11.3 Radiologic Surface Anatomy, Body Habitus & Sectional Body Cuts
Key Takeaways
- Palpable bony landmarks convert a written request into a centring point: the vertebra prominens marks C7, the jugular notch T2-T3, the sternal angle T4-T5, the xiphoid process T9-T10, the lowest costal margin L2-L3, the iliac crest L4-L5, the anterior superior iliac spine S1-S2, and the greater trochanter and pubic symphysis lie at approximately the same transverse level.
- The four body habitus types are hypersthenic (about 5 percent), sthenic (about 50 percent), hyposthenic (about 35 percent) and asthenic (about 10 percent), and they determine the position of the gallbladder, stomach, colon and diaphragm and therefore the centring and film orientation for abdominal work.
- Sectional imaging uses three cardinal planes: sagittal divides right from left, coronal divides anterior from posterior, and transverse or axial divides superior from inferior; oblique planes lie at an angle to two of these.
- Radiographic anatomy is described in the anatomical position — erect, facing forward, arms at the sides with palms forward — regardless of how the patient is actually positioned during the examination.
- A projection is named by the path of the central ray through the body from entrance to exit, a position is named by the part of the body closest to the image receptor or by the general body posture, and a view describes what the image receptor sees, a term reserved for the radiograph itself.
11.3 Radiologic Surface Anatomy, Body Habitus & Sectional Body Cuts
The Patient Care and Management subject opens with Human Anatomy and Physiology, and its first sub-topic is Radiologic Surface Anatomy and Body Cuts (4 items), with competencies to illustrate the surface anatomy of the human body and analyze positions and body cuts. This is short in item count but load-bearing: without landmarks you cannot centre, and without planes you cannot describe an oblique or a cross-sectional image.
1. The Anatomical Position and Reference Terms
All radiographic description assumes the anatomical position: the body erect, facing the observer, head and feet directed forward, arms at the sides with the palms facing forward. Anatomical right and left always mean the patient's right and left, never the observer's.
| Term | Meaning |
|---|---|
| Anterior / ventral | Toward the front |
| Posterior / dorsal | Toward the back |
| Superior / cephalad / cranial | Toward the head |
| Inferior / caudad | Toward the feet |
| Medial | Toward the midline |
| Lateral | Away from the midline |
| Proximal | Nearer the point of attachment or origin |
| Distal | Farther from the point of attachment or origin |
| Superficial / external | Nearer the surface |
| Deep / internal | Farther from the surface |
| Ipsilateral / contralateral | Same side / opposite side |
| Plantar / dorsum (foot) | Sole of the foot / top of the foot |
| Palmar (volar) / dorsum (hand) | Palm of the hand / back of the hand |
2. Projection, Position and View — Keep Them Separate
These three are examined as a set because candidates routinely blur them.
- Projection is named by the path of the central ray through the body, entrance to exit. Posteroanterior (PA) means the ray enters the posterior surface and exits the anterior surface. Anteroposterior (AP), lateral, axial (any ray angled along the long axis of the body), and tangential (skimming a curved surface) are all projections.
- Position is named by the part of the body closest to the image receptor, or by the general posture of the body. Right anterior oblique (RAO) means the patient's right anterior surface is against the receptor. Postures such as supine, prone, erect, recumbent, Trendelenburg (head lower than feet), Fowler (head higher than feet), Sims (recumbent oblique for enema tip insertion) and lithotomy are also positions.
- View describes what the image receptor sees. In the British and American conventions it is correctly applied only to the radiograph itself, not to the act of positioning. The PRC blueprint asks you to "explain how anatomic terms, view, and projection are used to determine the patient, film, and central ray relationship" — so know that a PA projection produces a "PA view" of the chest but that you do not "position the patient in a PA view".
Decubitus deserves special attention because it combines both. The patient is recumbent, the central ray is horizontal, and the decubitus is named for the dependent (down) side: a left lateral decubitus means the patient lies on the left side. The horizontal ray is what demonstrates air-fluid levels and free intraperitoneal air.
3. Palpable Surface Landmarks and Their Vertebral Levels
Memorise this table; it is the single most usable page in positioning.
| Landmark | Vertebral level |
|---|---|
| Mastoid tip | C1 |
| Gonion (angle of the mandible) | C3 |
| Thyroid cartilage (upper margin) | C4-C5 |
| Vertebra prominens (most prominent spinous process at the base of the neck) | C7 |
| Jugular (suprasternal) notch | T2-T3 |
| Sternal angle (angle of Louis) | T4-T5 |
| Inferior angle of the scapula | T7 |
| Xiphoid process (tip) | T9-T10 |
| Lowest (tenth) costal margin | L2-L3 |
| Iliac crest | L4-L5 |
| Anterior superior iliac spine (ASIS) | S1-S2 |
| Greater trochanter | Level of the pubic symphysis / coccyx |
| Ischial tuberosity | Roughly 4 cm below the pubic symphysis |
How they are used in practice:
- Chest PA: centre at T7, the inferior angle of the scapula.
- Abdomen KUB supine: centre at the iliac crest, including the symphysis pubis inferiorly.
- Acute abdomen erect: centre roughly 5 cm above the iliac crest so both hemidiaphragms are included.
- Thoracic spine: centre midway between the jugular notch and the xiphoid, roughly T7.
- Lumbar spine AP: centre at the iliac crest for L4-L5, or at the lower costal margin for the upper lumbar segments.
- Cervical spine AP axial: centre at the thyroid cartilage, C4.
- Hip: locate the femoral head roughly 4 cm distal and 2.5 cm medial to the midpoint of a line drawn from the ASIS to the pubic symphysis.
4. Body Habitus
Body habitus is the general form of the body. It is not the same as body weight, and it determines where the viscera sit — which is why it changes centring, receptor orientation and even how many exposures a barium series requires.
| Habitus | Approximate share of the population | Build | Consequences |
|---|---|---|---|
| Hypersthenic | About 5% | Massive, broad and deep thorax; short and wide abdomen | Diaphragm high; heart transverse; lungs short and wide; gallbladder high, lateral and nearly transverse; stomach high and transverse; colon peripheral and high. Chest often needs landscape (crosswise) receptor orientation |
| Sthenic | About 50% | The athletic average build | The reference standard for textbook centring points |
| Hyposthenic | About 35% | Slighter build, more vertical organ orientation | Organs slightly lower and more medial than sthenic |
| Asthenic | About 10% | Slender, narrow thorax, long and shallow abdomen | Diaphragm low; heart narrow and vertical; lungs long; gallbladder low, medial and near the vertebral column; stomach low, J-shaped and medial; colon low and medial, folded on itself |
The two examples examiners use most: the gallbladder (high, lateral and transverse in the hypersthenic; low, medial and vertical in the asthenic) and the stomach (high and transverse versus low and J-shaped). Getting these two right answers most habitus items.
5. Body Planes and Sectional Cuts
| Plane | Divides | Sectional imaging term |
|---|---|---|
| Sagittal | Right from left; the midsagittal (median) plane divides the body into equal right and left halves | Sagittal reformat |
| Coronal (frontal) | Anterior from posterior; the midcoronal (midaxillary) plane divides the body into equal front and back halves | Coronal reformat |
| Transverse (axial, horizontal, cross-sectional) | Superior from inferior | The native acquisition plane of CT |
| Oblique | At an angle to two of the cardinal planes | Oblique reformat |
Two further planes matter in skull work and in CT positioning:
- Interpupillary (interorbital) line — connects the pupils; used to check for head rotation.
- Orbitomeatal line (OML) — from the outer canthus to the external auditory meatus, the primary skull baseline. The infraorbitomeatal line (IOML) lies roughly 7-8 degrees below the OML, and the glabellomeatal line (GML) roughly 8 degrees above it. The acanthiomeatal line (AML) runs from the acanthion to the EAM. The mentomeatal line (MML) runs from the mental point to the EAM and is used for the Waters projection.
- Frankfort horizontal plane — from the infraorbital margin to the superior border of the external auditory meatus, kept parallel to the floor in panoramic dental radiography and in many cranial studies.
Directional terms for sectional images
When a transverse CT image is displayed, the convention is that the image is viewed from the patient's feet looking toward the head, so the patient's right appears on the viewer's left. Anterior structures are at the top of the image and posterior at the bottom. This convention is the reason a left-sided lesion appears on the right of the monitor, and it is a favourite item.
6. Body Cavities and Quadrants
| Cavity | Contents |
|---|---|
| Thoracic | Pleural cavities (lungs) and the mediastinum (heart, great vessels, trachea, oesophagus, thymus) |
| Abdominal | Stomach, small and large intestine, liver, gallbladder, pancreas, spleen, kidneys, adrenals |
| Pelvic | Rectum, urinary bladder, and the reproductive organs |
The abdomen is divided for description into four quadrants by a vertical and a horizontal line through the umbilicus — right upper, left upper, right lower and left lower — or into nine regions (right and left hypochondriac with the epigastric between them; right and left lumbar with the umbilical between them; right and left iliac or inguinal with the hypogastric between them). Quadrant description dominates clinical requests; region description appears in anatomy items.
7. Putting It Together
| Request | Landmark you palpate | Centring |
|---|---|---|
| PA chest, sthenic adult | Inferior angle of the scapula | T7, receptor top about 4-5 cm above the shoulders |
| PA chest, hypersthenic adult | Same | T7, but consider a crosswise receptor to include the full width |
| KUB | Iliac crest | Iliac crest, include the symphysis |
| Erect acute abdomen | Iliac crest | About 5 cm above the crest to include both hemidiaphragms |
| AP lumbar spine | Iliac crest | L4-L5 at the crest |
| AP pelvis | ASIS and symphysis | About 5 cm below the ASIS, or midway between the ASIS and the symphysis |
| Lateral hip | ASIS-to-symphysis line | 4 cm distal and 2.5 cm medial to the midpoint of that line |
| AP thoracic spine | Jugular notch and xiphoid | Midway between, about T7 |
A request asks for an AP lumbar spine centred at the level of the fourth and fifth lumbar vertebrae. Which palpable landmark identifies this level?
A hypersthenic patient presents for an oral cholecystographic-style evaluation of the gallbladder. Compared with a sthenic patient, where should the gallbladder be expected?
A transverse CT image of the abdomen is displayed on the workstation. A lesion appears on the left side of the monitor. Where is the lesion in the patient?
Which statement correctly distinguishes projection from position?