Incision and drainage vs minimally invasive catheter drainage on pain and anal function in high perianal abscess patients

Abstract

BACKGROUND

Perianal abscess (PA) is a common and debilitating condition that requires prompt surgical intervention. Conventional incision and drainage, while standard, often results in significant postoperative pain, tissue trauma, and potential impairment of anal sphincter function, prompting the need for alternative approaches.

AIM

To compare the effect of incision and drainage with selective seton placement (ID) vs minimally invasive catheter drainage (MICD) on postoperative pain control and anal function preservation in patients with high PA.

METHODS

This retrospective study included 226 patients with high PA (defined as abscesses located above the levator ani muscle, confirmed by imaging) who underwent ID (n = 122) or MICD (n = 104). Primary outcomes were pain intensity identified using the visual analogue scale (preoperatively and on postoperative days 1, 7, and 14) and anal function according to Wexner score on postoperative day 30. Secondary outcomes included inflammatory cytokine levels [interleukin (IL)-4, IL-6, IL-10, and tumor necrosis factor-alpha], operative time, blood loss, wound healing time, and hospital stay. Anal fistula formation and abscess recurrence were evaluated as exploratory endpoints.

RESULTS

The MICD group demonstrated significantly lower visual analogue scale at all postoperative time points (all P < 0.001). A significantly higher proportion of patients in the MICD group achieved normal anal function (69.2% vs 48.4%, P = 0.002). On postoperative day 7, the MICD group showed lower levels of IL-4, IL-6, and tumor necrosis factor-alpha and higher levels of IL-10 (all P < 0.01). Operative time, blood loss, wound healing, and hospital stay were significantly reduced in the MICD group (all P < 0.01). Exploratory analysis showed a lower rate of anal fistula formation (8.7% vs 24.6%, P = 0.002) and abscess recurrence (3.8% vs 12.3%, P = 0.023) with MICD. However, these findings are limited by inherent differences in internal opening management between the techniques. Multivariate analysis identified MICD as a protective factor against anal incontinence (odds ratio = 0.334, P = 0.003), whereas diabetes and deep abscess were risk factors (both P < 0.01).

CONCLUSION

MICD is associated with better postoperative pain control, better preservation of anal sphincter function, a more favorable anti-inflammatory response, and faster recovery than conventional ID in patients with high PA. The potential benefit regarding fistula risk reduction requires further validation in prospective studies with standardized internal opening protocols.

Key Words: Perianal abscess; Incision and drainage; Minimally invasive catheter drainage; Pain; Anal function

Core Tip: This retrospective study compared incision and drainage with selective seton placement vs minimally invasive catheter drainage (MICD) for high perianal abscesses. MICD demonstrates significant advantages in reducing postoperative pain and preserving anal sphincter function. Notably, the observed lower fistula rate with MICD is confounded by differing intraoperative management of the internal opening between techniques. These findings support MICD as a promising, patient-centered alternative, though further validation with standardized protocols is required.

INTRODUCTION

Perianal abscess (PA) is a common and debilitating condition that can cause considerable pain and discomfort, severely affecting patients’ quality of life. These abscesses typically arise from an infection in the anal glands, leading to localized collections of pus that require prompt surgical intervention. Without appropriate treatment, PA can progress to more severe complications such as anal fistulas, chronic pain, and impaired bowel function[1-3]. Traditional management of PA involves incision and drainage with selective seton placement (ID), which has been the standard approach for many years[4]. However, this method is associated with persistent pain and risk iatrogenic sphincter injury. These sequelae directly affect patients’ quality of life, yet remain inadequately addressed by existing management guidelines[5].

ID is a straightforward procedure that involves making an incision over the abscess site to allow the pus to drain. This technique provides immediate relief of symptoms by decompressing the abscess cavity. Despite its simplicity, ID often results in considerable tissue trauma, which can lead to severe postoperative pain[6,7]. The extensive dissection required to locate the internal opening often disrupts the anal sphincter complex, contributing to postoperative incontinence rates as high as 11% in published cohorts[8,9]. Frequent dressing changes for the open wound further exacerbate pain and burden patients and providers. Additionally, ID has a high incidence of postoperative anal fistula formation, occurring in up to 50% of cases[1,5,10]. Fistulas develop when the tract created during drainage fails to close properly, leading to a persistent connection between the skin and the anal canal[11].

Minimally invasive catheter drainage (MICD) offers a promising alternative to traditional ID. MICD involves inserting a small catheter into the abscess cavity under ultrasound or fluoroscopic guidance, allowing for continuous drainage without the need for extensive surgical intervention. This approach aims to minimize tissue damage while ensuring effective drainage of the abscess by using a smaller incision and maintaining continuous drainage through the catheter. Furthermore, the continuous drainage provided by the catheter helps prevent fluid accumulation and secondary infection, potentially leading to accelerated healing and enhanced patient outcomes. MICD also allows for earlier mobilization and discharge from the hospital, reducing the overall burden on healthcare resources[12,13].

The effect of surgical techniques on postoperative pain is a critical aspect of PA management. Pain control is essential for patient comfort and compliance with postoperative care[14-16]. Traditional ID often results in higher levels of postoperative pain than less invasive methods like MICD due to its more invasive nature. Moreover, anal function preservation is a key consideration in the treatment of PA[17]. Postoperative anal incontinence is another considerable concern for patients undergoing surgical treatment[18]. The preservation of anal sphincter integrity is crucial for maintaining normal bowel control. Traditional ID, with its larger incisions, poses a higher risk of damaging the anal sphincter muscles, leading to increased rates of incontinence. By contrast, the minimally invasive nature of MICD may result in less disruption to the surrounding tissues, including the anal sphincter, thereby preserving its function.

This study aims to evaluate the effect of ID and MICD on postoperative pain control and anal function preservation, providing valuable insights for clinical practice. By comparing these two methods, this study aims to identify the most effective strategy for managing PA and reducing the burden of associated complications.

MATERIALS AND METHODS

Study population

A retrospective analysis was conducted on 226 patients with PA who underwent surgical inpatient treatment at our hospital from August 2019 to July 2024. The study was approved by the Medical Ethics Committee of Wuxi Ninth People’s Hospital Affiliated to Soochow University (approval No. KS2026-033-01). Given the retrospective design of the study and the anonymity of the data, the Ethics Committee waived the requirement for informed consent.

Inclusion criteria: (1) Age ≥ 18 years; (2) Meeting the diagnostic criteria for high PA as outlined in the Chinese Expert Consensus on Clinical Diagnosis and Treatment of Perianal Abscess, defined as the abscess cavity located above the levator ani muscle (including high intersphincteric, pelvirectal, retrorectal, and high submucosal abscesses with supralevator extension), confirmed by transrectal ultrasonography (TRUS) or magnetic resonance imaging (MRI); (3) First episode; and (4) Complete clinical and follow-up data.

Exclusion criteria: (1) Individuals with other perianal diseases such as hidradenitis suppurativa, perianal boils and folliculitis, or sacrococcygeal teratomas, or pre-existing chronic anal fistula; (2) PA associated with Crohn’s disease, tuberculosis, human immunodeficiency virus infection, or other causes of immunosuppression; (3) History of previous perianal surgery; (4) Severe heart, liver, or kidney dysfunction; (5) Immunosuppressive status; (6) History of fecal incontinence; (7) History of malignant tumors; (8) Pregnant or lactating women; and (9) Presence of mental illness.

In accordance with the different surgical treatments, the 226 patients were categorized into ID (n = 122) and MICD groups (n = 104). Treatment allocation was based on clinical decision-making rather than randomization. MICD was preferentially offered when the abscess cavity was suitable for catheter placement and when the patient consented to the procedure and its associated costs. ID was generally performed in cases where anatomy was less favorable for catheter drainage, when equipment was unavailable, or when urgent or emergent drainage was required.

Surgical treatments

Preoperative preparation: Both groups of patients were given a low-residue soft diet 1 day before surgery, took sitz baths with warm water twice daily, and underwent mechanical bowel preparation. Prophylactic antibiotics (second-generation cephalosporin combined with metronidazole) were administered 30 minutes before surgery. All surgeries were performed by the same team of senior colorectal surgeons.

Operating procedure: (1) ID group: The ID procedure for PA was performed. After the patients received satisfactory spinal or epidural anesthesia, they were placed in a jackknife or lateral position, and the operative field was routinely disinfected and draped. The extent of the abscess and the site of maximal fluctuance were identified by digital rectal examination. A radial incision (approximately 3-5 cm long) was made at this site, cutting through the skin and subcutaneous tissue. Curved forceps were used to bluntly dissect into the abscess cavity, ensuring adequate drainage of pus. The depth and course of the abscess cavity were explored with the index finger, and any fibrous septa within the cavity were separated. Once the internal opening (which did not indicate a pre-existing chronic fistula but rather the primary infection site) was identified, a rubber band was passed through it, tightened, and secured with silk sutures, performing seton placement. If no definite internal opening was found, only drainage of the abscess cavity was performed. The abscess cavity was then irrigated repeatedly with normal saline and 0.5% metronidazole solution, necrotic tissue was removed, and the cavity was packed with Vaseline gauze for drainage. The procedure was concluded; (2) MICD group: The procedure involved minimally invasive catheter placement with irrigation combined with vacuum-sealed drainage (VSD) (Figure 1). The anesthesia and patient positioning were the same as in the ID group. Under the guidance of preoperative imaging (TRUS or MRI) and digital rectal examination, the highest point (apex) and the most dependent (lowest) point of the abscess cavity were identified and marked on the perianal skin. The surgeon aspirated at the marked points to confirm the presence of pus by using a puncture needle. Two small incisions (approximately 0.3-0.5 cm long) were then made at these locations. Curved forceps were used to bluntly dilate the incisions and enter the cavity. A septum breaker was inserted to disrupt any fibrous loculations and remove necrotic tissue fragments. A 14F double-lumen catheter with multiple side holes was prepared. The catheter features two independent internal lumens – one for irrigation and one for drainage. The catheter was inserted through the incision and advanced along the cavity wall until its tip reached the apex of the abscess cavity. The irrigation port (located at the catheter tip) was thus positioned at the apex for postoperative continuous irrigation, while the drainage port (located more proximally along the catheter shaft) was positioned at the most dependent portion of the cavity, approximately 0.5-1.0 cm from the cavity floor, and was connected to the negative pressure drainage device. Catheter position was confirmed by gentle irrigation with normal saline, which demonstrated free flow from the irrigation port through the cavity and out of the drainage port. After adequate drainage was confirmed, the catheters were secured with sutures. If a definite low internal opening (near the dentate line) was identified during the procedure, it was trimmed and closed using absorbable 3-0 sutures. If the internal opening was too high or could not be clearly identified, no special treatment was performed, allowing it to heal naturally after sufficient drainage. Medical foam dressings were trimmed and packed into the abscess cavity to ensure full contact with the cavity walls, and the wound was sealed with a semi-permeable membrane. The negative pressure drainage device was connected, and after good sealing was ensured, continuous negative pressure suction was applied, maintaining a negative pressure ranging from -200 mmHg to -250 mmHg; and (3) Identification of the internal opening: In both groups, the internal opening was identified intraoperatively by using a standardized protocol. A blunt probe was gently inserted from the external drainage site through the abscess cavity toward the anal canal while the surgeon’s contralateral index finger was placed in the anal canal to palpate the probe tip and locate the corresponding anal crypt at the dentate line. In cases where the internal opening could not be clearly identified by probing alone, 3% dilute hydrogen peroxide was injected into the abscess cavity. The appearance of bubbles from a specific anal crypt confirmed the location of the internal opening. Notably, the internal opening identified intraoperatively in these acute abscess cases represents the infected anal gland – the primary source of infection – rather than a pre-existing chronic epithelialized fistula tract. At the time of surgery, no patient had a history of chronic fistula or a pre-existing external opening.

Figure 1 Representative images showing minimally invasive catheter drainage technique. A: Catheter placement; B: Irrigation and drainage.

Postoperative management: Both groups routinely received antibiotics until 3-5 days after their body temperature returned to normal. They were instructed to take sitz baths with warm water after defecation to maintain local cleanliness. In the ID group, the wound was dressed once daily; it was cleaned with normal saline, and Vaseline gauze was reinserted to maintain adequate drainage. The seton (rubber band) was removed when the following criteria were met: (1) 24 hours drainage volume < 10 mL with clear, non-purulent fluid; (2) Resolution of local perianal inflammation (no erythema, tenderness, or induration) and systemic inflammatory markers (normal body temperature, white blood cell count, and C-reactive protein levels); (3) Considerable reduction in abscess cavity size confirmed by TRUS/MRI, with no residual fluid collection; and (4) Easy mobility of the seton without surrounding fibrous encapsulation. In the MICD group, the irrigation lumen of the double-lumen catheter was connected to an intravenous infusion set for continuous normal saline irrigation at 20-40 drops/minute to irrigate the abscess cavity. The drainage lumen was connected to a negative-pressure suction device to maintain unobstructed drainage. Patients were instructed to maintain a residue-free diet for 5-7 days postoperatively and were prohibited from defecation. Patients were allowed limited sitting on soft cushions and could ambulate in the room when switched to the portable negative-pressure bottle clipped to clothing. When the abscess resolved and drainage became clear, the double-lumen catheter was removed and treatment was concluded.

Research indicators

Pain intensity: The degree of anal pain was assessed using the visual analogue scale (VAS) before surgery and on postoperative days 1, 7, and 14. Scores ranged from 0 to 10, with patients selecting a score on the basis of their subjective pain perception. Higher scores indicated more severe anal pain. The intraclass correlation coefficient was 0.99[19].

Anal function: On postoperative day 30, anal function was assessed using the Wexner score (also known as the Cleveland Clinic Incontinence Score). The Wexner scale consists of five dimensions: (1) Incontinence to solid stool; (2) Incontinence to liquid stool; (3) Flatus incontinence; (4) The need to wear pads; and (5) Lifestyle changes (frequency of lifestyle modifications due to incontinence). Each dimension is scored from 0 to 4 on the basis of the frequency of occurrence, with a total possible score ranging from 0 to 20. A score of 0 indicates normal function and 1-20 indicates anal incontinence, with a Cronbach’s α of 0.932[20].

Inflammatory cytokine levels: The levels of interleukin (IL)-4, IL-6, IL-10, and tumor necrosis factor-alpha (TNF-α) were measured using ELISA kits (ab215089, ab178013, ab185986, and ab181421; Abcam, China) before surgery and 7 days after surgery.

Surgical indicators: The operative time, intraoperative blood loss, wound healing time, and hospital stay were recorded for both groups.

Anal fistula and recurrence: Both groups were followed up for 12 months postoperatively, during which the formation of anal fistulas and recurrence of abscesses were recorded. Postoperative anal fistula was defined as an abnormal epithelialized tract persisting for more than 3 months after surgery, confirmed by a combination of clinical, imaging, and/or surgical findings: (1) Persistent purulent or serous discharge from the perianal wound/skin opening, or induction of granulation tissue with probing revealing a definite tract; (2) Identification of a continuous hypoechoic/hypodense tubular structure connecting the anal canal/rectum to the perianal skin on TRUS or MRI; and (3) Visualization of a mature fistulous tract during re-operation (if performed). A diagnosis of fistula was established if at least two of the above three criteria were met[11]. Abscess recurrence was defined as the reappearance of acute infection symptoms such as redness, swelling, and pain in the original surgical area, confirmed by imaging studies to show the formation of a new abscess cavity requiring further surgical intervention[21].

Statistical analysis

Data analysis was conducted using SPSS statistical software (version 29.0; developed by SPSS Inc., Chicago, IL, USA). The Shapiro-Wilk test confirmed that all continuous variables followed a normal distribution, and these variables were expressed as mean ± SD, with between-group comparisons performed using independent sample t-tests. Categorical variables were expressed as n (%) and compared between groups using χ² test. A P value less than 0.05 was considered statistically significant. Univariate and multivariate logistic regression analyses were performed with postoperative anal abnormal function as the dependent variable (normal = 0, abnormal function = 1) to identify independent risk factors for postoperative anal abnormal function in patients with PA.

RESULTS

General information

A total of 226 patients were included in the analysis, with 122 in the ID group and 104 in the MICD group. As shown in Table 1, no statistically significant differences were observed between the two groups in terms of gender distribution; age; body mass index; comorbidities, such as hypertension, diabetes, or constipation; disease course; abscess location; abscess diameter; and the proportion of deep abscesses (all P > 0.05). These findings indicated that the baseline characteristics were comparable between the two groups.

Table 1 Comparison of general information between two groups, n (%)/mean ± SD.

Parameter	ID group (n = 122)	MICD group (n = 104)	t/χ2	P value
Gender			0.102	0.750
Male	96 (78.69)	80 (76.92)
Female	26 (21.31)	24 (23.08)
Age (years)	52.34 ± 7.13	52.41 ± 7.06	0.071	0.944
BMI (kg/m2)	24.12 ± 3.35	24.18 ± 3.29	0.125	0.901
Hypertension	36 (29.51)	32 (30.77)	0.042	0.837
Diabetes	17 (13.93)	12 (11.54)	0.288	0.591
Constipation	24 (19.67)	20 (19.23)	0.007	0.933
Course of disease (days)	5.32 ± 1.54	5.29 ± 1.51	0.151	0.880
Abscess location			0.239	0.971
High intersphincteric abscess	28 (22.95)	24 (23.08)
Pelvirectal abscess	31 (25.41)	28 (26.92)
Submucosal abscess	29 (23.77)	22 (21.15)
Retrorectal abscess	34 (27.87)	30 (28.85)
Abscess diameter (cm)	1.44 ± 0.46	1.47 ± 0.43	0.463	0.644
Deep abscess	50 (40.98)	44 (42.31)	0.041	0.840

ID: Incision and drainage with selective seton placement; MICD: Minimally invasive catheter drainage; BMI: Body mass index.

Pain intensity

Pain levels, assessed using VAS, were compared between the two groups at multiple time points, as detailed in Figure 2. The preoperative VAS scores were similar between the ID and MICD groups (5.21 ± 1.53 vs 5.37 ± 1.52, P = 0.438). However, on postoperative day 1, the MICD group reported significantly lower pain scores than the ID group (2.41 ± 0.47 vs 3.42 ± 0.51, P < 0.001). This difference persisted at postoperative days 7 (1.63 ± 0.26 vs 2.15 ± 0.48, P < 0.001) and 14 (0.91 ± 0.22 vs 1.36 ± 0.34, P < 0.001), indicating that MICD was associated with sustained pain relief during the early postoperative period.

Figure 2 Comparison of visual analogue scale scores between two groups (points). ID: Incision and drainage with selective seton placement; MICD: Minimally invasive catheter drainage; VAS: Visual analogue scale.

Anal function

Anal function, evaluated using the Wexner score, showed significant differences between the two groups at 30 days post-surgery, as summarized in Table 2. A higher proportion of patients in the MICD group achieved normal anal function than in the ID group (69.23% vs 48.36%, P = 0.002). This finding suggests that MICD may offer better preservation of anal function.

Table 2 Comparison of anal function between two groups, n (%).

Parameter	ID group (n = 122)	MICD group (n = 104)	χ2	P value
Normal function	59 (48.36)	72 (69.23)	10.036	0.002
Anal incontinence	63 (51.64)	32 (31.37)	10.036	0.002

ID: Incision and drainage with selective seton placement; MICD: Minimally invasive catheter drainage.

Inflammatory cytokine levels

Changes in serum inflammatory cytokine levels before and after surgery are shown in Table 3. The preoperative levels of IL-4, IL-6, IL-10, and TNF-α were comparable between the two groups (all P > 0.05). At postoperative day 7, the MICD group exhibited significantly lower levels of IL-4 (32.05 ± 2.94 vs 33.18 ± 3.24, P = 0.007), IL-6 (100.98 ± 8.53 vs 105.32 ± 14.67, P = 0.006), and TNF-α (1.49 ± 0.31 vs 1.62 ± 0.34, P = 0.005), along with significantly higher levels of IL-10 (39.73 ± 11.64 vs 35.46 ± 9.35, P = 0.003), indicating a more favorable anti-inflammatory response following MICD.

Table 3 Comparison of inflammatory cytokine levels between two groups (pg/mL), mean ± SD.

Parameter	ID group (n = 122)	MICD group (n = 104)	t value	P value
IL-4
Preoperative	47.32 ± 4.18	47.41 ± 4.22	0.159	0.874
Postoperative 7 days	33.18 ± 3.24	32.05 ± 2.94	2.737	0.007
IL-6
Preoperative	249.67 ± 37.51	250.14 ± 37.49	0.095	0.925
Postoperative 7 days	105.32 ± 14.67	100.98 ± 8.53	2.761	0.006
IL-10
Preoperative	21.85 ± 6.32	21.96 ± 6.41	0.122	0.903
Postoperative 7 days	35.46 ± 9.35	39.73 ± 11.64	3.010	0.003
TNF-α
Preoperative	3.44 ± 1.05	3.42 ± 1.07	0.107	0.915
Postoperative 7 days	1.62 ± 0.34	1.49 ± 0.31	2.822	0.005

ID: Incision and drainage with selective seton placement; MICD: Minimally invasive catheter drainage; IL-4: Interleukin-4; IL-6: Interleukin-6; IL-10: Interleukin-10; TNF-α: Tumor necrosis factor-alpha.

Surgical indicators

Perioperative outcomes were compared between the two groups, as presented in Figure 3. The MICD group had a significantly shorter operative time than the ID group (27.86 ± 4.15 minutes vs 33.27 ± 5.48 minutes, P < 0.001). Intraoperative blood loss was lower in the MICD group (19.45 ± 3.58 mL vs 20.94 ± 4.62 mL, P = 0.007). Furthermore, the MICD group experienced faster wound healing (9.47 ± 2.32 days vs 12.75 ± 3.36 days, P < 0.001) and a shorter hospital stay (10.78 ± 2.19 days vs 14.82 ± 2.61 days, P < 0.001). In addition to these surgical indicators, the mean duration of seton placement in the ID group was 12 days (range: 7-21 days), with 97/122 (79.51%) patients with identified internal openings underwent loose seton placement. In the MICD group, the double-lumen catheter was removed at a mean of 6 days postoperatively. These durations reflect the different postoperative drainage strategies inherent to each technique.

Figure 3 Comparison of surgical indicators between two groups. A: Operative time; B: Intraoperative blood loss; C: Wound healing time; D: Hospital stays. ID: Incision and drainage with selective seton placement; MICD: Minimally invasive catheter drainage.

Anal fistula and recurrence

The incidence of postoperative anal fistula formation and abscess recurrence in both groups is presented in Table 4. The MICD group exhibited a significantly lower rate of anal fistula formation than the ID group (8.65% vs 24.59%, P = 0.002). Similarly, the abscess recurrence rate was markedly reduced in the MICD group (3.85% vs 12.30%, P = 0.023). These results suggest that MICD may be associated with a lower risk of postoperative complications.

Table 4 Comparison of anal fistula formation and abscess recurrence rate between two groups, n (%).

Parameter	ID group (n = 122)	MICD group (n = 104)	χ2	P value
Anal fistula formation	30 (24.59)	9 (8.65)	9.986	0.002
Abscess recurrence	15 (12.30)	4 (3.85)	5.205	0.023

ID: Incision and drainage with selective seton placement; MICD: Minimally invasive catheter drainage.

Univariate and multivariate logistic regression analyses

Univariate logistic regression analysis (Table 5) revealed that MICD was associated with a reduced risk of postoperative anal incontinence [odds ratio (OR) = 0.415, 95%CI: 0.294-0.585, P < 0.001]. By contrast, higher age (OR = 1.028, 95%CI: 1.004-1.053, P = 0.019), male gender (OR = 1.366, 95%CI: 1.029-1.813, P = 0.03), BMI (OR = 1.156, 95%CI: 1.019-1.311, P = 0.026), the presence of diabetes (OR = 2.335, 95%CI: 1.326-4.112, P = 0.003), abscess diameter (OR = 1.684, 95%CI: 1.143-2.481, P = 0.009), and deep abscess (OR = 2.499, 95%CI: 1.595-3.915, P < 0.001) were identified as risk factors.

Table 5 Univariate logistic regression analysis of risk factors for postoperative anal incontinence in patients with perianal abscess.

Parameter	Coefficient	SE	Wald	P value	OR	95%CI
MICD	-0.883	0.176	25.171	< 0.001	0.415	0.294-0.585
Age	0.028	0.012	5.444	0.019	1.028	1.004-1.053
Male	0.312	0.145	4.630	0.031	1.366	1.029-1.813
BMI	0.145	0.065	4.976	0.026	1.156	1.019-1.311
Diabetes	0.848	0.289	8.610	0.003	2.335	1.326-4.112
Abscess diameter	0.521	0.198	6.924	0.009	1.684	1.143-2.481
Deep abscess	0.916	0.229	16.000	< 0.001	2.499	1.595-3.915

OR: Odds ratio; MICD: Minimally invasive catheter drainage; BMI: Body mass index.

In the multivariate analysis (Table 6), after adjusting for potential confounders, MICD remained an independent protective factor against postoperative anal incontinence (OR = 0.334, 95%CI: 0.177-0.630, P = 0.003). Diabetes (OR = 2.000, 95%CI: 1.037-3.856, P = 0.006) and deep abscess (OR = 2.255, 95%CI: 1.127-4.512, P < 0.001) were confirmed as independent risk factors, whereas age, male gender, BMI, and abscess diameter did not retain statistical significance in the multivariate model (all P > 0.05).

Table 6 Multivariate logistic regression analysis of risk factors for postoperative anal incontinence in patients with perianal abscess.

Parameter	Coefficient	SE	Wald Stat	P value	OR	OR CI lower	OR CI upper
MICD	-1.096	0.322	11.585	0.003	0.334	0.177	0.630
Age	0.015	0.014	1.148	0.285	1.015	0.988	1.043
Male	0.198	0.162	1.494	0.223	1.219	0.889	1.673
BMI	0.098	0.055	3.175	0.074	1.103	0.991	1.227
Diabetes	0.693	0.335	4.279	0.006	2.000	1.037	3.856
Abscess diameter	0.285	0.221	1.663	0.197	1.330	0.862	2.053
Deep abscess	0.813	0.264	9.484	< 0.001	2.255	1.127	4.512

OR: Odds ratio; CI: Confidence interval; MICD: Minimally invasive catheter drainage; BMI: Body mass index.

DISCUSSION

This study compared the effect of ID vs MICD on postoperative pain control and anal function preservation in patients with high PA. The findings demonstrate that MICD is associated with better pain relief, better preservation of anal sphincter function, a more favorable anti-inflammatory response, and faster recovery than conventional ID.

MICD was found to provide better pain relief during the early postoperative period. Pain management is crucial for patient comfort and compliance with postoperative care. The reduced pain levels observed in the MICD group could be attributed to several factors. First, the smaller incision used in MICD likely causes less immediate postoperative pain than the larger incision required for ID[3,6,22]. Second, the continuous drainage provided by the catheter may reduce inflammation and pressure within the abscess cavity, leading to less discomfort[23]. These mechanisms collectively contribute to improved patient-reported pain scores in the MICD group[16,24].

Anal function was better preserved in patients treated with MICD. Postoperative anal incontinence is a significant concern for patients undergoing surgical treatment for PA. The preservation of anal sphincter integrity is essential for maintaining normal bowel control[25,26]. MICD’s minimally invasive approach may result in less damage to the surrounding tissues, including the anal sphincter, thereby preserving its function[27,28]. By contrast, ID involves a more extensive surgical intervention, which can disrupt the sphincter muscles and lead to higher rates of incontinence. By minimizing tissue disruption, MICD appears to offer better protection against anal dysfunction.

Inflammatory cytokine levels differed between the two groups. The MICD group exhibited a more favorable anti-inflammatory response, characterized by lower levels of pro-inflammatory cytokines, such as IL-6 and TNF-α, and higher levels of the anti-inflammatory cytokine IL-10. This finding suggests that MICD may modulate the inflammatory response more effectively than ID. The less invasive nature of MICD could result in reduced local tissue injury and a subsequent decrease in the release of pro-inflammatory mediators. Additionally, continuous drainage through a catheter may help remove inflammatory exudates more efficiently, contributing to a more balanced inflammatory response. This modulation of inflammation may play a role in the overall improvement in pain and functional outcomes observed in the MICD group[29-31].

Surgical indicators, including operative time, intraoperative blood loss, wound healing time, and hospital stay, were evaluated. The MICD group had shorter operative times, less intraoperative blood loss, faster wound healing, and shorter hospital stays than the ID group. These differences can be attributed to the minimally invasive nature of MICD, which requires smaller incisions and less extensive manipulation of tissues. The use of a catheter for continuous drainage eliminates the need for repeated dressing changes and allows for earlier discharge from the hospital[12]. Furthermore, the reduced tissue trauma associated with MICD may accelerate the healing process, resulting in faster recovery times. Notably, the relatively prolonged hospital stays observed in both groups reflect the standard inpatient management protocol for high PA at our institution, which includes intravenous antibiotics until afebrile for 72 hours, daily specialized wound care, and, in the MICD group, supervised management of the VSD system until catheter removal.

A critical methodological consideration must be acknowledged. The management of the internal opening differed between the two groups: In the ID group, identified internal openings were managed with seton placement, whereas in the MICD group, low openings were primarily closed with sutures and high openings were left to heal spontaneously. While these approaches reflect the distinct drainage principles of each technique – seton placement ensuring patency in an open cavity vs negative pressure allowing secondary collapse and healing – they represent an inherent confounding variable when comparing anal fistula formation rates. Consequently, the lower fistula rate observed in the MICD group (8.7% vs 24.6%) cannot be solely attributed to the minimally invasive nature of the catheter drainage itself; it may be partially or largely influenced by the different strategies employed for internal opening management. This confounder substantially limits the validity of direct comparisons of fistula formation between the two techniques.

Multivariate analysis identified MICD as an independent protective factor against anal incontinence, whereas diabetes and deep abscess were independent risk factors. Other risk factors included diabetes and deep abscesses. The association between diabetes and poor postoperative outcomes is well-established; patients with diabetes experience delayed wound healing and increased infection risk due to systemic metabolic disturbances and altered wound microbiota[32]. Deep abscesses pose greater surgical challenges due to their anatomical complexity and extent of tissue involvement, making functional preservation more difficult. The identification of these risk factors may help clinicians stratify patients and optimize surgical strategies accordingly.

Despite the promising results, this study has several limitations. First, the nonrandomized, retrospective design introduces potential selection bias. Although baseline characteristics were well balanced between the two groups for all measured variables, unmeasured confounders, such as subtle differences in abscess complexity, surgeon experience, or patient preferences, may have influenced treatment allocation. This is a particular concern for the exploratory fistula-related endpoints. However, for the primary outcomes postoperative pain and anal function, the potential effect of selection bias is substantially mitigated by the balanced baseline characteristics and the fact that these outcomes are primarily determined by the intrinsic tissue trauma and drainage efficiency of each technique. Nonetheless, residual confounding cannot be entirely excluded, and future prospective randomized trials are necessary to confirm the comparative benefits of MICD over ID. Second, the anal continence outcomes were assessed at a single time point (postoperative day 30) by using the Wexner score, which may not fully capture the long-term functional trajectory following PA surgery. Recovery of sphincter function is a gradual process that may continue for several months as postoperative edema subsides and tissues remodel. The 30-day assessment in this study provides meaningful information regarding early functional recovery, which is clinically relevant for patients’ immediate postoperative quality of life and represents a pragmatic endpoint in our retrospective design. However, the possibility of late-onset functional changes or continued improvement beyond this time point cannot be excluded. Future prospective studies should incorporate longer follow-up with serial Wexner or Vaizey score assessments (e.g., at 3 months, 6 months, and 12 months) to provide a more comprehensive evaluation of anal function outcomes. Third, while several important outcomes were evaluated, other aspects, such as patient satisfaction and quality of life, were not assessed. Including these measures in future studies could provide a more comprehensive evaluation of treatment effectiveness. Fourth, a formal cost-effectiveness analysis was not performed. While the MICD procedure involves higher initial consumable costs (catheters and VSD materials), the shorter hospital stay and reduced rates of fistula formation may offset these expenses. Future prospective studies incorporating comprehensive health-economic evaluations are warranted to determine the overall cost-effectiveness of MICD. Fifth, while fistula formation was objectively captured using composite diagnostic criteria, a formal risk assessment model for this endpoint was not performed. The inherent differences in internal opening management between the two techniques represent a fundamental confounding factor that precludes reliable risk prediction. Therefore, the findings regarding fistula rates are limited to descriptive comparison, and they should not be interpreted as a rigorous evaluation of fistula risk. Future prospective studies with standardized internal opening protocols are essential for any meaningful risk assessment. Sixth, postoperative fistula outcomes were not stratified in accordance with recognized anatomical classification systems such as the St. James’s University Hospital MRI classification, primarily because the relatively small number of fistula events precluded meaningful sub-group analyses. Furthermore, systematic postoperative MRI for fistula subtyping was not part of the retrospective protocol, with many fistulas diagnosed by clinical examination alone. Future prospective studies should incorporate standardized postoperative MRI evaluation to enable detailed fistula classification and enhance the interpretability of comparative outcomes between drainage techniques.

In conclusion, this study suggests that MICD may offer significant advantages over conventional ID in the management of high PA, including superior postoperative pain control, better preservation of anal sphincter function, a more favorable inflammatory response, and faster recovery. These findings support MICD as a promising patient-centered alternative, though prospective randomized trials with standardized protocols are warranted to confirm these benefits.

CONCLUSION

This study suggests that MICD may offer potential advantages over traditional ID in the management of PA. MICD appears to be associated with reduced postoperative pain and better preservation of anal function during the early postoperative period. Patients treated with MICD may experience a more favorable inflammatory response and faster recovery (shorter operative time, less blood loss, quicker wound healing, and shorter hospital stay than those treated with ID). Regarding anal fistula formation, while MICD was associated with a lower rate in this cohort, this finding is remarkably confounded by the different intraoperative strategies used to manage the internal opening between the two groups. Therefore, the superiority of MICD in reducing fistula risk remains inconclusive, warranting further investigation through well-designed prospective studies with standardized internal opening protocols.