What does an empty rectum mean in a per rectal (PR) examination?

Empty Rectum in Per Rectal Examination: Clinical Significance and Interpretation

An empty rectum on per rectal examination typically indicates the absence of stool in the rectal vault, which is actually the normal physiological state in healthy individuals without diarrheal disease. 1

Physiological Basis of Rectal Emptiness

The rectum functions as both a conduit and a storage organ in the digestive system. Contrary to what some might expect, the rectum is usually empty in healthy individuals. This occurs because:

• The rectum normally remains empty until just before defecation when stool moves from the sigmoid colon into the rectum
• When stool enters the rectum, it triggers the rectoanal inhibitory reflex, which normally leads to the urge to defecate
• After defecation, the rectum returns to its empty state

Research shows that in subjects without diarrhea, the rectum is empty approximately 69% of the time 1. This supports the concept that the rectum primarily serves as a conduit rather than a continuous storage organ in normal physiology.

Clinical Significance of Empty Rectum

An empty rectum during digital rectal examination can indicate several clinical scenarios:

Normal Findings:

• Recent bowel movement (typically within the past 5-6 hours) 2
• Normal bowel function with appropriate emptying

Potential Pathological Findings:

1. Proximal obstruction: May indicate blockage above the rectum, preventing stool from reaching the rectal vault
2. Constipation with incomplete descent: Stool may be present in the upper rectum but not palpable on digital examination 2
3. Complete evacuation in diarrheal conditions: In active diarrhea, the rectum may be empty due to frequent emptying

Comparison with Abnormal Findings

When interpreting an empty rectum finding, it's important to contrast it with other potential findings:

• Loaded/full rectum: May indicate constipation, fecal impaction, or poor rectal emptying
• Presence of blood: May indicate gastrointestinal bleeding, hemorrhoids, or rectal lesions 3
• Abnormal sphincter tone: May suggest neurological issues affecting defecation 4

Assessment During Digital Rectal Examination

During a proper digital rectal examination, the American Gastroenterological Association recommends the following components 4:

1. Position the patient in left lateral position with buttocks separated
2. Observe perineal descent during simulated evacuation
3. Evaluate resting tone of the sphincter and its augmentation during squeezing
4. Assess the puborectalis muscle, which should contract during squeeze
5. Ask the patient to attempt to expel your finger to evaluate expulsionary forces

Clinical Decision Making

When encountering an empty rectum on examination:

• If expected (recent defecation): No further action needed
• If unexpected (patient reports constipation): Consider:
  • Possible proximal obstruction requiring further evaluation
  • Potential defecatory disorders
  • Need for additional diagnostic testing such as anorectal manometry or defecography

Diagnostic Value

The digital rectal examination finding of an empty rectum has important diagnostic implications:

• High negative predictive value (99%) for excluding certain conditions 5
• Should be interpreted in conjunction with other clinical indicators for maximum diagnostic utility 6
• May help differentiate between slow-transit constipation and rectal evacuation disorders when combined with other findings 6

Conclusion

An empty rectum on per rectal examination is a normal finding in most healthy individuals and represents the physiological state of the rectum between defecation cycles. However, when interpreted in the context of the patient's symptoms and other clinical findings, it can provide valuable diagnostic information about potential gastrointestinal disorders.