ANATOMICAL PLANIMETRY: PLANES, AXES, ORIENTATION TERMS - ANATOMY AND PHYSIOLOGY - 2024

The anatomical mapping is the set of coordinates, and points conventional terms used to describe the orientation position of an anatomical structure within the body and its relationship with the rest of the anatomical elements present in the body.

Knowledge of all the planes, axes and anatomical orientation system is essential to allow fluid and error-free communication between medical teams, either in the description of imaging studies or during the execution of invasive procedures.

Source: CFCF - Own work, CC BY-SA 3.0, The location of an organ or anatomical structure in the body is based on three planes (coronal, sagittal, and transverse) and three axes (vertical, transverse, and anteroposterior). In this way, when describing the position of a structure, it can always be located, regardless of the position of the patient or health personnel.

Starting from this anatomical orientation system, not only normal anatomy but also imaging studies (tomography, nuclear magnetic resonance, etc.) and surgical procedures are described.

It is therefore a standardized and universal system, which guarantees precision in anatomical descriptions of any kind.

Anatomic position

To understand anatomical planimetry, it is first essential to know the anatomical position, since all the terms used in the orientation system are in relation to said position.

Once the anatomical position and the reference points it offers are known, it does not matter if the body position is later changed, since the reference points remain constant.

It is considered that the human body in anatomical position is in a standing position, with the face facing forward, with the arms extended to the sides of the trunk forming an angle of 45º with respect to it and with the palms of the hands oriented towards ahead.

The lower extremities are extended with the heels attached and the parallel toes facing forward.

In this position, a series of lines (axes) and planes will be drawn that will subsequently allow unequivocal anatomical orientation, regardless of the change that the body may have with respect to the base anatomical position.

Axles

Three axes are considered for anatomical orientation in the human body:

- Longitudinal (also known as axial).

- Transversal (also called latero-lateral).

- Anteroposterior.

These axes allow the orientation of the body in space. They are also used as a reference for drawing the planes, and as orientation vectors to indicate the position of various structures.

Longitudinal axis

Also known as the sagittal axis, it is an imaginary line that extends from the head to the feet, dividing the body into two equal parts, a right half and a left half.

By convention, the line passes through the center of the head, intersecting in the middle the imaginary line connecting the two ears. From there it extends downward, passes through the middle of the pelvis and reaches the feet without crossing any anatomical structure.

This line divides the body into two symmetrical parts (left and right). It also constitutes the intersection between the sagittal and coronal planes, which are described later.

Transverse axis

It is the imaginary line that passes through the navel running from right to left. It is also known as the lateral-lateral axis.

The middle of the transverse axis is marked by its intersection with the longitudinal axis, so that both form a cross.

This line divides the body into two asymmetric parts (superior or cephalic and inferior or caudal). In addition, it will be taken as a reference for the cephalo-caudal orientation as described below.

Anteroposterior axis

The third axis, known as the anteroposterior axis, also passes through the navel; but the stroke of the line is from front to back.

At its midpoint it intersects the two anterior axes (longitudinal and transverse), and is used for the orientation of anatomical structures from front to back.

In this way, everything that is towards the anterior end of the line is considered ventral, and everything that is towards its posterior end is called dorsal.

Blueprints

Although the axes are very useful for the spatial orientation of the body and its division into interconnected regions, as they have only one dimension, they are insufficient for the precise location of the anatomical structures.

Therefore, the information provided by the axes must be complemented by that provided by the plans.

Graphically the planes are rectangles that intersect each other forming 90º angles. They are also two-dimensional, so they offer greater precision when locating structures.

In anatomical planimetry, three basic planes are described:

- Sagittal.

- Coronal.

- Transversal.

Each of them is parallel to two axes and divides the body into two well-defined parts.

Sagittal plane

It is also known as the anteroposterior plane. It is parallel to the longitudinal axis and the anteroposterior axis and perpendicular to the transverse axis.

It is oriented from front to back passing through the midline of the body dividing it into two equal parts: left and right.

From this plane two more can be described, known as parasagittal planes. Their orientation is identical to that of the sagittal plane, but they differ from it in that they do not pass through the midline. Instead they do it to the right and left of it. Therefore, two parasagittal planes are described: right and left.

Although parasagittal planes are not commonly used in normal anatomy, they are essential for the design of surgical techniques, especially when planning approach points; that is, the areas where the incisions will be made.

Coronal plane

The coronal plane is parallel to both the longitudinal and transverse axes and parallel to the anteroposterior.

It is projected from top to bottom passing through the imaginary line that joins both ears. In this way it divides the body into two slightly asymmetrical parts: anterior and posterior.

Multiple forward and backward planes are derived from the coronal plane, known as paracoronal planes. They are projected on the same axes as the coronal plane, but they differ from this in that they pass either in front of or behind the line that joins the ears.

Paracoronal planes are not commonly used in conventional anatomical descriptions, but they are indispensable for the description of radiological anatomy, especially when nuclear magnetic resonance is performed. This is because this study can virtually "slice" the body into several overlapping planes from front to back.

Transverse plane

The last of the planes is the only one perpendicular to the longitudinal axis. Known as the transverse plane, it is parallel to the anteroposterior and transverse (lateral-lateral) axes.

It passes through the navel, dividing the body into two asymmetric parts: cephalic and caudal. Therefore, all the structures that are between the transverse plane and the feet are described as caudal, while those that are located between the head and this plane are considered cephalic.

Terms used for orientation

Once the axes and planes that intersect and divide the body in anatomical position are known, it is possible to establish relationships between these and the various anatomical structures.

Furthermore, it is possible to determine relative relationships between structures and planes according to the position of the body if it is different from the anatomical position. This is very useful when performing surgical approaches.

The terms used to describe the location of the anatomical elements according to the planes and axes are the following:

- Cephalic.

- Flow.

- Proximal.

- Distal.

- Ventral.

- Dorsal.

- Medial.

- Side.

To locate any anatomical structure it is necessary to indicate at least two of the previously mentioned characteristics as well as a reference point. If this is not indicated, one of the axes and planes previously described is considered as a universal reference point.

Cephalic and c audal

The terms cephalic and caudal refer to the position of the structures of the head and trunk along the longitudinal axis, as well as their relation to the transverse plane.

Absolute position

If the absolute position (with respect to the transverse plane) is considered, the structures are cephalic as they move away from this plane and approach the head, while they are considered caudal when they approach the feet and move away from the transverse axis.

Relative position

Considering the relative position, that is, with respect to a reference point other than the transverse plane, the structures are considered to be cephalic as they approach the head and move away from the given reference point. Therefore, the same anatomical element can be cephalic or caudal depending on the reference point used.

This is much easier to understand with an example considering any organ, such as the thyroid gland.

Example

The absolute position of the thyroid gland is cephalic, since it is closer to the head than to the transverse plane.

However, when the position of the thyroid is considered relative to other anatomical structures, for example the sternum and jaw, its relative position changes.

Thus, the thyroid gland is caudal to the jaw, since it is closer to the feet than the latter; but if the sternum is considered, the position of the gland is cephalic, since it is closer to the head than to the reference point.

It can be seen that in both the absolute and relative position, the location of the structure along the longitudinal axis is used to determine if it is cephalic or caudal, varying only the reference point.

Proximal and d istal

This is a variation of the "cephalic" and "caudal" nomenclature that applies only to the extremities.

In this case, a median line is considered that extends from the root of the limb (the point where it joins the trunk) to where it ends, this axis being equivalent to the longitudinal axis of the body.

Thus, structures close to the root of the limb are considered proximal while those further away are distal.

Once again there is an absolute position (when the root of the member is taken as a reference) and a relative position (relationship of two structures to each other).

Example

Using an example again, it will be easier to understand these relationships. Take the humerus as a case study.

This bone is part of the proximal skeleton of the arm, since it is very close to the root of the limb. However, when its relationship with neighboring structures such as the shoulder and elbow is considered, the description of the location of the humerus varies.

Thus, the humerus is distal to the shoulder and proximal to the elbow. This spatial localization system is extremely useful in surgery, although it is not as widely used in descriptive anatomy, where relationships with respect to planes are preferred.

Ventral and d Orsal

The location of an organ in relation to the anteroposterior axis and the coronal plane is described using the terms ventral and dorsal.

Structures in front of the coronal plane are described as ventral, while those behind it are considered dorsal.

As with the cephalo-caudal and proximal-distal references, when speaking of ventral and dorsal it can be considered an absolute reference (coronal plane) or a relative reference.

Example

If the urinary bladder is considered, it can be said that it is ventral (absolute position), since it is in front of the coronal plane. However, when the relationship of this organ to the abdominal wall and rectum is taken into consideration, its relative position changes.

Thus, the bladder is dorsal to the abdominal wall (it is behind it), and ventral to the rectum (it is in front of it).

Lateral and medial

The lateral and medial references have to do with the position of a structure with respect to the midline of the body and the sagittal plane.

In the head, neck and trunk, any structure that is far from the midline (longitudinal axis) is considered lateral, while those that are closer to said axis (and therefore the sagittal plane) are medial.

In the extremities, the midline of the body cannot be taken as a reference, since all the structures are lateral to it. Therefore, an imaginary line is drawn that divides the limb into two equal parts.

Everything that is located between this line and the midline of the body is considered medial, while everything that is outside it is lateral.

Absolute and relative position

As with all previous references, when speaking of lateral and medial, the absolute position with respect to the midline or the location relative to other structures can be taken as a reference.

Example

The gallbladder is lateral to the midline of the body (absolute position). However, if its position relative to the right lobe of the liver is described, it will be found to be medial to it (the gallbladder is between the liver and the midline).

On the other hand, if its relationship with the bile duct is considered, it should be noted that the gallbladder is lateral to this structure.

As you can see, the anatomical location taking planimetry into account is very easy as long as the basic concepts are mastered, being possible to accurately describe the location of any structure of the anatomy no matter how complex and intricate it may be.

References

1. Hellebrandt, FA, Tepper, RH, Braun, GL, & Elliott, MC (1938). The location of the cardinal anatomical orientation planes passing through the center of weight in young adult women. American Journal of Physiology-Legacy Content, 121 (2), 465-470.
2. Cappozzo, A., Catani, F., Della Croce, U., & Leardini, A. (1995). Position and orientation in space of bones during movement: anatomical frame definition and determination. Clinical biomechanics, 10 (4), 171-178.
3. Mirjalili, SA, McFadden, SL, Buckenham, T., Wilson, B., & Stringer, MD (2012). Anatomical plans: are we teaching accurate surface anatomy ?. Clinical Anatomy, 25 (7), 819-826.
4. Açar, HI, Cömert, A., Avsar, A., Çelik, S., & Kuzu, MA (2014). Dynamic article: surgical anatomical plans for complete mesocolic excision and applied vascular anatomy of the right colon. Diseases of the Colon & Rectum, 57 (10), 1169-1175.
5. Dodson, MG, & Deter, RL (1990). Definition of anatomical planes for use in transvaginal sonography. Journal of Clinical Ultrasound, 18 (4), 239-242.
6. Evans, AC, Beil, C., Marrett, S., Thompson, CJ, & Hakim, A. (1988). Anatomical-functional correlation using an adjustable MRI-based region of interest atlas with positron emission tomography. Journal of Cerebral Blood Flow & Metabolism, 8 (4), 513-530.
7. Uzun, C., Atman, ED, Ustuner, E., Mirjalili, SA, Oztuna, D., & Esmer, TS (2016). Surface anatomy and anatomical planes in the adult turkish population. Clinical Anatomy, 29 (2), 183-190.
8. Reynolds, HM, & Hubbard, RP (1980). Anatomical frames of reference and biomechanics. Human factors, 22 (2), 171-176.