What are the possible causes of bright red rectal bleeding in a 54‑year‑old woman with a normal colonoscopy one month ago?

Bright Red Rectal Bleeding After Recent Normal Colonoscopy

In a 54-year-old woman with bright red rectal bleeding and a normal colonoscopy one month ago, the most likely causes are internal hemorrhoids or anal fissures that were either missed or have developed since the examination, though you must still rule out missed proximal lesions and consider post-polypectomy bleeding if polyps were removed. 1, 2

Most Likely Anorectal Causes

• Internal hemorrhoids are the leading cause of isolated bright red rectal bleeding, appearing as scanty blood that is bright red in color on the stool surface or toilet paper. 1, 2

• Anal fissures present with bright red blood on toilet paper or stool surface, typically accompanied by anal pain during and after defecation. 3

• These anorectal conditions can develop rapidly or may have been present but not adequately visualized during the initial colonoscopy, particularly if dedicated anoscopy was not performed. 1

Critical Diagnostic Steps Required Now

• Perform direct visual inspection with anoscopy or proctoscopy to identify thrombosed external hemorrhoids, skin tags, prolapsed internal hemorrhoids, anal fissures, abscesses, or fistulas—this is essential even with a recent normal colonoscopy. 4, 1

• Digital rectal examination must be performed to assess for masses, fissures, and hemorrhoids, though a normal DRE does not eliminate the need for direct visualization. 1

• Check complete blood count to assess for anemia, which would suggest more significant or chronic bleeding. 1

When the Recent Colonoscopy May Have Missed Pathology

• Up to 9% of bright red rectal bleeding originates from lesions beyond the reach of standard examination, including more proximal colonic sources that may have been inadequately visualized. 5

• Vascular lesions (arteriovenous malformations, angiodysplasia) are notoriously difficult to detect and may only bleed intermittently; urgent CT angiography before repeat colonoscopy increases detection rates by approximately 15% for vascular lesions. 4

• Small or flat polyps and early cancers can be missed even on careful colonoscopy, particularly in the right colon or if bowel preparation was suboptimal. 5, 6

• Post-polypectomy bleeding can occur up to 2-3 weeks after polyp removal—verify whether any polyps were removed during the recent colonoscopy. 4

Red Flags Requiring Urgent Re-evaluation

• Blood mixed throughout the stool rather than just on the surface suggests a more proximal colonic source. 1

• Presence of mucus with blood, watery diarrhea, cramping, urgency, or abdominal pain suggests inflammatory bowel disease or infectious colitis. 1

• Anemia or ongoing significant bleeding warrants repeat colonoscopy within 24 hours, as the colorectal cancer risk in patients with rectal bleeding ranges from 2.4-11%. 4, 2

• Any systemic symptoms (fever, weight loss, altered bowel habits) mandate immediate comprehensive re-evaluation. 1

Common Diagnostic Pitfall to Avoid

• Never attribute all rectal bleeding to hemorrhoids without proper anoscopic examination, even with a recent normal colonoscopy, as hemorrhoids are extremely common and may coexist with more serious pathology that was missed. 1, 2

• The presence of hemorrhoids on examination does not exclude other pathology—colonoscopy findings in patients with intermittent rectal bleeding show concomitant significant lesions in 48% of cases regardless of anorectal findings. 6

Recommended Diagnostic Algorithm

1. Immediate anoscopy/proctoscopy to visualize the anal canal and distal rectum for hemorrhoids, fissures, or other anorectal pathology. 4, 1

2. If no clear anorectal source is identified or bleeding continues despite treatment of identified hemorrhoids/fissures, proceed to repeat colonoscopy to evaluate for missed lesions, particularly vascular malformations. 4, 5

3. Consider CT angiography before repeat colonoscopy if bleeding is ongoing or recurrent, as this increases detection of vascular lesions that may have been missed. 4

4. If bleeding is severe or associated with hemodynamic changes, perform upper endoscopy as well, since 10-15% of severe hematochezia originates from upper GI sources. 4, 1