Sectional and Cross-sectional Anatomy

Sectional and Cross-sectional Anatomy - Slicing & Dicing

• Anatomical Planes & Orientation: 📌 Mnemonic for Planes: Coronal: Crown; Sagittal: Side; Axial: Across.

  Plane	Division	View Analogy
  Axial	Superior/Inferior	CT slice / Across
  Sagittal	Right/Left	Side view
  Coronal	Anterior/Posterior	Crown / Front-Back

  • Orientation Terms:
    • Anterior (Ventral) / Posterior (Dorsal): Front / Back
    • Superior (Cranial) / Inferior (Caudal): Above / Below
    • Medial / Lateral: Towards / Away from midline
    • Proximal / Distal: Nearer / Further from trunk (limbs)

• Sectional Imaging Basics:
  • CT (Computed Tomography): X-rays; density in Hounsfield Units (HU).
    • Air: -1000 HU
    • Fat: -100 to -50 HU
    • Water: 0 HU
    • Soft Tissue: +40 to +80 HU
    • Bone: +700 to +3000 HU
  • MRI (Magnetic Resonance Imaging): Magnetic fields & radio waves; superior soft tissue detail.

⭐ Windowing in CT (e.g., lung, bone, soft tissue windows) is crucial for optimal visualization of different structures based on their densities.

Sectional and Cross-sectional Anatomy - Chest Checkpoints

Key Thoracic Axial Levels & Structures:

• Lungs, pleura, fissures.
• Heart chambers, pericardium.
• Great vessels: Aorta (ascending, arch, descending), SVC, IVC, pulmonary trunk/arteries/veins.
• Trachea, esophagus.

Mediastinal Divisions:

• Superior: Above sternal angle (T4).
• Inferior: Anterior, Middle (heart), Posterior.

⭐ The azygos vein arches over the root of the right lung to drain into the superior vena cava (SVC).

Sectional and Cross-sectional Anatomy - Gut Reactions

Key axial vascular landmarks:

-   Liver: Right/left lobes, caudate, quadrate. Segments I-VIII (Couinaud).
-   Spleen: LUQ, posterior to stomach.
-   Pancreas: Head, neck, body, tail; retroperitoneal (except tail).
-   Kidneys & Adrenals: Retroperitoneal.
-   Stomach: J-shaped, LUQ.
-   Small Bowel: Duodenum (retroperitoneal parts), jejunum, ileum.
-   Large Bowel: Cecum, colon (ascending, transverse, descending, sigmoid), rectum.
-   Bladder, Uterus/Prostate: Pelvic.

• Major Vessels: Aorta, IVC, Portal Vein.
• 📌 Retroperitoneal (SAD PUCKER): Suprarenal glands, Aorta/IVC, Duodenum (2nd-4th parts), Pancreas (except tail), Ureters, Colon (ascending/descending), Kidneys, Esophagus (lower 2/3), Rectum (lower 2/3).
• Key Peritoneal Spaces:
  • Morison's Pouch (Hepatorenal recess).
  • Pouch of Douglas (Rectouterine or Rectovesical pouch).
  • Lesser Sac (Omental bursa).

⭐ Morison's pouch (hepatorenal recess) is the most dependent part of the upper peritoneal cavity in the supine position, a common site for fluid collection.

Sectional and Cross-sectional Anatomy - Brainy Views

Key Axial Levels & Structures:

• Cerebral Lobes: Frontal, Parietal, Temporal, Occipital.
• Ventricles:
  • Lateral (anterior, posterior, inferior horns; body, atrium).
  • Third (between thalami).
  • Fourth (posterior to pons/medulla, anterior to cerebellum).
• Basal Ganglia: (📌 Caudate, Putamen, Globus Pallidus - "CaPuG").
• Thalamus: Relay station for sensory/motor signals.
• Internal Capsule: Anterior limb, Genu, Posterior limb.
• Corpus Callosum: Genu, Body, Splenium.
• Brainstem: Midbrain (cerebral peduncles, colliculi), Pons, Medulla.
• Cerebellum: Vermis, Hemispheres.
• Circle of Willis Components: ACA, MCA, PCA, ACom, PCom.

⭐ The posterior limb of the internal capsule, supplied by lenticulostriate arteries (branches of MCA), is a common site for lacunar infarcts leading to contralateral hemiparesis and hemisensory loss.

High‑Yield Points - ⚡ Biggest Takeaways

• Axial (transverse) plane: Divides body into superior/inferior parts; common in CT/MRI.
• Coronal (frontal) plane: Divides body into anterior/posterior parts.
• Sagittal plane: Divides body into left/right sides; midsagittal is midline.
• CT windowing is crucial: bone window for skeletal structures, soft tissue window for organs.
• Contrast media enhance visibility of vessels and various pathologies.
• Key thoracic landmarks: Aortic arch, carina, 4-chamber heart view.
• Key abdominal landmarks: Celiac trunk, SMA, renal hilum, aortic bifurcation.