Selective Use of the Perineal Artery Fasciocutaneous Flap (Singapore) in Urethral Reconstruction L

19 Selective Use of the Perineal Artery Fasciocutaneous Flap (Singapore) in Urethral Reconstruction L. Zinman Basics of the Fasciocutaneous Flap – 154 History of Singapore Flaps – 154 Flap Design and Elevation – 155 Urethral Reconstruction – 156 Technique of Onlay Patch Urethroplasty – 156 Techniques of Tube Flaps Urethral Replacement – 157 Perineal Artery – 158 Multistage Flap Urethroplasty – 158 Clinical Experience – 160 Conclusion – 160 References – 160 154 Chapter 19 · Selective use of the Perineal Artery Fasciocutaneous Flap (Singapore) in Urethral Reconstruction Complex bulbar and bulbomembranous strictures that vascular characteristics permit reliable, predictable flaps are compromised by extensive periurethral fibrosis with that can be raised by simple dissections with minimal avascular tissue beds, prior radiation, perineal decubitis, blood loss and no loss of function. Fasciocutaneous flaps pelvic fracture, distraction defects greater than 6 cm or are a significant advance in flap design and were develo- extensive perineal trauma present a surgical challenge ped because a myocutaneous flap is not often available, that will not often respond to traditional genital flaps not expendable, or is too bulky. They do not possess the and grafts. These patients with such demanding urethral superior immunologic qualities seen with muscle and pathology are candidates for a number of local peninsular musculocutaneous flaps, but have the advantages of less or free flaps from the thigh and forearm that can combine bulk, ease of elevation and are thinner and more expedi- the resolution of a urethral stricture, need for supporting tiously used for smaller defects such as those involving the skin cover and the filling of soft tissue defects. The graci- urethra and vagina. lis myocutaneous flap has been the most widely used for The Singapore medial thigh flap is an example of perineal reconstruction, but has the disadvantage of an a Cormack Type B fasciocutaneous flap with a single unpredictable skin vasculature and an extremely bulky septocutaneous perforator that permits it to be used as a cutaneous island for urethral substitution. hinged or island flap with consistently predictable measu- We first brought attention to the perineal artery fasci- rements. ocutaneous flap in male urethral reconstruction and urethral replacement in 1997, where it was employed in nine patients with high-risk, complex (bulbomembranous) History of Singapore Flaps urethral stricture management [1]. This flap provided a reliable skin island substitution onlay that could be readily The primary impetus for the development of the perineal transferred into the proximal bulb and posterior urethra artery flap was the need for reliable, one-stage, sensate with minimal donor site morbidity. vaginoplasty for acquired and congenital absence of the The perineal artery flap belongs to a class of axial vagina [5]. The concept was first applied for vaginal fasciocutaneous constructs that are ubiquitous and have reconstruction in two patients with congenital adrenal extended the role of thigh flaps in pelvic and perineal hyperplasia and vaginal atresia by Morton in 1986 [6]. reconstruction. It is often referred to as the Singapore Cadaveric injection studies by Hagerty et al. [7] first iden- Flap since its boundaries were anatomically defined by the tified the perineal branch of the internal pudendal artery Singapore surgeons, Wee and Joseph in 1989 [2]. as the vascular basis for the flap and defined the medial border as the groin crease. In 1989, Wee and Joseph [2] established the definitive boundaries (cutaneous vascular Basics of the Fasciocutaneous Flap territory) and the design of the pudendal flap as well as its neurovascular anatomy. Injection studies showed that the The perineal artery or Singapore flap belongs to a group internal pudendal artery supplies the perineum by its first of tissue segments referred to as axial fasciocutaneous branch, the inferior rectal. The perineal artery, its second flaps first described by Ponten [3] in 1981 for lower leg branch, then courses lateral to the labia majora in women reconstruction and subsequently classified by Cormack and the scrotum in men. The scrotal branches anastomose and Lamberty, who defined their vascular anatomy and with branches of the deep external pudendal artery as well the variation of fascial and skin components. The flap as the medial circumflex femoral artery and obturator consists of a unit of skin, subcutaneous tissue, and a artery over the proximal adductors. By arborizing with the well-developed fascial undersurface that acts as a vehicle deep external pudendal artery and the random subdermal or trellis for supporting that circulation and its arbori- circulation, the distal limit of the flap reaches the medial zing plexi and perforators. These well-defined composites border of the femoral triangle (⊡ Fig. 2). The deep fascia of transferable tissue are supplied by a circulation that and epimysium over the adductors were noted to be an consists of three vascular patterns. Their common ana- integral part of this reliable flap. Giraldo et al. [8], using a tomic feature is the inclusion of a deep fascial floor that 3×10-cm flap, confirmed that the surface landmarks, with preserves the interconnecting vascular network arising the center on the inguinal fold, were a reliable reflection from septocutaneous, musculocutaneous, or direct cuta- of the flap circulation and that the deep external pudendal neous arterial trunk sources. These vessels form a fasci- vessels could be cut at the superior apex without loss of ocutaneous plexus that may be found at the subfascial, skin. The first account of the use of a pudendal perineal 19 suprafascial, subcutaneous, or subdermal levels and ulti- artery-based flap in reconstruction of a post-traumatic mately arborizes and provides sustenance to the skin. The urethral stricture was in a patient with gender dysphoria, suprafascial component of the flap circulation is regarded reported by Tzarnas et al. [9] in 1994. Subsequent clinical as the major blood supply to these axial skin flaps regard- reports have confirmed the value of this approach to com- less of the type of vascular anatomy. These anatomic and plex proximal urethral stricture disease [10]. 155 19 Flap Design and Elevation Flap Design and Elevation a 1-cm area of the distal margin to identify a bleeding dermis. This step is followed by intravenous injection of two The perineal artery medial thigh flap is a vertically orien- ampoules of fluorescein dye and examined with a Wood’s ted composite of skin, subcutaneous tissue, deep fascia, light. The tissue bridge between the base of the flap and the and adductor epimysium that measures 15×6 cm, with its urethral exposure is divided rather than attempt tunneling proximal base in the male located at the level of the mid during transfer of the flap. This will prevent a compres- perineum 3 cm distal to the anal margin (⊡ Fig. 19.1). The sion effect and potential compromise of flap circulation. medial border is the crease of the groin lateral to the edge This technique provides ease of transfer of the somewhat of the scrotum. Wee and Joseph [6] described the maxi- tenuous distal island to the deep proximal urethra and mal safe dimensions of the flap as less than 6 cm in width release of tension on the closure of the donor wound site. from the base and 15 cm in length reaching the femoral triangle, including some random circulation at the distal point. The vascular basis of this flap is the superficial perineal artery, which is centered just medial to the groin crease with branches going to the scrotum and skin of the thigh. These vessels interconnect with branches of the deep external pudendal artery and the medial circumflex femoral artery, which arises directly from the profunda femoralis. A connection to the anterior branch of the obdurator artery exists near the proximal region of the adductor muscle (⊡ Fig. 19.2). The innervation of the proximal flap is supplied by branches of the pudendal nerve and perineal rami of the posterior cutaneous nerve of the thigh, which create a partially sensate structure. This flap is elevated with the patient in the exaggerated lithotomy position and the thigh abducted using well- padded Direct OR stirrups. The lower abdomen, genitalia, perineum, and both thighs are prepared and exposed. The proximal and distal limits of the urethral stricture are marked on the skin surface, and the margins of the flap are outlined carefully with an indelible skin scribe. The initial incisions are made in parallel vertical lines and deepened down to the fascia on both sides, raising the epimysium ⊡ Fig. 19.2. Vascular basis of the medial thigh perineal artery fasciocu- 4 with the fascia and suturing them to the dermis to prevent taneous flap centers around perineal artery ( ), which arises proximally from an internal pudendal artery. This courses lateral to the scrotum shearing injury to the segmental vessels. The flap is lifted and arborizes with branches from the deep external pudendal (2), until the proximal transverse margin is reached. The vas- medial circumflex (3), femoral (1),and obturator (5), which arises from cularity of the distal edge is confirmed by de-epithelializing common and profunda femoralis ⊡ Fig. 19.1. Medial thigh flap measurements are consistently 15×6 cm, with the proximal base located at the level of the mid-perineum. The medial border is the crease lateral to the edge of the scrotum. The distal border is the mid-femoral triangle 156 Chapter 19 · Selective use of the Perineal Artery Fasciocutaneous Flap (Singapore) in Urethral Reconstruction Urethral Reconstruction A running locked hemostatic suture of 5-0 chromic catgut is used to approximate the adventitia to the ure- Four different variations of the Singapore fasciocutaneous thral edge, thus controlling the bleeding spongiosa edge flap transfer have been used in the management of a group while permitting more precise fixation of the flap onlay. of high-risk, complex proximal strictures.

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