Anatomy Layering and Sectional Anatomy

Directional Terminology and Sectional Planes

• Key directional terms and sectional planes used in anatomy:
  • Coronal (or Frontal): Divides the body into anterior and posterior portions.
  • Sagittal: Divides the body into right and left portions.
  • Transverse: Divides the body into superior and inferior portions.
  • Superior: Towards the head.
  • Inferior: Away from the head.
  • Anterior: Towards the front.
  • Posterior: Towards the back.
  • Medial: Towards the midline.
  • Lateral: Away from the midline.
  • Proximal: Closer to the point of attachment or origin.
  • Distal: Farther from the point of attachment or origin.
  • Midsagittal: Divides the body into equal right and left halves.
  • Oblique: Any plane that is not sagittal, transverse, or coronal.

Scanning Planes

• In ultrasound, it is common to scan in an oblique plane rather than perfectly sagittal or transverse.

Long and Short Axis

• Transverse, Coronal, and Sagittal (Long) are scanning planes relative to the body.
• Long axis and short axis are relative to the organ.
• The axis of the organ and scanning plane may not be the same.
• Examples:
  • Short Axis image of Right Kidney taken in Transverse plane.
  • Long axis Right Kidney taken in Sagittal plane.
  • Long Axis image of Pancreas taken in the Transverse plane.
  • Short Axis of Pancreas taken in Sagittal Plane.

Orientation Examples

• Transverse:
  • Transverse CT and Ultrasound image at the level of the mid right kidney.
  • In the TRV plane CT image, we see a short axis of the kidneys, aorta, and IVC but a long axis of the renal veins and arteries.
• Horizontal Orientation:
  • Renal arteries and veins.
  • Hepatic artery.
  • Splenic vein and artery.
• Horizontal Oblique Orientation:
  • Pancreas (the lateral end of the pancreas is slightly more superior than the medial end).
  • Liver
• Sagittal:
  • Sagittal (Long) Right Kidney CT and Ultrasound.
  • We see the right kidney in long axis, and the renal arteries are not included in this slice.
• Vertical Orientation:
  • Aorta.
  • Superior mesenteric artery.
  • Inferior vena cava.
  • Common carotid artery.
  • Internal jugular vein.
• Vertical Oblique Orientation:
  • Kidneys.
  • Common hepatic duct and common bile duct.
  • Portal vein.
  • Common iliac arteries.
• Variable Orientation:
  • Gallbladder (the variable position of the gallbladder is dependent on the amount of bile it contains and/or the length of its mesenteric attachment).
  • Ovaries.

Body Divisions

• Dorsal and Ventral body cavities.
• Thoracic, Abdominal, and Pelvic regions.
• False (Greater) pelvis: Pelvic portion of abdominopelvic cavity.
  *Superiorlly
  *Space divider
  *Linea terminalis
  Sacral promontory
• Ala \ of \ Sacrum
  *Arcuate \ line
• Iliopubic \ eminence
  *Pecten \ pubis
• (Pectineal \ line)
• True (Lessor) pelvis
  Right Reseverd Inferior
• Anterior muscle layer: Includes muscles such as the external oblique, internal oblique, transversus abdominis, and rectus abdominis
  • Sternum
    *Linea alba
    *External oblique (cut)
    *External oblique
    *Aponeurosis of external obliques
    *-Internal oblique (cut)
    *-Tranversus abdominis
    *-Rectus abdominis
    *-Inguinal ligament
    *Inguinal canal
    *Copyright ©2021 by Elesvier, Inc.
• Pubic symphysis

Anatomical Relationships

• Anterior to posterior, the image demonstrates the abdominal wall, liver, gallbladder, and right kidney.

Gastrointestinal Tract

• Key anatomical structures of the gastrointestinal tract and related organs.
• Includes the liver, gallbladder, right kidney, duodenum, pancreas head, inferior vena cava, aorta, spleen, stomach, and left kidney.

Gallbladder and Biliary Tract

• Image demonstrates a transverse slice at the level of the left renal vein.

Inferior Vena Cava (IVC)

• Longitudinal plane image of the long axis IVC demonstrating the heart superior to the liver and diaphragm.
• From anterior to posterior, we see the abdominal wall, liver, hepatic vein, and IVC.
• The IVC lies slightly right of midline posterior to the liver.

Abdominal Aorta

• The Aorta is seen just left of midline posterior to the left lobe of the liver.
• Sagittal plane image demonstrates the long axis aorta posterior to the liver.

Kidneys and Adrenal Glands

• Location and relationship of the kidneys and adrenal glands.
• Also shows surrounding muscles such as the quadratus lumborum and psoas major.

Celiac Trunk

• Celiac Trunk: 1st major branch of abdominal aorta.
• Transverse ultrasound of aorta and Celiac Axis (Seagull sign).
• The splenic artery courses to the patient’s left, and the hepatic artery to the right.

Superior Mesenteric Artery (SMA)

• Second major branch of abdominal aorta.
• In TRV, appears as a circle anterior to the aorta.
• In Long, appears as a tube running anterior to the aorta.

Renal Vessels

• Renal Arteries: third major branches off abdominal aorta.
• Left Renal Vein passes between the SMA & Aorta.
• Right Renal Artery passes behind the IVC.

Pancreas

• Transverse view at the level of the Pancreas.
• Transducer in the TRV position yields a “long axis” image of the Pancreas.
• GDA (anterior) and CBD (posterior) are seen passing through the head.
• Splenic vein seen posterior to body & tail.
• Portal Splenic Confluence where Splenic Vein meets the Superior Mesenteric Vein.

Portal Venous System

• Anterior to posterior, we see the liver, portal veins, and IVC.
• Notice the echogenic (bright white) walls of the portal vein.

Biliary Ducts

• CBD is seen anterior to the Portal vein.
• Portal vein has Echogenic (thick white) walls.
• Top right image: “long” CBD.
• Transducer usually oblique towards the patient’s right shoulder.
• Bottom right image TRV CBD.
• Turn on color to tell CBD from HA.

Hepatic Veins

• Transverse ultrasound image of hepatic veins.
• IVC Posterior behind the liver.
• 3 hepatic veins coursing anterior into the liver.
• Note thin vessel walls.

IVC and Hepatic Veins

• TRV image of IVC and hepatic veins.
• Sagittal image of IVC and left hepatic vein.
• Note that we are seeing the long axis of the IVC.

Posterior Muscle Layer

• Includes muscles such as the psoas major, psoas minor, quadratus lumborum, transversus abdominis, and iliacus.
  Lumber vessels

True Pelvis Muscle Layer

• Includes muscles such as the coccygeus, puborectalis, iliococcygeus, and obturator internus.
  *Ischium
  *Ischial
  tuberosity
  *Rectum
  *Urethra
  *Vagina
  *R
  *Coccygeus
  muscle
  *Coccyx
  *Sacnim
  *Pubis
  *Puborectalis
  muscle
  *-Pubococcygeus
  muscle
  *Iliococcygeus
  muscle
  *Obturator
  internus
  muscle
  *Tendon of obturation
  internus muscle
  *Copyright © 2021 by Elesvier, Inc.
  *Levator ani
  muscle

Body Structure Relationships

• In a sagittal scanning plane image, the target organ or area of interest is always related to a structure immediately:
  • Anterior to it.
  • Posterior to it.
  • Superior to it.
  • Inferior to it.
• Examples of relationships in a sagittal plane:
  • Anterior: Muscle and tissue layers.
  • Posterior: Spine.
  • Superior: Lung, Diaphragm.
  • Inferior: Esophagogastric junction.
  • Aorta
• In a coronal scanning plane image, the target organ or area of interest is always related to a structure immediately:
  • Right or left lateral to it.
  • Medial to it.
  • Superior to it.
  • Inferior to it.
• Examples of relationships in a coronal plane:
  • Lateral: Spleen.
  • Medial: Aorta.
  • Superior: Diaphragm.
  • Inferior: Psoas major muscle.
• In a transverse scanning plane image from an anterior or posterior approach, the target organ or area of interest is always related to a structure immediately:
  • Anterior to it.
  • Posterior to it.
  • Right lateral to it.
  • Left lateral to it.
• Examples of relationships in a transverse plane:
  • Anterior: Duodenum, Pancreas head.
  • Posterior: Spine, Superior mesenteric artery.
  • Right: Liver.
  • Left: Stomach, Pancreas tail.
    Right crus
    of diaphragm
• Liver
  Stomach
  Pancreas
  tail
  Left
  renal vein
  Aorta
  Spine
  Superior mesenteric artery
  Posterior