Phallic Urethra: Tube-in-Tube and Pars Pendulans Construction
The phallic urethra, or pars pendulans, is the distal neourethral segment that runs through the neophallus from its base to the neomeatus. Unlike the pars fixa, which is built from local perineal tissue, the pars pendulans is determined primarily by flap choice and phalloplasty design.[1][2][3]
This is the atlas page for tube-in-tube phallic urethral construction and the main alternatives when tube-in-tube RFFF is not used. For full donor-flap anatomy and non-GAS applications, see Radial Forearm Free Flap. For the phalloplasty-specific donor-site page, see RFFF Phalloplasty.
Concept
The neourethra can be divided into two operative segments.[1][4]
| Segment | Location | Main Technical Driver |
|---|---|---|
| Pars fixa | Native urethral meatus to phallus base | Anterior vaginal-wall flap, labia minora / vestibular tissue, buccal mucosa graft, vaginectomy, buttress coverage |
| Pars pendulans | Phallus base to neomeatus at phallus tip | Tube-in-tube RFFF, separate urethral flap, prelaminated flap, or staged graft urethroplasty |
The pars pendulans must be long, hair-free, supple, well vascularized, and positioned so its suture line does not sit directly under the outer shaft closure. It also has to meet the pars fixa without tension; the pars fixa-to-pars pendulans junction remains a major stricture site.[1][3][5]
Tube-in-Tube RFFF
The classic tube-in-tube radial forearm free flap (RFFF) creates the phallic urethra and shaft from one fasciocutaneous flap. It remains the reference standard for simultaneous shaft, urethra, and sensory reconstruction because forearm skin is thin, pliable, and reliably perfused by the radial artery system.[2][6][7]
| Step | Technical Point |
|---|---|
| Design | A broad volar forearm flap is divided into a narrow urethral strip and a wider shaft segment |
| Inner tube | The urethral strip is rolled skin-side-in around a catheter to create the pars pendulans |
| Outer tube | The remaining flap is rolled around the inner tube, skin-side-out, to create the phallic shaft |
| Vascularity | Inner and outer tubes share the radial artery / venae comitantes and superficial venous drainage |
| Nerve coaptation | Forearm sensory nerves are coapted to dorsal clitoral nerve, ilioinguinal nerve, or other local targets according to center protocol |
| Suture-line planning | Inner and outer suture lines should be offset to reduce overlapping ischemia and fistula risk |
The key strength is that the urethra and shaft travel as one vascularized unit. The key vulnerability is that the inner skin tube has a long ventral suture line, and any hair-bearing skin left in the urethral strip can become a lifelong obstructive and infectious problem.
Advantages and Tradeoffs
| Advantage | Why It Matters |
|---|---|
| Single-flap urethra and shaft | Avoids a second free flap or staged phallic urethral graft bed |
| Thin pliable tissue | Forearm skin tubularizes more predictably than thick thigh tissue |
| Reliable vascular anatomy | Radial artery anatomy is usually consistent and familiar to microsurgical teams |
| Sensory potential | Forearm sensory nerves support tactile and erogenous reinnervation planning |
| Established outcomes literature | RFFF has the largest phalloplasty evidence base |
| Tradeoff | Counseling Point |
|---|---|
| Visible forearm donor site | The donor scar is often the decisive disadvantage |
| Microsurgery required | Requires reliable microsurgical team, recipient vessels, and postoperative monitoring |
| Urethral suture-line morbidity | Fistula and stricture remain common even when flap survival is excellent |
| Forearm size and hair pattern matter | Small forearms, thick adiposity, or dense hair can compromise design |
| Radial artery sacrifice | Requires vascular assessment and hand-perfusion safety checks |
Alternatives to Tube-in-Tube RFFF
When RFFF tube-in-tube is not used, the surgeon must choose how the phallic urethra will be supplied. This choice is separate from the shaft flap choice and should be made before committing to donor-site scars or staging.
| Technique | Best Use | Main Limitation |
|---|---|---|
| Second free flap for urethra | ALT shaft with a dedicated RFFF or other thin urethral flap | Adds a second donor site and additional microsurgery |
| SCIP urethral flap | ALT or revision phalloplasty when a thin concealed-donor urethral flap is desired | Requires favorable groin tissue and flap-specific experience |
| Prelaminated ALT | Patient wants ALT shaft and a planned graft-lined urethra | Historically high complication rates from graft take, contracture, and vascular-interface problems |
| Staged split-thickness skin-graft urethroplasty | ALT shaft without reliable tube-in-tube urethra | Requires three-stage pathway and delayed standing voiding |
| Pedicled labia minora flap | Selected ALT / SCIP phalloplasty with usable local genital tissue | Limited length and substantial stricture / fistula rates in early series |
| Tube-in-tube ALT | Rare thin-thigh candidate with favorable hair pattern | Usually not feasible; ALT is often too thick and hair-bearing |
Second Free Flap
Double-flap phalloplasty pairs a pedicled ALT shaft with a separate RFFF used only for urethral reconstruction. Van der Sluis and colleagues reported 19 transgender men undergoing pedicled ALT phalloplasty with RFFF urethral reconstruction; long-term urinary complications occurred in 53%, including strictures in 47%, and total RFFF failure occurred in two patients.[8]
D'Arpa and colleagues reported a 37.9% urethral complication rate when RFFF was used for urethral reconstruction in ALT phalloplasty, compared with 26.3% for SCIP urethra in the same 93-case ALT urethral-reconstruction experience.[9] A second RFFF can also salvage loss of a tube-in-tube urethra after partial flap necrosis, but it spends the contralateral forearm and should be reserved for carefully selected salvage situations.[10]
Prelaminated Flap
Prelamination places a graft onto the planned flap before phalloplasty, allows it to vascularize, and later tubularizes it as the phallic urethra. It is appealing in theory, but the outcome signal has been poor in ALT urethral reconstruction. D'Arpa reported an 87.5% urethral complication rate for prelaminated ALT urethra, and the Hu meta-analysis found prelaminated flaps associated with significantly higher stricture rates than tube-in-tube approaches.[9][11]
Staged Skin-Graft Urethroplasty
Bluebond-Langner's staged ALT pathway avoids forcing a thick thigh flap into a tube-in-tube urethra. Stage I creates a single-tube ALT phallus without urethra. Stage II opens the ventral phallus, grafts a urethral plate, and completes vaginectomy / pars fixa / scrotoplasty. Stage III tubularizes the grafted plate to complete the pars pendulans.[12]
Robinson and colleagues reported 24 patients treated with staged split-thickness skin-graft ALT urethroplasty: standing micturition was achieved in 87.5%, with 33.3% fistula and 20.8% stricture rates.[12]
Labia Minora and SCIP Urethral Flaps
Pedicled labia minora flaps can form both fixed and pendulous urethral components when local tissue length is adequate. In the Amsterdam / Belgrade first-experience series of 16 patients undergoing ALT or SCIP phalloplasty with pedicled labia minora flap urethral lengthening, fistula occurred in 25%, stricture in 37.5%, and standing micturition in 56.3%.[13]
SCIP can be used as a dedicated thin urethral flap, especially with ALT shaft reconstruction. D'Arpa reported the most favorable non-RFFF urethral signal in that 93-case ALT series for SCIP urethra, with a 26.3% urethral complication rate.[9] For flap-specific selection, see SCIP Phalloplasty.
Tube-in-Tube ALT
Tube-in-tube ALT is uncommon because thigh tissue is often thick and hair-bearing. In D'Arpa's 93-case ALT series, tube-in-tube ALT was feasible in only 5 patients, with a 20% urethral complication rate in that highly selected subgroup.[9]
Comparative Outcomes
| Pars Pendulans Strategy | Largest Cited Series / Context | Urethral Signal |
|---|---|---|
| Tube-in-tube RFFF | Largest evidence base; RFFF remains reference standard | Lower stricture risk than prelaminated approaches in meta-analysis, but combined urethral complications remain common[2][7][11] |
| Second RFFF urethral flap with ALT shaft | van der Sluis 2017, 19 patients; D'Arpa 2019, 29 patients | 53% urinary complications / 47% strictures in van der Sluis; 37.9% urethral complications in D'Arpa[8][9] |
| SCIP urethral flap | D'Arpa 2019, 38 patients | 26.3% urethral complication rate in ALT urethral-reconstruction series[9] |
| Staged skin-graft ALT urethroplasty | Robinson 2023, 24 patients | 87.5% standing micturition; 33.3% fistula; 20.8% stricture[12] |
| Prelaminated ALT urethra | D'Arpa 2019, 8 patients; Hu 2022 meta-analysis | 87.5% urethral complications in D'Arpa; higher stricture rate than tube-in-tube in meta-analysis[9][11] |
| Pedicled labia minora flap | Al-Tamimi 2020, 16 patients | 25% fistula; 37.5% stricture; 56.3% standing micturition[13] |
Complications
| Complication | Mechanism / Pattern | Prevention or Repair Direction |
|---|---|---|
| Urethrocutaneous fistula | Long inner-tube suture line, ischemia, distal obstruction, or overlapping closures | Offset suture lines, ensure vascularized coverage, treat distal obstruction before fistula closure |
| Stricture | Pars fixa-to-pars pendulans anastomosis, neomeatus, graft contracture, or ischemic tube | Define with cystoscopy / contrast imaging; avoid repeated low-yield dilation |
| Intraurethral hair | Hair-bearing donor skin in urethral strip | Preoperative depilation; endoscopic laser epilation for postoperative hair-bearing grafts |
| Neomeatal stenosis | Tip ischemia, scar, glansplasty / meatal configuration | Meatoplasty or staged revision when persistent |
| Urethral loss after partial flap necrosis | Inner tube ischemia or partial flap loss | Salvage with staged graft urethroplasty or second flap in selected cases |
Veerman and colleagues reported that urologic complications after genital gender-affirming surgery with urethral lengthening often present early, with strictures occurring at a median of about 3 months in that cohort.[14] Revision algorithms should therefore keep the urethra decompressed, identify distal obstruction, and avoid definitive repair through inflamed tissue; advanced revision may require staged grafting, local flaps, or second-flap salvage depending on tissue loss and patient goals.[18]
Hair Removal
Hair-bearing urethral skin can cause recurrent urinary tract infection, obstructive symptoms, encrustation, stone formation, and difficult cystoscopy. Hair clearance must be planned before flap elevation, especially for RFFF and ALT urethral strips.[15][16]
| Modality | Practical Point |
|---|---|
| Electrolysis | Most definitive method for permanent follicle destruction; slow and operator-dependent |
| Laser hair removal | Faster and less painful for dark terminal hair, but produces permanent reduction rather than guaranteed removal |
| Timing | Start early; multiple sessions and a regrowth observation interval are usually needed before surgery |
| Postoperative hair | Nd:YAG laser epilation via cystoscopy has been described for hair-bearing urethral grafts |
Single-Tube Phalloplasty Without Pars Pendulans
Some patients choose phalloplasty without urethral lengthening and continue voiding from the native perineal meatus. This avoids pars pendulans and pars fixa morbidity but sacrifices standing micturition. Miller and colleagues described a single-tube RFFF modification that creates an aesthetic distal neomeatal pouch without a functional urethral connection, preserving the appearance of a meatus while avoiding urethral lengthening.[17]
Operative Pearls
- Decide whether standing micturition is worth the urethral risk before choosing the shaft flap.
- For tube-in-tube RFFF, plan the urethral strip first; hair, width, and suture-line position are not afterthoughts.
- Offset inner and outer suture lines so fistula-prone closures do not stack directly over each other.
- Do not force tube-in-tube construction into a thick ALT flap; choose a staged graft or separate flap pathway when tissue is unfavorable.
- Treat prelaminated ALT urethra cautiously; the complication signal is worse than its conceptual elegance.
- Always evaluate the pars fixa-to-pars pendulans junction when a patient presents with pendulous urethral symptoms.
- For patients who do not prioritize standing voiding, no-UL phalloplasty is a legitimate morbidity-sparing endpoint.
References
1. Berli JU, Monstrey S, Safa B, Chen M. Neourethra creation in gender phalloplasty: differences in techniques and staging. Plast Reconstr Surg. 2021;147(5):801e-811e. doi:10.1097/PRS.0000000000007898
2. Gottlieb L, Cripps C. An update on gender-affirming phallus construction using the radial forearm free-flap. Neurourol Urodyn. 2023;42(5):963-972. doi:10.1002/nau.25103
3. Elyaguov J, Isakov R, Nikolavsky D. Evaluation and management of urologic complications following transmasculine genital reconstructive surgery. Neurourol Urodyn. 2023;42(5):979-989. doi:10.1002/nau.25100
4. Dabela-Biketi A, Mawad K, Li H, et al. Urethrographic evaluation of anatomic findings and complications after perineal masculinization and phalloplasty in transgender patients. Radiographics. 2020;40(2):393-402. doi:10.1148/rg.2020190143
5. Waterschoot M, Claeys W, Hoebeke P, et al. Treatment of urethral strictures in transmasculine patients. J Clin Med. 2021;10(17):3912. doi:10.3390/jcm10173912
6. Monstrey S, Hoebeke P, Selvaggi G, et al. Penile reconstruction: is the radial forearm flap really the standard technique? Plast Reconstr Surg. 2009;124(2):510-518. doi:10.1097/PRS.0b013e3181aeeb06
7. Garaffa G, Christopher NA, Ralph DJ. Total phallic reconstruction in female-to-male transsexuals. Eur Urol. 2010;57(4):715-722. doi:10.1016/j.eururo.2009.05.018
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. 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
10. Tchang LA, Largo RD, Babst D, et al. Second free radial forearm flap for urethral reconstruction after partial flap necrosis of tube-in-tube phalloplasty with radial forearm flap: a report of two cases. Microsurgery. 2014;34(1):58-63. doi:10.1002/micr.22168
11. 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
12. Robinson I, Chao BW, Blasdel G, et al. Anterolateral thigh phalloplasty with staged skin graft urethroplasty: technique and outcomes. Urology. 2023;177:204-212. doi:10.1016/j.urology.2023.03.038
13. 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
14. Veerman H, de Rooij FPW, Al-Tamimi M, et al. Functional outcomes and urological complications after genital gender affirming surgery with urethral lengthening in transgender men. J Urol. 2020;204(1):104-109. doi:10.1097/JU.0000000000000795
15. Yanes DA, Smith P, Avram MM. A review of best practices for gender-affirming laser hair removal. Dermatol Surg. 2024;50(12S):S201-S204. doi:10.1097/DSS.0000000000004441
16. Finkelstein LH, Blatstein LM. Epilation of hair-bearing urethral grafts using the neodymium:YAG surgical laser. J Urol. 1991;146(3):840-842. doi:10.1016/s0022-5347(17)37937-5
17. Miller TJ, Saberski ER, Safa B, Watt AJ. Modification of the single-tube radial forearm phalloplasty technique to allow for urinary meatal reconstruction: a report of two cases. Microsurgery. 2022;42(7):728-731. doi:10.1002/micr.30950
18. Loughran A, Coon D. Advanced phalloplasty: management of complications and techniques for revision. Clin Plast Surg. 2025;52(4):507-514. doi:10.1016/j.cps.2025.06.007