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 phalloplasty series, tube-in-tube ALT was feasible in only 5 patients (5.4%), making a separate urethral strategy necessary for most ALT candidates.[1]
This is the atlas page for separate-flap phallic urethral construction. 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 | Bring new vascularized tissue into a scarred urethral bed |
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 | Excellent tubularization tissue, but microsurgery and forearm donor scar remain |
| Pedicled labia minora flap | Local genital-tissue urethral lengthening in ALT / SCIP pathways | Limited length and lower standing-micturition signal in early series |
| 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 | Not applicable to most transmasculine patients |
Pedicled SCIP Urethral Flap
The superficial circumflex iliac artery perforator (SCIP) flap is the most important contemporary separate urethral flap for ALT phalloplasty. 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 | Rolled around a catheter to create the pars pendulans |
| Donor site | Typically closes primarily, leaving a concealed groin scar |
| Limitation | Short pedicle or unfavorable anatomy can require conversion to a free flap |
D'Arpa and colleagues reported the strongest non-tube-in-tube signal for SCIP in their 93-case ALT urethral-reconstruction experience: 38 SCIP urethras had a 26.3% combined urethral complication rate, lower than RFFF urethra and far lower than prelaminated ALT in that series.[1]
De Gelder and colleagues' 10-year Ghent SCIP experience reported 55 SCIP flaps used for urethra and / or shaft reconstruction in gender-diverse patients. Among patients with a SCIP urethra, 82% achieved standing micturition; complete SCIP urethral failure occurred in 8 flaps, and 3 SCIP flaps were converted to free flaps. 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 | Sensory reinnervation is less established than RFFF |
| 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 RFFF is harvested only for urethral reconstruction, tubularized, and inset within the ALT phallus.[8]
| Feature | Practical Point |
|---|---|
| Urethral tissue | Forearm skin is thin and pliable, with reliable radial-artery anatomy |
| 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 | Lateral antebrachial cutaneous nerve may be used for sensory planning |
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, total ALT failure in 1 patient, and long-term urinary complications occurred in 53%, including strictures in 47%.[8]
D'Arpa's Ghent series reported a 37.9% combined urethral complication rate for RFFF urethras in ALT phalloplasty, intermediate between SCIP urethra and prelaminated ALT.[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. This is not a simple pedicled ALT plus urethral flap; it is a highly complex combined free-flap strategy.[9]
In 21 patients, Staud reported 100% flap survival, 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 cisgender male patients. Urethral options included pudendal-thigh flaps, pedicled scrotal septum flaps, and other revision strategies; urethral complication rates remained substantial, underscoring that "separate flap" is a tissue-supply strategy rather than a guarantee of urethral success.[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 25%, stricture in 37.5%, and standing micturition in 56.3%.[11]
Native penile skin flaps can have low complication rates in D'Arpa's mixed penile-reconstruction dataset, but they apply to cisgender penile reconstruction with residual penile tissue, not standard transmasculine phalloplasty.[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 urethral complication rate in D'Arpa; 82% standing micturition 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 | 100% flap survival; 38.1% fistula; 23.8% stenosis; 95.2% standing micturition[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, selected cisgender ALT penile reconstruction | Useful salvage options, but not generalizable to transmasculine phalloplasty[10] |
For context, tube-in-tube RFFF remains the largest evidence base and reference standard for simultaneous shaft-plus-urethra construction, while prelaminated urethral strategies have the worst clinical stricture signal in meta-analysis.[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 | Usually grafted forearm closure |
| 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 | Less established | LABCN or other forearm nerve options |
| 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 attraction is clear: 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%. The sensory limitation remains important because SCIP lacks the established major sensory nerve coaptation pathway of RFFF.[3]
Operative Pearls
- Choose the urethral flap for urethral function, not donor-site aesthetics alone.
- In ALT phalloplasty, assume tube-in-tube is unlikely unless pinch thickness, hair pattern, and center experience are favorable.
- Map SCIP anatomy before committing to a pedicled SCIP urethra; pedicle reach is the critical limitation.
- Remember that buried urethral flaps are hard to monitor, especially when the urethral flap is free and enclosed by another flap.
- 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.
- Present perineal urethrostomy or no-UL phalloplasty as valid options when standing micturition is no longer worth the revision burden.
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