Five years of experience with the FiLaC™ laser for fistula-in-ano management: long-term follow-up from a single institution

Minimally invasive fistula management, which balances clinical effectiveness with an absence of post-operative functional disturbance has been the “holy grail” of anal fistula treatment since Tasci first presented a novel “fistulectome” device in 2003, designed to mechanically core out the primary fistula track [15]. This approach has been extended by Rojanasakul and others with the ligation of the intersphincteric fistula tract (LIFT) procedure [16, 17]. Further extension of this idea towards totally endofistular therapy was advanced by our group’s preliminary report of the FiLaC™ procedure [7] with success in 9/11 cases over a median follow-up of 7.4 months and by Meinero and Mori [3, 18], with their "video-assisted anal fistula treatment” (VAAFT™) technique. These latter two methods were first reported in 2011 in Techniques in Coloproctology.

This study reports the long-term outcomes of a cohort of 117 patients presenting with anal fistulae where there was a unit policy towards formal flap closure of the internal fistula opening and as such represents (as far as we are aware) the largest series of FiLaC™—treated anal fistula cases currently available. The primary success rate over a median follow-up of 25.4 months was moderate, and the secondary success rate was high regardless of whether the fistula is cryptoglandular or Crohn’s related in origin. Primary and secondary healing is more likely if the initial fistula is less complicated, and there is no specific advantage of a particular flap technique (when used to close the internal fistula opening definitively). Patient demographics, the number of prior operations or the timing of definitive surgery have no effect on successful outcome. In our study, as in other available reports, no major faecal incontinence was reported [8, 10].

It is recognized that although many sphincter-preserving techniques have provided encouraging preliminary results, over time they have failed to live up to their initial promise [19]. As an outcome measure, a high secondary healing rate is an essential gauge of success of any novel fistula therapy particularly when patients referred to a tertiary institution have had multiple prior failed procedures and where continence may already be partially disturbed. The lack of formal prospective continence assessment is lacking limitation of our study, but it will be a specific focus in future work. Moreover, although the cohort size is comparatively small, it is particularly encouraging that Crohn’s disease does not seem to have any influence on either primary or secondary outcomes following FiLaC™ treatment. The distalization of the primary fistula track in half of the cases where an initial FiLaC™ procedure had failed also permits a much easier repeat fistulectomy with or without the need for a subsequent sphincter repair. In our operative strategy to avoid any kind of faecal incontinence, only two cases of a very low persistent fistula were suitable for a lay-open procedure. In cases with muscular involvement of up to 30% on clinical examination, we did a fistulectomy with “partial” and, in patients with up to 50% involvement, a fistulectomy with a “major” sphincter reconstruction. If a high fistula track persisted and involved more than 50% of the muscle, a second sphincter-saving procedure like “re-FiLaC™” or “Gore^®-Plug” was performed. The precise mechanism of this shift from a high to a low anal fistula is unclear, but it may be a specific feature of the tissue-modulating effect of the laser.

Lasers have been used as surgical tools for anal diseases for the past four decades [20] with the first report of a CO₂ laser in 1981 [21] being used to treat three cryptogenic anal fistulae by coring out the fistula track followed by a 2001 Saudi Arabian study reporting six anal fistula cases treated with a KTP solid-state laser combined with fibrin glue instillation [22]. Similar success rates using a CO₂ laser therapy in complex Crohn’s-related anal fistulae have also been previously reported [23]. In the past, a range of bare-tip diode lasers with variable wavelengths (810, 940 and 980 nm) were used for anal fistulae, borrowing from the effect observed with these types of lasers in a range of endovenous procedures [24]. In the present study, we used a diode laser with a wavelength of 1470 nm and a circular emitting laser fibre, which is estimated to have a 60 times higher efficiency to shrink and seal the fistula track by interacting with water and blood at a lower energy compared to 980 nm. Earlier diode lasers with lower wavelengths (around 980 nm) have been reported to be successful because of their enhanced coagulating effect [8]. The photothermal effect and the optimal shrinkage obtained with a radial-tip fibre result in a more controlled damage, which is confined to the fistula lumen so that the limited radial penetration depth (2–3 mm beyond the fistula track) results in minimal collateral sphincter injury. The reduction in laser energy with the shift from a 980-nm to a 1470-nm probe has also resulted in lower pain scores in a study reported by Giamundo et al. treating 35 patients with the FiLaC™ probe [8].

The use of definitive closure of the internal fistula opening en passant with the FiLaC™ procedure remains controversial. Although the flap technique appears to be unassociated with primary or secondary FiLaC™ success rates, our approach has been formally to close the internal fistula orifice and to choose the type of flap closure on a case-by-case basis. It is recognized that formal fistula excision combined with sphincter reconstruction is associated with a 20% rate of post-operative faecal incontinence [25] and that in management of complex fistulas even the traditional flap techniques alone can be associated with incontinence rates of up to 43% [26]. The prospective assessment of the recurrence rate is dependent upon the ability of the laser alone to completely seal the inner part of the fistula track. Giamundo et al. [8, 10] have treated anal fistulae entirely with the laser probe without the need for closure of the internal opening. In this respect, most recurrences appear to occur relatively early following FiLaC™ treatment and are likely the result of fistula reopening with a linking up of the epithelial remnants of small undetected secondary tracks before the denaturation effect of the laser can take effect.

The role of preliminary seton deployment before definitive FiLaC™ therapy requires further examination possibly in a randomized, controlled trial. In our study, the majority of patients had an indwelling seton. In the most recent studies by Giamundo et al. [8, 10], the presence of the seton resulted in a better success rate (although this did not reach statistical significance in a small group of patients). One other study by Özturk et al. [9] reporting high success rates with FiLaC™ therapy did not include seton management as part of a first operative stage. The laser fibre is easier to insert in those patients which already have an indwelling seton, and in this setting the seton can be used to railroad the laser probe across the fistula (Seldinger manoeuvre) and to assist maturation of the principal track by inducing a more homogeneous fibrotic reshaping of the fistula lumen. Such an effect would permit a more uniform shrinkage distribution along the fistula track when the laser is employed in the second-stage procedure. The use of a seton and conversion of a “one-stage” to a “two-stage” procedure will have the benefit of preliminary drainage of abscesses and the intersphincteric space and should encourage small secondary tracks to close improving the likelihood of advancement flap healing if this is used as a supplementary technique.

The FiLaC™ procedure combines the aims of fistula management, namely clinical effectiveness and the maintenance of continence function. Although it is essentially a “blind” procedure that has the potential of missing some small secondary tracks, it is clearly safe and does not induce short-term post-operative sepsis. The long-term results show moderate primary and high secondary healing rates for the majority of fistula types and success rates unaffected by the nature and number of prior procedures or by the presence of Crohn’s disease. The minimally invasive FiLaC™ approach may therefore represent a sensible first-line treatment option for anal fistula repair. Randomized, controlled trials are needed to assess its performance against other minimally invasive fistula therapies.