Chapter 24: Sectional Anatomy for Radiographers

Detailed Chapter Overview

Chapter 24 provides an essential introduction to sectional anatomy, a field that is foundational to understanding modern medical imaging. As technology has evolved beyond traditional planar radiography, modalities like Computed Tomography (CT), Magnetic Resonance Imaging (MRI), and Sonography have become central to diagnosis. These technologies visualize the body in "slices" or cross-sections, and this chapter serves as the radiographer's guide to interpreting this three-dimensional information. The central theme is the reorientation of anatomical thinking—moving from the two-dimensional shadowgraphs of conventional x-ray to a comprehensive understanding of anatomical relationships in the axial, sagittal, and coronal planes. The chapter meticulously defines these planes and provides a systematic, region-by-region tour of the human body as seen in cross-section. It begins with the intricate structures of the brain and cranium, moves through the complex relationships of the organs in the thorax and abdomen, and concludes with the musculoskeletal system. For each body part, the text highlights key anatomical landmarks and their appearance in different sectional planes, enabling the student to build a mental 3D model of human anatomy. Mastering this content is not just an academic exercise; it is a prerequisite for becoming a competent technologist in CT or MRI and is essential for passing advanced certification exams.

In-Depth Study Guide

The Three Cardinal Planes of Sectional Anatomy

Sectional anatomy requires a strong understanding of the three primary planes used to "slice" the body. All cross-sectional images are presented in one of these three orientations.

1. Axial (Transverse) Plane

• Definition: A horizontal plane that divides the body into superior (upper) and inferior (lower) portions.
• Visualization: Axial images are viewed as if you are standing at the patient's feet and looking up toward their head. Therefore, the patient's right side appears on the viewer's left, and the anterior aspect of the patient is at the top of the image.
• Significance: This is the primary plane of acquisition for most CT scans.

2. Sagittal Plane

• Definition: A vertical plane that divides the body into right and left portions. A **midsagittal** plane divides the body into equal right and left halves.
• Visualization: Sagittal images are viewed as if you are looking at the patient from their side.
• Significance: Excellent for visualizing the vertebral column and the midline structures of the brain.

3. Coronal Plane

• Definition: A vertical plane that divides the body into anterior (front) and posterior (back) portions.
• Visualization: Coronal images are viewed as if you are standing in front of the patient and looking at them. The patient's right side appears on the viewer's left.
• Significance: Often provides a more familiar, "AP-like" view of the anatomy that is intuitive for radiographers.

Region-by-Region Sectional Anatomy

The Head and Brain

Key Structures in Axial View:

• Ventricles: The lateral ventricles, third ventricle, and fourth ventricle are clearly identifiable CSF-filled spaces.
• Gray and White Matter: The outer cortex (gray matter) can be differentiated from the inner white matter.
• Basal Ganglia: Deep gray matter structures like the thalamus and caudate nucleus are visible.
• Sella Turcica: Best visualized on sagittal and coronal images, showing the pituitary gland.
• Orbits: Axial slices clearly show the globe, optic nerve, and extraocular muscles. Coronal views are excellent for demonstrating orbital floor fractures ("blowout" fractures).

The Thorax

Key Structures in Axial View:

• Lungs: The branching patterns of the bronchi and pulmonary vessels can be traced through sequential slices. The different lobes are identifiable.
• Heart and Great Vessels: The four chambers of the heart (atria and ventricles) are clearly delineated. The ascending and descending aorta, pulmonary artery, and vena cava are key landmarks. Coronal views are often used to see the aortic arch.
• Mediastinum: The esophagus, trachea, and major vessels are seen in cross-section, showing their relationship to each other and the vertebral column.

The Abdomen

The abdomen is a complex region where sectional imaging excels at differentiating soft tissue organs.

Key Structures in Axial View (from superior to inferior):

• Liver and Spleen: The large liver dominates the right upper quadrant, while the smaller spleen is seen in the left upper quadrant.
• Pancreas: This retroperitoneal organ is seen stretching across the abdomen. The head is nestled in the C-loop of the duodenum, while the tail extends toward the spleen.
• Kidneys and Adrenal Glands: The retroperitoneal kidneys are easily identified, along with the small adrenal glands situated on their superior poles.
• Stomach and Bowel: The stomach, small bowel, and large bowel can be traced. Oral contrast is often used in CT to opacify the bowel loops and differentiate them from other structures.
• Aorta and Inferior Vena Cava (IVC): These two great vessels are prominent anterior to the vertebral column. The aorta is typically on the left and circular, while the IVC is on the right and more ovoid.

The Pelvis

Key Structures in Axial View:

• Bladder: A fluid-filled structure located in the anterior pelvis.
• Reproductive Organs: In females, the uterus, ovaries, and fallopian tubes can be visualized. In males, the prostate gland is seen inferior to the bladder, and the seminal vesicles are posterior to it.
• Rectum: The terminal portion of the large intestine, located posteriorly.
• Musculature: The powerful gluteal and iliopsoas muscles are clearly demonstrated.

The Spine

• Axial View: Provides the best view of the relationship between the **vertebral body**, the **intervertebral disk**, the **spinal canal**, and the exiting **nerve roots**. It is the primary view for assessing disk herniations and spinal stenosis (narrowing of the canal).
• Sagittal View: The ideal plane for assessing the overall alignment of the vertebral column, vertebral body height (for compression fractures), and visualizing the spinal cord.
• Coronal View: Best for evaluating scoliosis (lateral curvature of the spine).