3.3 Small & Large Bowel Disorders (IBD, Diverticulitis, Obstruction)

Small and Large Bowel Disorders

Intestinal disorders are heavily tested on the PANCE. Clinicians must be able to differentiate inflammatory bowel diseases, recognize the presentation and management of acute diverticulitis, and identify the hallmark radiographic and clinical features of small bowel obstruction.

Inflammatory Bowel Disease: Crohn's vs. Ulcerative Colitis

Inflammatory Bowel Disease (IBD) consists of Crohn's disease and Ulcerative Colitis, two chronic inflammatory conditions with distinct clinical, endoscopic, and histopathological features.

• Crohn's Disease: Crohn's disease can affect any segment of the gastrointestinal tract from the mouth to the anus, though the terminal ileum and colon are the most common sites. Rectal sparing is typical. The inflammation is transmural, involving the entire thickness of the bowel wall, which leads to complications like strictures, fistulae, perianal disease, and intra-abdominal abscesses. Endoscopy characteristically demonstrates "skip lesions" (areas of active inflammation interspersed with normal-appearing mucosa) and a "cobblestone" mucosal pattern. Histopathology shows non-caseating granulomas, which are pathognomonic but not always present. Serologically, it is associated with anti-Saccharomyces cerevisiae antibodies (ASCA). Common extraintestinal manifestations include aphthous stomatitis, erythema nodosum, uveitis, episcleritis, and nephrolithiasis (calcium oxalate stones due to fat malabsorption in the terminal ileum).
• Ulcerative Colitis: Ulcerative Colitis is strictly limited to the colon and rectum, presenting as continuous mucosal and submucosal inflammation that starts at the rectum and extends proximally. Endoscopy reveals friable mucosa, superficial ulcerations, and pseudopolyps. Barium or contrast studies may show a loss of haustral markings, creating a "lead pipe" appearance. Histopathology reveals crypt abscesses and mucosal inflammation, with no granulomas. Serologically, it is associated with perinuclear anti-neutrophil cytoplasmic antibodies (p-ANCA). Complications include toxic megacolon (defined as colonic dilation >6 cm on abdominal radiograph with systemic toxicity) and a significantly elevated risk of colorectal adenocarcinoma. The most specific extraintestinal manifestation is primary sclerosing cholangitis (PSC), a chronic progressive cholestatic liver disease. Total proctocolectomy is curative for Ulcerative Colitis, whereas surgery in Crohn's disease is reserved for complications due to high recurrence rates at anastomotic sites.

Pharmacological Management of IBD

First-line therapy for the maintenance of mild-to-moderate Ulcerative Colitis and colonic Crohn's disease is 5-aminosalicylic acid (5-ASA) derivatives, such as mesalamine or sulfasalazine. Topical formulations (suppositories or enemas) are preferred for distal colitis, while oral agents are used for proximal disease. Corticosteroids (e.g., oral prednisone, budesonide, or IV methylprednisolone) are indicated for the rapid induction of remission during acute flares but are strictly contraindicated for long-term maintenance due to adverse systemic effects. For moderate-to-severe or steroid-refractory disease, immunomodulators (e.g., azathioprine, 6-mercaptopurine) or biologic agents (e.g., anti-TNF-alpha antibodies like infliximab or adalimumab) are indicated.

Acute Diverticulitis

Diverticulitis is localized microperforation and inflammation of a diverticulum, which is a herniation of the mucosa and submucosa through the muscular layers of the colonic wall. It is most common in the sigmoid colon. Patients present with constant, severe left lower quadrant (LLQ) abdominal pain, low-grade fever, nausea, vomiting, and leukocytosis. The diagnostic imaging modality of choice is computed tomography (CT) of the abdomen and pelvis with intravenous contrast, which typically shows colonic wall thickening (>3 mm), pericolic fat stranding, and diverticula. Colonoscopy and barium enemas are strictly contraindicated in the acute phase of diverticulitis due to the high risk of converting a microperforation into a free perforation. Uncomplicated diverticulitis is managed with bowel rest (clear liquid diet) and oral broad-spectrum antibiotics, typically a combination of fluoroquinolones (e.g., ciprofloxacin) and metronidazole, or amoxicillin-clavulanate. Complicated diverticulitis, characterized by abscess formation (>4 cm), free perforation, or peritonitis, requires hospitalization, intravenous fluids, IV antibiotics (e.g., piperacillin-tazobactam), and potentially surgical intervention (such as a Hartmann's procedure or primary anastomosis).

Small Bowel Obstruction (SBO)

Small bowel obstruction is mechanical blockage of the small intestine. The most common etiology is postoperative adhesions from prior abdominal surgeries, followed by hernias (inguinal or femoral) and neoplasms. Patients present with crampy, paroxysmal abdominal pain, early bilious vomiting, abdominal distention, and obstipation (inability to pass flatus or stool). Physical examination reveals abdominal distention and tympany to percussion. Auscultation of bowel sounds demonstrates hyperactive, high-pitched, "tinkling" sounds in early stages, which progress to hypoactive or silent bowel sounds as the bowel fatigues. Diagnostic workup begins with plain abdominal radiographs (upright and supine views). Characteristic findings include:

1. Dilated loops of small bowel (>3 cm in diameter).
2. Air-fluid levels in a "step-ladder" pattern on the upright view.
3. Paucity or complete absence of gas in the colon. If radiographs are inconclusive or to determine the transition point and check for strangulation, a contrast-enhanced CT scan of the abdomen and pelvis is performed. Initial management of uncomplicated SBO is conservative, consisting of bowel rest (NPO), aggressive intravenous fluid resuscitation with isotonic crystalloids, and nasogastric (NG) tube decompression to relieve gastric distention. Emergency surgical intervention (laparotomy or laparoscopy) is indicated for signs of strangulated or ischemic bowel, such as fever, persistent tachycardia, leukocytosis, localized peritonitis (rebound, rigidity), or free air on imaging.

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Anorectal Disorders: Hemorrhoids and Anal Fissure

Anorectal complaints are common in primary care and appear under the GI/Nutrition blueprint (colorectal disorders).

Hemorrhoids

Hemorrhoids are engorged, fibrovascular cushions in the anal canal. They are classified by their relationship to the dentate (pectinate) line.

• Risk Factors: Constipation, straining, prolonged sitting, pregnancy, obesity, chronic cough, heavy lifting.
• Clinical Presentation: Painless bright red hematochezia on toilet paper or dripping into the toilet bowl (internal). Painful anal lump, especially when thrombosed (external).
• Management:
  1. Conservative: High-fiber diet, adequate fluid intake, stool softeners, warm sitz baths, topical hydrocortisone (short courses).
  2. Rubber band ligation — first-line procedural treatment for symptomatic internal hemorrhoids.
  3. Excision — for thrombosed external hemorrhoids within 48-72 hours of onset.
  4. Hemorrhoidectomy — for grade III-IV internal hemorrhoids or mixed internal-external disease.

Anal Fissure

An anal fissure is a linear tear in the anoderm, most commonly caused by passage of hard stools.

• Location: 90% are in the posterior midline (because the posterior anal canal has relatively poor blood supply). Anterior midline fissures are more common in women and may indicate Crohn disease or trauma.
• Clinical Presentation: Sharp, tearing pain during defecation that persists for hours afterward, with bright red blood on the toilet paper. A sentinel skin tag may be present externally.
• Diagnostic Clue: The fissure is typically too painful to allow digital rectal exam — the history alone often establishes the diagnosis.
• Management:
  1. First-line: Fiber supplementation, stool softeners, warm sitz baths, and topical agents.
  2. Topical nitroglycerin ointment (0.2-0.4%) or calcium channel blocker ointment (diltiazem 2%) — relax the internal anal sphincter, reduce resting anal pressure, and improve blood flow to promote healing. Headache is the main side effect of nitroglycerin.
  3. Botulinum toxin injection — for refractory fissures; chemically denervates the internal sphincter.
  4. Lateral internal sphincterotomy — surgical option for chronic, refractory fissures. Risk: incontinence.
• PANCE Trap: Multiple fissures, fissures off the midline, or non-healing fissures suggest Crohn disease, HIV, tuberculosis, syphilis, or anal carcinoma — biopsy and evaluate for underlying disease.