S-Shaped Coaxial Dilators
Double-curve ("S-shaped") urethral dilators passed over a pre-placed guidewire — the engineering compromise between the anatomical conformity of the curved Van Buren sound and the safety of guidewire-assisted dilation historically delivered by straight coaxial dilators or the Balloon Dilator. The S-shape matches the natural double curve of the male urethra (pendulous urethra curving inferiorly, then bulbar urethra curving superiorly around the perineal body); the coaxial track over a guidewire constrains the dilator to the true lumen and eliminates the principal complication of blind metal-bougie dilation — false-passage creation. Originally described by Herschorn and Carrington (2007).[1]
Design and Rationale
- Double-curve (S-shaped) profile along the working length — matches the pendulous → bulbar urethral curvature without the blind manipulation required by the single-curve Van Buren.[1]
- Coaxial central lumen for over-the-wire passage — designed for a standard 0.035" guidewire (PTFE-coated or hydrophilic Glidewire) pre-placed across the stricture under cystoscopic or fluoroscopic vision.
- French sizing in sequential graduated increments, allowing stepwise dilation from baseline caliber to the therapeutic endpoint.
- Single-instrument-per-size simplicity — no threaded follower assembly as with filiform and follower systems.
The Herschorn / Carrington design emerged from prototype iteration to settle on the S-curve geometry and insertion technique that allowed smooth passage from meatus to bladder neck in routine practice.[1]
Reconstructive-Urology Uses
- Recurrent bulbar or pan-urethral stricture requiring dilation when blind metal-bougie passage has previously created false passage or carries high risk.
- Anterior-urethral dilation in the patient with prior failed DVIU where preservation of the true lumen is critical for the next intervention.
- Pediatric urethral dilation — guidewire-assisted dilation is particularly safe in pediatric patients (Dewan 2003: 32 pediatric cases, no false passages, no sepsis), and the S-shape adapts the same advantage to the adult urethra.[3]
- As a bridge to definitive urethroplasty in the symptomatic patient awaiting reconstruction.
- Catheter exchange over wire through a difficult-to-access stricture — the S-shape navigates the urethra without re-instrumenting blindly.
For full procedural context, see DVIU and Urethral Dilation.
Comparison of Urethral Dilation Methods
| Feature | S-shaped coaxial | Van Buren | Straight coaxial | Filiform + followers | Balloon dilator |
|---|---|---|---|---|---|
| Curvature | Double curve (S) matching pendulous + bulbar | Single distal J-curve | Straight | Flexible filiform tip | N/A (inflatable balloon) |
| Guidewire-guided | Yes | No (blind) | Yes | No (threaded coaxial assembly) | Yes |
| Conforms to male urethra | Excellent | Good | Poor | Variable | N/A |
| False-passage risk | Low — wire-constrained | Higher — blind, rigid | Low — wire-constrained, but fights the curve | Moderate | Lowest (direct vision) |
| Force mechanism | Axial (shearing) | Axial (shearing) | Axial (shearing) | Axial (coaxial) | Radial |
| Setup overhead | Single instrument over wire | Single instrument blind | Single instrument over wire | Multi-component threaded assembly | Wire + balloon + inflator |
The defining advantages over the Van Buren are guidewire-tracked safety and better anatomic fit. The defining advantage over the straight coaxial dilator is anatomic conformity — the straight coaxial fights the bulbar curve and demands more axial force.[1] The defining advantage over the balloon dilator is mechanical simplicity and lower cost; the balloon retains the advantage of radial-vs-axial force and direct-vision dilation.[2][4]
Technique
- Cystoscopic or fluoroscopic guidewire placement across the stricture into the bladder. The AUA 2023 guideline explicitly notes that urethral strictures may be dilated over a guidewire to prevent false-passage formation — Freid and Smith's Glidewire technique is the standard.[5][6]
- Sequential dilation — pass S-shaped dilators in ascending French sizes over the wire, oriented so the S-curve tracks the pendulous → bulbar bend.
- Catheter placement — after the desired caliber is achieved, a Foley can be passed over the same guidewire to maintain access.
- Antibiotic prophylaxis — standard for any urethral instrumentation.
Safety Profile
- False passage — markedly reduced vs blind metal-bougie dilation because the dilator is constrained to the wire-defined true lumen.[1][3]
- Urethral hemorrhage, UTI, bacteremia — standard urethral-instrumentation risks; comparable to other dilation modalities.
- Stricture recurrence — the underlying biologic problem (mucosal rupture → fibroblast activation) is not solved by changing the instrument; durability remains determined by stricture length, etiology, and prior treatment burden. Balloon dilation has been proposed to improve healing via radial rather than axial force, but published data have not shown a clear long-term recurrence advantage over sound-based methods.[4]
Current Practice Context
Despite the theoretical advantages of guidewire-assisted dilation, blind metal-bougie dilation remains the majority practice: the Kaçtan 2026 Turkish urology survey found 47% blind metal-bougie, 23% plastic dilator over guidewire, and 26% disposable catheter — with non-metal, guidewire-based methods significantly more common in academic centers (p = 0.04).[7] The 2026 EAU guideline emphasizes that single-session dilation offers outcomes similar to DVIU with reduced complications when visually controlled.[8]
Limitations
- Does not address the fibrotic substrate — like all axial-shearing dilators, the S-shaped coaxial stretches and ruptures scar; recurrence remains the limiting factor in long, dense, or radiation-induced strictures.
- Requires a guidewire to be passable — in a completely obliterated stricture, a filiform-and-follower system or open exploration may still be necessary before any coaxial dilator can be used.
- Not a substitute for urethroplasty in recurrent, long, penile, ischemic, or radiation-induced disease — durability is best for short bulbar strictures regardless of dilation method.
See also: Van Buren Sound, Dittel Sound, Haygrove Sound, Balloon Dilator, DVIU and Urethral Dilation.
References
1. Herschorn S, Carrington E. "S-shaped coaxial dilators for male urethral strictures." Urology. 2007;69(6):1199–201. doi:10.1016/j.urology.2007.02.066
2. Wong SS, Aboumarzouk OM, Narahari R, O'Riordan A, Pickard R. "Simple urethral dilatation, endoscopic urethrotomy, and urethroplasty for urethral stricture disease in adult men." Cochrane Database Syst Rev. 2012;12:CD006934. doi:10.1002/14651858.CD006934.pub3
3. Dewan PA, Gotov E, Chiang D. "Guide wire-assisted urethral dilatation for urethral strictures in pediatric urology." J Pediatr Surg. 2003;38(12):1790–2. doi:10.1016/j.jpedsurg.2003.08.035
4. González-Espinosa C, Castro-Nuñez P, Averbeck MA, et al. "Diagnosis and treatment of urethral stricture in men with neurogenic lower urinary tract dysfunction: a systematic review." Neurourol Urodyn. 2022;41(6):1248–57. doi:10.1002/nau.24982
5. Freid RM, Smith AD. "The Glidewire technique for overcoming urethral obstruction." J Urol. 1996;156(1):164–5.
6. Wessells H, Morey A, Souter L, Rahimi L, Vanni A. "Urethral stricture disease guideline amendment (2023)." J Urol. 2023;210(1):64–71. doi:10.1097/JU.0000000000003482
7. Kaçtan Ç, Abali T, Vosoughi O, et al. "Management of urethral stricture: translating guidelines into clinical practice." World J Urol. 2026;44(1):212. doi:10.1007/s00345-026-06312-5
8. Campos-Juanatey F, Barratt R, Chan G, et al. "European Association of Urology guidelines on urethral strictures: summary of the 2026 guidelines. Update in recommendations for endoluminal management of male anterior urethral strictures." Eur Urol. 2026. doi:10.1016/j.eururo.2026.04.021