Patología Gastrointestinal 11/11

Gastrointestinal Pathology and Imaging

Core Imaging Principles

• The lecture focuses on using imaging to assess the gastrointestinal tract, from the esophagus through the large intestine.
• A key question is whether the bowel wall is abnormally thickened. The lecture gives a normal wall thickness of approximately 3–5 mm. Thickening can reflect inflammation, infection, or a tumor.
• Thickening may narrow the bowel’s lumen and help explain symptoms such as difficulty swallowing or intestinal obstruction.
• The bowel wall has several layers. Their differing blood supply affects how they appear after contrast:
  • More vascular layers generally enhance more.
  • The less vascular submucosa tends to enhance less.
  • Fluid or edema between layers can make the layers distinguishable on imaging.
• Adequate distension matters. A collapsed stomach or bowel segment can appear falsely thickened. Studies assessing the stomach or other digestive segments should distend them sufficiently—often with fluid or air—before wall thickness is judged.

Abdominal X-Rays: Uses and Limitations

Plain abdominal radiographs are quick and relatively inexpensive, but they have limited sensitivity and specificity for acute abdominal conditions. A normal X-ray does not rule out serious disease, and abnormal findings may not identify the cause.

They are most useful for selected questions, including:

• Bowel dilation and obstruction.
• Free air suggesting perforation, particularly on an upright image.
• Some volvulus patterns, especially cecal or sigmoid volvulus.
• Certain radiopaque foreign bodies, calcifications, or stones.
• Indirect signs of fluid, masses, trauma-related bleeding, or infection.

Many findings are indirect: X-rays may show that something is abnormal without showing exactly what caused it. CT, MRI, ultrasound, endoscopy, or other tests may be needed for further evaluation.

Suggested Approach to Reading an Abdominal X-Ray

1. Assess fat planes and anatomical outlines.

   • Check whether the expected fat lines are visible and symmetric.
   • Look for blurring or loss of outlines, which may indicate fluid, inflammation, blood, or a mass replacing normal fat.
   • Relevant outlines discussed include the liver edge, kidney contours, psoas muscles, bladder, and paracolic gutters.
   • A low-lying liver edge may suggest hepatomegaly; loss of a psoas outline may point to a retroperitoneal process.

2. Assess the distribution and amount of gas.

   • Determine whether gas is within bowel loops or outside them.
   • Look for bowel dilation, abnormal gas distribution, and multiple air–fluid levels.
   • Free intraperitoneal air can indicate perforation; bowel-wall or portal venous gas can be a sign of advanced bowel ischemia.

3. Search for calcifications.

   • Possible examples include renal or ureteral stones, appendicoliths, chronic pancreatitis-related calcifications, calcified fibroids, and some gallbladder calcifications.
   • The lecture notes that most gallstones are not visible on X-ray because many are cholesterol-based.

4. Review the bones and soft tissues, particularly when trauma is suspected.

Obstruction, Volvulus, and Ischemia

Mechanical Obstruction

• In a mechanical obstruction, bowel proximal to the blockage dilates, while bowel distal to it tends to collapse.
• For small-bowel obstruction, the lecture identifies adhesions—often related to previous surgery—as a common cause. Hernias and torsion are other causes.
• For large-bowel obstruction, the lecture emphasizes colon cancer as a frequent cause, as well as hernias and volvulus.
• X-ray findings can include dilated loops, multiple air–fluid levels, and reduced gas beyond the obstruction. A “string of beads” appearance may occur when small bubbles of gas collect between folds.
• A high-grade obstruction is suggested by numerous abnormal air–fluid levels and marked differences in their height or width.

Paralytic Obstruction (Ileus)

• In a paralytic obstruction, the problem is impaired peristalsis rather than a physical blockage. Gas and contents may accumulate throughout the affected bowel rather than only upstream from a focal obstruction.
• The lecture links this pattern to loss of blood supply in mesenteric ischemia. Lack of perfusion can stop bowel movement and, if prolonged, cause tissue infarction and necrosis.

Volvulus

• A volvulus is twisting of the bowel, which can also compromise its blood supply.
• Sigmoid volvulus may produce the “coffee bean” sign: a markedly dilated sigmoid loop extending upward from the pelvis, often without normal haustral markings.
• Cecal volvulus can cause a markedly enlarged cecum that shifts toward the midline.
• CT may show a whirlpool or swirl pattern as bowel and mesenteric vessels converge toward the point of torsion. The lecture also describes a closed-beak appearance near the obstruction.

Mesenteric Ischemia

• Mesenteric ischemia is a serious condition caused by impaired blood flow through mesenteric vessels.
• The lecture describes an early inflammatory or hyperemic phase with wall thickening, followed by thinning and infarction if perfusion remains inadequate.
• Advanced findings may include pneumatosis (gas in the bowel wall), portal venous gas, paralytic dilation, and free air. These are serious signs but may not be visible early.
• Because X-rays show mainly indirect or late signs, they are not adequate to exclude acute mesenteric ischemia.

Esophageal Disorders

• A narrowed esophageal lumen can cause dysphagia and weight loss.
• Benign tumors: Leiomyoma is described as the most common benign esophageal tumor, often in the distal third. It arises from smooth muscle and may cause symptoms if it narrows the lumen.
• Malignant tumors: The lecture describes squamous cell carcinoma as the most frequent primary malignant esophageal tumor. It can cause progressive dysphagia and substantial weight loss, and may spread to nearby structures and distant organs.
• The lecture contrasts growth patterns of gastrointestinal cancers, emphasizing that adenocarcinomas often grow concentrically and narrow the lumen.
• Barrett esophagus is described as a metaplastic change associated with chronic gastroesophageal reflux. It is a precancerous condition that can increase the risk of adenocarcinoma.
• Diverticula are pouches in the esophageal wall:
  • Pulsion diverticula are associated with increased pressure within the esophagus; examples discussed are Zenker and epiphrenic diverticula.
  • Traction diverticula are associated with fibrosis and are commonly described in the middle esophagus.

Stomach Disorders

• Gastric imaging must be performed with adequate distension to avoid mistaking a collapsed stomach for abnormal wall thickening.
• Gastric adenocarcinoma arises from the mucosa and may progress from a polypoid lesion. Its growth can constrict the lumen and cause bleeding or impaired eating.
• Endoscopy can directly assess the mucosa and obtain tissue; cross-sectional imaging helps evaluate tumor extent, lymph nodes, and spread to other organs. The lecture discusses staging using the TNM framework and notes that enlarged perigastric nodes may suggest involvement.
• Gastric lymphoma is described as arising in the submucosa, with more longitudinal wall thickening and relatively low contrast enhancement.
• Gastrointestinal stromal tumor (GIST) is discussed as a tumor associated with markers CD117 and CD34. It may grow outward from the stomach wall into the abdominal cavity and become large.
• Menetrier disease is described as diffuse thickening of the gastric mucosa, associated in the lecture with protein loss.
• A bezoar is accumulated foreign material, such as a hair mass. Unlike a tumor attached to the wall, it may shift position when the patient moves.
• Gastric polyps are generally benign but may be precancerous.

Small-Bowel Disorders

The lecture discusses several small-bowel lesions and inflammatory diseases:

• Lipomas are benign fatty lesions that may arise in the submucosa and protrude into the lumen.
• Adenocarcinoma can produce concentric wall thickening and luminal narrowing.
• Carcinoid/neuroendocrine tumors often occur in the distal small bowel. The lecture describes them as vascular and capable of metastasis, with a characteristic surrounding desmoplastic (fibrotic) reaction.
• The lecture also mentions that metastatic disease can reach the bowel from other primary sites.

Inflammatory Bowel Diseases

• Crohn disease

  • Can affect different parts of the gastrointestinal tract in discontinuous (“skip”) areas.
  • Often involves the distal small bowel and proximal colon.
  • Active inflammation can thicken the wall and produce edema between layers, making the wall’s layered appearance visible.
  • The lecture discusses increased vascularity in the surrounding tissues and the “comb sign” during active disease.

• Ulcerative colitis

  • Is described as continuous inflammation beginning in the distal colon and extending proximally.
  • Imaging may show thickening and layered enhancement of the inflamed bowel wall.

• Celiac disease

  • Is presented as an immune-mediated response to gluten, mainly affecting the duodenum and jejunum.
  • The lecture describes loss or shortening of villi and an altered distribution of intestinal folds.
  • It also notes an increased risk of certain small-bowel malignancies.

Colon Disorders and Polyps

• Colorectal adenocarcinoma can grow concentrically, narrowing the lumen and causing mechanical obstruction.
• Polyps protrude from the mucosa and may be precursors to cancer. Colonoscopy can detect and remove them; virtual CT colonography is discussed as a less invasive method for detection.
• The lecture emphasizes particular attention to polyps around 10 mm or larger, which may require removal and further assessment.
• Diverticula are pouches that commonly occur in the colon, especially the sigmoid region. Their presence alone is called diverticulosis; inflammation or infection of a diverticulum is diverticulitis.

Acute Abdomen: Appendicitis and Diverticulitis

Appendicitis

• The lecture describes a progression in which obstruction of the appendix—often related to lymphoid tissue or an appendicolith—causes secretions to build up and pressure to rise.
• Rising pressure can cause pain and impair venous drainage. Progression may lead to inflammation of surrounding fat, arterial compromise, tissue necrosis, and perforation.
• Imaging features include:
  • An enlarged appendix, typically over approximately 6–7 mm.
  • Thickened, enhancing wall.
  • Inflammatory change or “dirty fat” around the appendix.
  • An appendicolith in a subset of cases.
• Perforation can spread infection into the peritoneal cavity, causing peritonitis.

Diverticulitis

• Diverticulosis is common, but diverticulitis occurs when a diverticulum becomes inflamed or infected.
• The lecture relates diverticula to increased intraluminal pressure and discusses low-fiber diets and refined carbohydrates as contributing factors.
• Uncomplicated diverticulitis may show colonic wall thickening and inflammatory change in the surrounding fat without an abscess, fistula, or perforation.
• Complicated diverticulitis may involve an abscess, perforation, fistula, or more widespread infection.
• The lecture mentions a size-based approach to abscess treatment: smaller abscesses may be treated with antibiotics, whereas larger ones may need image-guided drainage. It also refers to a classification system for complicated disease.

Ascites and Fluid in Abdominal Spaces

• The abdomen contains potential spaces normally occupied by fat. Free fluid—whether blood, inflammatory fluid, or another fluid—can replace that fat and blur normal anatomical lines on radiographs.
• The lecture names spaces including the subphrenic spaces, Morrison’s pouch, paracolic gutters, and lesser sac.
• Fluid distribution follows these anatomical spaces rather than appearing randomly. Cross-sectional imaging can show its location and extent more clearly than a plain radiograph.

Speakers and Sources Featured

• Speaker: One unnamed lecturer presenting a gastrointestinal pathology and imaging lesson. No additional speaker is identifiable in the subtitles.
• Illustrative material: The lecturer refers to radiographs, CT, MRI, ultrasound, endoscopic images, diagrams, and clinical imaging cases. The subtitles do not identify their original sources.