Anal fissure is a linear crack or tear in the squamous epithelium of the lower half of the anal canal, usually extending from below the dentate line to the anal verge. Fissures occur in all age groups, with equal prevalence in men and women. Because of sensory innervations to this area, the fissure is a painful condition.

The pathophysiology of chronic anal fissures has not been clearly established.

Possible causes include infections and traumatic injury to the anal canal such as passage of a hard stool or severe diarrhea.¹ Its relationship to hypertonic anal sphincter is controversial. The majority of investigators have found significantly elevated resting anal pressures in patients with fissure.^2–7 Other studies have found no significant difference in resting pressures.^8,9

Since the introduction of lateral internal sphincterotomy by Eisenhammer in 1951,¹⁰ this procedure has been used with increasing frequency and is now considered the treatment of choice for anal fissure. The procedure reduces the pathologically raised pressure profile within the anal canal.

The main purpose of this study was to evaluate long-term manometric results of sphincter healing following left lateral internal sphincterotomy during 1 year of follow-up.

This prospective study, conducted at the Division of General Surgery in Rabin Medical Center between the years 2000 to 2003, included all patients with chronic anal fissure requiring surgery. The study was approved by the hospital's ethics committee.

Manometric evaluations were performed at the Pelvic Floor Physiologic Laboratory Unit.

Exclusion criteria were: acute anal fissure, coexisting Crohn's disease or ulcerative colitis, prior history of anorectal surgery, chronic diarrheal illness, and pelvic radiotherapy or anorectal malignancies.

Fifty patients (23 females and 27 males; mean age, 40.5 years; range, 25–60 years) were included in this study. A control group included 12 normal volunteers: 5 women and 7 men (mean age, 40 years; range, 25–54 years). All patients had a limited bowel preparation with one Fleet (Dexxon) enema 250 mL. Manometric evaluation was carried out using a 6-channel water perfusion polyvinyl catheter (Zinetics AMC), with 60° angle radial at 5 cm from tip. The catheter's outside diameter was 4.5 mm and the inside diameter 0.8 mm radial lumens with 1.8 mm center lumen. The catheter was connected to the Mui Scientific perfusion pump, and the pressure was recorded by PC Polygraf system (Medtronic) through a pressure transducer. The lubricated catheter was introduced manually into the rectum, with patients in the left lateral decubitus position with flexed knees and hips. Water was perfused at a flow rate of 0.2 mL/min. The continuous pull-through technique was used with the catheter puller at a constant speed of 0.5 cm/s. Each investigation was repeated 3 times, and the mean value was taken as the result. For patients with anal fissure, the examination was performed 1 month before surgery and 1, 3, 6, and 12 months following surgery. In the control group, 3 examinations were performed, 6 months apart (ie, at 0, 6, and 12 months). The site of the fissure was located and recorded in all anal fissure patients.

The study included 50 patients with anal fissures who underwent sphincterotomy and 12 healthy patients who served as controls. Average age was 40.4 ± 9.6 years. The fissure group comprised 27 males and 23 females and the control group 7 males and 5 females. There were no significant age differences between genders (Table 1).

TABLE 1. Patient Characteristics and Resting Anal Pressure Measurements Between Genders and in Fissure Patients Versus Control

Baseline manometric measurements in the fissure group were significantly higher than in the control group (138 ± 28 mm Hg versus 73 ± 5.9 mm Hg, P < 0.0001, t test). At 12 months follow-up, there was a significant decline in manometric measurements as compared with baseline (138 ± 28 mm Hg versus 110 ± 18 mm Hg, P < 0.0001, t test paired). However, at the 12-month follow-up, the measurements in the fissure group were still significantly higher than in the control group (110 ± 18 mm Hg versus 73 ± 4.8, P < 0.0001, t test) (Fig. 1).

FIGURE 1. Changes in resting anal pressure, baseline versus 12-month follow-up.

In the fissure group, there was a significant drop in manometric measurements at 1 month compared with baseline (from 138 ± 28 mm Hg to 86 ± 15 mm Hg, P < 0.001). From that point on, a steady rise in pressure was observed at 3 and 6 months up to a plateau at 12 months (95.4 ± 17, 102.2 ± 18, and 109.6 ± 18 mm Hg, respectively, P < 0.0001 for each step, t test paired). The resting pressure remained steady but significantly lower than the first measurement before surgery (P < 0.0001) (Figs. 1–3).

FIGURE 2. Resting anal pressure changes over time in fissure patients.

FIGURE 3. Resting anal pressure changes during 1 year.

In most patients, after 12 months, the anal tone was reduced between 5 and 40 mm Hg, average 28.3 mm Hg (10%–25% from baseline) (Fig. 4).

FIGURE 4. Histogram of resting anal pressure improvement at 12 months.

The baseline measurements for females were significantly lower than for males in both the fissure and control groups (Fig. 5). However, in the fissure group, there were no significant differences in measurements between genders at follow-up. Thus, the postoperative changes in manometric measurements from baseline are lower for females (Table 1).

FIGURE 5. Monthly change in resting anal pressure between genders and in fissure patients versus control.

During 1 year of follow-up, all the patients were free of symptoms. Only 1 patient (2%) had temporary soiling, which resolved after 3 months. There were no other postoperative complications.

The etiology of anal fissure is not fully understood, and the reason why some fissures heal spontaneously and others become chronic remains obscure.

The source for the high anal resting pressure in patients with anal fissure has not been fully explained, but internal sphincter hypertonia may be one of the reasons.^7,11,12 High anal resting pressure has previously been proposed as a cause of ischemia of the anal lining and contributes to the pain of anal fissures and their failure to heal.¹²

Chronic anal fissure has traditionally been treated by surgery once conservative measures failed. Lateral internal anal sphincterotomy is the standard treatment of chronic anal fissures. Postoperative impairment of continence is not uncommon. Lewis et al¹³ found some degree of incontinence in 17% of their patients; in two thirds of these patients, this complication was only temporary. Khubchandani and Reed¹⁴ reported postoperative soiling in 22% of their study patients after lateral sphincterotomy and grade 1 incontinence in 35.1%. Hsu and MacKeigan¹⁵ reported no postoperative soiling or incontinence following lateral sphincterotomy. In our study, only 1 patient (2%) had soiling, which resolved after 3 months.

The alternative therapeutic procedure of sphincter dilatation is associated with uncontrolled tearing of the internal sphincter muscle and portions of the external anal sphincter may also be damaged. Recent endosonographic studies^16–18 of the sphincter apparatus after sphincter dilatation confirm these findings.

Postoperative impairment of continence is common. The healing process of the anal fissure has been documented clinically and to some extent also by manometric measurements, but the duration of these studies did not exceed 5 months follow-up postoperatively. McNamara et al¹⁹ demonstrated that resting pressure returns to normal values after sphincterotomy. To the best of our knowledge, the present study is the first long-term manometric evaluation that describes the healing process of the internal anal sphincter over a period of 1 year following lateral internal sphincterotomy.

In our study, we confirmed that all the patients with chronic anal fissure had significantly higher anal resting pressure than the control group. This finding has been well established by other investigators.^7,11,12 We showed that, 1 month after lateral internal anal sphincterotomy, there was a sharp decline in the anal resting pressure as expected. At 3 months of follow-up, a consistent rise in pressure measurements had begun. Between 3 and 6 months, there was a marked increase in pressure, but the increase in pressure measurements then became very slight, up to a plateau at 12 months. One year following surgery, the pressure measurements still remained significantly lower than before surgery (but higher than in the controls). Romano et al²⁰ found 1 month after surgery that only 52% of patients had normal anal resting pressure and 32% had hypertonus. These findings are not in agreement with ours. In our series, all the patients had higher pressure than the control group postoperatively. The decline in pressure in our patients, although not reaching normal pressure, was low enough to enable fissure healing and symptom relief.

Lateral internal sphincterotomy causes significant decline in the resting pressure. During the first year following surgery, the tone of the internal anal sphincter gradually increased, showing recovery, but still remained significantly lower than before surgery. However, postoperative resting pressures were higher than those in the control, and no patient suffered any permanent problems with incontinence, so this decrease may not be clinically significant.

The authors thank Mrs. Carmela Cohen for her administrative assistance.