Filiforms & Followers
Two-component coaxial urethral-dilation system. A thin, flexible filiform leader (2–6 Fr) negotiates a tight or near-obliterative stricture, followed by threaded hollow "followers" in graduated French sizes that screw onto the filiform's proximal threaded end and dilate the stricture sequentially. It is the classic instrument for a stricture too tight to admit a standard sound or catheter, and the historical fallback when bladder drainage is needed but a Foley will not pass.[1][2]
Design
Filiforms (leaders)
- Diameter. Extremely thin, typically 2–6 Fr (0.66–2 mm); the smallest urethral instruments available.
- Material. Traditionally woven silk or gum-elastic ("bougie"); modern leaders are plastic / polyethylene.
- Flexibility. Semi-rigid to flexible, allowing negotiation of tortuous strictures that rigid sounds cannot enter.
- Tip configurations, selected to match stricture geometry:
- Straight. For axially aligned strictures.
- Coudé (curved). Angled tip to clear an elevated bladder neck or eccentric stricture.
- Spiral / corkscrew. For irregular or eccentric lumens.
- Filiform bougie. Tapered whip-like tip for tight obliterative segments.
- Proximal end. Threaded male connector that accepts the screw-on followers.
- Length. Approximately 35 cm, reaching from meatus to bladder.
Followers
- Diameter. Graduated, typically 6–8 Fr up to 24 Fr in 2-Fr increments.
- Material. Historically gum-elastic; modern followers are metal or rigid plastic.
- Hollow design with a threaded female connector at the tapered leading end that mates with the filiform.
- Smooth taper at the leading end matches the filiform diameter, creating a seamless transition that limits mucosal trauma during passage.
Reconstructive-Urology Uses
Filiforms-and-followers are the dilation system for strictures too tight for any other instrument and the historical fallback for failed catheterization:[1][3]
- Very tight or near-complete urethral stricture. Luminal diameter too narrow for the smallest Van Buren or Dittel sound.
- Failed catheterization with urgent need for bladder drainage. Before flexible cystoscopy this was the standard fallback before suprapubic tube; it is now generally supplanted by bedside flexible cystoscopy with guidewire-assisted catheter placement when available.[3]
- Tortuous / irregular strictures. The flexible filiform tip can find eccentric lumens that a rigid sound cannot.
- Resource-limited / equipment-unavailable settings. When flexible cystoscopy and fluoroscopy are not at hand, filiform-and-follower remains a valid blind technique.
For procedural context, see DVIU and Urethral Dilation.
Technique
- Topical 2% lidocaine instilled per urethra; supine position; generous sterile lubricant.
- Filiform passage. Advance the leader gently through the urethra. If resistance is met at the stricture:
- Try a different tip configuration (coudé, spiral) before forcing.
- Multiple-filiform technique. Insert several filiforms simultaneously (up to 5–6). They fill the false passages and dead-ends; the next leader is more likely to find the true lumen. A classic urologic maneuver.
- Confirm intravesical position by loss of resistance as the filiform enters the bladder and by the length of filiform advanced (should approximate expected urethral length).
- Follower attachment. Once the filiform is confirmed in the bladder, screw the smallest follower onto its proximal end and advance.
- Sequential dilation. Exchange followers in ascending French sizes. The filiform stays in place throughout as the guide rail. Typical endpoint is approximately 24 Fr.[4]
- Catheter placement. Pass a Council-tip catheter (with an open tip) over the filiform or an exchanged guidewire for bladder drainage.
Comparison with Other Dilation Methods
| Feature | Filiform + Followers | Van Buren | S-Shaped Coaxial | Balloon Dilator |
|---|---|---|---|---|
| Minimum stricture caliber | 2–6 Fr (tightest accommodated) | ~ 8 Fr (smallest sound) | Must accept guidewire (~ 3 Fr) | Must accept guidewire |
| Guidance | Blind (tactile, flexible leader) | Blind (tactile, rigid) | Over guidewire ± fluoroscopy | Direct vision or fluoroscopy |
| Flexibility | Semi-flexible filiform | Rigid | Flexible guidewire | Flexible balloon |
| Components | Multi-component (filiform + threaded followers) | Single instrument per size | Single instrument over wire | Wire + balloon + inflator |
| Force mechanism | Axial (coaxial shearing) | Axial (shearing) | Axial (shearing) | Radial |
| False-passage risk | Blind; the flexible tip may help | Rigid and blind | Wire-guided | Visualized and wire-guided |
| Best use | Very tight / near-obliterative stricture, failed catheterization | Routine moderate stricture; intraoperative calibration | Recurrent stricture with prior false-passage risk | Direct-vision dilation, drug-coated delivery |
Outcomes
In the Heyns 1998 RCT, 210 men were randomized to filiform dilation (106) or internal urethrotomy (104). Among men still stricture-free at 3 months after a single treatment (about 70% of the cohort), the estimated stricture-free rate was 55–60% at 24 months and 50–60% at 48 months. A second treatment for recurrence at 3 months added little at 24 months and nothing at 48 months, and a third treatment had no value.[7] The Cochrane review of this trial found no significant difference between dilatation and urethrotomy in the proportion stricture-free at three years or in median time to recurrence.[4]
The 2014 SIU/ICUD consultation reviewed dilation, internal urethrotomy and stenting of male anterior urethral strictures and graded the evidence.[8]
Safety Profile
Complications specific to filiforms-and-followers (these are practical hazards of the design, not figures from a trial):[1][6]
- Filiform knotting in the urethra or bladder. Particularly with excessive advance or intravesical coiling.
- Filiform breakage. Leaves a retained intraurethral or intravesical fragment that needs endoscopic retrieval.
- Filiform bending / deformation. Prevents follower passage and aborts the procedure.
- False-passage creation. Lower than with rigid sounds because of the flexible tip, but still possible with forceful blind passage.[1]
- Urethral hemorrhage, UTI, bacteremia. Standard urethral-instrumentation risks.[6]
Modern Alternatives and Declining Use
Filiform-and-follower use has declined as wire- and vision-based alternatives have spread:[3][5]
- Hydrophilic Glidewire technique (Freid & Smith 1996). A hydrophilic guidewire passed per urethra in filiform-like fashion, exchanged for a standard wire, then coaxial dilation. Successful in 19 of 20 attempts in a small series, several after failed filiform passage. The authors recommended it over filiforms and followers when cystourethroscopy is not immediately available.[5]
- Bedside flexible cystoscopy with guidewire-assisted catheter placement (Beaghler 1994). Successful in 52 of 54 patients with failed catheterization, with no complications reported; it has largely replaced the traditional filiform-and-follower role in the acute "can't pass a catheter" setting wherever a flexible scope is available.[3]
- Direct-vision balloon dilation. Radial force under endoscopic vision.[1]
- S-shaped coaxial dilators. Single-instrument guidewire-tracked alternative for the curved male urethra.[2]
Filiforms and followers remain on the urology tray for the case where modern equipment is unavailable or the stricture admits nothing else.
See also: Van Buren Sound, Dittel Sound, S-Shaped Coaxial Dilators, Balloon Dilator, DVIU and Urethral Dilation.
References
1. Gelman J, Liss MA, Cinman NM. "Direct vision balloon dilation for the management of urethral strictures." J Endourol. 2011;25(8):1249–51. doi:10.1089/end.2011.0034
2. 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
3. Beaghler M, Grasso M, Loisides P. "Inability to pass a urethral catheter: the bedside role of the flexible cystoscope." Urology. 1994;44(2):268–70. doi:10.1016/s0090-4295(94)80148-7
4. 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
5. Freid RM, Smith AD. "The Glidewire technique for overcoming urethral obstruction." J Urol. 1996;156(1):164–5.
6. Verla W, Oosterlinck W, Spinoit AF, Waterloos M. "A comprehensive review emphasizing anatomy, etiology, diagnosis, and treatment of male urethral stricture disease." Biomed Res Int. 2019;2019:9046430. doi:10.1155/2019/9046430
7. Heyns CF, Steenkamp JW, De Kock ML, Whitaker P. "Treatment of male urethral strictures: is repeated dilation or internal urethrotomy useful?" J Urol. 1998;160(2):356–8. doi:10.1016/s0022-5347(01)62894-5
8. Buckley JC, Heyns C, Gilling P, Carney J. "SIU/ICUD consultation on urethral strictures: dilation, internal urethrotomy, and stenting of male anterior urethral strictures." Urology. 2014;83(3 Suppl):S18–22. doi:10.1016/j.urology.2013.08.075