Esophagus

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  Cervical and thoracic segments

Stomach

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  Hollow muscular organ between esophagus and small intestine

  
  
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  Location: Intraperitoneal, in left upper quadrant, bordered superiorly by left hemidiaphragm, posterolaterally by spleen, posteroinferiorly by pancreas

  
  
  
  
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    Greater omentum attached from greater curvature and drapes over small and large intestines

    
    
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    Lesser omentum attached from lesser curvature to porta hepatis, covers lesser sac

  
  
  
  
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  Function

  
  
  
  
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    Gastric acid production for breakdown of large molecules of food into smaller molecules in preparation for small intestinal absorption

    
    
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    Storage of food

  
  
  
  
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  Sections

  
  
  
  
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    Gastroesophageal junction/cardia, lower esophageal sphincter

    
    
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    Fundus and body: Delineated by horizontal plane passing through cardia

    
    
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    Antrum/pylorus: Lower section facilitating entry of gastric contents into duodenum

  
  
  
  
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  Curvatures

  
  
  
  
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    Greater curvature: Lateral wall of stomach

    
    
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    Lesser curvature: Medial wall of stomach

  
  
  
  
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  Rugae/internal ridges increase surface area for digestion

  
  
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  Arterial supply

  
  
  
  
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    Right and left gastric arteries supply lesser curvature

    
    
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    Right and left gastroepiploic arteries supply greater curvature

    
    
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    Short gastric artery supplies fundus

  
  
  
  
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  Venous drainage

  
  
  
  
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    Follow arteries and drain into portal vein and its tributaries

  
  

Small bowel

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  Between stomach and large intestine

  
  
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  ~ 4-7 meters in length

  
  
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  Centrally located in abdomen

  
  
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  Intraperitoneal, except for 2nd-4th portions of duodenum

  
  
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  Function: Further breakdown of food molecules from stomach with eventual absorption

  
  
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  Intraluminal extensions/folds valvulae conniventes increase surface area for absorption

  
  
  
  
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    Abundant in proximal small bowel, decrease in number in distal small bowel loops

  
  
  
  
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  Duodenum

  
  
  
  
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    C-shaped hollow tube connecting stomach with jejunum

    
    
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    Begins with duodenal bulb, ends in ligament of Treitz (duodenojejunal junction)

    
    
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    Arterial supply and venous drainage: Superior and inferior pancreaticoduodenal artery, pancreaticoduodenal veins

  
  
  
  
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  Jejunum

  
  
  
  
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    Connects duodenum with ileum

    
    
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    ~ 2.5 meters in length

    
    
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    Begins at ligament of Treitz

    
    
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    Along with ileum, suspended by mesentery

    
    
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    Arterial supply and venous drainage: Superior mesenteric artery and vein

  
  
  
  
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  Ileum

  
  
  
  
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    Connects jejunum with ascending colon

    
    
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    ~ 3.5 meters in length

    
    
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    Along with jejunum, suspended by mesentery

    
    
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    Arterial supply and venous drainage: Superior mesenteric artery and vein

  
  

Large bowel

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  Between small bowel and anus

  
  
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  ~ 1.5 meters in length

  
  
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  Peripherally located in abdomen

  
  
  
  
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    Cecum and appendix, transverse colon, and rectosigmoid intraperitoneal

    
    
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    Ascending colon, descending colon, and middle rectum retroperitoneal

    
    
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    Distal rectum extraperitoneal

  
  
  
  
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  Function: Absorption of remaining water, storage, and elimination of waste

  
  
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  Sections

  
  
  
  
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    Ascending colon: Located in right side of abdomen, includes cecum where appendix arises

    
    
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    Hepatic flexure: Turn of colon at liver

    
    
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    Transverse colon: Traverses upper abdomen

    
    
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    Splenic flexure: Turn of colon at spleen

    
    
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    Descending colon: Left side of abdomen

    
    
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    Sigmoid/rectum: At posterior pelvis

  
  
  
  
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  With taenia coli: 3 bands of smooth muscle just under serosa

  
  
  
  
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    Haustration: Sacculations in colon resulting from contraction of taenia coli

    
    
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    Epiploic appendages: Small fat accumulations on viscera

  
  
  
  
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  Arterial supply

  
  
  
  
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    Superior mesenteric artery supplies colon from appendix through splenic flexure

    
    
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    Ileocolic branch supplies cecum

    
    
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    Right colic branch supplies ascending colon

    
    
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    Middle colic branch supplies transverse colon

    
    
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    Inferior mesenteric artery supplies descending colon through rectum

    
    
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    Left colic branch supplies descending colon

    
    
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    Sigmoid branches supply sigmoid

    
    
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    Superior rectal artery supplies superior rectum

    
    
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    Middle and inferior rectum supplied by arteries of same name originating from internal iliac artery

  
  
  
  
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  Venous drainage

  
  
  
  
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    Superior and inferior mesenteric veins

  
  

Anus

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  External opening of rectum

  
  
  
  
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    Termination of gastrointestinal tract

  
  
  
  
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  With sphincters for controlling defecation

  
  
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  Internal anal sphincter

  
  
  
  
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    Thin ring of smooth muscle surrounding anal canal, deep to submucosa

    
    
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    Under involuntary control

    
    
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    Continuous with muscularis propria of rectum

    
    
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    Forms incomplete ring in females

  
  
  
  
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  External anal sphincter

  
  
  
  
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    Thick ring of skeletal muscle around internal anal sphincter

    
    
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    Under voluntary control

    
    
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    3 parts from superior to inferior: Deep, superficial, and subcutaneous

  
  
  
  
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  Longitudinal muscle

  
  
  
  
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    Thin muscle between internal and external anal sphincters

    
    
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    Conjoined muscle from muscularis propria of rectum and levator ani

  
  

Bowel wall throughout GI tract has uniform general histology, comprised of 4 layers

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  Mucosa

  
  
  
  
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    Functions for absorption and secretion

    
    
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    Composed of epithelium and loose connective tissue

    
    
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    Lamina propria

    
    
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    Muscularis mucosa (deep layer of mucosa)

  
  
  
  
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  Submucosa

  
  
  
  
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    Consists of fibrous connective tissue

    
    
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    Contains Meissner plexus

  
  
  
  
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  Muscularis externa

  
  
  
  
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    Muscular layer responsible for peristalsis or propulsion of food through gut

    
    
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    Contains Auerbach plexus

  
  
  
  
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  Serosa

  
  
  
  
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    Epithelial lining continuous with peritoneum

  
  

GI tract extends from mouth to anus

Esophagus, which is intrathoracic, is difficult to visualize with external ultrasound due to rib cage and air-containing lungs

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  Endoluminal ultrasound performed to assess mural pathology

Stomach to rectum lie within abdomen and pelvis

Stomach, 1st part of duodenum, jejunum, ileum, transverse colon, and sigmoid colon suspended within peritoneal cavity by peritoneal folds and are mobile

2nd-4th parts of duodenum, ascending colon, descending colon, and rectum typically extraperitoneal/retroperitoneal

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  Retroperitoneal structures have more fixed position and are easy to locate

Stomach located in left upper quadrant

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  Identified by presence of rugae/mural folds

  
  
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  Prominent muscular layer facilitates identification of pylorus

Small bowel loops are located centrally within abdomen

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  Abundant valvulae conniventes helps identify jejunal loops

  
  
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  Jejunalization of ileum seen in celiac disease to compensate for atrophy of folds in proximal small bowel

  
  
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  Contents of jejunal loops usually liquid and appear hypoechoic/anechoic

Cecum and colon identified by haustral pattern

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  Located peripherally in abdomen

  
  
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  Contain feces and gas

  
  
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  Haustra seen as prominent curvilinear echogenic arcs with posterior reverberation

  
  
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  Cecum identified by curvilinear arc of hyperechogenicity (representing feces and gas) in right lower quadrant blind ending caudally

  
  
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  Not uncommonly, cecum high lying and may be horizontally placed

  
  
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  Sigmoid colon variable length and mobile

  
  
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  Junction of left colon with sigmoid colon identified in left iliac fossa by tracing descending colon

  
  
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  Rectosigmoid junction has fixed position and is identified with full bladder, which acts as acoustic window

Appendicular base normally located in right lower quadrant

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  Length and direction of tip vary

  
  
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  Retrocecal appendix and pelvic appendix can be difficult to locate transabdominally

  
  
  
  
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    Transvaginal ultrasound examination useful to identify pelvic appendix

  
  

Normal measurements of bowel caliber

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  Small bowel < 3 cm

  
  
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  Large bowel

  
  
  
  
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    Cecum < 9 cm

    
    
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    Transverse colon < 6 cm

  
  

Stratified appearance of bowel wall on histology is depicted by 5 distinct layers on ultrasound as alternating echogenic/sonolucent (hypoechoic) appearance (gut signature)

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  Interface of lumen and mucosa: Echogenic

  
  
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  Muscularis mucosa: Hypoechoic

  
  
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  Submucosa: Echogenic

  
  
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  Muscularis propria/externa: Hypoechoic

  
  
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  Serosa: Echogenic

Normal bowel wall thickness < 3 mm

Bowel is hollow viscus and is constantly mobile due to peristalsis

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  Assessing direction of flow of contents often challenging

  
  
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  When visibility permits, direction of flow can be determined by following long segments of bowel in continuous fashion

Different bowel pathologies have potential to alter normal gut motility

Real-time dynamic ultrasound provides useful information regarding bowel mobility, which can aid in diagnosis of underlying condition

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  Cine function useful to store dynamic images for review

Ultrasound is the initial study of choice for gastrointestinal conditions in children and young adults and for select indications in adults

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  Focused survey for acute appendicitis, pyloric stenosis, intussusception, and malrotation

  
  
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  Extended systematic survey in Crohn disease

5- to 8-MHz curvilinear probe for wider field of view and deeper penetration

7- to 12-MHz linear probe for higher resolution

12- to 18-MHz linear probe for delineation of 5 bowel layers

Fixed points of bowel easy to assess with transabdominal ultrasound: Pylorus, “C loop” of duodenum, and ileocecal junction

Abnormal bowel identified as thickened or dilated segments, ± disturbance of gut signature

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  Thickened bowel demonstrates reduced peristalsis, which stands out among normally peristalsing loops of normal bowel

Optimize settings, evaluate abnormal bowel in 2 planes

Slow, graded compression

Evaluate surrounding tissues for secondary signs: Echogenic fat, fluid, enlarged lymph nodes, tracts

Color Doppler: Increased vascularity in acute inflammation, may be helpful in malrotation