Pathogenesis and treatment of fistula in ano

Anal fistula is a common problem1, although there is wide variation in estimates of incidence in the general population. This ranged from 1·04 to 2·32 new patients per 100 000 inhabitants in four European countries2. In the UK in 2005, over 6000 surgical procedures were performed for anal fistula3. It is now 50 years since the seminal publication of the paper that has probably had the most influence on surgical practice for anal fistula4. ‘Pathogenesis and treatment of fistula-in-ano’, by Professor Sir Alan Parks, established the pathological basis of this condition, introducing the concept that the origin of anal fistula was in the anal glands of the intersphincteric space. Based initially on cadaveric findings, with confirmatory histopathology, he provided a detailed description of a surgical approach that followed his theory of fistula development. Parks held that the crux of the operation was removal of the infected anal gland and its surrounding abscess deep to the internal sphincter. For most patients it was believed that this could be achieved via the lumen of the anal canal with excision of as much of the subsidiary track to the exterior as possible4. The description of the anal glands was not in itself new as they had been recognized since the 19th century5. It was Parks, however, who proposed that chronic infection of these glands, duct blockage and the subsequent formation of granulation tissue led to the development of a subsequent fistulous track. The specific anatomy and function of these glands and their relationship to disease is poorly understood. They predominate in the posterior half of the anal canal and this is used to explain the greater frequency of posterior tracks, but it is not known why the glands are distributed in this way6. Similarly, although it is recognized that the anal glands secrete mucin and are different from glands sited on the rectal mucosa, their specific function is still debated7. Sepsis being unable to drain into the anal canal owing to obstruction of the ducts was also used to account for the occasional extension of sepsis beyond the intersphincteric space8,9. Most studies seem to confirm this theory10, but as long ago as 1967 Goligher and colleagues11 disputed its validity, taking into account the lack of clinical evidence of intersphincteric abscess in the majority of patients. Recently, studies focusing on the microbiology of infected anal glands have added further doubt to Parks' hypothesis and suggested the importance of track epithelialization as the main component in persistence of the fistula, as in other sites12. There have been more than 5000 publications on anal fistula in the past 50 years, but only a few involve new approaches to management based on a sound understanding of the pathophysiology13,14. Conversely, a huge number of papers have described new techniques in recent years including advancement flaps, special glues, different designs of plugs, ligation of the intersphinteric tract, several types of seton, topical treatments as well as new methods of treating the fistulous track1. If cicatrization constituted the only endpoint in anal fistula surgery, fistulotomy would probably be the standard treatment, but at the expense of impaired continence when the track includes a significant external sphincter component as well as the internal sphincter. This is the main reason for the introduction of sphincter-preserving techniques. Although these procedures reduce the risk of incontinence, in the longer term they tend to be associated with high recurrence rates14. The use of glues or plugs is based on the hypothesis that they act as a scaffold or matrix to allow infiltration of the patient's connective tissue15. Continence disturbance with these procedures is conceptually difficult to imagine and has not been reported so far. Most of these treatments have not been developed from any type of experimental basis that has shed new light on the pathophysiology of this condition, and enthusiasm for their adoption seems ‘industry driven’. The result is that anal fistula remains a clinical problem with no established standards for management. Published outcomes still fall below those that a professional association might consider desirable in a modern era. There remains a dearth of research in proctology. It has been suggested that, although colorectal surgeons may operate daily on the anus, they prefer to read and write about colorectal procedures rather than proctology. This may well account for the poor quality of papers in this area and the lack of scientific evidence to deal with a common problem like anal fistula. Only by investing effort into studying the origin of clinical problems are we likely to improve surgical outcomes. The author declares no conflict of interest.