Skull Views And Anatomy

Question 1

What are the 4 main types of skull radiographs?

Answer 1

Occipitomental
Postero anterior mandible
Reverse Townes

True lateral skull (very similar to lateral ceph except not standardised with cephalostat)

Question 2

What is the primary use for occipito mental radiographs?

Answer 2

Fractures of the mid face

Question 3

What is the primary use for postero anterior mandible radiographs?

Answer 3

Fractures of the posterior mandible (excluding condyle)

Question 4

What is the primary use of reverse Townes radiographs?

Answer 4

Fractures of mandibular condyles

Question 5

What is the main reference line in skull radiographs?

Answer 5

Orbitomeatal line
- outer can thus of eye to center of external auditory meatus

Question 6

When is a occipitomental radiograph indicated?

Answer 6

Middle third fractures:
- le fort fractures
- zygomatic complex
- orbital blow out

Coronoid process fractures

Question 7

How are patients positioned for OM radiographs?

Answer 7

Head tipped back so orbitomeatal line is parallel to floor and 45 degrees to receptor.
Patient facing receptor.

Beam 0 degrees (perpendicular to receptor and centered through occipitus) or 30 degrees (above perpendicular line, centered through lower border of orbit).

Question 8

What are the indications for a PA mandible?

Answer 8

Lesions and fractures involving:
- posterior third of body
- angles
- rami
- low condylar necks

Mandibular hyperplasia/ hypoplasia
Maxillofacial deformities

Question 9

What is patient positioning for PA mandible?

Answer 9

Face towards receptor
Head tipped forward so orbitomeatal line is perpendicular to receptor and parallel to floor.
(Forehead nose position)

Beam perpendicular to receptor and centered through cervical spine at level of rami

Question 10

In OM radiograph, which direction does the skull base move with higher angulation of beam?

Answer 10

Skull base moves down

Question 11

Why is the beam projected from behind the patient?

Answer 11

Reduced magnification of face (as closer to receptor)- less space to diverge

Reduced effective dose - beam partially attenuated by back of skull, before reaching face (radio sensitive tissues eg eyes).

Question 12

What are the indications for a reverse Townes?

Answer 12

High fractures of condylar necks
Intra capsular fractures of TMJ
Condylar hyperplasia/ hypoplasia

Question 13

What is the difference between reverse Townes and PA mandible?

Answer 13

Reverse Townes has mouth open and beam angulation from below (30 degrees below perpendicular, through condyles)

Question 14

What does a reverse Townes image?

Answer 14

Condylar heads and necks

Question 15

What does PA mandible image?

Answer 15

Posterior parts of mandible

Question 16

What does OM image?

Answer 16

Facial skeleton (avoids superimposition of skull base)

Question 17

How is the patient positioned for reverse Townes?

Answer 17

Face receptor
Head tipped forward so orbitomeatal line is parallel to floor, mouth open

Beam 30 degrees below perpendicular line to receptor and centered through condyles

Question 18

Why is the mouth open for reverse Townes?

Answer 18

Moves condylar heads out of glenoid fossa