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 or bulbar segment of urethral lengthening and one of the most technically demanding portions of metoidioplasty and phalloplasty.[1][2][3]
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] In Chesson and colleagues’ staged technique, 3–4 cm of anterior vaginal wall was mobilized from the distal urethra and rolled to extend the urethra to the clitoral base; the labia minora were sutured over the lengthened urethra before later phalloplasty.[8]
| Feature | Practical Implication |
|---|---|
| Mucosal-lined local tissue | Better conceptual match to urethral lining than hair-bearing skin |
| Pedicled vascularity | Its vaginal-wall vascular supply permits a long, narrow flap.[6] |
| 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 |
In Chesson and colleagues’ early series, all five initial phalloplasties without urethral lengthening developed fistulas; after a change to staged colpocleisis with anterior vaginal-wall preservation and urethral lengthening, 14/20 phalloplasties had no fistula (p = 0.0087).[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. A labia minora ring flap can form the fixed urethra in RFFF phalloplasty or the entire lengthened urethra in metoidioplasty; a separate pedicled labia minora flap has been described for ALT and SCIP phalloplasty.[24][9] A 2024 retrospective ring-flap series reported fistula in 71/242 RFFF phalloplasties and 11/69 metoidioplasties, and stricture in 44/242 and 4/69, respectively, at mean 37-month follow-up; 56/71 RFFF fistulas closed spontaneously.[24]
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. The series is retrospective and has no comparator.[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.[10][11][12] This is the Belgrade / modified Belgrade concept.[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 2 fistulas in 38 patients (median follow-up 22 months) with combined buccal mucosa graft and labia minora flap urethral lengthening in metoidioplasty. A later retrospective comparison included 207 regular follow-up participants from 298 patients who underwent metoidioplasty (median follow-up 39 months), all with a buccal graft; fistulas were less frequent (5.7% vs 14.3%) and standing voiding more frequent (93% vs 87.8%) with the labia minora flap than with a dorsal clitoral skin flap.[11][12]
Vaginal Mucosal Graft
Vaginal mucosa can also be used as a free graft for prefabrication of the phallic urethra (pars pendulans). Zhang and colleagues found vaginal mucosa histologically similar to buccal mucosa and closer to urethral epithelium than forearm skin, with good revascularization after prefabrication. Their retrospective series of 22 patients (median follow-up 25 months) reported a 4.5% stricture rate and a 31.8% fistula rate.[13]
A 2025 seven-patient report of vaginal-mucosal graft metoidioplasty found one fistula requiring closure and one mild stricture under observation at median five-month follow-up. The combined metoidioplasty, hysterectomy, oophorectomy and vaginal-closure operation had median blood loss of 1,610 mL; the authors described blood loss during flap and graft harvest as high.[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, in 24 patients, 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, in a 21-patient series, and remains a specialized pathway.[16]
Vaginectomy and Buttressing
Vaginectomy is a reconstructive maneuver that can improve pars fixa coverage. In a 224-patient phalloplasty-with-urethral-lengthening series, Massie and colleagues reported in a retrospective comparison that urethral complications occurred in 27% of patients with vaginectomy (215) and 67% of those with vaginal preservation (9), with lower odds of both stricture and fistula after vaginectomy.[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. A vaginal mucosa and gracilis flap was used in all 36 patients in whom a pars fixa was created; median estimated blood loss was 200 mL, median length of stay was 3 days, and 4 of 42 patients had vaginectomy-related complications, all resolved conservatively.[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 who underwent revision surgery with a reconstructive urologist for complications of masculinizing genital reconstruction performed elsewhere, 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] A two-center retrospective series of 41 pars fixa strictures used Heineke–Mikulicz repair for mobile strictures <20 mm (44% success; 16 patients), ventral onlay buccal graft for strictures <40 mm unsuitable for that repair (92%; 13 patients), and two-stage Johanson repair for complex or at least 40-mm strictures (75%; 12 patients).[25] Mean follow-up was 30.2 months, and success meant no reintervention after at least 12 months.[25]
| Stricture Scenario | Typical Repair Direction |
|---|---|
| Very short, early, non-obliterative narrowing | After neophalloplasty, defer endoscopic incision or urethroplasty until at least six months after surgery ; use suprapubic diversion for severe obstruction, recurrent UTI, or retention during healing. Once tissues stabilize, one cautious endoscopic attempt may be considered for a short non-obliterative anastomotic stricture, although recurrence is common; the EAU 2026 guideline recommends against more than two endoscopic incisions unless treatment is palliative .[22] |
| Anastomotic stricture with healthy adjacent tissue | For a very short (<1.5 cm), low-grade narrowing, Heineke–Mikulicz repair is an option. For a nearly or completely obliterative anastomosis, consider excision and primary anastomosis, graft augmentation, or staging according to length, tension, and tissue quality.[22] |
| Long or scarred segment | Select repair by site and tissue quality. For a neophallic stricture requiring open reconstruction, EAU 2026 recommends staged urethroplasty ; for an isolated fixed-part stricture, single-stage dorsal inlay graft repair is possible. Buccal mucosa graft and local flap reconstructions have also been reported, with local flap support when ventral tissue is insufficient. A systematic review reported 0–25% recurrence after staged repair, mainly for long pendulous strictures, in heterogeneous retrospective series.[3][22][23] |
| 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 |
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 single-surgeon series with at least six months’ follow-up: 71 of 73 patients proceeded to stage 2; the authors reported stricture in 8% and urethrocutaneous fistula in 16.4% after stage 2, while 96% of the full cohort ultimately achieved standing voiding.[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.
- 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
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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
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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
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22. European Association of Urology. "EAU Guidelines on Urethral Strictures: 8. Disease Management in Transgender Patients." EAU Guidelines. 2026. Guideline chapter.
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24. Sun HH, Gupta S, Chen ML. "Urethral outcomes of the labia minora ring flap for metoidioplasty and phalloplasty." Urology. 2024;188:156-161. doi:10.1016/j.urology.2024.03.028
25. Jung H, Chen ML, Wassersug R, et al. "Urethroplasty outcomes for pars fixa urethral strictures following gender-affirming phalloplasty and metoidioplasty: a retrospective study." Urology. 2023;182:89-94. doi:10.1016/j.urology.2023.07.009