Anatomy and Imaging of the Abdomen Flashcards
Which layer of an embryo forms the majority of the gut?
The Endoderm, and Mesoderm
- most of the GI originates around week 3
What is found in the Foregut?
- Oesophagus
- Stomach
- Proximal half Duodenum
- Liver
- Pancreas
What is found in the Midgut?
- Distal half Duedenum
- Jejunum
- Ileum
- Cecum
- Asc. Colon
- 3/4 Trans. Colon
What is found in the Hindgut?
- 1/4 Trans. Colon
- Desc. Colon
- Sigmoid Colon
- Rectum
Label the parts of the primitive gut?
What is Mesentery?
- A double layer of peritoneum around a specific organ
Label the parts of the primitive gut
What is the role of Mesentery?
- Suspends gut organs
- originates from the mesoderm
- Provides a pathway for blood, innervation, lymphatics etc to the gut
- Only the foregut has dorsal and ventral mesentery after development, ventral mesentery degrades
What is the result of abnormal gut rotation during development and what are the symptoms?
- duodenum constrictions
- midgut volvulus leading to ischaemia, necrosis and death
Symptoms
- vomiting
- pain
- abdominal distention
Label the diagram, what happened to result in this?
- formed as a result of organ rotation
Explain the role of Dorsal Mesentery
- attaches organs to the posterior abdominal wall
Gives rise to
- Gastrosplenic ligament
- Lienorenal ligament
- Greater omentum
- The mesentery of small & large intestine
Label the diagram, what is it depicting?
The Ventral Mesentery which is only found in the foregut
What are the regions of the abdomen?
- Abdomen proper
- Greater pelvis
- Lesser pelvis
Label the diagram, what plane is it in?
- Sagittal Plane of the Pelvis
Label the diagram, what does ASIS stand for?
Anterior Superior Illiac Spine
What is part of Ventral mesentry?
- The falciform ligament
- lesser omentum
What is the name of the gap between the greater and lesser sacs?
- the Epifloic foreman
What are the muscles of the anterior abdominal wall?
- External oblique
- Internal Oblique
- Transversus abdominis
- Rectus abdominis
Describe the location of the external oblique
From the outer surface of the lower eight ribs
To the linea alba transversely and the iliac crest and pubic tubercle inferiorly
Describe the location of the Internal oblique
From the lateral 1/3 of the inguinal ligament to the anterior 2/3 of the iliac crest
To the Linea alba costal margin and crest of the pubic bone
Describe the location of the Transversus Abdominis
From the lateral 1/3 inguinal ligament, the interior surface of the lower 6 ribs and the iliac crest
To the linea alba and the crest of the pubic bone
Describe the location of the Rectus Abdominis
From the pubic symphysis and pubic crest
To the Xiphoid process and the 5th-7th costal cartilage
What is the blood supply of the muscles of the anterior abdominal wall?
Arteries: Sup. and Inf. epigastric, intercostal, circumflex iliac
Veins: thoracoepigastric (between the lat. thoracic and sup. epigastric vein)
What is the innervation of the muscles of the anterior abdominal wall?
- Thoracoabdominal nerves
- subcostal nerves for the rectus abdominis
What is the function of the muscles of the anterior abdominal wall?
Ext Obl: work with Int Obl for torsional movement of the trunk
Int Obl: flex and rotate trunk; compresses the viscera
Transv Abd: compress and supports the viscera
Rectus Abd: flexes trunk; compresses the viscera
What is the difference between the fibre pattern of the internal and external obliques?
- External obliques, fibres travel down towards the pelvis
- Internal obliques, fibres run mainly upwards
What is the purpose fo the Inguinal canal?
Allows passage for
- the spermatic cord is able to reach the scrotum
- the round ligament of the uterus is able to reach the labia majora
- the genital nerve and other blood and lymphatic vessels
- this passage is limited by the superficial and deep inguinal sings
As the spermatic cord passes through the abdominal wall what three layers does it take with it?
- Transversalis fascia => contributes the innermost covering of the spermatic cord – the internal spermatic fascia
- Internal oblique => contributes the middle covering layer to the cord – the cremasteric fascia
- External oblique => contributes the outer covering of the cord – the external spermatic fascia
What are the 9 anatomical subdivisions of the abdomen? How are they marked out?
Right hypochondriac | Epigastric | Left hypochondriac
Right lumbar | Umbilical | Left lumbar
Right inguinal (iliac) | Hypogastric (pubic) | Left Inguinal (Iliac)
- Right and left regions are measured from the midclavicular lines
- 1st horizontal demarcation is the subcostal line, 2nd is the Transtubercular line
What is the contents of the right upper abdomen?
Right lobe of the liver
Gallbladder
Duodenum
Head of Pancreas
Hepatic flexure of the colon
Part of the ascending and transverse colon
What is the contents of the Left upper abdomen?
Stomach
Spleen
Left lobe of the liver
Body of pancreas
Splenic flexure of the colon
Part of the transverse and descending colon
What is the contents of the Right lower Abdomen?
Cecum
Appendix
Ascending colon
Small intestine
What is the contents of the Left lower abdomen?
Small intestine
Descending colon
Sigmoid Colon
What is the purpose of the Serous membrane of there peritoneum?
- the outer membrane; encloses several body cavities; secretes a lubricating fluid;
- the outer epithelial layer (secretory) and the inner layer (connective tissue with vessels
What is the purpose of the Muscular membrane of the peritoneum?
- longitudinal or circular;
- responsible for the movement of the contents of the lumen
What is the purpose of the mucosal layers of the peritoneum?
- inner layer; lines internal organs or cavities exposed to external environment;
- secretes mucus; also involved in absorption
What are the three basic membranes of the peritoneum?
Serous
Muscular
Mucosal
Name the 5 anatomical regions of the stomach ( not including the fundus)
- Cardial orifice – link to the oesophagus
- Pyloric orifice – link to the small intestine
- Lesser curvature (superior border)
- Greater curvature (inferior border)
- Pyloric and cardial sphincters
What are the 3 layered muscle types in the stomach
- longitudinal
- circular
- oblique
Describe the anatomy of the duodenum
- Retroperitoneal organ (have peritoneum on their anterior side only)
- 20-25 cm long
- C-shaped and split into four parts: superior, descending, horizontal ascending
- the pancreatic and gall bladder ducts open into it
- ends at the duodenal-jejunal flexure
Describe the anatomy of the large intestine
- 1.5 m long
- M shaped with 4 parts: ascending, transverse, descending, sigmoid
- the ascending and descending section or retroperitoneal
What is the VAN-L of the Foregut?
Vein: Portal
Artery: Celiac
Symp Nerve: Celiac ganglia (prevertebral)
Parasymp Nerve: Vagus - CN X
Lymphatics: Celiac nodes
What is the VAN-L of the Midgut?
Vein: Sup Mesenteric
Artery: Sup Mesenteric
Symp Nerve: Sup Mesenteric ganglia ( prevertebral)
Parasymp Nerve: Vagus - CN X
Lymphatics: Sup Mesenteric nodes
What is the VAN-L of the Hindgut?
Vein: Inf Mesenteric
Artery: Inf Mesenteric
Symp Nerve: Inf Mesenteric Ganglia (paravertebral)
Parasymp Nerve: Pelvic Splanchnic - S2-4
Lymphatics: Inf Mesenteric Nodes
Where do the branches of the Superior Mesenteric Artery supply?
- the Distal part of the duodenum to the proximal 2/3 of the transverse colon
- the Hehunal and ileal branches
- Middle Colic branch
- the Right Colic branch
- The Ileocaecal branch
(all in the midgut)
Where do the branches of the Inferior Mesenteric Artery supply?
- the distal 1/3 of the transverse colon to halfway down the anal canal
- the Left colic
- the Sigmoid
- Superior rectal
( all in the hindgut)
What are the 4 main gut-associated glands?
- Liver
- Spleen
- Gall bladder
- Pancreas
What are the main two types of imaging sequences for MRI?
- T1 and T2 weighted
- T1: fluid is black
T2: fluid is white
What are the Pros for X-Rays
- Cheap, Quick
- Easy for patient
- High spatial resolution (good for bone)
- Low radiation dose
What are cons for X-rays?
- Poor contrast resolution (poor for soft tissue)
- Planar imaging (superimposes structures)
What are pros for CT imaging?
- Quick, widely available
- Cross-sectional images
- High Contrast resolution (good for soft tissue)
What are cons for CT imaging?
- Radiation dose
- IV Contrast risks: excreted through the kidney, therefore there is a temporary reduced kidney function
What are pros for Ultrasound imaging?
● Cheap, Quick, No radiation
● Cross sectional images
● US guided interventions
What are cons of ultrasounds?
● Saved images are only a snapshot of examination (report operator dependant)
What are pros for MRI imaging?
- Contrast resolution
- Specific applications (e.g. Spine, MSK)
- No radiation
What are cons of MRI imaging?
- Limited availability
- Patient experience (duration, claustrophobia)
- Expense
- Magnet / Contrast risks
What paired opposing factors need to be accounted for when carrying out abdominal imaging?
- Solid vs Hollow viscera: bladder vs kidney
- Intraperitoneal vs Retroperitenal: jejunum vs ascending/descending colon
- Systemic vs Portal circulation
Describe the organisation of the hepatic segments
Divided by the portal vein horizontally
Divided by the hepatic vein vertically
- the middle hepatic vein operates the right and left liver lobes
- the right hepatic vein separates the anterior and posterior liver
- the left hepatic vein separates the medial and lateral segments of the left liver lobe
What is posterior acoustic shadowing and when would you encounter this?
- seen in ultrasounds of the liver/ gallbladder
- creates dark shoeing behind a gallstone
- the gall bladder wall may also appear thickened
What radiological interventions are there for gallstones?
ERCP: Endoscopic retrograde cholangiopancreatography
PTC: Percutaneous transhepatic cholangiogram
DSA: Digital subtracted angiogram
What would be seen in a CT of a shattered spleen?
- there wouldn’t be a clear divide between the stomach and the spleen
- the gastrosplenic ligament wouldn’t be seen
What would be seen on an axial cross looking at the pancreas and the surrounding structures?
What would be seen in a CT of Pancreatitis?
- a poor gastro-splenic border
What is this an image of and when would it be identified?
- free gas in the hemidiaphragm when standing erect
- seen in an X-ray
- bowel perforation
What modalities are good for imaging the hollow viscera (the bowel)?
- X-ray: good as a first-line
- CT colonography replaces Ba enema &
- MRI as they avoid endoscopy
- Fluoroscopy, barium follow-through, barium meal (double-contrast; difficult for frail patients)
