Anatomical planes and directional terms: sagittal, coronal, transverse and ipsilateral vs contralateral

Every plane and directional term is defined from the anatomical position. In this position the body stands upright with the feet at shoulder width and parallel, toes pointing forward, the upper limbs held at the sides and the palms of the hands facing forward. (OpenStax Anatomy and Physiology 2e, 1.6: Anatomical Terminology.)

Anatomists use these terms as if the body were in the anatomical position even when it is not. A patient lying face down (prone) or face up (supine) still has an anterior surface that is the front of the body, and the heart is still superior to the stomach. Right and left always mean the subject's own right and left, not the viewer's. (OpenStax Anatomy and Physiology 2e, 1.6: Anatomical Terminology.)

That last rule matters for every diagram on this page. When you face a person or an anterior view, their right side is on your left. The figures here mark the subject's right with an R so you can check yourself.

A plane is an imaginary two-dimensional surface that passes through the body. A section is the flat surface you would see if the body or an organ were actually cut along that plane. There are three basic planes, set at right angles to each other: the sagittal, frontal (coronal) and transverse planes. (OpenStax Anatomy and Physiology 2e, 1.6: Anatomical Terminology.)

The sagittal plane runs vertically and divides the body or an organ into right and left sides. The frontal plane runs vertically at right angles to the sagittal plane and divides the body into an anterior (front) and a posterior (back) portion. The transverse plane runs horizontally and divides the body into upper and lower portions. (OpenStax Anatomy and Physiology 2e, 1.6: Anatomical Terminology.)

Kenhub gives the same three planes with their common synonyms: median or midsagittal for the sagittal plane through the midline, coronal for the frontal plane, and axial or horizontal for the transverse plane, which lies at right angles to both the sagittal and frontal planes. (Kenhub: Anatomical terminology.)

There are many possible sagittal planes, because a vertical plane can cut the body anywhere from one side to the other. If the plane runs directly down the middle of the body it is the midsagittal or median plane, and it divides the body into equal right and left halves. If it divides the body into unequal right and left sides it is a parasagittal plane. (OpenStax Anatomy and Physiology 2e, 1.6: Anatomical Terminology.)

So the midsagittal plane is one particular sagittal plane, and every other sagittal plane parallel to it is parasagittal. Kenhub describes a sagittal plane as any vertical plane passing through the body parallel to the midline, dividing it into left and right parts; only the one through the centre is the median (midsagittal) plane. (Kenhub: Anatomical terminology.)

The midline defined by the median plane is also the reference for the terms medial and lateral. TeachMeAnatomy describes the midline as a line in the sagittal plane that splits the right and left halves evenly. (TeachMeAnatomy: Anatomical Terms of Location.)

The frontal plane divides the body or an organ into an anterior (front) portion and a posterior (back) portion. It is often called the coronal plane. Like the sagittal plane it is vertical, but it faces the opposite way: it runs from one side of the body to the other. (OpenStax Anatomy and Physiology 2e, 1.6: Anatomical Terminology.)

Kenhub defines the frontal (coronal) plane as a vertical plane at right angles to the sagittal plane. Because it runs from side to side, a single coronal slice can include structures of both the right and left sides of the body. (Kenhub: Anatomical terminology.)

The transverse plane divides the body or an organ horizontally into upper (superior) and lower (inferior) portions. Images made in transverse planes are called cross sections. (OpenStax Anatomy and Physiology 2e, 1.6: Anatomical Terminology.)

In radiology the transverse plane is usually called the axial or transaxial plane: a horizontal plane perpendicular to the long axis of the body. Radiopaedia notes that some authors keep the two words apart, using axial for the plane perpendicular to the long axis of the CT or MRI scanner and transverse for the plane perpendicular to the long axis of the body. The two are usually the same, but not when a patient cannot lie in the standard position. (Radiopaedia: Radiographic positioning terminology.)

When someone searches for an axial view, they almost always mean this kind of horizontal slice, such as an axial CT image through the abdomen. The same word appears elsewhere in anatomy, so do not confuse an axial view with the axial skeleton, which is made up of all the bones of the head, neck, chest and back. (OpenStax Anatomy and Physiology 2e, 7.1: Divisions of the Skeletal System.)

Movements happen in a plane and around an axis, and the axis is always at right angles to the plane. In Kinetic Anatomy the sagittal plane rotates about a frontal horizontal axis (bending the knee is an example), the frontal plane rotates about a sagittal horizontal axis (raising the arm out to the side), and the horizontal (transverse) plane rotates about a vertical or longitudinal axis (turning the head from side to side). (Human Kinetics: Anatomical planes and axes of movement (excerpt from Kinetic Anatomy, 5th ed.).)

OpenStax links the main movements to these planes. Flexion and extension, which decrease and increase the angle between bones, typically take place in the sagittal plane. Abduction, which moves a limb laterally away from the midline, and adduction, which brings it back toward or across the midline, occur in the coronal plane. (OpenStax Anatomy and Physiology 2e, 9.5: Types of Body Movements.)

Rotation, such as medial (internal) and lateral (external) rotation of the limbs, happens in the horizontal plane around the vertical axis. At the ankle, dorsiflexion and plantarflexion are sagittal-plane movements, while inversion and eversion of the foot are frontal-plane movements. (Human Kinetics: Anatomical planes and axes of movement (excerpt from Kinetic Anatomy, 5th ed.).)

Directional terms come in opposite pairs. Anterior (ventral) means the front or toward the front of the body, and posterior (dorsal) means the back or toward the back. Superior (cranial) means above or higher than another part, and inferior (caudal) means below or lower. (OpenStax Anatomy and Physiology 2e, 1.6: Anatomical Terminology.)

Medial means toward the middle of the body and lateral means toward the side. Proximal describes a position in a limb nearer to its point of attachment to the trunk, and distal a position farther from it. Superficial means closer to the surface of the body and deep means farther from it. (OpenStax Anatomy and Physiology 2e, 1.6: Anatomical Terminology.)

Examples make the pairs easier to remember. The heart lies posterior to the sternum, the nose is superior to the mouth, the eye is lateral to the nose, the wrist is distal to the elbow and the knee is proximal to the ankle. Proximal and distal are used for structures with a beginning and an end, such as limbs and blood vessels. (TeachMeAnatomy: Anatomical Terms of Location.)

Anatomical terms are built on Greek and Latin roots. OpenStax points out that because these languages are no longer used in everyday conversation, the meanings of their words do not drift over time, which keeps the terminology stable. (OpenStax Anatomy and Physiology 2e, 1.6: Anatomical Terminology.)

Ipsilateral means on the same side of the body, and contralateral means on the opposite side. Your right hand and right foot are ipsilateral to each other; your right hand and left foot are contralateral. (Radiopaedia: Radiographic positioning terminology.)

The terms are used most in neurology. Axons of the corticobulbar tract are ipsilateral, meaning they project from the cortex to motor nuclei on the same side of the nervous system. The axons of the corticospinal tract are largely contralateral: they cross the midline and synapse on the opposite side of the body. Axons that act on both sides at once are described as bilateral. (OpenStax Anatomy and Physiology 2e, 14.3: Motor Responses.)

Most spinal pathways that connect to the brain are contralateral, so the right side of the body is connected to the left side of the brain, while cranial nerve systems are mostly ipsilateral, with some exceptions. (OpenStax Anatomy and Physiology 2e, 14.1: Sensory Perception.)

Because most corticospinal fibres cross to the opposite side, the right motor cortex of the cerebrum controls muscles on the left side of the body, and the left motor cortex controls the right side. (OpenStax Anatomy and Physiology 2e, 14.3: Motor Responses.)

Clinicians also use the pair for paired organs. A tumour in the left breast with an enlarged lymph node in the left axilla describes ipsilateral spread; a finding in the right axilla would be contralateral. Unilateral means affecting one side only, and bilateral means affecting both.

Anatomical illustrations and 3D models are usually shown from standard directions named with the same terms. An anterior view shows the body from the front, a posterior view from the back, and a lateral (side) view from the right or left. A superior view looks down from above, as when you look at the top of the skull. (OpenStax Anatomy and Physiology 2e, 1.6: Anatomical Terminology.)

In a right lateral view the subject's right side faces you and the anterior surface points to one side of the picture, so the frontal plane appears edge-on as a vertical line, as in the centre panel of the planes diagram. X-ray projections are named by the direction the central ray travels: in an AP (anteroposterior) projection it passes from anterior to posterior, perpendicular to the coronal plane, in a PA projection from posterior to anterior, and in a lateral projection from one side of the body to the other. (Radiopaedia: Radiographic positioning terminology.)

On EasyAnatomyLab's 3D human model you can switch between anterior, posterior, left and right views. Try finding a structure in one view and then predicting where it will appear in another: it is one of the fastest ways to make the planes and directional terms automatic.