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GIT

The Gastrointestinal Tract Overview

  • Also known as the alimentary canal.

  • Comprises the mouth, pharynx, esophagus, stomach, small intestine, and large intestine.

  • Approximately 30-foot muscular tube, varying in diameter from lips to anus.

  • Supplied by the celiac axis, SMA (Superior Mesenteric Artery), and IMA (Inferior Mesenteric Artery).

Stomach

Location and Anatomy

  • Under the ribs in the left upper abdomen.

  • Extends from the left hypochondriac region into the epigastric and umbilical regions.

  • Sonographic appearance varies based on contents.

Structural Features

  • J-shaped structure with:

    • Openings: Cardiac and pyloric orifices.

    • Curvatures: Lesser and greater.

    • Surfaces: Anterior and posterior.

Parts of the Stomach

  • Divided into:

    • Fundus

    • Body

    • Pyloric antrum

    • Pylorus

  • Mucosa and submucosa folds known as Rugae.

Small Intestine

  • Major site for digestion and absorption of food.

  • Divided into three parts:

    • Duodenum

    • Jejunum

    • Ileum

Duodenum

  • C-shaped tube curving around the pancreas.

  • First few centimeters covered with peritoneum, rest is retroperitoneal.

  • Divided into four parts.

Jejunum and Ileum

  • Arises from the duodenum, extends for about 2 meters into the ileum.

  • Ileum is the lower part of the small intestine.

Large Intestine

  • Comprised of:

    • Appendix

    • Cecum

    • Ascending colon

    • Transverse colon

    • Descending colon

    • Rectum

  • Segments of the colon called haustra.

Sections of the Large Intestine

  1. Ascending: Begins with cecum, connects to ileum, extends to hepatic flexure.

  2. Transverse: From hepatic flexure to splenic flexure.

  3. Descending: From splenic flexure to sigmoid.

  4. Sigmoid/Rectum: Terminal segment of the large bowel.

Appendix

  • Located at the junction of small and large intestines.

  • Thin tube, approximately four inches long; situated in the lower right abdomen.

  • Function is currently unknown.

Sonographic Instrumentation

  • Specialized instruments for endorectal, endovaginal, and endoscopic sonographic evaluations.

Types of Sonographic Examinations

  • Transabdominal and Endoluminal examinations.

Transabdominal Sonography

  • Used as a screening procedure for:

    • Abdominal or pelvic pain.

    • Causes of fever.

    • Palpable abdominal mass.

    • Follow-up on abnormal lab and imaging results.

Endoluminal Sonography

  • Conducted by trained sonographers and gastroenterologists.

  • Utilizes specialized endoscopes with sonographic transducers.

  • Provides images from within the lumen and adjacent GI wall.

Endosonography

  • Primarily focuses on upper GI tract: esophagus, stomach, and duodenum.

  • Also examines rectum and anal sphincter; aids in managing rectal cancer.

  • Endovaginal transducers help locate the appendix in females, especially useful in larger body types.

Patient Preparation

  • Preparation varies by evaluation segment of the GI tract.

  • Recommended fasting for 8-12 hours prior to exams to reduce stomach gas.

  • Patients can drink water (10-40 oz) to improve visualization unless they have GI obstruction.

Sonographic Technique and Challenges

  • Examination may be difficult due to:

    • Gas obscuring bowel wall details.

    • Large patient body habitus.

    • Operator dependence.

  • Fluid administration can help delineate lumen and wall characteristics.

  • A cross-section of gut appears as a target or bull’s eye.

Sonographic Features

  • Normal bowel should compress easily and exhibit peristalsis.

  • Normal wall thickness: 3-5 mm (3 mm when distended, 5 mm when non-distended).

  • Haustra identified as echogenic lobulations in the colon.

Histologic Layers of the GI Tract

  • Five histologic layers appearing as alternating echogenic and hypoechoic segments (Gut Signature):

    1. Superficial mucosa: Echogenic (innermost layer)

    2. Deep mucosa: Hypoechoic

    3. Submucosa: Echogenic

    4. Muscularis propria: Hypoechoic

    5. Serosa: Echogenic (outermost layer)

Sonography of Stomach

  • Antrum is target-shaped, located anterior to the pancreas body.

Imaging Characteristics

  • Gastroesophageal Junction marks where distal esophagus meets proximal stomach.

  • Assessed on sagittal scans as a target or bull’s eye pattern.

Sonography of Appendix

  • Appendix is a long, narrow blind-ended tube, commonly in right lower quadrant.

  • Maximum outer diameter of normal appendix: up to 6 mm.

  • Techniques for evaluation include compression to confirm non-inflammation.