ICG-Guided Flap / Graft Perfusion Assessment in Urethral Reconstruction
ICG-guided flap and graft perfusion assessment is an emerging intraoperative adjunct in urethral reconstruction that uses indocyanine green near-infrared fluorescence angiography (ICG-FA) to provide objective, real-time, semiquantitative evaluation of tissue perfusion — replacing or augmenting the surgeon's traditional reliance on subjective visual and tactile assessment.[1] The evidence base is early but growing across adult urethroplasty, pediatric hypospadias repair, and ureteral reconstruction, and an international Delphi consensus has declared the technology no longer experimental in plastic and reconstructive surgery.[2]
For ICG mechanism, FDA dosing limits, safety profile (iodine-allergy contraindication), camera hardware, broader GU applications (ureteral identification, lymphatic mapping, VUA, fistula localization), and adverse events, see the canonical Indocyanine Green (ICG) hub. This page is intentionally limited to urethral-reconstruction-specific applications, perfusion thresholds, and outcomes.
Applications in Urethral Reconstruction
1. Graft-bed assessment in substitution urethroplasty
Zhang 2024 described a standardized protocol for ICG use in open urethral reconstruction with two imaging modes: a black-and-white qualitative brightness mode and a quantitative perfusion mode comparing the tissue of interest to a control area of similar tissue type.[1] In dorsal onlay buccal mucosal graft urethroplasty, graft-bed perfusion was compared to the proximal erectile bodies. A proposed perfusion cutoff of ≥ 60% of control correlated with the surgeon's clinical judgment of adequate graft-bed quality. This matters because graft take depends entirely on imbibition and inosculation from the recipient bed — an objectively hypoperfused bed predicts graft failure.
2. Flap perfusion in perineal urethrostomy (Blandy flap)
In the same Zhang series, ICG was used to assess a Blandy flap during perineal urethrostomy both before and after mobilization. A flap-perfusion cutoff of ≥ 40% of control was proposed based on existing flap-reconstruction literature, with the goal of tailoring flap design to avoid ischemia and necrosis.[1]
3. Staged urethroplasty after failed hypospadias repair
In complex staged substitution urethroplasty after prior hypospadias repair, ICG facilitated a more limited excision and shorter graft inlay by objectively delineating well-perfused from poorly perfused tissue, preserving viable tissue that might otherwise have been excised on visual inspection alone.[1]
4. Onlay preputial-island-flap hypospadias repair
Paraboschi 2023 first reported ICG-guided assessment of a preputial island flap during onlay urethroplasty in a 13-month-old with mid-shaft hypospadias. Using the EleVision IR system (Medtronic) and ICG 0.15 mg/kg, fluorescence appeared within 80 seconds of injection and helped define the proximal resection margin of the preputial flap to ensure adequate vascularization of the tissue used for urethral reconstruction.[3]
5. Neourethral coverage in TIP (tubularized incised plate) urethroplasty
Wang 2026 evaluated ICG-FA with the SPY Elite system in 14 boys undergoing TIP hypospadias repair. Perfusion was categorized as well-perfused or poorly perfused based on grayscale fluorescence intensity:[4]
| Cohort | n | Necrosis | Urethrocutaneous fistula |
|---|---|---|---|
| Well-perfused | 10 | 0% (1 glans dehiscence only) | 0% |
| Poorly perfused | 4 | 100% (ventral necrotic crust) | 75% (3/4) |
No ICG-related adverse events were observed.
6. Open ureteral reconstruction — instructive parallel
Hebert 2024 provides the most rigorous reconstructive parallel. In 39 patients (80% radiation-induced strictures), ICG-NIFI changed intraoperative decision-making in 63% of cases. Discordance between subjective white-light and objective ICG ureteral perfusion occurred in 61% of ureters, and ICG drove significantly longer ureter resection (mean 3.6 vs 1.8 cm, p = 0.001). The ureteroenteric / ureteroneocystostomy stricture rate was only 1.8% at median 23.4 months — supporting the hypothesis that ICG-guided resection margins improve outcomes.[5]
For the technique-page on this application, see Ureteroenteric Anastomotic Stricture Repair and the broader Upper Tract Reconstruction atlas.
Perfusion Thresholds
| Context | Proposed Threshold | Source |
|---|---|---|
| Graft bed (dorsal onlay urethroplasty) | ≥ 60% of control | Zhang 2024[1] |
| Blandy flap (perineal urethrostomy) | ≥ 40% of control | Zhang 2024[1] |
| Perforator flap (animal model) | ~27% predicts necrosis; ~59% predicts survival; viability threshold ~40–50% | Monahan 2014[6] |
| Head & neck free flaps | 20–50% reduction from reference = impaired | H&N reconstruction SR[7] |
These thresholds are preliminary and not yet validated in large prospective urethral cohorts. Standardization across camera systems, tissue types, and clinical contexts remains an open challenge.[7]
Practical Workflow
- Dose — pediatric hypospadias 0.15 mg/kg; adult perfusion 1.25–5 mg IV per FDA label, with cumulative ceiling 2 mg/kg / day. Per the international Delphi consensus, image 20–60 seconds after injection at a camera-to-tissue distance of 20–30 cm.[2][3]
- Hardware — SPY Elite (Stryker), EleVision IR (Medtronic), and the da Vinci Firefly mode have all been used in published urethroplasty cases.[1][3][4]
- Repeatability — short hepatic clearance allows repeat injections within a single procedure.
- Confounders — vasopressors, hypothermia, ambient light, and tissue edema all affect perfusion readings; document conditions when interpreting borderline values.[2]
For full FDA-label dosing, iodine-allergy contraindication, anaphylaxis precautions, and camera-system technical detail, refer to the foundations ICG hub.
Where It Fits in Urethral Reconstruction
ICG-FA is best understood as an intraoperative quality-assurance adjunct, not a stand-alone technique. Its value is highest in scenarios where tissue quality is uncertain and the cost of graft / flap failure is high:
- Failed prior hypospadias repair with a depleted, scarred urethral plate.
- Radiated or otherwise hostile graft beds in adult substitution urethroplasty.
- Staged BMG repairs where conservative excision preserves usable tissue.
- Perineal urethrostomy / flap-based reconstruction with concern for apical ischemia.
- Pedicled preputial / fasciocutaneous flap design where margin viability is the failure-mode of interest.
Direct outcome benefit vs unguided reconstruction has not yet been established in randomized urethral data; the strongest supportive evidence is the Wang 2026 TIP-cohort signal (0% vs 75% fistula by perfusion category) and the Hebert 2024 ureteral parallel (63% decision-change, 1.8% stricture).
Limitations
- Urethroplasty-specific evidence is limited to case reports, small feasibility series, and one TIP cohort.
- Perfusion thresholds are not yet standardized across camera systems, tissue types, and clinical contexts.[7]
- Vasopressor use, body temperature, ambient light, and tissue edema confound perfusion readings.[2]
- The technology adds cost (camera systems, ICG dye) and requires familiarity with interpretation.
- Iodine-allergy hypersensitivity is the only absolute contraindication; see foundations ICG for full safety detail.
References
1. Zhang X, Lin JS, Raines A, et al. Semiquantitative tissue perfusion assessment using indocyanine green in complex open urethral reconstruction. Urology. 2024;185:e149-e151. doi:10.1016/j.urology.2023.11.032.
2. Schols RM, Dip F, Lo Menzo E, et al. Delphi survey of intercontinental experts to identify areas of consensus on the use of indocyanine green angiography for tissue perfusion assessment during plastic and reconstructive surgery. Surgery. 2022;172(6S):S46-S53. doi:10.1016/j.surg.2022.04.015.
3. Paraboschi I, Gnech M, Minoli DG, et al. Indocyanine green (ICG)-guided onlay preputial island flap urethroplasty for the single-stage repair of hypospadias in children: a case report. Int J Environ Res Public Health. 2023;20(13):6246. doi:10.3390/ijerph20136246.
4. Wang Y, Du G, Guo F, et al. Preliminary use of ICG-FA in predicting the blood perfusion of neourethra covering in TIP hypospadias repair. Urology. 2026. doi:10.1016/j.urology.2026.04.044.
5. Hebert KJ, Bearrick E, Anderson KT, Viers BR. High rates of discordant ureteral perfusion during open ureteral reconstruction with indocyanine green: does near-infrared fluorescence imaging change management or stricture outcomes? Urology. 2024;190:117-122. doi:10.1016/j.urology.2024.04.055.
6. Monahan J, Hwang BH, Kennedy JM, et al. Determination of a perfusion threshold in experimental perforator flap surgery using indocyanine green angiography. Ann Plast Surg. 2014;73(5):602-606. doi:10.1097/SAP.0b013e318276da2d.
7. Poen WAFM, Nijssen DJ, van 't Hof LWP, et al. The role of indocyanine green fluorescence angiography in head and neck reconstruction: a systematic review. J Craniomaxillofac Surg. 2026;54(6):104477. doi:10.1016/j.jcms.2026.104477.