Disease
Etiologies
Risk factors
Clinical presentation
Diverticulosis (30–50 %)
Arterial bleed from vasa recta at base of diverticula
Advanced age, lack of fiber, obesity
Painless bright red blood per rectum (hematochezia) in the absence of stool
90 % of diverticula in sigmoid colon, but 60 % of diverticular bleeds from right colon
Neoplastic (10–20 %)
Colorectal adenocarcinoma may erode or ulcerate
Age >50, African-American race, inflammatory bowel disease, family history, sedentary lifestyle, smoking, obesity, diabetes mellitus type 2
Large LGIB rare
Iron-deficiency anemia and/or change in bowel habits
Iatrogenic
Up to 2 weeks post-polypectomy or biopsy
History of recent colonoscopy
Variable amount of bleeding occurring either immediately or days to weeks after the procedure (likely due to sloughing off of eschar)
Colitis (10–20 %)
Infectious
CMV, Kaposi’s
Enteroinvasive organisms: Salmonella, Campylobacter, Shigella, EHEC, E. histolytica
History of eating undercooked or contaminated foods or drinks
Immunosuppression
Travel history
Bloating
Crampy abdominal pain and tenderness
Fever and chills
Bloody diarrhea
Ischemic
Nonocclusive mesenteric ischemia secondary to low-flow state
Post-op complication of aortic surgery
Hypoperfusion secondary to hypotension, pressors, extreme exercise
Dialysis
History of aortoiliac procedures
Acute abdominal pain and tenderness
Bloody diarrhea
Chronic ischemia can result in stricture formation
Inflammatory
Ulcerative colitis or Crohn’s
Family history of IBD
Bloody diarrhea and mucus in stool
Abdominal pain and cramping
Previous episodes
Radiation
Direct mucosal damage from radiation exposure resulting in arteriolitis
History of pelvic radiation
Bloody diarrhea, tenesmus (feeling of incomplete defecation), mucus discharge
Angiodysplasia (5–10 %)
Aberrant blood vessels in the GI tract
Venous in origin
Usually right sided (cecum or ascending colon)
Advanced age
Associated with von Willebrand’s disease, CKD, aortic stenosis
Painless
Often present with iron-deficiency anemia
Anorectal (5–10 %)
Hemorrhoids—bleeding from the hemorrhoidal venous plexus within the anus
Pregnancy, constipation, straining
4.4 % of US population
Painless bright red blood with straining at bowel movement
Anal fissures
Constipation
Trauma, IBD, malignancies
Minimal blood usually on toilet paper
Tear most commonly posterior midline
Severe, tearing pain with defecation
Rectal varices—bleeding is more proximal (within the rectum)
Portal hypertension
Painless bright red blood per rectum
Rectal ulcers
Advanced age, debilitation, constipation
History of Crohn’s disease
Anterior location
Blood and mucus per rectum, sense of incomplete evacuation
Watch Out
LGIB can be due to a large upper GI bleed (UGIB), always place nasogastric tube to aspirate for blood or coffee grounds (refer to chapter on UGI bleed) and confirm that bile is obtained so that you know you have assessed for duodenal bleeding.
Watch Out
Diverticulosis is the most common cause of lower GI bleed.
Watch Out
Patients with watery progressing to bloody diarrhea and no fever should always be evaluated for EHEC.
What Is the Most Likely Diagnosis?
An elderly patient with a recent normal colonoscopy who presents with a large amount of bright red blood per rectum most likely has a lower GI bleed and is most likely due to colonic diverticulosis.
Mnemonic for Most Common Causes of a LGIB Is H-DRAIN
Hemorrhoids
Diverticular bleeds
Radiation colitis
Angiodysplasia
Infectious/ischemic/IBD
Neoplasms/polyps
History and Physical
Why Is Age an Important Factor in a Patient with a LGIB?
Acute LGIB in patients over age 50 is more likely to be diverticulosis, angiodysplasia, or malignancy, whereas in younger patients, the most common causes are infectious, hemorrhoids, anal fissures, and IBD.
Why Are the Onset and Duration of Bleeding Important?
Diverticular bleeding is arterial and as a result tends to present acutely with relatively large amounts of blood. Angiodysplasia and cancer are more chronic, and are more likely to present only with anemia or dark stools.
What Do the Color and Amount of Blood Tell us About the Source of Bleeding?
Color, amount of bleeding | Possible source(s) |
Dark maroon, mixed with stools | Upper GI, small intestine, right colon |
Copious bright red blood (hematochezia) a | Right colon (e.g., diverticulum), rectum, anus, massive upper GI bleed with rapid transit |
Spots of blood on toilet paper, dripping after defecation | Rectum, anus |
Scant, dark red blood | Angiodysplasia |
Occult | Polyp, colorectal cancer |
Watch Out
Right colonic diverticula are more likely to bleed while left colonic diverticula are more likely to get infected.
What Is an Occult Bleed?
Occult bleeding means that the patient does not see any blood per rectum. The bleeding is only detected by fecal occult blood testing or by finding iron-deficiency anemia. Occult bleeding (particularly in older patients) raises suspicion for malignancy (especially colorectal cancer), and in younger patients, it may be due to inflammatory bowel disease or due to familial cancer syndromes (e.g., Familial Adenomatous Polyposis, Hereditary nonpolyposis colorectal cancer).
What Associated Symptoms Are Important to look for and How Do They Help in the Differential Diagnosis?
Systemic symptoms such as fever and bloody diarrhea may indicate an infectious or inflammatory cause. Recurrent symptoms in younger patients are suspicious for IBD. Weight loss should raise suspicion for malignancy, especially in older patients who have changes in bowel habits and/or iron-deficiency anemia. Bleeding that follows straining at stool suggests an anorectal cause. In this latter setting, painless bleeding suggests internal hemorrhoids, whereas anal pain is suggestive of anal fissures (bleeding with fissures is usually minimal). Tenesmus, a sense of incomplete evacuation of stool, is most often seen with ulcerative colitis and infectious etiologies. Bleeding from diverticulosis and angiodysplasia tends to be painless. Abdominal pain (especially in elderly patients) should raise suspicion for ischemic colitis (particularly in the setting of low-flow states).
Watch Out
Bloody diarrhea with recent travel to endemic areas raises suspicion for infectious causes.
Why Is a Past History of LGIB on prior colonoscopy Important?
Patients with angiodysplasia tend to present with recurrent, painless bleeds. Patients with diverticulosis may also have chronic bleeding, although larger, acute bleeds are more typical. Colon cancer typically arises from a polyp and takes many years to transform to a malignant lesion. Thus, a history of a recent (<5 years) normal screening colonoscopy makes colon cancer very unlikely.
Why Is a History of Pelvic Radiation on Prior Aortic Surgery Important?
Radiation can cause damage to the rectal mucosa, leading to radiation proctitis. Aortic surgery rarely results in erosion of the aortic graft into the duodenum, leading to an aortoduodenal fistula.
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