pt 1 Sectional Anatomy of the Abdominopelvic Cavity – Imaging & Anatomical Planes

Imaging: An Integrated, Non-Siloed Approach

• Imaging of the abdominopelvic cavity is now viewed as an inter-connected discipline; modalities routinely inform and complement one another.

• Core modalities referenced:

  • Computerized Tomography (CT)

  • Diagnostic Sonography (Ultrasound, US)

  • Magnetic Resonance Imaging (MRI)

  • Nuclear Medicine (mentioned as part of the spectrum)

• Ultrasound often selected over CT (ionizing radiation) and MRI (costly, time-consuming).

• Sonographer responsibilities:

  • Tailor each examination to exploit US strengths and minimize limitations.

  • Integrate findings from prior CT/MRI for targeted, follow-up evaluation.

Modality-Specific Summaries

Ultrasound (US)

• Physics & Image Creation

  • Uses high-frequency sound waves emitted from a piezoelectric crystal in a transducer (surface or internal).

  • Echoes from acoustical interfaces create 2-D images; real-time cine loops allow dynamic assessment.

• Strength Areas

  • Real-time visualization of vascular flow, moving structures, and guidance for interventional procedures.

  • Excellent for gallbladder evaluation and rapid trauma assessment ("FAST" scan).

• Advantages

  • Portable (hand-held to cart-based systems).

  • Completely non-ionizing → safe from fetus to geriatrics.

  • Distinguishes cystic vs. solid lesions instantly.

  • Rapid survey in ER, OR, ICU, nursery.

• Limitations

  • Sound waves do not traverse bone or gas → limited in lungs, bowel, skull.

Computerized Tomography (CT)

• Physics & Image Creation

  • 360^\circ x-ray tube rotation + computer reconstruction = cross-sectional slices of bone, vessels, soft tissue.

• Clinical Uses

  • Acute trauma (especially head), complex fractures, chronic vascular disease, pre-operative mapping.

  • Fusion imaging for interventional guidance.

• Advantages

  • Superior inherent contrast resolution between tissue types.

  • Post-processing: zoom, multiplanar reformatting (MPR), 3-D volume rendering.

  • Speed: whole-body scans in seconds → ideal for unstable patients.

• Disadvantages / Risks

  • Ionizing radiation; pediatric & pregnant exposure concerns.

  • Iodinated contrast may impair renal function over time.

Magnetic Resonance Imaging (MRI)

• Physics & Image Creation

  • Strong static magnetic field + radiofrequency pulses align hydrogen nuclei; differences in precession/spin rates between healthy vs. diseased tissue generate signal.

• Advantages

  • Exceptional soft-tissue contrast and multi-planar capability.

  • Non-ionizing.

• Considerations / Limitations

  • Long acquisition time → motion sensitivity; images largely static.

  • Gadolinium contrast sometimes required; contraindicated in severe renal impairment & pregnancy.

  • Loud gradients, enclosed bore → claustrophobia, acoustic protection.

  • Installation demands specialized, shielded suites.

X-Ray (Plain Radiography)

• Uses external x-ray beam; differential attenuation yields 2-D projection image.

• Applications: lung pathology, skeletal fractures/dislocations, tumors.

• Contrast Principle:

  • Air/fluid -> minimal attenuation -> dark.

  • Bone/metal -> maximal attenuation -> light.

Cross-Sectional Anatomy & Scanning Geometry

Importance for Sonographers

• Quality scanning depends on mental 3-D reconstruction of anatomy in transverse, sagittal, coronal, and oblique planes.

• Normal organs vary markedly in size/position; operator must display those variations convincingly.

Anatomic Position (Reference Standard)

• Patient standing erect, gaze forward, arms at sides, palms & toes facing anteriorly.

Anatomic Directions & Definitions

• Superior (Cephalic/Cranial) ↔ Inferior (Caudal).

• Anterior (Ventral) ↔ Posterior (Dorsal).

  • Example: Aorta is anterior to vertebral column; right kidney posterior to head of pancreas.

• Medial ↔ Lateral.

  • Hepatic artery medial to common bile duct; adnexa lateral to uterus.

• Proximal ↔ Distal.

  • Hepatic duct proximal to common bile duct; sphincter of Oddi distal to CBD.

• Superficial ↔ Deep.

  • Rectus abdominis superficial to transversus abdominis.

Fundamental Planes / Body Sections

• Transverse (Axial): horizontal; separates superior from inferior portions.

• Sagittal: longitudinal front-to-back; divides right from left.

  • Midsagittal = equal halves.

• Coronal: side-to-side; divides anterior from posterior.

• Oblique: any non-orthogonal cut; often used for vessel/duct trajectories.

Abdominal Mapping Systems

Four Quadrant Model

• Defined by one midsagittal and one transverse line through the umbilicus.

  1. Right Upper Quadrant (RUQ)

  2. Left Upper Quadrant (LUQ)

  3. Right Lower Quadrant (RLQ)

  4. Left Lower Quadrant (LLQ)

Nine Region Model

• Borders

  • Two vertical lines through each mid-inguinal point (midway between pubic symphysis & ASIS).

  • Two horizontal lines:

  • Subcostal plane (lowest costal margin).

  • Intertubercular plane (joining iliac tubercles).

  • Additional landmark: Transpyloric plane (passes pylorus, duodeno-jejunal junction, pancreatic neck, renal hila).

• Resulting Regions (right → left, superior → inferior):

  • Right Hypochondrium | Epigastrium | Left Hypochondrium

  • Right Lumbar | Umbilical | Left Lumbar

  • Right Iliac (Inguinal) | Hypogastrium (Suprapubic) | Left Iliac (Inguinal)

Practical & Ethical Considerations

• Radiation stewardship: minimize CT/x-ray in pediatrics and pregnancy; favor US/MRI when diagnostic yield is equivalent.

• Contrast-induced nephropathy: weigh risks vs. benefits, especially in renal compromise (both iodinated and gadolinium-based agents).

• Patient comfort & compliance: MRI noise/claustrophobia, CT speed for unstable cases, US immediacy at bedside.

• Inter-modality communication: reporting should acknowledge prior imaging, clarify discrepancies, and suggest best next test.