STEPTRACKERGASTROINTESTINAL | PATHOLOGY + MICROBIOLOGY | HIGH-YIELD REVIEW

Colon Disorders

Pouches, bleeding vessels, the inflamed appendix, the colitis you can't see and the colitis antibiotics cause.

FOCUS ON
Diverticulosis = false pouches in the sigmoid, painless bleeding. Diverticulitis = LLQ pain + fever ("left-sided appendicitis"). Angiodysplasia = right colon, elderly, aortic stenosis. Microscopic colitis = watery diarrhea with a normal colonoscopy. C difficile = after antibiotics, pseudomembranes.
DISORDER
MECHANISM · CAUSE
FEATURES
CLUE · TREATMENT
Diverticulosis
False diverticula (mucosa + submucosa) where vasa recta pierce the muscularis; low fiber → ↑ intraluminal pressure
Usually sigmoid; asymptomatic or painless hematochezia
Most common cause of lower GI bleed in older adults
Diverticulitis
Obstruction of a diverticulum → inflammation, microperforation
LLQ pain, fever, leukocytosis
CT · complications: abscess, perforation, stricture, colovesical fistula (pneumaturia) · no colonoscopy acutely
Angiodysplasia
Dilated, tortuous submucosal vessels; acquired with age
Cecum / ascending colon; recurrent painless bleeding, iron deficiency
Heyde syndrome: aortic stenosis (vWF cleaved by shear) · ESRD
Appendicitis
Luminal obstruction: fecalith (adults), lymphoid hyperplasia (children) → distension, ischemia, infection
Periumbilical pain → McBurney point (RLQ); anorexia, nausea, fever
Rovsing, psoas, obturator signs · CT / US · appendectomy
Pseudomembranous colitis
C difficile toxins A and B after antibiotics (clindamycin, fluoroquinolones, cephalosporins) or PPIs
Watery diarrhea, cramps, fever; yellow-white pseudomembranes
Stool PCR/toxin · oral vancomycin or fidaxomicin · fecal transplant for recurrence
Microscopic colitis
Immune-mediated; drugs (NSAIDs, PPIs, SSRIs); autoimmune associations
Older women, chronic watery diarrhea; normal colonoscopy
Collagenous: thick subepithelial collagen band · lymphocytic: ↑ intraepithelial lymphocytes
Irritable bowel syndrome
Functional disorder: altered gut-brain signaling, visceral hypersensitivity
Recurrent pain related to defecation + change in stool frequency or form; diarrhea, constipation or mixed
No weight loss, blood or nocturnal symptoms · women; anxiety, depression
Hemorrhoids
Dilated vascular cushions; straining, pregnancy, constipation
Internal (above dentate line, visceral nerves): painless bleeding · external (below, pudendal): painful if thrombosed
Not portal hypertension
Anal fissure
Tear in the anoderm below the dentate line; hard stool
Severe pain with defecation, bright red blood; posterior midline
Off-midline fissure → Crohn, HIV, cancer
Acute colonic pseudo-obstruction
Ogilvie syndrome: autonomic imbalance in sick, postoperative, elderly patients
Massive colonic (cecal) dilation without obstruction
Cecum > 12 cm → perforation risk · neostigmine

Mechanism — why the sigmoid pouches out

Low-fiber dietSmall hard stool
→
Segmental contraction↑ Intraluminal pressure
→
Weak pointsWhere vasa recta enter
→
False diverticulaSigmoid (narrowest)
Vasa recta stretched over the dome
→
Painless bleed
Obstruction → diverticulitis

Lower GI bleeding by age

AGE
MOST LIKELY
CLUE
Infant / toddler
Meckel, intussusception, fissure
Painless vs currant jelly vs painful
Child / teen
Juvenile polyp, IBD
Painless rectal polyp
Young adult
Hemorrhoids, fissure, IBD
Blood on paper
Older adult
Diverticulosis, angiodysplasia, cancer
Painless large bleed vs iron deficiency
After hypotension
Ischemic colitis
Pain then blood

How it's tested

COMMON CONFUSIONDiverticulosis bleeds without pain. Diverticulitis hurts (LLQ) and rarely bleeds. Angiodysplasia also bleeds painlessly but sits on the right.
THE TRAPA patient with chronic watery diarrhea and a normal-looking colonoscopy still needs biopsies. Microscopic colitis is only seen under the microscope.
YOUR APPROACHPain or not + location (left or right) + age + drug or antibiotic history + bleeding vs watery stool → narrow to one diagnosis.

If you see… think…

Elderly patient, large painless hematochezia → diverticulosis
LLQ pain, fever, leukocytosis → diverticulitis — CT
Air in urine in a man with past diverticulitis → colovesical fistula
Aortic stenosis + recurrent GI bleeding → angiodysplasia (Heyde)
Periumbilical pain moving to the RLQ → appendicitis
Diarrhea a week after clindamycin, yellow plaques on colonoscopy → C difficile
Older woman on NSAIDs, watery diarrhea, normal colonoscopy → microscopic colitis
Thick subepithelial collagen band on colon biopsy → collagenous colitis
Painless bright red blood on toilet paper → internal hemorrhoids
Severe pain with stool, posterior midline tear → anal fissure