What is the evidence comparing microenema versus no bowel prep for prostate MRI image quality?

1. The evidence base: study types and endpoints

The literature includes retrospective cohort comparisons, paired prospective designs, multi‑reader quality‑assurance studies and systematic/critical reviews; common endpoints are rectal gas level, gas‑related artifacts on DWI, subjective image quality scores, PI‑QUAL assessments and, less commonly, diagnostic outcomes such as false‑negative rates for clinically significant cancer ^{[1] [7] [8] [9]}. Several studies rely on blinded reader scoring with interobserver agreement reported as moderate for artifact and image quality metrics ^{[10] [1]}.

2. What the positive studies report

Multiple reports conclude that microenema administered immediately before scanning significantly reduces rectal gas and associated susceptibility artifacts and improves DWI quality; one multi‑reader retrospective series of 171 patients showed significant DWI image‑quality gains and higher PI‑QUAL scores after microenema versus none ^{[1] [3]}. A preliminary study synthesizing several institutions’ results likewise concluded that microenema “seems to significantly improve image quality of DWI and the whole mpMRI image set of the prostate,” and related work documents reduced stool/gas and fewer DWI artifacts after microenema ^{[2] [11] [12]}.

3. Conflicting findings and limitations in effect size

Not all data are unequivocal: some prospective paired and cohort studies report only modest effects of enemas on DWI distortion and overall image quality, and at least one study found that enema preparation did not decrease false‑negative PI‑RADSv2 findings for clinically significant cancer ^{[7] [13]}. Reviews and critical appraisals note mixed results across studies and emphasize heterogeneity in enema type/timing, MRI field strength and sequences, reader scoring systems and outcome measures—factors that limit pooling and clear generalization ^{[9] [5] [14]}.

4. Mechanisms, practical tradeoffs and alternative interventions

The rationale for microenema is straightforward: evacuation of stool/air reduces air–tissue interfaces that induce susceptibility artifacts that most profoundly degrade DWI, especially at higher field strengths ^{[2] [5]}. Alternative or adjunct approaches studied include Fleet’s cleansing enemas, dietary restrictions, and antispasmodics (hyoscine butylbromide); results show that antispasmodics and dietary restriction generally lack benefit, while cleansing enemas may reduce distention but often have only modest downstream gains in DWI or overall image quality ^{[2] [7] [4]}.

5. What this means for diagnostic performance and guidelines

Crucially, improved image quality metrics do not automatically equate to better diagnostic accuracy; few studies link microenema use to meaningful changes in clinically important endpoints such as detection of clinically significant prostate cancer or biopsy outcomes, and some paired designs failed to show reduced false negatives ^{[13] [7]}. PI‑RADSv2.1 and recent reviews note the absence of consensus and call for standardized prospective trials that measure diagnostic yield rather than only artifact scores ^{[5] [6]}.

6. Bottom line and research priorities

Current evidence supports that a microenema immediately before prostate mpMRI reliably reduces rectal gas and often improves subjective and PI‑QUAL measures of DWI image quality compared with no bowel prep, but effect sizes vary and the impact on diagnostic accuracy is insufficiently proven; heterogeneity in study methods and outcomes undercuts a universal recommendation ^{[1] [2] [9]}. High‑quality randomized or paired prospective trials that standardize enema type/timing, MRI protocols and that link image‑quality changes to biopsy or clinical outcomes remain the critical next step flagged in reviews and editorials ^{[14] [6]}.