Appendiceal Onlay / Interposition
The appendix is a pedicled tissue source for upper-tract reconstruction, used either as a tubular interposition conduit or as a spatulated onlay flap for ureteral augmentation. It is most useful for selected right-sided proximal or mid-ureteral strictures where primary ureteroureterostomy would be under tension, but ileal ureter substitution or renal autotransplantation would be excessive.[1][2][3]
This page covers appendiceal ureteroplasty. For oral mucosa alternatives, see Buccal Mucosa Graft Onlay (Ureter) and Augmented Anastomotic Ureteroureterostomy. For bowel substitution of long defects, see Ileal Ureter Substitution. For catheterizable-channel use of the appendix, see Continent Catheterizable Channels.
Why the Appendix Works
The appendix offers a rare combination: small caliber, close proximity to the right ureter, and a vascular pedicle through the mesoappendix.
| Property | Reconstructive Importance |
|---|---|
| Appendicular artery from the ileocolic artery | Makes the appendix a pedicled flap with intrinsic blood supply, unlike free oral mucosa grafts that require graft take from the recipient bed[1][2] |
| Ureter-like caliber | The lumen is often close enough to ureteral diameter for interposition or patch augmentation[2][3] |
| Typical length 6-9 cm, with wide variation | Can bridge many moderate right-sided strictures, but short appendices limit use[2][4] |
| Mucus-producing columnar mucosa | Produces less mucus burden than ileal substitution, but not zero mucus[3] |
| Muscular wall | Permits pro-peristaltic orientation when used as a tubular conduit[3] |
| Right lower-quadrant location | Makes right proximal/mid-ureteral reconstruction natural; left-sided use is exceptional[2][4] |
The key advantage over buccal or lingual mucosa grafts is vascular independence: the appendix arrives with its own blood supply. The key limitation is geography: the appendix usually belongs to the right ureter.
Historical Position
Appendiceal ureteral substitution was described in the early 20th century but remained uncommon while ileal ureter substitution and standard reimplantation dominated long-segment reconstruction. Modern interest has returned for two reasons: robotic suturing makes intracorporeal appendiceal reconstruction feasible, and graft/flap ureteroplasty has created a reconstructive niche between short primary repair and ileal substitution.[1][2]
Yarlagadda et al. reported robotic intracorporeal appendiceal interposition for ureteral stricture disease in 2017, helping launch the contemporary robotic era for this operation.[6]
Configurations
Appendiceal interposition
The appendix is harvested on its mesentery as a tubular conduit. The diseased ureteral segment is excised, and the appendix is interposed between healthy ureteral ends, or occasionally between ureter and renal pelvis or bladder depending on defect location.[6][7][8]
Interposition is a replacement operation: the appendix substitutes for the missing ureteral segment.
Appendiceal onlay flap
The appendix is harvested on its mesentery, opened longitudinally along the antimesenteric border, and laid as a pedicled patch over a longitudinal ureterotomy. The ureter is not fully replaced; the flap augments the narrowed ureteral plate.[5][8][9]
Onlay is an augmentation operation: the appendix widens a narrowed ureter while preserving native ureter continuity.
Augmented roof ureteroplasty
Appendiceal onlay can also be combined with an augmented anastomotic design: the obliterated portion is excised, the posterior ureteral wall is reanastomosed, and the appendix is placed as an anterior or roof onlay to complete the circumference.[5]
Indications
Appendiceal ureteroplasty is considered when all of the following are favorable: right-sided disease, moderate defect length, usable appendix, and a need for vascularized tissue.[1][2][5][11]
| Indication | Why Appendix Is Attractive |
|---|---|
| Right proximal or mid-ureteral stricture | Appendix is nearby and can reach without bowel interposition |
| Defect about 2-8 cm | Too long for primary UU but often short enough for appendix |
| Failed balloon dilation or endoureterotomy | Moves from endoscopic treatment to tissue reconstruction |
| Post-stone-surgery or ureteroscopy stricture | Common right-sided benign indication in series |
| Radiation-induced or fibrotic stricture | Pedicled blood supply may outperform free graft take in hostile beds |
| Need to avoid oral graft harvest | No second donor site |
| Need to avoid ileal ureter morbidity | Less mucus and metabolic burden than ileal substitution |
Published etiologies include nephrolithiasis, iatrogenic injury, failed pyeloplasty or ureteroscopy, radiation, and idiopathic strictures.[7][10][11]
Contraindications and Caution Zones
- prior appendectomy,
- diseased, fibrotic, atretic, inflamed, or ischemic appendix,
- left-sided ureteral disease unless an exceptional lengthening strategy is planned,
- appendix needed for Mitrofanoff appendicovesicostomy or MACE,
- very long stricture beyond appendiceal length,
- active appendiceal/cecal disease,
- extensive right lower-quadrant adhesions or mesenteric limitation,
- malignant ureteral disease requiring oncologic excision and margins.
In patients with neurogenic bladder, bladder augmentation, or anticipated continent catheterizable channel need, preserving the appendix for Mitrofanoff may be more valuable than using it for ureteral reconstruction.[12][16]
Preoperative Planning
Preoperative planning should define:
- Stricture length and location by CT urogram, MR urogram, retrograde/antegrade pyelography, and ureteroscopy when needed.
- Renal salvageability by renal scan, cortical thickness, symptoms, infection burden, and patient goals.
- Appendix availability from surgical history and intraoperative assessment.
- Competing appendix needs such as Mitrofanoff or MACE.
- Backup plan if the appendix is absent or unusable: buccal/lingual mucosa graft, Boari flap, ileal ureter, transureteroureterostomy, or renal autotransplantation.
Intraoperative ureteroscopy and ICG fluorescence can help delineate the stricture and assess ureteral and appendiceal perfusion, particularly during robotic onlay or augmented roof reconstruction.[5]
Appendiceal Interposition Technique
- Expose the right ureter. Position and ports follow right upper/mid-ureteral reconstruction.
- Define the stricture. Use ureteroscopy, stent, ICG, and/or ureterotomy as needed.
- Excise the diseased segment. Debride to healthy ureteral mucosa and preserve periureteral blood supply.
- Harvest the appendix. Mobilize it on the mesoappendix while preserving the appendicular artery; divide from the cecum and close the cecal base.
- Open both appendiceal ends. Tailor length and caliber to the ureteral defect.
- Orient pro-peristaltically. The cecal/base end is typically placed proximally and the tip distally so peristalsis travels toward the bladder.[3][5]
- Perform proximal and distal anastomoses. Use fine absorbable sutures, typically 4-0 or 5-0, over a double-J stent.
- Drain and follow. Stent removal is commonly around 6 weeks, individualized by tissue quality and leak risk.
Interposition is best when the ureteral segment is too diseased to preserve as a plate and the appendix is long enough to replace it.
Appendiceal Onlay Technique
- Expose the strictured right ureter.
- Open the ureter longitudinally across the stricture, preserving continuity whenever possible.
- Harvest the appendix on its mesentery.
- Open the appendix longitudinally along the antimesenteric border to create a flat vascularized flap.
- Lay the appendiceal mucosa toward the ureteral lumen.
- Suture the flap to the ureterotomy edges as an anterior/ventral onlay.
- Place a double-J stent across the reconstruction.
- Confirm vascularity of the appendix and ureteral margins, using ICG if available.
Onlay is best when the ureter is narrowed but still worth preserving as a native plate. It is analogous to oral mucosa onlay ureteroplasty, but with a pedicled flap instead of a free graft.[5][9]
Cecal Flap Extension and Left-Sided Use
Appendiceal ureteroplasty is overwhelmingly right-sided. Komyakov et al. described a modification that uses a flap from the cecal dome to increase the appendiceal reach and anastomotic diameter, including 4 left-sided cases in a 26-patient series. This is an important proof of possibility but remains uncommon and should not be generalized to routine left ureteral reconstruction.[4]
Outcomes
| Series | N | Approach / Configuration | Stricture Length | Success |
|---|---|---|---|---|
| Yarlagadda et al. 2017 | 1 | Robotic interposition | 5 cm | Successful at 10 months[6] |
| Wang et al. 2020 | 9 | Robotic/laparoscopic onlay | 3-4.5 cm | 100% initial success[9] |
| Burns et al. 2020 | 11 | Open/robotic interposition | Not specified | No recurrent stricture at median 363 days[7] |
| Jun et al. 2020 | 13 | Robotic; 62% onlay, 38% interposition | Mean 6.5 cm | 92% among evaluable patients; 1 balloon dilation; 1 unrelated POD0 cardiovascular death[10] |
| Komyakov et al. 2020 | 26 | Open interposition, many with cecal flap extension | Long-segment | 96.2% long-term success over 1-21 years[4] |
| Cho et al. 2024 | 14 | Robotic; 71% onlay, 29% interposition | Mean 4.75 cm | 92.9%; hydronephrosis improved without significant creatinine change[11] |
| Zhang et al. 2025 | 16 | Laparoscopic; 62.5% interposition, 37.5% onlay | 2-5 cm | 93.8% at mean 14.9 months; no significant difference between configurations[8] |
Across modern series, success is generally reported around 92-100%, but the evidence base remains small, retrospective, and concentrated in reconstructive centers.[1][8][10][11]
Complications
| Complication | Notes |
|---|---|
| Recurrent stricture | Main failure mode; may require balloon dilation, endoureterotomy, stenting, re-anastomosis, or alternative reconstruction |
| UTI or pyelonephritis | Cho et al. reported UTI readmission in the multi-institutional robotic experience[11] |
| Urinary leak | Managed with drainage, stent duration, nephrostomy, or reoperation depending on severity |
| Major complications | Higher in some mixed open/robotic series; lower in small robotic series, but numbers are too small for firm comparisons[7][10] |
| Anastomotic stricture at appendiceal junction | Reported in long-term interposition experience[4] |
| Mucus | Usually far less clinically important than ileal substitution, but appendiceal mucosa is not mucus-free[3] |
Advantages
- Pedicled flap with intrinsic blood supply.
- No dependence on recipient-bed graft take.
- No oral donor site.
- Avoids ileal harvest, bowel anastomosis, and classic ileal ureter metabolic complications.
- Appropriate caliber for ureteral reconstruction.
- Less mucus burden than ileal substitution.
- Can be used as interposition, onlay, or augmented roof ureteroplasty.
- Same operative field for right-sided ureteral disease.
Limitations
- Usually right-sided only.
- Requires an intact, healthy, adequately long appendix.
- Competes with Mitrofanoff and MACE needs.
- Length is variable and sometimes inadequate.
- Evidence remains small and retrospective.
- Once used, the appendix is no longer available for future channel construction or re-reconstruction.
- Left-sided use with cecal flap extension is exceptional, not routine.
Comparison With Alternatives
| Feature | Appendiceal Flap | Oral Mucosa Graft | Ileal Ureter |
|---|---|---|---|
| Tissue type | Pedicled vascularized flap | Free graft | Pedicled bowel segment |
| Laterality | Mostly right-sided | Bilateral | Bilateral |
| Best length range | Moderate, limited by appendix length | Moderate, usually up to about 8 cm | Long or pan-ureteral |
| Omental wrap | Usually not required for graft take | Strongly favored | Not a graft-take issue |
| Donor morbidity | Appendectomy/cecal closure | Oral pain, numbness, tightness | Bowel resection/anastomosis |
| Metabolic effects | Minimal | None | Acidosis, mucus, stones, B12/absorption issues depending on segment |
| Evidence maturity | Small series | Growing multi-institutional series | Larger historical experience |
Meta-analysis comparing oral mucosal graft ureteroplasty with ileal ureter replacement found lower complication burden with oral mucosal grafts than ileal ureter, reinforcing why appendix and oral mucosa occupy the tissue-sparing middle ground before bowel substitution.[13]
Appendix in Other Urologic Reconstruction
Mitrofanoff appendicovesicostomy
The appendix is the classic conduit for a continent catheterizable channel from bladder to skin. This is often its most valuable reconstructive use in children and patients with neurogenic bladder, exstrophy, cloacal anomalies, or complex bladder reconstruction.[12][16]
Robot-assisted Mitrofanoff appendicovesicostomy is feasible, and large catheterizable-channel experience supports appendix as first-choice channel when available.[14][15][17][18]
Malone antegrade continence enema
The appendix can also be used for MACE/appendicostomy in patients with fecal incontinence or severe bowel-management needs. If a patient may need both urinary and bowel catheterizable channels, appendix allocation must be planned before using it for ureteral reconstruction.
Decision Framework
Choose appendix when:
- the stricture is right-sided,
- the defect is moderate length,
- the appendix is intact and healthy,
- the patient does not need appendix for Mitrofanoff or MACE,
- a pedicled vascularized flap is preferable to a free graft,
- ileal substitution would be excessive.
Choose oral mucosa graft when the appendix is absent, the stricture is left-sided, or a graft is more anatomically straightforward. Choose ileal ureter when the defect is too long or complex for appendix or oral mucosa. Choose renal autotransplantation or transureteroureterostomy only when substitution and bladder-based options are poorly suited.
Operative Pearls
- Inspect the appendix before committing; have a backup plan ready.
- Preserve the appendicular artery and mesoappendix.
- Do not sacrifice a future Mitrofanoff casually in a neurogenic-bladder patient.
- Onlay works best when the ureteral plate is worth preserving.
- Interposition works best when the diseased segment should be removed.
- Place interposition in pro-peristaltic orientation when feasible.
- Do not force left-sided reconstruction unless the appendix truly reaches without tension and the team has a mature plan.
References
1. Bello D, Van Shufflin M, Hofer MD. Expanding the armamentarium: perspectives on buccal mucosal grafts and appendiceal flaps in ureteral reconstructive surgery. J Clin Med. 2025;14(21):7681. doi:10.3390/jcm14217681.
2. O'Rourke TK, Gm M, Patel HV, et al. The urologist and the appendix: a review of appendiceal use in genitourinary reconstructive surgery. Urology. 2022;159:10-15. doi:10.1016/j.urology.2021.10.007.
3. Xiong S, Zhu W, Li X, et al. Intestinal interposition for complex ureteral reconstruction: a comprehensive review. Int J Urol. 2020;27(5):377-386. doi:10.1111/iju.14222.
4. Komyakov B, Ochelenko V, Guliev B, Shevnin M. Ureteral substitution with appendix. Int J Urol. 2020;27(8):663-669. doi:10.1111/iju.14268.
5. Gabrielson A, Li O, Cohen AJ. Robotic-assisted augmented roof ureteroplasty with appendiceal onlay flap. Urology. 2023;176:243-245. doi:10.1016/j.urology.2023.02.027.
6. Yarlagadda VK, Nix JW, Benson DG, Selph JP. Feasibility of intracorporeal robotic-assisted laparoscopic appendiceal interposition for ureteral stricture disease: a case report. Urology. 2017;109:201-205. doi:10.1016/j.urology.2017.08.017.
7. Burns ZR, Sawyer KN, Selph JP. Appendiceal interposition for ureteral stricture disease: technique and surgical outcomes. Urology. 2020;146:248-252. doi:10.1016/j.urology.2020.07.078.
8. Zhang B, Chen J, Chen X, et al. Laparoscopic ureteroplasty for the treatment of long ureteral strictures with appendiceal interposition and appendiceal onlay flap: technical description and initial experience. World J Urol. 2025;43(1):678. doi:10.1007/s00345-025-06048-8.
9. Wang J, Xiong S, Fan S, et al. Appendiceal onlay flap ureteroplasty for the treatment of complex ureteral strictures: initial experience of nine patients. J Endourol. 2020;34(8):874-881. doi:10.1089/end.2020.0176.
10. Jun MS, Stair S, Xu A, et al. A multi-institutional experience with robotic appendiceal ureteroplasty. Urology. 2020;145:287-291. doi:10.1016/j.urology.2020.06.062.
11. Cho EY, Chaudry AE, Puri D, et al. Outcomes of robot-assisted appendiceal ureteroplasty from a multi-institutional experience. Urology. 2024;192:136-140. doi:10.1016/j.urology.2024.07.042.
12. Cain MP, Casale AJ, King SJ, Rink RC. Appendicovesicostomy and newer alternatives for the Mitrofanoff procedure: results in the last 100 patients at Riley Children's Hospital. J Urol. 1999;162(5):1749-1752. doi:10.1016/s0022-5347(05)68230-4.
13. You Y, Gao X, Chai S, et al. Oral mucosal graft ureteroplasty versus ileal ureteric replacement: a meta-analysis. BJU Int. 2023;132(2):122-131. doi:10.1111/bju.15994.
14. Cerchia E, Serpentino M, Nguyen Duy V, et al. Minimally invasive Mitrofanoff in children: versatile laparoscopic strategies-from low-resource to non-robotic high-cost settings in an exploratory case series. J Clin Med. 2026;15(5):1954. doi:10.3390/jcm15051954.
15. Barashi NS, Rodriguez MV, Packiam VT, Gundeti MS. Bladder reconstruction with bowel: robot-assisted laparoscopic ileocystoplasty with Mitrofanoff appendicovesicostomy in pediatric patients. J Endourol. 2018;32(S1):S119-S126. doi:10.1089/end.2017.0720.
16. Sumfest JM, Burns MW, Mitchell ME. The Mitrofanoff principle in urinary reconstruction. J Urol. 1993;150(6):1875-1877. doi:10.1016/s0022-5347(17)35921-9.
17. Famakinwa OJ, Rosen AM, Gundeti MS. Robot-assisted laparoscopic Mitrofanoff appendicovesicostomy: technique and outcomes of extravesical and intravesical approaches. Eur Urol. 2013;64(5):831-836. doi:10.1016/j.eururo.2013.05.007.
18. Wille MA, Zagaja GP, Shalhav AL, Gundeti MS. Continence outcomes in patients undergoing robotic assisted laparoscopic Mitrofanoff appendicovesicostomy. J Urol. 2011;185(4):1438-1443. doi:10.1016/j.juro.2010.11.050.