Comparison of inconclusive rates between suction rectal biopsy and open strip rectal biopsy in children of different age groups: a single-center retrospective study

Introduction

First described in 1887, Hirschsprung’s disease (HD) is a condition characterized by the lack of ganglion cells normally found in the myenteric and submucosal plexuses of the colon. This aganglionic segment leads to a failure to relax resulting in a functional obstruction. It typically presents in neonates with features of complete bowel obstruction with delayed passage of meconium (greater than 48 hours of life), abdominal distension and vomiting.1 In addition to these clinical features, the NICE guidelines (2017) also recommend that the presence of either chronic constipation, a family history of HD and/or faltering growth would necessitate further evaluation for HD.2

The gold-standard test for diagnosing HD is rectal biopsy, which requires histological evaluation of the submucosal plexus and myenteric plexus to delineate an absence of ganglion cells and hypertrophic nerve trunks.3 The first suction rectal biopsy (SRB) technique was introduced by Dobbins and Bill in 1961 and built on by Noblett in 1969 including side apertures and a cylindrical knife.4–6 Our institution uses the newer rbi2 model which has been shown to be superior to the Noblett forceps at producing lower rates of inconclusive samples and being more cost-effective.7

There is no recognized age cut-off for using SRB, but current notions suggest that it should not be used in older infants due to the increased fibrous tissue in their rectal wall leading to higher rates of inconclusive results.5 8 Previous studies have reported that SRB were suitable for use in patients less than 6 months old8 9 while others found conclusive results in patients up to one year of age.10 11 One study even recommended the use of SRB in children above the age of five.12 Open strip biopsy (OSB) is currently the preferred method for older infants who require a general anesthetic to obtain rectal samples. Our institution, similarly, does not have a specific age limit for when each rectal biopsy technique should be used but has trend toward using SRB in the first instance due to its relative ease of use, cost-effectiveness and lower risk of complications compared with OSB.

This single-center study aims to compare the diagnostic accuracy of SRB with that of OSB in children of different age groups.

Methods

Results

A total of 87 rectal biopsies were performed on 77 patients during the study period. One open biopsy performed during laparotomy and one forceps biopsy from two different patients were excluded. A further six rectal biopsies (three SRB and three OSB) from four different patients were excluded due to the history of endorectal pull-through surgeries for HD. A total of 79 biopsies (57 SRB and 22 OSB) from 71 patients were thus included in the study.

Sixty-two per cent (49/79) of patients were male while 38% (30/79) of patients were female overall. The study population had a median age of 34 (IQR 6–64) months overall. Nine neonates (aged <1 month) were included with SRB performed on all of them. Eight neonates were referred due to clinical and radiological features consistent with large bowel obstruction while one was referred due to delayed passage of meconium. Moreover, 93.5% (58/62) of patients aged 1 month and above were referred for constipation while 6.5% (4/62) were referred for suspected bowel obstruction.

Eight patients were ultimately diagnosed with HD and underwent endorectal pull-through surgery while two patients were diagnosed with anorectal malformations and underwent anorectoplasty surgery. There were no complications associated with either biopsy technique.

Twelve biopsies (nine SRB and three OSB) from ten patients were deemed inconclusive. Table 1 shows a breakdown for each biopsy by number, type, age at time of procedure and final diagnosis.

One patient had a conclusive SRB performed at 3 years old with the sample reporting minimal submucosa for assessment but with three definite ganglions identified, effectively ruling out HD. The patient continued to suffer from chronic constipation and subsequently underwent an MRI which raised the possibility of a transition zone. He had a further conclusive OSB at 4 years old which again ruled out HD.

A further breakdown of all the histological reasons why biopsies were deemed inconclusive is given in table 2.

Table 3 shows no significant differences in gender distribution between the SRB and OSB groups (p=0.121). Patients in the OSB group had a higher median age in months compared with the SRB group, but this was not statistically significant (p=0.096). One hundred per cent of neonates included in the study had SRB performed. Notably, there was no significant difference in the rate of inconclusive results between SRB and OSB overall (15.8% vs 13.6%, p=1.000).

Table 4 shows no significant difference in the rate of inconclusive results between SRB and OSB when patients were further divided into those aged under 1 year (30% vs 33.3%, p=1.000) and those aged 1 year and above (8.1% vs 10.5% p=1.000).

Similarly, table 5 shows no significant difference in the rate of inconclusive results between SRB and OSB in patients aged 1–2 years (16.7% vs 0%, p=1.000), aged 3–4 years (0% vs 22.2%,p=0.471) and those aged 5 years and above (6.3% vs 0%, p=1.000).

Discussion

Our study set out to find whether SRB produced similar rates of inconclusive results as OSB in patients with different age groups. Earlier studies suggested that SRB should only be performed in children younger than 6 months of age.8 9 This age limit was subsequently increased with children up to 1 year of age deemed suitable for SRB.10 11 Croffie et al found that SRBs, when performed in children older than 3 years, were less likely to provide adequate submucosa to identify ganglion cells compared with uterine grasper forceps.5 Even more recently, Brady et al found that SRB yielded accurate results even in children older than 5 years.12

Overall, our study found no significant difference in rates of inconclusive results between SRB and OSB (15.8% for SRB vs 13.6% for OSB, p=1.000). We also found no significant difference when patients were further divided into those aged under 1 year and those aged over 1 year or when subdivided into different age groups. This finding suggests that SRB provides comparable rates of inconclusive results with OSB in patients of all age groups as recently demonstrated in a study by Muise et al.13 They, however, found that SRB produced equivalent submucosa to OSB which differed from our own study’s finding that SRB specimens were less thick than OSB specimens (2 mm vs 3 mm, p<0.001) leading to a higher proportion of inconclusive results due to being superficial with limit to no submucosa present (77.8%). Previously established consensus for any rectal biopsy specimen included a depth of 1 mm with equal mucosa and submucosa,14–16 and our study’s median thickness of 2 mm for SRB was still within range.

Interestingly, a higher proportion of patients with an inconclusive and superficial SRB were aged less than 1 year compared with more than 1 year (57.1% vs 42.9%, p=1.000). Despite the small sample size, this finding contradicts the popular belief that SRB yields more superficial and inconclusive results in older infants due to their thicker and more fibrous rectal wall.

Our study’s operative records reported that OSB was taken at least 1–2 cm from the estimated dentate line. However, all inconclusive results for OSB resulted from specimens being obtained too distal in the rectum with the presence of anorectal junction mucosa. This was due to inaccurate estimation of the dentate line by the operator resulting in the specimen being obtained closer than estimated. SRB, on the other hand, typically involved at least two or three samples, each 1 cm apart, starting 2 cm from the dentate line. Moreover, the rbi2 disposable capsule contained 1 cm markings which made it easier to gauge the distance required. This greatly reduceed the likelihood for samples obtained too distally.

The retrospective nature of our study makes it susceptible to various inherent biases which impact on the accuracy of the data. The relatively small population size also restricts its ability to demonstrate statistical significance. Certain variables which could potentially alter the findings of the study were either inconsistently reported or not reported at all. The distance from the dentate line where each SRB was obtained was inconsistently reported. This was also true to a lesser degree for OSB.

From a histological point of view, inconsistently reported features such as calretinin stain (which was not introduced at our institution until 2016 and performed in only 60.8% of biopsies) and nerve diameter (reported in only 46.8% of biopsies) have potential to alter our primary outcome if recorded accurately. Furthermore, the submucosa is qualitatively assessed by the pathologist and whether the submucosal tissue is deemed adequate may vary from one pathologist to another.

Despite the above limitations, our study supports newer literature advocating for use of SRB in children of all ages. Its relative ease of use, cost-effectiveness and lower risk for complications make it an ideal technique for obtaining rectal biopsies. Future research would ideally consist of multicenter prospective cohort studies looking at replicating or further emphasizing the current study’s findings on a larger scale. Standardized recording of specific operative details (such as distance from dentate line and operator level) and histological features (such as calretinin stain, nerve diameter, quantity of submucosa) also have potential to affect the outcome of each biopsy sample. A cost-analysis study would help quantify how effective SRB is compared with other biopsy techniques while a survey distributed to pediatric surgical trainees could look at how easy the rbi2 biopsy gun is to use.