Anatomical planes are imaginary flat surfaces used to describe the orientation of the body and its structures. A section is a cut or image made along one of these surfaces. Sagittal, coronal and transverse planes provide a consistent framework for understanding anatomy in specimens, three-dimensional models and medical images.
What is the difference between an anatomical plane and a section?
A plane describes orientation rather than a particular cut. A section shows the structures intersected at a chosen position along that orientation. Moving a section through the body without changing its angle produces different views in parallel planes with the same orientation.
Anatomical planes are described relative to the anatomical position: the body stands upright, faces forwards, and has the arms at the sides with the palms facing forwards. This reference remains the same when a person lies down or a model is rotated. Right and left always refer to the person's own right and left.
Several directional terms help describe sections:
- Anterior means towards the front; posterior means towards the back.
- Superior means towards the head; inferior means towards the feet.
- Medial means towards the body's midline; lateral means away from it.
The midline is the central reference separating the body's right and left sides. These directions describe anatomical relationships, not necessarily the top, bottom or sides of a displayed image.
What does a sagittal section show?
A sagittal plane runs vertically from front to back and divides the body into right and left portions. A sagittal section therefore presents a side-oriented view, showing anterior–posterior and superior–inferior relationships within the selected slice.
The median plane, also called the midsagittal plane, passes through the midline and divides the body into right and left halves. This does not mean that the halves contain identical structures: many organs are asymmetrical or lie mainly on one side.
A parasagittal plane is parallel to the median plane but lies to its right or left. Its position determines which structures it intersects. A section near the midline and one farther laterally may look very different despite sharing the same orientation.
A median section of the brain reveals the cut surfaces of structures lying at the midline. A median section through the vertebral column can show the stacked vertebral bodies, the weight-bearing anterior portions of the individual spinal bones. Within the skeletal system, the body's framework of bones and associated cartilages, this view makes the column's front-to-back curves easier to follow.
What does a coronal section show?
A coronal plane, also called a frontal plane, runs vertically from side to side and divides the body into anterior and posterior portions. A coronal section shows right–left and superior–inferior relationships within the selected slice.
This orientation is useful for comparing structures on opposite sides of the body. A section at an appropriate depth may intersect both kidneys, allowing their positions to be compared. Each kidney lies towards the back of the abdomen, with the right usually slightly lower than the left.
A coronal section through the liver can demonstrate its extent across the upper abdomen, mainly on the right. However, one section does not show the organ's complete shape: portions lying in front of or behind the selected plane are absent from that section.
Moving a coronal section from anterior to posterior changes the structures encountered. The plane's orientation stays constant, but its depth through the body changes.
What does a transverse section show?
A transverse plane, commonly called an axial plane in imaging, divides the body into superior and inferior portions. In anatomical position, it is horizontal. A transverse section shows right–left and anterior–posterior relationships at a selected level.
The level of the section is essential to its meaning. A transverse section through the chest intersects different structures from one through the abdomen. Even within one region, nearby sections may show different parts of the same organ.
For example, successive transverse sections through the heart intersect different parts of its chambers and connecting vessels. Because the heart lies obliquely in the chest, a transverse body section is not necessarily perpendicular to the heart's own long axis, the direction along its length.
A transverse section through a long structure is often described as a cross-section when it cuts across that structure's length. However, a body transverse section is not automatically a true cross-section of every structure it intersects: vessels, muscles and organs may run at an angle.
What is an oblique section?
An oblique section is made at an angle to the standard sagittal, coronal or transverse planes. It is useful when a structure's orientation does not align neatly with the body's principal planes.
A longitudinal section follows a structure's length, whereas a cross-section cuts across it. These terms describe the cut relative to the structure itself, rather than relative to the whole body. A longitudinal section of an angled structure may therefore be oblique to the standard body planes.
Cutting a circular cylindrical tube obliquely can produce an oval profile rather than the round profile expected from a perpendicular cut. This illustrates why apparent shape depends on both the structure's anatomy and the angle of the section.
How do anatomical planes relate to CT and MRI slices?
Computed tomography, abbreviated CT, uses X-rays to produce sectional images. Magnetic resonance imaging, abbreviated MRI, uses a magnetic field and radiofrequency signals to produce images that can also be displayed as sections. Both methods use anatomical planes to describe image orientation.
A displayed slice represents a thin layer of tissue rather than an infinitely thin mathematical plane. A series of slices allows anatomy to be followed through a region. A structure may appear, change shape and disappear as the slice position moves beyond its boundaries.
CT images are commonly viewed in the axial plane, with coronal and sagittal views reconstructed from the acquired image data. Reconstruction here means producing an image in a chosen orientation from those data. MRI images can be acquired in different orientations, and suitable datasets can also be reconstructed into other planes.
Axial images are conventionally displayed as though viewed from the person's feet towards the head, placing the person's right on the image's left. Coronal images are commonly displayed as though facing the person. Orientation labels remain important, particularly for sagittal and oblique views, because screen position alone does not reliably identify anatomical direction.
How can you compare the planes in a 3D model?
The principal planes are perpendicular to one another, meaning that they meet at right angles. Each highlights a different set of relationships, so no single orientation gives a complete account of a three-dimensional structure.
| Plane | What it divides | Typical anatomical use |
|---|---|---|
| Median sagittal | Right and left halves | Examining midline structures and front-to-back relationships |
| Parasagittal | Unequal right and left portions | Examining structures lateral to the median plane |
| Coronal or frontal | Anterior and posterior portions | Comparing right and left structures at a selected depth |
| Transverse or axial | Superior and inferior portions | Comparing structures at a selected body level |
| Oblique | Portions determined by the chosen angle | Following structures angled to the principal planes |
In the 3D model next to this article, you can rotate and zoom, select a structure, and cut a section along the sagittal, coronal or transverse plane. You can also hide, isolate or fade a selected structure, switch layers on and off, or pull parts apart.
When comparing sections, distinguish orientation, the direction of the cut, from position, its location through the body. Then identify which surfaces are cut and which structures lie outside the section. Keeping these distinctions separate makes it easier to relate a flat sectional view to the surrounding three-dimensional anatomy.