Pars Fixa Urethral Construction
The pars fixa is the fixed proximal neourethral segment that bridges the native urethral meatus to the base of the neophallus, where it anastomoses with the pars pendulans or phallic urethra. In masculinizing gender-affirming surgery, it is the perineal / bulbar segment of urethral lengthening and one of the most technically unforgiving portions of metoidioplasty and phalloplasty.[1][2][3]
This is the atlas page for pars fixa urethral construction. For phalloplasty-first staging, see Big Ben Method. For metoidioplasty with buccal mucosa graft and labia minora flap, see Modified Belgrade Metoidioplasty. For flap-specific phallic urethra choices, see RFFF Phalloplasty, ALT Phalloplasty, and SCIP Phalloplasty.
Terminology
The gender-affirming neourethra is best discussed as two segments because each segment has different tissue sources, blood supply, mobility, and failure modes.[1][4]
| Segment | Definition | Usual Tissue Source |
|---|---|---|
| Pars fixa | Fixed perineal / bulbar segment from native urethral meatus to phallus base | Anterior vaginal-wall flap, labia minora flap, buccal mucosa graft, vaginal mucosa graft, or skin graft depending on operation |
| Pars pendulans | Mobile phallic urethra through the neophallus to the neomeatus | Tube-in-tube flap, separate flap, prelaminated graft, or staged skin-graft urethroplasty |
The pars fixa-to-pars pendulans junction is a dominant stricture site after phalloplasty with urethral lengthening. Any technique plan should therefore be judged by the tissue quality, vascularized coverage, dead-space management, and tension at this junction.[2][3][5]
Tissue Sources
Anterior Vaginal-Wall Flap
The anterior vaginal wall flap is the classic local flap for pars fixa construction in phalloplasty and metoidioplasty with urethral lengthening. It is elevated on its submucosal vascular plexus, separated from the posterior urethral wall in the described anatomic cleavage plane, then tubularized around a catheter to form a mucosal-lined proximal neourethra.[1][6][7]
| Feature | Practical Implication |
|---|---|
| Mucosal-lined local tissue | Better conceptual match to urethral lining than hair-bearing skin |
| Pedicled vascularity | More reliable than a free graft when local tissue is healthy |
| Requires vaginectomy planning | Harvest and dead-space closure must be coordinated with gynecology / reconstructive urology |
| Buttress potential | Vaginectomy can provide vestibular / bulbospongiosus tissue for layered suture-line coverage |
Chesson and colleagues reported that colpocleisis with anterior vaginal-wall sparing and staged urethral lengthening reduced fistula rates compared with primary single-stage anastomosis, establishing the long-standing principle that the pars fixa benefits from thoughtful staging and vascularized local coverage.[8]
Labia Minora Flaps
Pedicled labia minora flaps can supply ventral urethral coverage, local vascularized tissue, or a more extensive urethral tube in operations where the main phalloplasty flap does not provide a tube-in-tube urethra. They are particularly relevant in ALT and SCIP-related urethral strategies.[9]
In the Amsterdam / Belgrade multicenter first-experience series of pedicled labia minora flap urethral lengthening for ALT and SCIP phalloplasty, 16 patients had a 25% fistula rate, 37.5% stricture rate, and 56.3% standing micturition rate. Those numbers should be framed as early feasibility data, not proof of superiority.[9]
Buccal Mucosa Graft
Buccal mucosa is most established in metoidioplasty urethral lengthening, where it can be quilted as a dorsal plate and combined with a labia minora flap for ventral closure. This is the Belgrade / modified Belgrade concept rather than the standard pars fixa solution for every phalloplasty.[10][11][12]
| Use Case | Role |
|---|---|
| Metoidioplasty with UL | Dorsal urethral plate over ventral corpora / released clitoral shaft |
| Revision urethroplasty | Graft substitute when local genital tissue is scarred or insufficient |
| Phalloplasty prelamination | More often used for the phallic urethra than the pars fixa |
Djordjevic and colleagues reported low fistula rates with combined buccal mucosa graft and labia minora flap urethral lengthening in metoidioplasty, and a later comparative series favored this combined method over dorsal clitoral skin flap urethral lengthening.[11][12]
Vaginal Mucosal Graft
Vaginal mucosa can also be used as a free graft for urethral prefabrication. Zhang and colleagues found vaginal mucosa histologically similar to urethral and buccal mucosa, with good revascularization after prefabrication; their 22-patient series reported a 4.5% stricture rate but a 31.8% fistula rate.[13]
A 2025 metoidioplasty report also describes vaginal-mucosal graft urethral reconstruction as a transmasculine technique, reinforcing that vaginal mucosa remains a relevant autologous substitute when tissue is available and patient goals permit harvest.[14]
Skin Grafts
Skin grafts are most relevant to staged phallic urethral construction, but they interact with the pars fixa because the fixed segment must eventually meet the grafted phallic urethra without tension. Robinson and colleagues described staged ALT phalloplasty with a local-tissue pars fixa and split-thickness skin-graft phallic urethroplasty, reporting 87.5% standing micturition, 33.3% fistula, and 20.8% stricture.[15]
Full-thickness skin grafting has also been described for elongating the pars fixa during colpectomy before combined RFFF / ALT phalloplasty, but this remains a specialized pathway rather than a general default.[16]
Vaginectomy and Buttressing
Vaginectomy is not only cavity obliteration; it is also a reconstructive maneuver that can improve pars fixa coverage. In a 224-patient phalloplasty-with-urethral-lengthening series, Massie and colleagues reported fewer urethral complications with vaginectomy than with vaginal preservation: 27% versus 67%, with lower odds of both stricture and fistula.[7]
| Adjunct | Reconstructive Purpose |
|---|---|
| Vaginectomy / colpoclesis | Removes epithelial dead space and supplies additional vascularized tissue |
| Bulbospongiosus / vestibular tissue flap | Buttresses pars fixa suture lines after anterior vaginal-wall flap harvest |
| Gracilis muscle flap | Fills vaginal dead space and wraps / covers the pars fixa in selected staged pathways |
| Layered closure | Separates urethral suture line from skin and perineal wound lines |
Cohen and colleagues described a split pedicled gracilis muscle flap during robotic-assisted vaginectomy and urethral lengthening: the inferior muscle portion fills the vaginal dead space, while the superior portion wraps the pars fixa. In their 16-patient series, no urethroplasty-site fistulas occurred at mean 361-day follow-up.[17]
Vaginectomy Approaches
| Approach | Best Fit |
|---|---|
| Open / perineal sharp excision | Direct local tissue control; useful when anterior vaginal-wall tissue is needed for pars fixa construction |
| Laparoscopic-assisted vaginectomy | Useful when combined with laparoscopic hysterectomy / BSO and when adequate mucosa can still be harvested |
| Robotic-assisted laparoscopic vaginectomy | Helpful in staged penile reconstruction pathways and when pelvic visualization / robotic colpoclesis is favored |
Jun and colleagues reported robotic-assisted vaginectomy during staged penile reconstruction in 42 patients. Vaginal mucosa and gracilis flap were used in most pars fixa constructions; median estimated blood loss was 200 mL, median length of stay was 3 days, and vaginectomy-related complications were uncommon and low grade.[18]
Complications
The pars fixa is vulnerable because it sits at the crossroads of local genital tissue, vaginectomy dead space, perineal wounds, and the mobile phalloplasty urethra. Referral populations are enriched for failures, but they reveal the failure pattern clearly. Dy and colleagues reported that among 55 patients presenting to a reconstructive urologist after masculinizing genital reconstruction, 86% had strictures, 56% had fistulae, 47% had vaginal remnants, and 73% had at least two simultaneous complications.[2]
| Complication | Typical Pattern | Key Management Concept |
|---|---|---|
| Stricture | Often at pars fixa-to-pars pendulans anastomosis | Define length and location with urethroscopy plus contrast imaging; avoid repeated ineffective dilation |
| Fistula | Anastomotic or suture-line leak, often after distal obstruction | Treat obstruction first; repair only after inflammation has settled |
| Vaginal remnant | Retained mucosa can communicate with neourethra or collect fluid | Identify with imaging / endoscopy; excise or obliterate when symptomatic |
| Mucocele | Retained mucosa in closed space | Prevention is meticulous epithelial removal and dead-space control |
| Revision cascade | Stricture, fistula, and remnant often coexist | Stage repairs when tissue quality is poor or defects are multiple |
Stricture Management
Waterschoot and colleagues' systematic review of transmasculine urethral stricture management found that strictures most commonly occur at the pars fixa-to-pars pendulans anastomosis. Reported techniques include endoscopic dilation / urethrotomy, staged Johanson-type urethroplasty, excision and primary anastomosis, buccal mucosa graft urethroplasty, and local pedicle flap urethroplasty. No repair method has been proven superior because comparative evidence is limited.[3]
| Stricture Scenario | Typical Repair Direction |
|---|---|
| Very short, early, non-obliterative narrowing | One cautious endoscopic attempt may be reasonable, but recurrence is common |
| Anastomotic stricture with healthy adjacent tissue | Excision and primary anastomosis or augmented repair depending on length and tension |
| Long or scarred segment | Buccal mucosa graft or local flap urethroplasty |
| Multiple defects / active fistula / poor tissue bed | Staged Johanson-type urethroplasty with later retubularization |
| Patient no longer prioritizes standing voiding | Perineal urethrostomy is a valid endpoint rather than a failure |
Comparison by Staging Strategy
| Strategy | Pars Fixa Tissue | Timing | Reported Urethral Signal |
|---|---|---|---|
| Single-stage phalloplasty | Anterior vaginal-wall flap + labia minora / vestibular buttress | Same operation as phalloplasty | Urethral complications remain high in many series[1][7][19] |
| Big Ben Method | Anterior vaginal-wall flap and local-tissue urethral lengthening | Deferred until after phallus healing | OHSU 2025: 8% stricture, 16.4% fistula, 96% standing micturition[20] |
| Metoidioplasty-first | Anterior vaginal-wall flap with or without buccal mucosa graft | Before any later phalloplasty | Lower complexity than phalloplasty UL, but UL still drives complications[10][21] |
| ALT staged skin-graft pathway | Vaginal flap / gracilis buttress for pars fixa; skin graft for phallic urethra | Middle stage of a three-stage plan | Robinson 2023: 20.8% stricture, 33.3% fistula[15] |
| Pedicled labia minora flap pathway | Labia minora flap, often with ALT / SCIP phalloplasty | At phalloplasty or staged urethral reconstruction | Al-Tamimi 2020: 37.5% stricture, 25% fistula[9] |
Operative Pearls
- Plan the pars fixa before choosing the phalloplasty urethral strategy; the junction fails when the two plans are mismatched.
- Favor mucosal tissue and vascularized local coverage when available.
- Treat vaginectomy as part of the urethral reconstruction, not a separate cosmetic step.
- Separate urethral, vaginal, and skin suture lines with vascularized tissue whenever possible.
- Avoid tension at the pars fixa-to-pars pendulans anastomosis; length deficiency becomes stricture.
- Look for combined pathology when a patient presents with one complication; stricture, fistula, and vaginal remnant commonly coexist.
- Offer perineal urethrostomy as a goal-concordant option when standing micturition is no longer worth the revision burden.
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. Dy GW, Granieri MA, Fu BC, et al. Presenting complications to a reconstructive urologist after masculinizing genital reconstructive surgery. Urology. 2019;132:202-206. doi:10.1016/j.urology.2019.04.051
3. 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
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. 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
6. Hage JJ, Torenbeek R, Bouman FG, Bloem JJ. The anatomic basis of the anterior vaginal flap used for neourethra construction in female-to-male transsexuals. Plast Reconstr Surg. 1993;92(1):102-108. doi:10.1097/00006534-199307000-00015
7. Massie JP, Morrison SD, Wilson SC, Crane CN, Chen ML. Phalloplasty with urethral lengthening: addition of a vascularized bulbospongiosus flap from vaginectomy reduces postoperative urethral complications. Plast Reconstr Surg. 2017;140(4):551e-558e. doi:10.1097/PRS.0000000000003697
8. Chesson RR, Gilbert DA, Jordan GH, et al. The role of colpocleisis with urethral lengthening in transsexual phalloplasty. Am J Obstet Gynecol. 1996;175(6):1443-1449. doi:10.1016/s0002-9378(96)70088-1
9. 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
10. Kocjancic E, Acar O, Talamini S, Schechter L. Masculinizing genital gender-affirming surgery: metoidioplasty and urethral lengthening. Int J Impot Res. 2022;34(2):120-127. doi:10.1038/s41443-020-0259-z
11. Djordjevic ML, Bizic M, Stanojevic D, et al. Urethral lengthening in metoidioplasty (female-to-male sex reassignment surgery) by combined buccal mucosa graft and labia minora flap. Urology. 2009;74(2):349-353. doi:10.1016/j.urology.2009.02.036
12. Djordjevic ML, Bizic MR. Comparison of two different methods for urethral lengthening in female to male (metoidioplasty) surgery. J Sex Med. 2013;10(5):1431-1438. doi:10.1111/jsm.12108
13. Zhang YF, Liu CY, Qu CY, et al. Is vaginal mucosal graft the excellent substitute material for urethral reconstruction in female-to-male transsexuals? World J Urol. 2015;33(12):2115-2123. doi:10.1007/s00345-015-1562-z
14. Nakamura K, Sakurai T, Sakamoto A, Watanabe K, Ogawa R. Vaginal-mucosal graft metoidioplasty: a novel surgical technique for urethral reconstruction in transmasculine surgery. J Sex Med. 2025;22(7):1275-1279. doi:10.1093/jsxmed/qdaf125
15. 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
16. 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
17. Cohen O, Stranix JT, Zhao L, Levine J, Bluebond-Langner R. Use of a split pedicled gracilis muscle flap in robotically assisted vaginectomy and urethral lengthening for phalloplasty: a novel technique for female-to-male genital reconstruction. Plast Reconstr Surg. 2020;145(6):1512-1515. doi:10.1097/PRS.0000000000006838
18. Jun MS, Shakir NA, Blasdel G, et al. Robotic-assisted vaginectomy during staged gender-affirming penile reconstruction surgery: technique and outcomes. Urology. 2021;152:74-78. doi:10.1016/j.urology.2021.01.024
19. Chen ML, Safa B. Single-stage phalloplasty. Urol Clin North Am. 2019;46(4):567-580. doi:10.1016/j.ucl.2019.07.010
20. Berli JU, Ferrin PC, Buuck C, Cylinder I, Putnam C, Dy GW, Peters BR, Llado-Farrulla M, Sajadi KP, Annen A. Long-term urologic outcomes using the Big Ben method for phalloplasty. Plast Reconstr Surg. 2025;156(2):279e-290e. doi:10.1097/PRS.0000000000012010
21. Waterschoot M, Hoebeke P, Verla W, et al. Urethral complications after metoidioplasty for genital gender affirming surgery. J Sex Med. 2021;18(7):1271-1279. doi:10.1016/j.jsxm.2020.06.023