Thank you to radiological technologist Will Pinter for your help with this article!
Anatomical directional terms are a method of communication which enable us to discern different parts of the body and discuss their locations relative to one another. These terms are precise and universal.
We colloquially use directional terms every day. We can’t just “go,” we drive forward or backwards. Being told to “turn” isn’t enough information, we need to know if we’re turning right or left. If our destination is north or south. If an object is up or down. But east or west, right or left, won’t help us navigate the human body or medical imaging. Anatomical directional terms are most easily learned through paired opposites, and always describes structures as if the subject were in anatomic position.
Anatomic Position – The following terms always assume the subject is in anatomic position: standing upright with feet together and arms out from their sides with palms facing forward. See these examples.
Supine/Prone – Directional terms always assume anatomic position unless otherwise specified, even if the subject is laying down. A person laying facing up is said to be in a supine position (facing sup’!); facing down would be prone. Supine/prone may describe pinpointed structures, too – a supine hand has the palm facing up (just imagine the hand’s orientation when the supine subject in anatomic position).
Right/Left – Right and left are colloquial directional terms which when used in anatomy will refer to the subject’s right and left, not the observer.
Anterior/Posterior – Anterior is towards the front; posterior towards the back. E.g., (and pardon the mnemonic) the posterior (the buttocks) is posterior. If looking at an image with the person facing you, the subject would be seen from an anterior view. These directional terms are sometimes substituted with ventral/dorsal, respectively, when describing animals. To avoid confusion due to posturing, use the spine as a reference.
Superior/Inferior – These opposites indicate proximity to one end or another. Superior indicates towards the head, or above something else (Remember to assume anatomic position – superior means “up” towards the head, even if the subject is technically laying down). Inferior means towards the feet, down, or below. E.g., torso is superior to legs; feet are part of the inferior extremities.
Medial/Lateral – Medial means towards the middle, and lateral conversely means to the sides. E.g., In anatomic position, your thumbs are lateral to your palms.
Proximal/Distal – See examples. Proximal is closer to an attached base (usually describing a part closer to or moving towards the torso), and distal is further from the base (or farther away, e.g. hands are distal to the forearm).
Cephalic/Caudal – Cephalic (cephalad or cranial) describes something towards the head; caudal identifies something towards the “tail” or tailbone (coccyx).
Superficial/Deep – Superficial anatomy are structures on or proximal to the body’s surface. To discuss depth, superficial means closer to the surface, whereas deep denotes deeper into a body region, closer to the structure’s center, E.g., the ribcage is superficial to the lungs.
Central/Peripheral – Central is the midpoint of the main part or organ. Peripheral refers to a part that is near the surface, edge, or outside of another body part. Whereas deep and superficial describe the degree of depth to the body, central and peripheral can further be outside the body.
Ipsilateral/Contralateral – Ipsilateral relates to things on the same right or left side of the body. Contralateral contrasts things on opposite sides of the body.
Unilateral/Bilateral – Unilateral identifies a condition affecting only one side of the body; bilateral describes something symmetrically affecting both right and left sides.
The abdomen and pelvis are divided into right upper (RUQ), right lower (RLQ), left upper (LUQ), and left lower (LLQ) quadrants (see examples). They may also be divided into nine tic-tac-toe style regions: beginning in the center of the gastrointestinal system and including the belly button is the umbilical region; superior is the epigastric region (above the gastric- region), inferior to the umbilical region is the hypogastric region (below the gastric-). The epigastric region contains the heart, which helps us remember the upper lateral regions are the right and left hypochondriac regions. The central umbilical region includes the lumbar area of our back, which helps us remember the right and left lumbar regions. The uppermost and largest part of our pelvis is the ilium, which helps us remember our final right and left iliac regions.
Finally, subjects or medical images may be cut/imaged from different angles/perspectives, such as an anterior view (looking at their front side) or an inferior view (as if viewing from the bottom of their feet). We can describe the body in three dimensions using these planes of reference: frontal (or coronal) divides front from back (allowing an anterior or posterior view), sagittal separates right side from left side, and transverse (or horizontal) cuts top from bottom (superior or inferior view). Oblique planes are diagonal cross sections in any direction.