Snodgrass procedure for primary hypospadias repair

Authors


Yun Zhou mschir, Department of Pediatric Surgery, Soochow University Affiliated Children’s Hospital, 303 Jingde Road, Suzhou, Jiangsu 215003, China. Email: cloudy2000s@yahoo.com

Abstract

Background: In this study, the authors’ experience in adaptation of the Snodgrass technique for primary hypospadias repair, with an alternative way to create a barrier layer of dartos flap for neourethral covering, is presented.

Methods: Between March 2000 and January 2001, Snodgrass urethroplasty was consecutively done on 24 boys aged between 14 months and 9 years (median: 3 years). The position of the meatus was coronal in one boy, at the distal shaft in two, at mid-shaft in eight, at the proximal shaft in five, penoscrotal in four, scrotal in three and perineal in one. Dorsal plication was carried out in nine patients (37.5%) to correct residual ventral curvature after penile degloving. Postoperatively the neourethra was stented for 10–12 days and suprapubic diversion was used for 12–14 days.

Results: Postoperative follow up ranged from 4 to 14 months (median: 8 months). All patients undergoing Snodgrass repair obtained a neourethra with a slit-like meatus at the tip of the glans. A small urethrocutaneous fistula occurred in one patient with mid-shaft and two with proximal-shaft hypospadias (an overall fistula rate of 12.5%). Urethral stricture had not been encountered at the time of this report. One patient developed mild meatal stenosis and was successfully managed by simple dilatation.

Conclusions: The results indicate that Snodgrass urethroplasty provides satisfactory cosmetic and functional results and is versatile in repairing almost all types of hypospadias.

Introduction

With changing concepts in modern hypospadiology, Snodgrass first described the tubularized, incised plate (TIP) urethroplasty for distal hypospadias repair in 1994 and recently extended its application to proximal hypospadias with promising results.1–3 The major principles are deep longitudinal incision of the urethral plate, which allows for its tubularization without the need for additional flaps, and the interposition of a barrier layer of dartos pedicle between the neourethra and overlying skin, which is crucial in reducing the likelihood of urethrocutaneous fistula. However, the extensive dissection of dartos flap from the dorsal prepuce and shaft skin may jeopardize blood supply to the edges of the dorsal skin that is later used for resurfacing closure. Mobilization of the dartos flap by rotating it around one side of the penile shaft may also predispose to penile torsion.

Dr Philip A. King from the Princess Margaret Hospital for Children, Perth, Western Australia, demonstrated  the original Snodgrass urethroplasty successfully on a 3-year-old boy with scrotal hypospadias at Soochow University Affiliated Children's Hospital,  Suzhou, China, in March 2000. We have adapted the surgical technique from our own experience, with a slight variation in transposition of the dorsal dartos flap ventrally to cover the neourethra by penile pull-through. Our surgical results are retrospectively evaluated in this study.

Methods

Clinical data

Between March 2000 and January 2001, we consecutively performed Snodgrass urethroplasty on 24 boys for primary hypospadias repair at Soochow University Affiliated Children’s Hospital. The boys’ ages at surgery ranged from 14 months to 9 years (median: 3 years). The severity of their conditions was evaluated in accordance with the Barcat classification. After penile degloving, the position of the hypospadiac meatus was coronal in one boy, at the distal shaft in two, at mid-shaft in eight, at the proximal shaft in five, penoscrotal in four, scrotal in three and perineal in one. One case was complicated with penile torsion and four with penoscrotal transposition and bifid scrotum.

Surgical technique

We adapted the Snodgrass operation with an alternative method in mobilization of a dorsal dartos flap for neourethral covering (Fig. 1). Briefly, a stay suture was placed at the dorsal skin of the glans for easy handling and then the urethral plate was outlined at a width of approximately 7–9 mm. A U-shaped incision was made, extending along the edges of the urethral plate from the tips of the glans to 2–3 mm or healthy skin proximal to the hypospadiac meatus. A circumferential incision 5–7 mm proximal to the coronal margin was extended from each edge of the urethral plate and the penile shaft was degloved. Artificial erection was performed and dorsal plication used to correct the disproportion of the corpora cavernosa if residual chordee persisted. A longitudinal relaxing incision was made at the midline from the distal extent of the urethral plate to the hypospadiac meatus, which widened the plate to approximately 13–16 mm. The urethral plate was then tubularized over a 6-Fr fenestrated silicone stent with a continuous 6–0 Dexon absorbable suture to create the neourethra that was extended to the tip of the glans. Instead of dissecting a dartos flap extensively, we slightly modified the Snodgrass technique by channeling beneath the dorsal preputial and shaft skin at the midline. The dorsal median part of the dartos layer was then transposed ventrally by pulling the penile shaft through a ‘buttonhole’ at the base of the dartos. The redundant dorsal skin was transferred for resurfacing closure. One end of the indwelling stent was placed just beyond the neourethra and the other end was secured to the glans. The neourethra was stented for approximately 10–12 days, which served for drainage of urethral discharge and local application of prophylactic antibiotic solution. A suprapubic diversion was used to drain the bladder for approximately 12–14 days. For postoperative dressing, a piece of nylon net was wrapped around the penis and it was maintained intact for 5–7 days to serve as immobilization and compression to control excessive edema and prevent postoperative bleeding.

Figure 1.

The Snodgrass urethroplasty for hypospadias with an alternative method for dartos flap mobilization. (a) The dotted lines represent skin incision used to create the urethral plate flap and for penile degloving. (b) Midline incision of the urethral plate is delineated by the dotted line from the hypospadiac meatus to the glanular tip. (c) A deep incision is made to widen the urethral plate. (d) The urethral plate is tubularized over a 6-Fr stent. (e) A flap of dartos is created by channeling beneath the dorsal prepuce and shaft skin. (f) Dorsal dartos tissue is transposed ventrally to cover the neourethra by penile pull-through. (g) The glanular wings are re-approximated and the skin incision is closed.

Results

Postoperative follow up was 4–14 months (median: 8 months). All patients obtained a functional neourethra with a vertically oriented, slit-like meatus at the tip of the glans. The length of the neourethra created after correction of chordee was 1.2–4.5 cm (mean: 2.4 cm). Dorsal tunica albuginea plication was done in nine patients (37.5%) to correct residual ventral curvature after penile degloving and release of the chordee tissue causing the ventral bending of the penis lateral to the urethral plate. Penile torsion was successfully corrected at the same time during urethroplasty in one patient and bifid scrotum was corrected in four. However, penoscrotal transposition persisted in two patients with severe hypospadias.

A small urethrocutaneous fistula occurred in one patient with mid-shaft and two with proximal-shaft hypospadias (resulting in an overall fistula rate of 12.5%). The location of these fistulae was subcoronal in two patients and penoscrotal in one. At follow up, the size of the neourethra was routinely calibrated with silicone catheters at outpatient clinics for all patients. The caliber of the neourethra was more than 8-Fr in 23 patients and 6-Fr in one. Recalibration in the latter patient with a urethral sound was done under anesthesia, and it was determined to be 12-Fr in size. Urethral stricture was not encountered in these patients at the time of this report. One patient developed mild meatal stenosis and had a thin and weak urinary stream 1 month after urethroplasty: that was successfully managed by regular dilatation for 3 months.

Discussion

The surgical objectives of modern hypospadiology have been complete straightening of the penis, creating a hairless, smooth urethra of uniform caliber with the position of the meatus at the tip of the glans, normalization of voiding and erection, and normal appearance of the penis with a minimum of complications. Regardless of the severity of the malformation, urologists strive to meet such demands. As a result, over 200 described operative procedures or modifications have emerged to manage boys with hypospadias, but no single procedure has been considered a panacea for all types of hypospadias, and it has remained one of the most challenging problems in urological surgery. Nonetheless, significant progress has been made in the field as staged repairs have given way to single-stage operations such as those described by Asopa et al.4 and Duckett.5,6 At the end of the 20th century, Snodgrass advocated a versatile TIP procedure for most cases of hypospadias repair, which showed favorable cosmetic and functional results.1,2,7The most common complications were fistulae and meatal stenosis, but these occurred at a relatively low incidence. Most encouragingly, few urethral strictures have, to our knowledge, been reported with the Snodgrass operation.

The longitudinal split of urethral groove described by Snodgrass is considered an innovation to urethral plate preservation surgery. It allows tension-free tubularization of the narrow urethral plate to form a neourethra of an adequate size. Recent histological studies have demonstrated that the urethral plate consists of epithelium overlying well-vascularized connective tissue with rich nerve supply.8,9 In an experimental study, Bleustein and co-authors confirmed that healing of the midline incision of the urethral plate during urethroplasty occurred by re-epithelialization with normal tissue in-growth and without scarring or contracture.10 These features may explain the few urethral strictures encountered using this technique.

Histologically, there has been no evidence of fibrous or dysplastic cords in the urethral plate traditionally believed to be responsible for chordee, which supports dorsal plication to achieve penile straightening without transection of the urethral plate.3,8,9 In our experience, penile bending can be simply corrected by the release of skin and fascia tether lateral to the urethral plate during penile degloving in many cases. Complete resection of so-called chordee tissue in alternative procedures may not always reliably straighten the penile curvature. If residual chordee persists, the corpora cavernosal disproportion is best corrected by dorsal plication.

Another key step in Snodgrass repair is the interposition of a barrier layer of subcutaneous dartos tissue between the neourethra and the overlying skin closure. However, the wide dissection of a layer of dartos pedicle from the dorsal prepuce and shaft skin may, at least theoretically, jeopardize blood supply to the skin that is used for resurfacing closure, and predispose to skin loss and dehiscence. Mobilization and ventral transposition of the dartos flap around one side of the penile shaft may also predispose to penile torsion. To address these potential hazards, we made a modification by channeling beneath the dorsal prepuce and shaft skin at the midline, and then pulling the penile shaft through so as to transfer the median part of the subcutaneous dartos layer ventrally to cover the neourethra. Neither skin necrosis nor wound dehiscence occurred in our present study.

The dartos flap created by our penile pull-through technique provides a sufficiently thick layer of dartos tissue to cover the neourethra for most penile and penoscrotal hypospadias. In more severe scrotal and perineal hypospadias, however, the transverse dartos bridge may not be adequate in width to cover the whole length of the neourethra. In such cases, we emphasize covering the penile portion of the neourethra adequately with the transposed dartos flap. The proximal portion of the neourethra can usually be buried deeply under the thick layers of scrotal dartos after concomitant correction of bifid scrotum (an anomaly commonly encountered with severe hypospadias). We believe that urethral fistula is unlikely to occur in the scrotal area, and instead there may be two spots vulnerable to fistula formation which deserve special attention during hypospadias repair with the Snodgrass procedure: one in the subcoronal region and the other at the penoscrotal junction.

Although routine urethral dilatation may not be necessary after Snodgrass repair, we carried out regular urethral calibration with silicone catheters at outpatient clinics every 2–3 weeks for approximately 3 months after the operation, and then optionally at later follow ups. At the time of this report, no urethral stricture had been recognized clinically. One patient with mild meatal stenosis was successfully managed by simple dilatation.

In spite of limited experience, we believe that the Snodgrass operation can be applied to a wide range of defects from distal to most severe perineal hypospadias. It creates a functional urethra of uniform caliber with a vertical slit-like meatus at the tip of the glans. The most common complication of urethral fistula occurs at an acceptably low rate and is much easier to handle than urethral stricture.

Ancillary