The proper surgical management of perianal Crohn’s disease is controversial. Ever since fistulas were first recognized as a manifestation of Crohn’s disease by Penner and Crohn, the specter of incontinence from aggressive perianal surgery has haunted its operative management. Given the often extensive presentation of Crohn’s disease, the decision of when to operate must be a collaborative effort among the patient, gastroenterologist, and surgeon.
Crohn’s disease typically presents in the following three ways: (1) ulceration, (2) fistula, and (3) stricture. There are reviews by Frizelle and colleagues (1996) and by Hughes (1978). The criteria for such a diagnosis include typical perianal lesions with histologic evidence of granulomata. Michelassi and colleagues (2000) observed that 23% of patients with Crohn’s disease manifested perineal fistulas, 18% stenosis, 16% abscess, 9% rectovaginal fistula, 5% incontinence, and 29% from a combination of problems.
The cumulative incidence of perianal fistulas in Crohn’s disease has been estimated by two population-based studies. Hellers and colleagues (1980) reported a cumulative incidence of perianal fistulas of 23%. In a Mayo series, Schwartz and colleagues (2002), showed that the cumulative incidence of fistulizing Crohn’s disease in Olmsted County, Minnesota, between 1970 and 1993, was 38%. The lifetime risk for developing a fistula is 20 to 40%.
The presence of perianal disease may also be affected by the location of proximal disease. Patients with disease confined to the colon have a higher incidence of perianal fistulas, with a rate approaching 100% in those with rectal involvement. Although rare, up to 5% of patients with perianal Crohn’s disease will have no evidence of proximal disease. Once treated the risk of recurrence remains high. It is estimated that the rate of recurrence of Crohn’s disease is 70% by 20 years.
Substantial morbidity, including scarring, continual seepage, and fecal incontinence, complicate perianal Crohn’s disease. Therapy is not standardized and debate continues on the role of operative intervention. The aim of this review is to discuss the perianal complications of inflammatory bowel disease and provide appropriate surgical solutions.
The anal canal consists of two separate and distinct muscles. The internal anal sphincter is a continuation of the circular smooth muscle of the rectum. The outer external sphincter is a continuation of the puborectalis muscle. Overlying the internal sphincter is the mucosa and the sub-mucosa of the anal canal. The dentate or pectinate line separates the transitional and columnar epithelium of the rectum. It is at this level that the anal crypts and glands may become infected, leading to perianal fistulas.
The appearance of active Crohn’s disease is classic. In active perianal disease, the lesions are swollen and take on a translucent pink or bluish hue. As inflammation resolves, the tissues become opaque and the ulcers heal with a fragile layer of epithelium. Chronically, the tissues become thickened, fibrotic, and scarred. When Crohn’s disease is in an active state, wound healing is significantly prolonged, but may be relatively normal when the disease is quiescent.
Hughes developed the first pathologic classification of fistula in ano based on morphology. This classification was based on structural abnormalities such as (1) ulceration, (2) fistula/abscess, and (3) stricture. More recently, several classification systems have been proposed. The most well known is, of course, Parks classic description of 1976. Park and colleagues developed the most anatomic and clinically relevant classification. Their use of the anatomy of the sphincter muscles as a reference point has made it the most surgically useful description to date.
It is important to remember that fistulas associated with Crohn’s disease rarely follow classically described pathways; indeed, it is the rare Crohn’s disease fistula that has a primary opening at the dentate line. Most fistulas associated with Crohn’s disease have a primary opening in the rectum proper and a secondary opening quite far removed (> 4 cm) from the anal verge.
Measurement of Fistula Disease Activity
The Perianal Disease Activity Index provides the most comprehensive measure of the morbidity caused by perianal Crohn’s disease. This index evaluates fistula disease in the following five categories:
- Restriction of sexual activity
- Type of perianal disease
- Degree of induration (Table Perianal Crohn Disease Activity Index).
Adequate evaluation of perianal disease in the setting of inflammatory bowel disease usually requires an examination under anesthesia. As is typical with perianal disease, an examination in the office setting is not only painful, but yields little. Examination under anesthesia facilitates the examining of the anal canal and distal rectum digitally; proctoscopical examination remains the current gold standard for assessment of perianal disease. Examination under anesthesia not only lends itself to the diagnosis of perianal pathology but also provides an opportunity to treat any pathology encountered.
TABLE. Perianal Crohn Disease Activity Index
|Categories Affected by Fistulas||Score|
|Minimal mucous discharge||1|
|Moderate mucous or purulent discharge||2|
|Gross fecal soiling||4|
|Pain and restriction of activities|
|No activity restriction||0|
|Mild discomfort, no restriction||1|
|Moderate discomfort, some limitation of activities||2|
|Marked discomfort, marked limitation of activities||3|
|Severe pain, severe limitation of activities||4|
|Restriction of sexual activity|
|Unable to engage in sexual activity||4|
|Type of perianal disease|
|None or skin tags||0|
|Anal fissure or mucosal tear||1|
|<3 perianal fistulas||2|
|>3 perianal fistulas||3|
|Anal sphincter ulceration or fistulas with substantial undermining||skin 4|
|Degree of induration|
|Gross fluctuance or abscess||4|
Other nonsurgical methods of assessing perianal disease include fistulography computed tomography (Computed tomography), magnetic resonance imaging (MRI), and endoscopic ultrasound (EUS). Fistulography has an accuracy ranging from 16 to 50%. Like fistulography Computed tomography is an imprecise test, providing accurate diagnoses in only 24 to 60% of patients. However, MRI and EUS accurately delineate fistulas in 76 to 100% of patients.
The Mayo series reported by Schwartz and colleagues (2001) is the most helpful study regarding accurate diagnostics. In this series, the accuracy of examination under anesthesia, MRI and EUS were all equal ranging from 87 to 91%. The differences between modalities were found to be insignificant. The interesting finding was that using any 2 of these 3 modalities increased the accuracy to 100%.
MRI or EUS combined with examination under anesthesia provides the highest diagnostic accuracy for perianal fistulous disease with the added benefit of enabling concomitant surgery if needed. As stated above, Computed tomography scan was only accurate in about half the patients with perianal abscesses.
The effect of fecal diversion or activity of perineal Crohn’s disease is controversial. Yamamoto and colleagues (2000) found no improvement in perianal disease with proximal diversion. Over the years, this practice had been frowned upon because of the historically low rates of restoration of continuity. This negative experience, however, predates combination therapy using antibiotics, azathioprine or 6-mercaptopurine, infliximab, cyclosporine, or tacrolimus. Given the current ease of laparoscopic loop ileostomy and the use of these newer medications, fecal diversion may again have a place in our overall treatment of perianal Crohn’s disease.
Proctectomy is uncommonly performed in patients with perineal Crohn’s disease; between 5 to 25% of patients will ultimately require proctectomy. In our own long term series of patients with anorectal Crohn’s disease, two groups have emerged. The first had suffered severe rectal involvement and proceeded to proctectomy very early in the disease process. The second group had more limited rectal disease and has been managed well with conservative treatment. Within this series, the cumulative probability of avoiding proctectomy was 92% at 10 years and 83% at 20 years. Despite good results with intensive medical and surgical therapy, a small percentage of patients will ultimately require proctectomy.
As perineal wound complications are a major source of morbidity, an intersphincteric dissection to decrease morbidity is performed routinely. In patients with severe perianal sepsis, a diverting laparoscopic ileostomy followed by proctocolectomy in 6 to 12 weeks results in fewer wound complications. For patients who have persistent perianal pain, discharge, or incontinence despite maximal medical therapy, proctectomy offers a substantially improved quality of life.
Oncologic Risk of Perianal Disease in inflammatory bowel disease
The risk of cancer developing in longstanding (decades) perianal disease is low indeed. There have been a few case reports of Crohn’s disease fistulas developing adenocarcinoma. Malignant degeneration should be considered in the differential diagnosis of all chronic nonhealing fistulas. If cancer is suspected, patients should undergo examination under anesthesia with curettage of the fistulous tract for diagnosis. There is a separate chapter by Brentrall on surveillance for dysplasia in Crohn’s disease, as well as in ulcerative colitis.
Most patients with rectal Crohn’s disease have concomitant perianal involvement. Conservative medical management works well in most patients and there is little risk of progression to proctectomy. In more complex disease, sepsis continues to cause discomfort and morbidity. Management of perianal disease continues to evolve. Aggressive surgical treatment alone has invariably lead to the serious complications of healing, incontinence, and need for permanent fecal diversion. Combining surgical drainage with aggressive anti-inflammatory and/or immunomodulators has become a powerful tool in the management of perianal Crohn’s disease. Surgery is indicated for the treatment of complications of perianal Crohn’s disease, and only when such combination therapy fails is proctectomy indicated.