Comparison of effect between dartos fascia and tunica vaginalis fascia in TIP urethroplasty: a meta-analysis of comparative studies

Hypospadias, resulting from the disruption of the normal urethral formation, is one of the most common congenital malformations in male infants, with an overall predicted prevalence of 20.9 cases per 10,000 male live births around the world [1]. The international total prevalence increased 1.6 times from 1980–2010, by 0.25 cases per 10,000 births per year [1]. The current purpose of hypospadias surgery is to improve the functional and cosmetic outcomes while minimizing the incidence of postoperative complications and avoiding reoperations. The tubularized incised plate (TIP) urethroplasty is the most commonly performed procedure for hypospadias [2]. Additional urethral coverage is now routinely used by most paediatric urologists to reduce the incidence of postoperative complications [3]. Dartos fascia (DF) and tunica vaginalis fascia (TVF) are the two most widely used urethral coverages with good surgical results while results reported by different studies vary [4‐6]. At present, there has been no consensus on the better choice between the DF and TVF flap techniques or on the short- and long-term outcomes of both techniques [3]. This meta-analysis aimed to compare the outcomes of TVF and DF as intermediate layers in TIP hypospadias repair.

This meta-analysis was the first comprehensive synthesis of evidence for currently available comparisons between DF and TVF flap techniques for TIP urethroplasty in primary hypospadias patients in comparative studies. We included 6 comparative studies, comprising 353 hypospadias patients who received TIP repair with the use of DF or TVF flaps. Evidence of our findings came from the pooled estimate size for the primary outcomes, which showed that TVF was better than DF for the repair of hypospadias in terms of total postoperative complications, urethrocutaneous fistula, and wound-related complications. No significant difference was found in meatal/urethral stenosis and prepuce-related complications. No significant difference was found in different hypospadias type, study design, and perioperative use of antibiotics subgroups. Additional, sensitivity analyses verified the robustness of the results in this meta-analysis.

Reoperation for failed hypospadias or fistula repair has been considered a serious problem because the dense fibrotic tissue causes difficulties in wound healing and increases the rate of complications [20]. Over 300 surgical methods and modifications have been developed for repairing the hypospadias, while various complications have occurred, especially urethrocutaneous fistula, one of the most common complications of these techniques [21]. In our study, the incidence of urethrocutaneous fistula was 9.63%, followed by meatal/urethral stenosis (4.25%), consistent with the 7.50% (fistula) and 4.40% (stenosis) incidence rates in a systematic review [22]. Patient age, glans size, urethral defect length, urethral operation history, surgical procedure, type of surgical repair, chordee degree, magnification technique, caudal anesthesia, preoperative hormonal stimulation, and other many factors may relate to the development of complications postoperatively [21‐25]. Additional soft coverages on the neourethra are also introduced to avoid these complications, especially to decrease the incidence of postoperative urethrocutaneous fistula. TVF, DF, Buck’s fascia, spongious tissue, external spermatic fascia, adipose tissue of the scrotum, adipose tissue of the spermatic cord, and a combination of tissues and platelet-rich plasma are used in different studies [26‐32] with various outcomes. Among them, TVF and DF are the most popular flaps used in the repair of hypospadias and fistula.

Objective and comprehensive assessments of the outcome of hypospadias repair may have a major impact on future clinical practice. Evaluations of outcome after hypospadias repair include complication rate, cosmetic outcome, functional outcome, and even the effects on psychology. In this study, we focused on assessing the effect of DF and TVF on the outcomes of complication rate after TIP urethroplasty in primary hypospadias. For functional and cosmetic results in our meta-analysis, the conclusions are uncertain due to the limited evidence. The assessment methods of cosmetic and functional outcomes in most published studies were thought to be prone to bias, subjectivity, or inaccuracy. Several assessment methods have been applied for evaluating cosmetic outcomes after TIP repairs, such as HOSE, PPPS, and HOPE [7‐9]. However, all of them are retrospectively assessed, and which method is the most reliable and valid to assess the outcome is uncertain. From the practical point of view, it is highly recommended that standardized assessment tools be used for comparability and reproducibility and to build up a prospective database that does not currently exist. Moreover, there are many measurement indexes applied for the assessment of functional outcome in TIP repair, including urinary stream direction, maximum flow rate, voided volume, average flow rate, voiding time, flow curve shape, and residual urine. However, the significance of these measurement indexes remains uncertain until long-term follow-up studies clarify the significance of abnormal flow parameters [33]. Moreover, the assessment of functional outcomes in non-toilet-trained boys is difficult. Therefore, large prospective studies and uniform assessment criteria for functional and cosmetic evaluation are needed. Other outcomes, such as life quality, sexual function, and sexual psychology, are also not reported in any of the included studies.

DF is a layer of connective tissue found in the penile dorsal or ventral area, foreskin, and scrotum and can be used in hypospadias or fistula repair in different techniques [34, 35]. TVF can be harvested through a penile incision by degloving up to the root of the penis [26] or with an additional scrotal incision that reaches and covers the neourethra through a subcutaneous scrotal tunnel [36]. Excellent vascularity, easy availability and adequate source are advantages of DF, making this flap technique more popular for many paediatric urologists, especially young surgeons. Penile rotation and preputial skin necrosis are commonly reported relevant complications in the use of DF and can be avoided by careful operation and technical improvement. However, harvest of TVF may damage the vas deferens or vessels of the testicles, resulting in scrotal abscess or scrotal haematoma, but were ultimately not reported in any of the included studies. Snodgrass described additional interposition of vascularized tissues between the tubularized plate and the glans closure dissected from the dorsal preputial and shaft skin [2]. Duckett has described that when dartos is separated from the skin, it compromises the vascularity of the overlying skin [37]. Thus, the dissection of DF may compromise the vascularity of the preputial skin covering and result in subsequent skin necrosis, which is consistent with the conclusion of our outcomes. The blood supply of the neourethra tissue may be affected due to the dissection and utilization of DF, which mainly comes from the shortage of dartos or preputial skin necrosis. Although skin necrosis was inconsequential in the long run, it did cause anxiety and distress to the families and resulted in more hospital visits. Moreover, dissection to raise DF may damage the intrinsic blood supply to the outer skin, which is transposed ventrally to provide skin cover and may consequently devitalize, leading to skin necrosis, and fistula formation. However, this is rarely affected in the TVF technique, as its ventral skin covering is almost never compromised. All of these factors can theoretically explain the advantage of TVF over DF. We performed this meta-analysis to prove the advantages of TVF over DF with the data.

The results of our meta-analysis were partially consistent with the results of a systematic review by Fahmy et al. [3]. However, there were several differences between the two studies. The study of Fahmy et al. included not only comparative studies but case series, which weakened the evidence. In addition, the literature retrieval process should be as comprehensive as possible, while there was only one database (PubMed) employed in his study. Our analysis included only comparative studies and searched 4 databases (PubMed, EMBASE, the Cochrane Library and Web of Science), a clinical trial register (clinicaltrials.gov) and several international meeting abstract archives. All of these sources enhanced our evidence.

There are several limitations in our meta-analysis. First, although a comprehensive retrieval was performed, only limited studies were included, and most included studies were nonrandomized clinical trials/studies without reporting prospective power calculations and non-inclusion of consecutive patients, which might bias the results. Given the diversity of types of included studies, the level of evidence for our findings is not high. Second, the duration of follow-up varied, ranging from 6 to 48 months. The relatively short length of follow-up limited the present study, as it is known that long-term follow-up is necessary to determine the true complication rate of hypospadias repair and Spinoit et al. [38] stated in their study that only 47.37% of complications appeared in the first year. Third, the definition of complications was inconsistent among all included studies which indicated that reporting complications also depended on different factors and a publication bias existed. A survey of North American paediatric urologists clearly showed that there is a discrepancy between complication rates reported in the literature and participants’ operative outcomes, regardless of practice setting, operative volume, or time in practice [39]. In addition, research aimed at studying the effects of different flaps on urethrocutaneous fistula postoperatively may result in bias in other complications. Last, other than follow-up periods and complications criteria, differences in other clinical characteristics, including study settings, patient age, thickness and width of flap, and hypospadias type existed, although the statistical heterogeneity was not high. The contribution of these differences to the outcomes was unknown. We performed subgroup analyses to identify potential sources of heterogeneity, but no significant results were found due to the limited number of studies.

Although many uncontrollable confounding factors may affect the hypospadias surgery outcomes, especially the wide variability for individual surgical experience and complexity for hypospadias cases, additional large sample size, well-designed, single-urologist prospective studies need to be conducted for optimal comparisons between these two flap techniques.

This meta-analysis revealed that compared to DF, TVF is a better option in TIP repair in terms of decreasing the incidence of the total complications, urethrocutaneous fistula, and prepuce-related complications. There is limited evidence for functional and cosmetic outcomes. However, there was substantial heterogeneity between studies indicating a lack of clarity in this field. There remains a need for high-quality prospective comparative trials for reliable evidence and clinical utility.