Anal fistula disease is a condition characterized by pain and discharge of purulent secretion from an opening in the anorectal region. There are two stages of the disease: abscess formation as the acute stage and fistula formation as the chronic stage [1, 2].
The most common cause of anal fistulas is inflammation of the proctodeal glands. For this reason, this type of fistula is also referred to as a cryptoglandular anal fistula. The second most common cause of anorectal fistulas is chronic inflammatory bowel diseases, particularly Crohn's disease. Less commonly, fistulas can occur after surgical procedures in the pelvis or in cases of malignancies. Fistulas in infants are a distinct entity and often have a congenital cause [3, 4].
Anal abscesses and fistulas occur primarily in younger adults aged between 30 and 50 years [5]. Men are more frequently affected than women. The incidence of this disease in Europe is 1-2 cases per 10,000 inhabitants per year and varies depending on the population [6].
The development of cryptoglandular anal fistulas begins in the proctodeal glands in the intersphincteric space [7, 8]. The number of glands is more concentrated posteriorly and is higher in men than in women [9, 10]. The duct of these glands opens in the anal canal at the level of the dentate line. Purulent inflammation in these glands can cause local necrosis, surrounded by granulation tissue (abscess capsule). Depending on the virulence of the germs, the abscess spreads in the direction of least resistance and breaks through the skin. The connection of the abscess with the body surface is lined with granulation tissue and is referred to as a fistula.
The acute inflammatory stage, where no secretion drains, is perceived as an anal abscess, while the chronic course with putrid secretion in the presence of an external opening is referred to as an anal fistula.
In chronic inflammatory diseases, fistulas arise through transmural inflammation, which may also include perianal and perirectal tissue and only partially respect anatomical structures [11]. It is not uncommon to find intersphincteric anal fistulas also associated with anal fissures.
Microbiological examinations are irrelevant for the treatment of anal fistulas and usually reveal a mixed flora [12, 13]. Risk factors for the formation of an abscess and thus a "common" anal fistula (as opposed to IBD) are not described in the literature.
The treatment of anal fistula is principally surgical.
Fistulectomy with Primary Sphincter Reconstruction
Fistulectomy with primary sphincter reconstruction (FPSR) is a safe and promising method, particularly for distal and intermediate transsphincteric anal fistulas, and can also be an option for proximal fistulas [16, 21, 22].
Suture dehiscence is a complication in high fistulas, associated with an increased risk of postoperative continence disorders, which is why a clinical examination should be performed 2 to 4 weeks after FPSR to allow for timely revision reconstruction if necessary [14]. In specialized centers, primary healing rates of 88% can be achieved with FPSR, and up to 96% after revisions [15, 16].
Impairment of continence is described with varying frequency. A 2012 study reported that there was no deterioration in continence performance after FPSR in preoperatively continent patients. In preoperatively incontinent patients, continence performance was even improved [17]. A systematic review from 2015 (14 studies, 666 patients) compared the results of fistulotomy with those of FPSR [18]. After FPSR, mild and severe incontinence occurred more frequently postoperatively (mild: 8.6% vs. 15.4%, severe 1.1% vs. 2.7%). In patients with preoperatively undisturbed continence, the rate of postoperative continence disorders was 12.4%. In a randomized study, no differences were found between FPSR and advancement flap regarding functional outcomes and recurrence rate [19].
De Hous et al. describe that FPSR avoids unfavorable keyhole deformities of the anus in most cases and has a high healing rate of almost 96% [20]. FPSR has low morbidity, good healing rates, and good postoperative continence performance [23 - 26].
The data from the studies are, however, insufficient to provide a definitive answer to the question of which surgical method is best suited for the treatment of higher or complex anal fistulas. In particular, additional controlled randomized studies are lacking. Although FPSR is now an established procedure, it should be reserved for proctological centers of excellence, as the individual expertise of the surgeon is also important [21].