is therefore required to excise precancerous lesions in these patients, which may lead to cervical stenosis. Cervical stenosis can make it difficult to check the deeper side of the cervical canal. Cervical stenosis can lead to unsatisfactory follow-up after conization with a risk of unseen relapse. Therefore, careful follow-up is required for older patients.
The surgical margin status is a well-known prognostic factor for persistent or recurrent disease. In the current study, the rate of positive surgical margin was 18.5%. In comparison to that in LEEP (11.2%) or cold knife conization (CKC) (8.1%), it seems higher [12–14]. However, the overall recurrence rate after S-T method was approximately 5%, which was comparable to LEEP (8.1%) and CKC (2.1%) [12–14]. Although the precise explanation for the low recurrence rate with S-T method is unclear, it may be associated with the use of a coagulation probe. A small flat probe, shown in Fig. 1, is applied to the entire cervical stump to coagulate the remaining part of the lesion. This step may contribute to preventing recurrence in patients with positive surgical margins.
We found that older age (≥ 45 years) was not only an independent prognostic factor for recurrence after conization but also an independent prognostic factor for cervical stenosis, which may lead to unsatisfactory follow-up. In particular, focusing on the surgical margin status, older patients with endocervical margin involvement showed a higher rate of recurrence (3-year recurrence rate: 28.1%) (Fig. 1). When residual disease exists in the endocervix, postsurgical stenosis could prevent adequate follow-up. Therefore, when endocervical margin involvement is confirmed in older patients, it is beneficial to offer subsequent hysterectomy.
A few studies have investigated the obstetric outcomes after S-T conization. In the current study, the rate of preterm delivery was 6.1%, which was consistent with the rate of preterm delivery in the Japanese general population (5.6%) [15]. We found that a short interval from conization to pregnancy (≤ 3 months) was associated with preterm delivery. Some authors suggested that a 3- to 4-month interval from conization to pregnancy increased the risk of preterm delivery [16, 17], while others suggested that time interval from conization was not associated with preterm delivery [18, 19]. Various other factors are potentially associated with preterm birth after conization, including the cone depth [20], the size of the resected specimen [21] and the pre- and post-treatment cervical length [22]. Therefore, whether the interval from conization to conception is associated with preterm birth is controversial. The cervical length reported to heal to nearly the same length as the pretreatment level at 6 months of posttreatment follow-up in patients who delivered at term in the subsequent pregnancy [22]. Although it is difficult to determine the optimal interval from conization to pregnancy, an interval of at least 6 months would be reasonable, considering the risk of preterm birth and the time required for regeneration of the cervical length.
The present study was associated with some limitations. First, the data used for this study were retrospective and the sample size was relatively small. A larger population should be analyzed to support our results. Second, confounding factors for recurrent disease, such as the preoperative and postoperative HPV infection status, were not analyzed. These types of information would have strengthened the results of our study. Third, comparison with a different surgical method, such as CKC and LEEP would be helpful for demonstrating the validity of S-T conization method.
In conclusion, Shimodaira-Taniguchi conization method is effective in terms of the surgical, oncological and obstetric outcomes. We found that older patients with endocervical margin involvement had a higher incidence of recurrence and postoperative cervical stenosis after therapeutic conization. Careful follow-up is required and secondary hysterectomy could be considered for older patients with endocervical margin involvement. Furthermore, to increase the likelihood of term pregnancy after conization, a short interval of ≤ 3 months from conization to conception should be avoided.