1 - Skull radiographic views and anatomy

Question 1

What are the main types of skull view radiographs?

Answer 1

• occipitomental
• posterior-anterior mandible
• reverse Townes
• true lateral skull

Question 2

Describe the equipment used for a skull radiograph.

Answer 2

• specialised skull unit that can be positioned to capture patient at different angles ie sitting or lying down
• receptor is digital and large enough to capture the entire head

Question 3

What is the orbitomeatal line?

Answer 3

• reference line used in positioning patients for most skull radiographs
• runs from outer canthus of eye to centre of external auditory meatus

Question 4

What do occipitomental radiographs show?

Answer 4

• facial skeleton avoiding superimposition of skull base
• middle third facial fractures

Question 5

At what angle are OM radiographs taken?

Answer 5

• 0°, 10°, 30°, 40°
• usually take two together to evaluate trauma

Question 6

What are the indications for an OM radiograph?

Answer 6

• middle third facial fractures (ie. Le fort, zygomatic complex, naso- ethmoidal complex, orbital blowout)
• coronoid process fracture

Question 7

Describe the positioning for an OM radiograph.

Answer 7

• face towards receptor
• head tipped back so OM line is at 45° to receptor (chin and nose to receptor)
• X-ray beam runs at angle specified (0° is perpendicular to receptor)

Question 8

What do postero-anterior mandible radiographs show?

Answer 8

Posterior parts of mandible

Question 9

What are the indications for a PA mandible radiograph?

Answer 9

• lesions or fractures to posterior third of body of mandible, angles, rami, low condylar necks
• mandibular hyperplasia/hypoplasia
• maxillofacial deformities

Question 10

Describe the positioning for a PA mandible radiograph.

Answer 10

• face towards receptor
• head tipped forwards so that OM line is perpendicular to receptor (forehead and nose to receptor)
• X-ray beam is perpendicular to receptor at level of rami

Question 11

Why is the X-ray beam projected from the posterior side?

Answer 11

• reduced magnification of face (reduced distortion of relevant structures)
• reduced effective dose to radiosensitive tissues (ie lens of eye)

Question 12

What does the reverse Townes radiograph show?

Answer 12

Condylar heads and neck

Question 13

What are the indications for a reverse Townes radiograph?

Answer 13

• high fractures of condylar necks
• intracapsular fractures of TMJ
• condylar hypoplasia/hyperplasia

Question 14

Describe the positioning of a reverse Townes radiograph.

Answer 14

• face towards receptor
• head tipped forward so that OM line is perpendicular to receptor (forehead and nose to receptor)
• mouth open (moves condylar heads out of glenoid fossa)
• X-ray beam 30° below OM line and centred through condyles