Phallic Urethra: Separate-Flap Technique
The separate-flap technique constructs the phallic urethra, or pars pendulans, from a dedicated second flap that is distinct from the shaft flap. It is most relevant when the shaft flap, usually pedicled ALT, is too thick, too hair-bearing, or otherwise unsuitable for tube-in-tube urethral construction. In D'Arpa's 93-case ALT series, only 5 patients (5.4%) received tube-in-tube ALT; the others received a second flap, skin-graft prelamination, residual penile skin, or no urethral reconstruction.[1]
For the reference single-flap approach, see Phallic Urethra: Tube-in-Tube and Pars Pendulans Construction. For SCIP-specific flap selection, see SCIP Phalloplasty. For the fixed urethral segment, see Pars Fixa Urethral Construction.
Rationale
Tube-in-tube RFFF works because the same thin, pliable, vascularized forearm flap supplies the shaft and the urethral tube. ALT phalloplasty solves a different problem: it gives a concealed donor site, avoids a full forearm scar, and can often be harvested as a pedicled flap, but the thigh skin and subcutaneous layer are frequently too thick for a reliable inner urethral tube.[1][2]
| Problem With Main Shaft Flap | Separate-Flap Solution |
|---|---|
| ALT too thick for tube-in-tube | Use a thin SCIP or RFFF urethral flap |
| Hair-bearing urethral skin risk | Select a better urethral donor site and depilate the urethral strip |
| Need to preserve shaft bulk / donor-site concealment | Use ALT for shaft and a separate thin flap for urethra |
| Revision after failed urethral construction | Complete flap loss may warrant a new vascularized flap or perineostomy, depending on patient goals.[3] In a 2024 retrospective series of 18 redo flap reconstructions after prior phalloplasty flap failure, no redo flap failed; 13/16 patients who had primary urethral lengthening voided standing.[14] For a stricture, plan repair by site, length, and tissue quality; EAU 2026 recommends no endoscopic incision or urethroplasty within six months after neophalloplasty , and staged urethroplasty for a neophallic stricture when open repair is indicated .[13] |
The tradeoff is that the urethra becomes its own reconstructive unit. It must be perfused, monitored, tubularized, inset within the shaft, and connected to the pars fixa without tension.
Main Separate-Flap Options
| Urethral Flap | Typical Role | Main Tradeoff |
|---|---|---|
| Pedicled SCIP | Dedicated urethral flap for ALT phalloplasty or revision | Concealed donor site and no microsurgery, but short pedicle and variable anatomy |
| Free RFFF urethral flap | Narrow forearm free flap inside ALT shaft | Thin, pliable tubularization tissue, but microsurgery and forearm donor scar remain |
| Pedicled labia minora flap | Local genital-tissue urethral lengthening in ALT / SCIP pathways | Requires adequate labia minora tissue; in the 16-patient initial series, mean pars pendulans length was 11.7 cm and 9/16 patients voided standing.[11] |
| Pudendal-thigh / scrotal septum flap | Selected penile reconstruction or revision contexts | Less applicable to standard transmasculine phalloplasty |
| Native penile skin | Cisgender penile reconstruction with residual penile tissue | — |
Pedicled SCIP Urethral Flap
The superficial circumflex iliac artery perforator (SCIP) flap was the most frequently used separate urethral flap in D'Arpa's historical ALT series (38 of 93 patients). In a later Ghent series, complete losses of SCIP urethras led the team to move away from the ALT-plus-SCIP combination in 2019 and usually suggest a free RFFF urethra for an ALT shaft.[1][3] The flap is based on perforators from the superficial circumflex iliac artery (SCIA), which arises from the femoral artery and divides into superficial and deep branches.[3][4][5]
| Technical Feature | Practical Point |
|---|---|
| Preoperative mapping | Color Doppler ultrasound or local imaging identifies usable SCIA perforators[6] |
| Design | Narrow groin / lower-abdominal fasciocutaneous flap sized for urethral tubularization |
| Transfer | Usually pedicled and rotated toward the perineum / phallus, avoiding microvascular anastomosis; pedicled SCIP has broader male genital-reconstruction experience beyond gender-affirming phalloplasty[7] |
| Tubularization | The Ghent team designed the SCIP urethral strip at least 4 cm wide for tension-free tubularization around a catheter. Avoid compressing it with the ALT wrap; when closure was too tight, the team temporarily used split-thickness skin coverage on the ventral shaft.[3] |
| Donor site | Typically closes primarily, leaving a concealed groin scar |
| Limitation | Short pedicle or unfavorable anatomy can require conversion to a free flap |
In D'Arpa's retrospective single-center series of 93 ALT phalloplasties, 38 SCIP urethras had a 26.3% combined fistula and stricture rate. The series also included 79 gender-affirming cases and 14 penile-insufficiency reconstructions; the unmatched RFFF (11/29, 37.9%) and prelaminated ALT (7/8, 87.5%) subgroups had higher observed fistula/stricture rates than the SCIP subgroup, without establishing comparative effectiveness.[1] A skin flap from a previous phalloplasty (n = 6) had 16.7% and tube-in-tube ALT (n = 5) had 20%.[1]
De Gelder and colleagues' 10-year Ghent series included 55 transgender men undergoing SCIP-based phalloplasty: 47 unilateral and eight bilateral reconstructions; mean follow-up was 26 months (range 1–97).[3] In the full 55-person SCIP cohort, 25 needed at least one additional urologic intervention and 36 needed additional plastic-surgery procedures; these groups may overlap.[3] After interventions, 37/45 recipients with a SCIP urethra (82%) could void standing. Complete urethral flap loss occurred in 8/45 (18%); the published 14% uses all 55 SCIP recipients as its denominator, including shaft-only reconstructions. Three SCIP urethral flaps were converted to free flaps because the pedicle did not reach; all three subsequently failed completely.[3] In the bilateral SCIP shaft-plus-urethra subgroup, urethral fistula / stricture occurred in 38%.[3]
SCIP Advantages and Cautions
| Advantage | Caution |
|---|---|
| Concealed groin donor scar | Groin skin can be hair-bearing and may require depilation |
| Primary donor closure in many patients | Short pedicle can limit reach |
| Pedicled transfer avoids microsurgery | SCIA anatomy varies and must be mapped |
| Thin pliable tissue for urethra | In the Ghent bilateral SCIP design, urethral innervation can be omitted to avoid troublesome neourethral sensation.[3] |
| Same operative field as ALT | Complete urethral flap failure remains possible |
Free RFFF as Dedicated Urethral Flap
Double-flap phalloplasty uses one flap for the shaft, commonly pedicled ALT, and a narrow RFFF as the urethral tube. The dedicated RFFF supplies only the urethra. In the cited 19-patient approach, a roughly 3-cm-wide strip was tubularized skin-in in two layers around an 18-Fr catheter, joined to the pars fixa with a spatulated two-layer anastomosis, and revascularized before the ALT shaft was wrapped around it.[8]
| Feature | Practical Point |
|---|---|
| Urethral tissue | Forearm skin is thin and pliable, with reliable radial-artery anatomy |
| Hand perfusion | Verify adequate ulnar collateral flow before radial-artery harvest (Allen test in the cited series); insufficient hand perfusion contraindicates RFFF.[8] |
| Microsurgery | Requires radial artery / venous anastomoses to recipient vessels |
| Monitoring | Inner flap is buried inside the shaft, making vascular compromise hard to detect |
| Donor site | Smaller forearm scar than total RFFF phalloplasty, but still visible and often grafted |
| Sensation | In the cited double-flap series, urethral RFFF sensory nerve coaptation was abandoned because catheterization became unpleasant; the ALT shaft nerve was coapted to a dorsal clitoral nerve.[8] |
Van der Sluis and colleagues reported 19 transgender men treated with pedicled ALT shaft plus RFFF urethral reconstruction. At median 35-month follow-up, total RFFF failure occurred in 2 patients and total ALT failure in 1. Long-term urinary complications occurred in 10/19 patients (53%). Nine (47%) developed urethral strictures: eight at the pars fixa–pars pendulans anastomosis and one within the phallic urethra due to hair growth; median onset was nine months (range 7–56) after surgery.[8]
D'Arpa's Ghent series reported a 37.9% combined urethral complication rate for RFFF urethras in ALT phalloplasty, between SCIP urethra (26.3%) and prelaminated ALT (87.5%).[1]
Modified Combined RFFF + ALT
Staud and colleagues described a modified microvascular tube-in-tube concept in which RFFF supplies the inner urethral tube and a free ALT flap supplies the outer shaft.[9]
In 21 patients, Staud reported 100% flap survival (with partial necrosis of three RFFFs and one ALT flap), 38.1% fistula, 23.8% stenosis, 52.4% overall complications, and standing micturition in all but one patient at mean 4.4-year follow-up.[9]
Other Separate-Flap Options
Wu and colleagues reported urethral reconstruction and revision urethroplasty after pedicled ALT penile reconstruction in patients with micropenis, iatrogenic defects or traumatic penile defects. Urethral options included pudendal-thigh flaps, pedicled scrotal septum flaps, and other revision strategies. The reported complication percentages combine flap necrosis, urinary fistula, and stricture.[10] Rates were 66.7% with tube-in-tube (n = 6), 46.2% with SCIAP (n = 26), 38.5% with pudendal-thigh (n = 11) and 50% with scrotal septum flaps (n = 6), and all patients could void standing after revision.[10]
Pedicled labia minora flap urethral lengthening is more directly relevant to transmasculine ALT / SCIP phalloplasty. Al-Tamimi and colleagues reported 16 patients with pedicled labia minora flap urethral lengthening; fistula occurred in 4/16 (25%), stricture in 6/16 (37.5%), and 3/16 underwent perineostomy (reported as temporary), while 9/16 (56.3%) voided standing.[11]
D'Arpa's group with a skin flap from a previous phalloplasty (n = 6) had a 16.7% urethral complication rate, and the authors advise using residual penile skin for the urethra when a penis is present.[1]
Comparative Outcomes
| Separate-Flap Technique | Largest Relevant Series | Urethral Signal |
|---|---|---|
| Pedicled SCIP urethra | D'Arpa 2019, 38 SCIP urethras; De Gelder 2025, 10-year SCIP experience | 26.3% combined fistula / stricture rate in D'Arpa; 37/45 (82%) SCIP-urethra recipients across shaft and revision pathways voided standing after any needed interventions, including salvage after flap failure, in De Gelder[1][3] |
| Free RFFF urethral flap | van der Sluis 2017, 19 patients; D'Arpa 2019, 29 RFFF urethras | 53% urinary complications / 47% strictures in van der Sluis; 37.9% urethral complications in D'Arpa[1][8] |
| Modified RFFF + ALT free-flap construct | Staud 2021, 21 patients | No complete flap loss, but partial necrosis in 3 RFFFs and 1 ALT; 8/21 (38.1%) fistula, 5/21 (23.8%) stenosis, and 20/21 (95.2%) standing micturition at mean 4.4-year follow-up[9] |
| Pedicled labia minora flap | Al-Tamimi 2020, 16 patients | 25% fistula; 37.5% stricture; 56.3% standing micturition[11] |
| Pudendal-thigh / scrotal septum flap | Wu 2022, 49 ALT penile reconstructions for micropenis or penile defects | The abstract reports a composite of flap necrosis, fistula or stricture in 38.5% of pudendal-thigh and 50% of scrotal-septum cases; its stated 11 pudendal-thigh recipients do not reconcile with 38.5%. The series includes primary reconstruction and revision[10] |
Tube-in-tube RFFF is the most frequently reported simultaneous shaft-plus-urethra technique, but a 2026 review found no established gold-standard method and inconsistent urinary-outcome reporting across studies.[12] In the earlier meta-analysis, prelaminated urethral strategies had more strictures than tube-in-tube and did not differ significantly from second-flap techniques.[2]
SCIP Versus RFFF Urethral Flap
| Feature | Pedicled SCIP Urethra | Free RFFF Urethra |
|---|---|---|
| Microsurgery | Usually no | Yes |
| Donor-site visibility | Concealed groin scar | Visible forearm scar |
| Donor-site closure | Often primary | In the 19-patient dedicated-RFFF series, 11/19 forearms closed primarily; 8/19 needed a small split-thickness graft[8] |
| Tissue thickness | Thin if patient anatomy favorable | Thin and pliable |
| Pedicle / reach | Shorter and anatomy-dependent | Longer free-flap pedicle |
| Monitoring | Buried urethral flap still difficult to monitor | Buried free urethral flap especially difficult to monitor |
| Sensory planning | Ghent's bilateral SCIP design permits omitting urethral innervation.[3] | The dedicated-RFFF series abandoned urethral sensory coaptation after unpleasant catheterization; ALT shaft sensation was planned separately.[8] |
| Published urethral complication signal | 26.3% in D'Arpa ALT series | 37.9% in D'Arpa ALT series; 53% urinary complications in van der Sluis |
Bilateral SCIP Shaft Plus Urethra
The Ghent group also described bilateral SCIP use, with one SCIP flap for shaft and another for urethra. The attractions are no forearm scar, possible avoidance of microsurgery, concealed donor sites, and primary closure. In the 8-patient bilateral SCIP subgroup, De Gelder reported no shaft reconstruction failures, but urethral fistula / stricture occurred in 38%. SCIP lacks the established major sensory nerve coaptation pathway of RFFF.[3]
Operative Pearls
- Choose the urethral flap for urethral function as well as donor-site aesthetics.
- In ALT phalloplasty, assume tube-in-tube is unlikely unless pinch thickness, hair pattern, and center experience are favorable.
- Map SCIA perforators and confirm pedicle reach. Assess groin or flank pinch thickness (the Ghent team listed <1 cm as a selection criterion); tubularized SCIP tissue may be compressed within a thick ALT shaft.[3][6]
- Buried urethral flaps are hard to monitor, especially when the urethral flap is free and enclosed by another flap. In pedicled ALT plus RFFF reconstruction, avoid tight ALT closure around the RFFF because postoperative swelling may compromise the inner flap’s blood supply.[8]
- Depilate any urethral skin strip before surgery, including groin-based SCIP tissue when hair-bearing.
- Minimize tension and caliber mismatch at the pars fixa-to-pars pendulans anastomosis.
- Discuss phalloplasty without urethral lengthening and perineal urethrostomy before flap selection, and revisit the option if standing micturition is no longer worth the revision burden. In de Rooij's retrospective cohort with different flap mixes, 74/91 (81%) with urethral lengthening and 12/45 (27%) without it underwent reoperation; after 80/91 completed a lengthening pathway, 60/80 (75%) voided standing, whereas all 45 without lengthening had a definitive perineostomy.[15]
References
1. D'Arpa S, Claes K, Lumen N, et al. Urethral reconstruction in anterolateral thigh flap phalloplasty: a 93-case experience. Plast Reconstr Surg. 2019;143(2):382e-392e. doi:10.1097/PRS.0000000000005278
2. Hu CH, Chang CJ, Wang SW, Chang KV. A systematic review and meta-analysis of urethral complications and outcomes in transgender men. J Plast Reconstr Aesthet Surg. 2022;75(1):10-24. doi:10.1016/j.bjps.2021.08.006
3. De Gelder A, Young-Afat D, Claes K, et al. Use of the superficial circumflex iliac artery perforator flap for urethra and/or shaft reconstruction in gender-diverse persons: 10-year single-center experience. Plast Reconstr Surg. 2025;155(6):1036e-1044e. doi:10.1097/PRS.0000000000011830
4. Zhang Y, Zeng A. An easy way to harvest a superthin SCIP flap with long pedicle: reappraisal of the inferolateral branches of the SCIA. Plast Reconstr Surg. 2023;152(5):1100-1104. doi:10.1097/PRS.0000000000010338
5. Gandolfi S, Postel F, Auquit-Auckbur I, et al. Vascularization of the superficial circumflex iliac perforator flap (SCIP flap): an anatomical study. Surg Radiol Anat. 2020;42(4):473-481. doi:10.1007/s00276-019-02402-9
6. Tashiro K, Harima M, Kato M, et al. Preoperative color Doppler ultrasound assessment in planning of SCIP flaps. J Plast Reconstr Aesthet Surg. 2015;68(7):979-983. doi:10.1016/j.bjps.2015.03.004
7. Scaglioni MF, Meroni M, Fritsche E. Pedicled superficial circumflex iliac artery perforator flap for male genital reconstruction: a case series. Microsurgery. 2022;42(8):775-782. doi:10.1002/micr.30933
8. van der Sluis WB, Smit JM, Pigot GLS, et al. Double flap phalloplasty in transgender men: surgical technique and outcome of pedicled anterolateral thigh flap phalloplasty combined with radial forearm free flap urethral reconstruction. Microsurgery. 2017;37(8):917-923. doi:10.1002/micr.30190
9. Staud CJ, Zaussinger M, Duscher D, et al. A modified microvascular "tube-in-tube" concept for penile construction in female-to-male transsexuals: combined radial forearm free flap with anterolateral thigh flap. J Plast Reconstr Aesthet Surg. 2021;74(9):2364-2371. doi:10.1016/j.bjps.2021.01.016
10. Wu Q, Yang Z, Ma N, Wang W, Li Y. Urethra reconstruction and revision urethroplasty in pedicled anterolateral thigh flap penile reconstruction. Ann Plast Surg. 2022;89(2):201-206. doi:10.1097/SAP.0000000000003100
11. Al-Tamimi M, Pigot GL, Ronkes B, et al. The first experience of using the pedicled labia minora flap for urethral lengthening in transgender men undergoing anterolateral thigh and superficial circumflex iliac artery perforator flap phalloplasty: a multicenter study on clinical outcomes. Urology. 2020;138:179-187. doi:10.1016/j.urology.2019.10.041
12. Tinajero JD, Liang DGK, Wasay S, Djordjevic ML, Di Taranto G. "The evolution of phalloplasty for masculinizing gender affirming surgery: a systematic review of surgical techniques and complications over the past 25 years." Microsurgery. 2026;46(6):e70273. doi:10.1002/micr.70273
13. European Association of Urology. "EAU Guidelines on Urethral Strictures: 8. Disease Management in Transgender Patients." EAU Guidelines. 2026. Guideline chapter.
14. van der Sluis WB, Al-Tamimi M, Pigot GLS, et al. "Redo phalloplasty and/or urethraplasty after previous flap failure in phalloplasty in transgender men: surgical considerations and outcomes." J Sex Med. 2024;21(11):1085-1093. doi:10.1093/jsxmed/qdae119
15. de Rooij FPW, van der Sluis WB, Ronkes BL, et al. "Comparison of surgical outcomes and urinary functioning after phalloplasty with versus without urethral lengthening in transgender men." Int J Transgend Health. 2023;24(4):487-498. doi:10.1080/26895269.2022.2110548