A perianal abscess (PA) in neonates is a relatively common disease, but it is poorly understood. It is usually considered a trivial disease by physicians. Nevertheless, the discovery of perianal swelling in a neonate can be a source of anxiety for parents. Parents' excessive worry and physicians' insufficient experience make the management of neonatal PA very challenging. However, only rare literature is devoted to it. Therefore, the treatment is usually based on the studies of PA in infants and children.

The management of PA in infants and children is controversial. It has traditionally been treated surgically by incision and drainage (ID) (1–11). However, in the past two decades, some studies have shown that the conservative management appears to be effective in selected cases (12–23). On the other hand, the other studies have recommended that the surgical procedure should involve a careful identification for the fistula and treatment of that by fistulotomy (24–32). Thus, at present, the optimal management has not yet been established.

At our center, PA in infants can be treated either in the department of anorectal surgery or in the department of pediatric surgery. Some infants experienced fistula formation after ID, and were transferred to the department of anorectal surgery. Is ID enough? Is incision and drainage with primary fistulotomy (IDF) better than ID? These ideas prompted us to complete this long-term comparative study.

To the best of our knowledge, no published study in PubMed has directly compared the outcomes of IDF vs. ID for neonatal PA. This study aimed to compare the efficacy and safety of IDF and ID for PA in neonates.

A retrospective case note review was carried out for all consecutive neonates with PA at a single tertiary center between January 2008 and December 2017. At our center, all neonates admitted to the department of anorectal surgery underwent IDF, while all neonates admitted to the department of pediatric surgery underwent ID. Patients with PA undergoing IDF were assigned to the IDF group, and those undergoing ID were assigned to the ID group. Although group allocation was not randomized, it was naturally formed according to the department in which the patients were hospitalized. Neonates with PA received intravenous antibiotics routinely (Ceftazidime in the IDF group and Cefathiamidine in the ID group) for 3–5 days.

The present study was approved by the Affiliated Hospital of Jining Medical University Institutional Review Board. Written informed consent was obtained from all parents.

A total of 147 hospitalized neonates with PA were identified from January 2008 to December 2017 (Figure 1). Of the 9 excluded patients, 5 were excluded because parents refused surgery. Of the 138 included patients, 65 (47.1%) underwent IDF and 73 (52.9%) underwent ID. Follow-up data were available for all but one who had been excluded according to exclusion criteria. The median follow-up was 6.5 years (range 4–13 years).

Patient and abscess characteristics are summarized in Table 1. The 2 groups were similar in respect of gender, age of onset, duration of symptoms, age at admission, number of the abscess, location of the abscess, and length of stay. Of note, inpatient costs were higher in the IDF group vs. the ID group (3,774.0 vs. 2,416.0 Yuan, p = 0.000). Healing time (the time needed for the complete epithelialization of the wound bed) was about 3 and 2 weeks for the IDF group and ID group, respectively.

A comparison of long-term outcomes between the 2 groups is shown in Table 2. The median follow-up for patients undergoing IDF and ID was 5.00 years (IQR, 4.00–7.50) and 7.00 years (IQR, 5.50–9.00), respectively (p = 0.000). Patients in the IDF group had a higher cure rate (98.46 vs. 80.82%, p = 0.001) and a lower fistula formation rate (1.54 vs. 13.70%, p = 0.01) than the ID group. After surgery, 11 patients developed FIA (Figure 2). Of the 3 patients developing FIA after ID, 2 patients were cured after more than 2 years of plaster and Chinese herbal preparations ointment (ingredients unknown), respectively. The third patient was cured with an ointment (ingredients and duration unknown).

None of the patients in the IDF group had a recurrence, while 4 patients in the ID group experienced recurrence (Table 3). Patients undergoing IDF seemed to have a lower abscess recurrence rate (0 vs. 5.48%; p = 0.12), albeit statistical significance was not achieved.

It is noteworthy that 2 (3.08%) patients developed new abscesses at the contralateral side of the anus in the IDF group, compared with 7 (9.59%) patients in the ID group (Table 4). However, the difference between the 2 groups is not statistically significant (p = 0.17).

No fecal incontinence was confirmed in any patients in our study. A 10-year-old boy (undergoing IDF in 2010) with mental illness was found to have stools in his underwear sometimes. It is not sure whether it was caused by surgery or mental illness.

Our long-term study showed that IDF was associated with a higher rate of cure and a lower rate of fistula formation compared with ID. In addition, patients in the IDF group seemed to have a lower rate of abscess recurrence and new-onset abscess, albeit statistical significance was not achieved.

In our study, the cure rate in the IDF group and ID group was 98.46 and 80.82%, respectively. That was similar to a previous report (29) that cure occurred in 61/66 (92%) in whom a fistula was identified and treated by fistulotomy at the initial operation, compared with 19/25 (76%) in whom a fistula was not identified (ID alone). The high cure rate is attributable to careful identification and laying opening of the coexisting fistula. The rate of fistula (between the PA and the anal crypt) identified at the time of primary drainage varies widely in different studies. The percentage of communication between the PA and the internal (anal) opening was <20% (1, 4, 6, 7, 11) or more than 60% (25, 27, 29–32). Our results (approximately 80%) support the latter.

In the IDF group, the fistula formation rate was 1.54% (1/65) and there were no recurrences after surgery. Our findings are supported by several studies. There were no recurrences (26, 27, 31) or the recurrence rate was <15% (29, 30, 32) in patients who underwent fistulotomy at the time of ID. These findings are in excellent agreement with ours. Given this, we recommend that ID and laying open of the coexisting fistulous tract be performed for PA in neonates.

Surprisingly, in the ID group, the rate of fistula formation and recurrence was 13.7 (10/73) and 5.48% (4/73), respectively. These results are better than we expected. Our study with a large sample size confirms that neonates may have a lower rate of fistula formation after ID than infants and children. We believe that our results are valuable to the clinician. In the literature, the rate of fistula formation and recurrence was 10.5 (4/38) and 7.9% (3/38) (5), 6 (2/33) and 12% (4/33) (7), 20 (20/100) and 27 (27/100) (8), 30 (15/50) and 4% (2/50) (9), 3.8 (1/26) and 3.8% (1/26) (23), and 28 (8/29) and 7% (2/29) (24), respectively. It is well-known that fistula formation and abscess recurrence are the two major challenges for PA therapy. Unfortunately, some studies did not distinguish between them (1–3, 11, 14, 18, 29–34). Of those studies, the rate of fistula formation or recurrence after ID varies widely, which was <20% in 2 studies (2, 3), between 20 and 50% in 7 studies (1, 18, 29–32, 34), and more than 50% in 2 studies (14, 33). Altogether, previous studies differed substantially regarding the rate of fistula formation or recurrence after ID. There are several potential reasons for this difference. First, some reports did not distinguish between fistula formation and abscess recurrence. Since fistula formation and abscess recurrence are different, we call for distinguishing them in future studies. Second, the indications for ID varied in the literature. Some surgeons argue that the abscess should be incised as soon as possible, while other surgeons recommend ID should be reserved for patients with failed conservative management, large abscess, or systemic signs of infection. Third, surgical techniques may differ in detail. Fourth, the sample size in some studies was small. Thus, these results should be viewed with caution.

Remarkably, in the present study, 6.5% (9/138) of patients developed new abscesses on the contralateral side of the anus. Several studies have previously reported a similar phenomenon (16, 21, 25, 35, 36), but the reason was unknown.

Some studies show that PA is a self-limited entity. In our study, 4 patients who were excluded, experienced spontaneous drainage, and their parents refused surgery. Notably, 3 patients among them were cured without surgery. Similar results have been reported in other studies (18, 22). However, two other studies have shown different results (10, 12). We believe that there is a possibility of a self-resolution of abscesses. In future studies, we will further investigate the safety and effectiveness of non-operative therapy for PA in neonates who spontaneously drained.

There are several strengths to our study. First, the subjects in this study were neonates with PA, excluding infants and children. It is well-known that different stages of life have different pathophysiological features. PA in neonates, infants, and children may have different clinical characteristics. Limiting the age to newborns helped reduce the potential confounding effects of age and made the conclusions more reliable. Second, to the best of our knowledge, this is the first study directly comparing the outcomes of IDF vs. ID for neonatal PA. Third, our sample size (138 neonates) was very large, which improved the power of the analysis and reduced the bias to a certain extent. Fourth, follow-up data were available for all but one who had been excluded according to exclusion criteria. This is a long-term study with a median follow-up time of 6.5 years. Although various difficulties were encountered, with the aid of the public security bureau, all but one patient were successfully contacted due to the ingenuity, perseverance, and intense effort of our team. Finally, our study included detailed characteristics and course of patients with fistula formation, abscess recurrence, and new-onset abscess after initial surgery, which have not been reported previously.

Of course, some limitations in our study need to be recognized. First, it is a single-center retrospective study, potentially limiting the generalizability of our results. Second, long-term follow-up data were mainly obtained by telephone interviews instead of outpatient reviews. Considering the COVID-19 pandemic, this may be a reasonable alternative method. Third, patients' assignment was not randomized. However, we could be rather certain that it was not assigned by disease severity. At our center, PA in neonates can be treated at the department of anorectal surgery or the department of pediatric surgery. Why patients are admitted to a ward or to another depends on the cognition of the parents, not the severity of the disease. In addition, because of changes in the electronic medical records system, much data were not recorded consecutively, such as body temperature, abscess size, body mass index, white blood cell count, C-reactive protein, procalcitonin, and pus cultures. However, our results showed that important clinical characteristics that might influence the outcome were considerable between the 2 groups (Table 1). Thus, there was no inclusion bias. Fourth, not all the surgeries were performed by the same surgeon. Nevertheless, all of those were performed by experienced surgeons using the standardized technique in each group. Finally, the children are too young to cooperate, so anorectal manometry was not performed, which should be performed in the near future.

Unfortunately, PA in neonates and infants is generally considered a trivial condition. However, there are considerable unresolved questions surrounding it. Long-term prospective studies will be necessary to determine the optimal treatment.

Our long-term follow-up study demonstrated that IDF and ID are both safe and effective treatments for PA in neonates. IDF is associated with a higher rate of cure and a lower rate of fistula formation compared with ID. Our findings support the value of careful identification and laying opening of the coexisting fistula when ID is performed.

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author/s.

The studies involving human participants were reviewed and approved by Affiliated Hospital of Jining Medical University. Written informed consent to participate in this study was provided by the participants' legal guardian/next of kin.

WY: study design, data collection, and drafting of the manuscript. LL: data collection and analysis, article revision, and quality control. LS: data collection, statistical analysis, and article revision. SW: study design, data collection, article revision, and overall responsibility for the article. All authors read and approved the final manuscript.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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