Genital flaps for anterior urethral reconstruction

Genital flaps can provide versatile options for complex penile, genital, and urethral reconstruction. Pedicled muscle flaps can be used in combination with grafting for urethral reconstruction, and genital skin flaps can also be utilized as urethral augmentation or replacement. Penile skin flaps, in particular, offer versatile options for the management of anterior urethral stricture disease. The choice of urethral reconstruction depends on surgeon expertise and patient disease. Given its surgical complexity, flap reconstruction is equally dependent on an appropriate understanding of patient disease and surgeon experience. It is crucial to understand the patients’ comorbid diseases (e.g., smoking status or lichen sclerosis), potential flap tissue quality (i.e., penile/preputial skin quality), and stricture anatomy (length, caliber, location). Of particular importance is any prior intervention that may alter the normal vascular supply to the proposed flap. The ideal skin flap will be (1) hairless; (2) accustomed to the aqueous environment; (3) adaptable; and (4) cosmetic. This review will cover the operative approaches and perioperative outcomes of genital flaps to manage urethral reconstruction. Particular attention will be paid to penile skin flap urethroplasty.


INTRODUCTION
Urethroplasty is the gold standard for the treatment of urethral stricture disease. While urethroplasty techniques can be technically demanding and have a significantly associated learning curve, the success rates are excellent and significantly better than endoscopic alternatives [1] . Urethral grafting, genital skin flaps, and combined tissue transfer provide durable options for single or two-stage repairs. However, there is no consensus on a single best reconstructive technique as the efficacy of each technique in restoring urethral patency varies with both patient disease and surgeon expertise [2,3] .
Anterior and posterior urethral strictures are considered separate disease processes, and flaps do not currently play a role in posterior urethral reconstruction. Therefore, this review will focus on the use of genital skin flaps, particularly those derived from penile skin, in anterior urethral reconstruction. Special consideration should be taken for cases of urethral reconstruction in patients with a neophallus. Urethral reconstruction in these patients is inherently complicated as the vascular supply of the neophallus is derived from a non-anatomic pedicled flap. The description of penile skin flaps is therefore not applicable in the reconstruction of the urethra in the neophallus as penile skin flaps depend on native penile vasculature. For the purposes of this review, the focus will be on male anterior urethral stricture disease with native penile tissue. Patient selection, flap characteristics, focused genital anatomy, and types of flaps will be discussed. Operative approaches and recommendations on the use of each flap will be provided in addition to an overview of published success rates.

PATIENT SELECTION
Appropriate understanding of patient comorbid diseases is essential in the choice of urethral reconstruction. The approach to genital flaps, in particular, can be surgically challenging, and appropriate patient selection is crucial. Patient comorbid diseases, particularly conditions that can compromise blood flow, are important to understand as they can affect flap failure and wound healing. For example, patients with a history of smoking, peripheral vascular disease, or radiation are at a higher rate of flap failure [4] . Physical examination to assess penile/genital skin integrity and concomitant wounds, fistulae, or abscesses is also important to select appropriate flap locations and counsel patients on post-operative expectations. The presence of lichen sclerosis (LS) bears particular mention. While there are reports of using flaps from uninvolved genital skin in patients with LS, the success rates are lower, and often a two-stage approach has been preferred in this population [5][6][7] . Therefore, skin involved with LS should not be used for urethral reconstruction.
Stricture location and length often indicate the surgical technique best suited for repair. Genital flaps with or without combined tissue transfer can play a role in bulbar urethroplasty, but generally, anastomotic or buccal mucosal grafting (BMG) is preferred in the bulbar urethra. The tunneling of penile skin into the perineum adds additional technical challenges -which makes this technique less favorable given the durable success rates of BMG [8][9][10][11][12] . In general, flaps have fallen out of favor as a mainstream reconstructive option in favor of BMG due to the risk of flap loss, increased technical demands, and patient satisfaction [13,14] . In the appropriately selected patient, however, flaps still offer excellent success. Obliterative strictures can be particularly challenging to manage as these have the insufficient dorsal urethral plate to perform onlay techniques. For short obliterative strictures (< 2 cm), particularly in the bulbar urethra, anastomotic urethroplasty with excision of the obliterated urethra is preferred due to the high published success rate. For longer obliterative strictures, the dorsal urethral plate requires reconstruction. Combined tissue transfer with dorsal graft (e.g., BMG) and ventral skin flap can be used in these cases. Two-stage repair, where the first stage reconstructs the dorsal plate, can also be considered. Tubularized repairs are not preferred and should be avoided if possible.
Patient age and goals are also important for patient counseling and choosing the appropriate reconstructive technique. For older men with significant comorbidities, operations with less time in lithotomy position or highest single-stage success may be preferred to the durability of repair. Paramount to this discussion is an understanding of patients' sexual function. There is emerging evidence that non-transecting techniques may preserve sexual function and may be favored in patients of younger age [15] . In addition, de novo persistent erectile dysfunction is rare following anterior urethroplasty (~1%) [16] .

Flap characteristics
There are four primary factors that characterize the ideal flap. Flaps should be (1) hairless; (2) accustomed to the aqueous environment; (3) adaptable; and (4) cosmetic [17] . Each factor will be discussed briefly, with more depth provided in the discussion of individual flaps.

Hairless
Flaps should be derived from non-hair bearing skin. Hair in chronic contact with urine will lead to bacterial urethral colonization, stone formation, and inflammation. Accordingly, penile prepuce and distal penile shaft skin are preferred over the proximal penile shaft and scrotal skin.

Aqueous environment
Choice of urethral augmentation should preferentially favor tissue that is accustomed to or adaptable to the aqueous environment. Skin not accustomed to this environment will become inflamed and will be prone to squamous metaplasia. Chronic inflammation and metaplastic changes are concerning for both stricture recurrence and malignant transformation. This includes skin that is already diseased with active inflammatory processes (e.g., LS).

Adaptable
Ideal flaps should provide adequate urethral caliber in varying locations and be mobile enough to treat strictures in variable locations in the urethra. This includes skip lesion strictures. While non-hair bearing skin can be found elsewhere in the groin, none is as adaptable as penile skin.

Cosmesis
The creation of suture lines that approximate anatomic skin markings is an important consideration in the choice of the flap. Concomitant skin conditions such as vitiligo should also be considered for the choice of flap location. Additionally, the possibility of debilitating another structure is another consideration for flaps, particularly for use in tissue transfer.

SCROTAL AND GENITAL ROTATION FLAPS
Scrotal and various rotational flaps (e.g., anterior thigh) were popularized prior to the wide use of penile skin flaps and BMG. Now primarily of historical importance, these flaps tend to fail to meet one or more of the four factors necessary for flap success. Scrotal flaps were widely used at one point, but the incorporation of hair-bearing skin into the urethra leads to unacceptable long-term outcomes with stones and infections [18][19][20][21][22][23][24] . Other flaps, including the incorporation of thigh skin which may not be hair-bearing, had comparatively short pedicles and were not appropriate in the reconstruction of the penile urethra. With rare exceptions, these skin flaps have been abandoned for use as the urethral replacement.
The use of non-skin pedicled rotational flaps (i.e., gracilis) as an interposition layer for fistula reconstruction and in combination with grafting continues to be actively used and investigated [25] . For example, rotational gracilis flaps have been combined with BMG to manage complex bulbar strictures [26] . A full discussion of these cases is outside the scope of this review.

Penile skin flaps
Penile skin flaps can provide single-stage reconstruction, even in long-segment anterior urethral stricture disease. Penile skin, particularly distal or preputial skin, in the appropriately selected patient will meet the four primary factors for an ideal flap. These flaps share a common blood supply from the external pudendal artery and involve the isolation of a skin island that is mobilized for urethral reconstruction. Penile flaps are best characterized by the location/orientation of the harvested skin island, the pedicle origin, and the way in which the flap is incorporated into the urethra [17] . Flap techniques have also acquired the eponym of the surgeon who first described that technique. Details and success rates of penile skin flaps are discussed below and are summarized in Table 1.

Penile anatomy
Appropriate utilization of penile skin flaps depends on an understanding of the penile blood supply. The cross-sectional anatomy of the penis is shown in Figure 1. Penile skin flaps depend on the subcutaneous plexus traveling in the tunica dartos just superficial to Buck's fascia. This plexus is derived from axial penile arteries, which arise from the superficial and deep branches of the external pudendal artery [ Figure 2].

Types of penile skin flaps
Penile skin flaps are described by anatomic classification. As described by Elliott and McAninch [17] , this classification should define the orientation of the harvested flap (longitudinal vs. transverse), the location where the skin island was derived (proximal vs. distal penile skin), the vascular supply (dorsal vs. ventrolateral pedicle), and how the flap is incorporated into the urethra (onlay vs. tube vs. combined tissue transfer). In addition to the anatomic description, the flap is also often described in the literature based on the eponym of the describing surgeon. For example, the longitudinal ventral penile skin flap with lateral pedicle placed as a ventral onlay is also referred to as the "Technique of Orandi" or "Orandi Flap" [27,28] . Further confusion can arise with modifications of classic descriptions, such as a tubularized "modified Orandi Flap" [29] . It is therefore important to adhere to the anatomic description described above.
Longitudinal ventral penile skin flap with lateral pedicle (Orandi flap) [28] With the penis on stretch, a vertical, ventral penile shaft incision is made over the strictured area that corresponds to the approximate stricture length [ Figure 3]. This incision should be carried lateral to the corpus spongiosum and will be the deep incision for flap harvest. On the contralateral side, a lateral urethrotomy is made until there is normal urethral mucosa is encountered at the proximal and distal aspects of the urethrotomy. A skin island is then dissected to match the urethrotomy defect. The superficial incision is then made and carried laterally to release the skin island and allow for suturing of the flap to the urethrotomy in a tension-free anastomosis [ Figure 4].
Longitudinal ventral penile skin flap with ventral pedicle (Turner-Warwick flap) [30] Similar to the Orandi [28] technique, this is a skin island flap derived from ventral skin. The Turner-Warwick [30] differs in that the pedicle is derived from bilateral ventrolateral arteries and used mostly in the bulbar urethra. Often the skin marking is made after perineal dissection and characterization of the bulbar urethral stricture. The deep plane of the skin island is developed distally, and the superficial layer is developed at the proximal flap apex. The island and pedicle are then raised and inverted through the scrotal tunnel and out the separate perineal incision to be incorporated into the bulbar urethra [ Figure 5]. This technique has been described most in modern literature as part of augmented anastomotic urethroplasty.  [34] 1998 66 79% Lower success with tubularized flap (58%) Alsikafi et al. [12] 2005 24 84% Forty-eight months follow-up. No significant difference compared to buccal grafting (nonrandomized) Dubey et al. [14] 2007 28 85.8% Randomized to skin flap vs. buccal mucosal graft. No sig difference in recurrence. PROMs favored BMG Whitson et al. [4] 2008 124 79% Success at 1 year (95%) declined over 10 years follow-up (79%). Smoking, prior hypospadias, and long strictures (7-10 cm) predictive of failure Kim et al. [36] 2014 29 69.9% Included combined tissue transfer Longitudinal ventral penile skin flap with lateral pedicle (Orandi Technique) Orandi [28] 1972 21 95% Proof of concept Goel et al. [27] 2015 10 80% Four years follow-up. Small sample size Hmida et al. [37] 2019 77 88% Younger age (45) than most studies. All recurrences managed with DVIU Ali et al. [38]   Ventral transverse penile island flap with ventral pedicle (Jordan flap) [31] Similar to the Orandi [28] and Turner-Warwick [30] flaps, this technique isolates a distal penile skin flap from ventral penile skin. The pedicle is derived from bilateral ventrolateral arteries similar to the Turner-Warwick [30] . This technique is utilized in distal penile and fossa novicularis strictures and differs from other techniques with a broader pedicle and comparatively smaller skin island. Like other techniques, this is  With the penis on stretch, a circumferential skin flap (width 2-2.5 cm based on stricture caliber) is taken from the distal penile skin or inner prepuce [ Figures 6 and 7]. First, the distal aspect of the flap should be dissected deep to the pedicle, leaving the pedicle with the proximal skin island. Next, the entire penile shaft should be degloved in this deep plane (superficial to bucks fascia). The proximal skin incision is then made superficial to the pedicle, creating a circumferential skin island that can be divided dorsally or ventrally to be rotated 90 degrees for urethral incorporation [ Figures 8-10]. The flap is traditionally divided ventrally. Additional length can be generated in this technique by modifying the circumferential incision into a Q incision.  Single-stage vs. two-stage One of the benefits of penile skin flaps for urethral reconstruction is the adaptability to achieve adequate urethral patency in a single stage. For complex stricture disease, a two-stage repair may be required. In nonrandomized series, there is a lower re-stricture rate with two-stage procedures; however, there is a higher surgical revision rate [33] . Therefore, two-staged procedures should be considered in cases where single-staged options would have an unacceptable risk of recurrence. Specifically, American Urological Association guidelines recommend against single-stage tubularized graft urethroplasty due to high recurrence rate, and alternatives -including staged repair -should be pursued [34,35] .

CONCLUSION
Anterior urethral reconstruction requires a detailed understanding of patient disease, penile anatomy, and multiple operative approaches. Though some reviews have suggested improved patency rates with BMG compared to penile skin flaps [8] , many of these studies have shorter follow-up for BMG, and multiple

Authors' contributions
Manuscript draft, literature review: Shaw NM Manuscript draft, editorial corrections: Amend G