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10.06: Zone M4 – Inferior Posterior Cheek

YOUR ASSIGNMENT FOR THIS LESSON

✅ Step #1: Review all content below.

✅ Step #2: Image the M4 zone on your own with your ultrasound, and using the checklist provided on this page, check off all key structures to be identified in this location

TRANSDUCER POSITION AT M4

Note: Clip is sped up.

STANDARD M4 ORIENTATION:
TRANSVERSE

The intersection of the vertical line from the lateral canthus to the horizontal line from labial mental crease is the location of M4.

QUICK TIP
  • First, identify the teeth or mandible (you may see either at this position depending on patient and angle of the probe) which will appear hyperechoic (bright). Adjust the depth of penetration so the teeth are visible at the bottom of the screen.
  • Next, identify a hypoechoic region just anterior and adjacently deep to the subcutaneous tissue, this is DAO muscle.
  • Coursing just posterior of the DAO muscle is a thin hypoechoic linear structure, this is the risorius muscle.
    • You may need to angulate the probe to visualize this structure optimally.

EXAMPLE OF TRANSVERSE IMAGE ACQUIRED AT M4

Standard image acquired at M4. (Transverse| Left side is patient's anterior). See key below for lables.*

ANATOMICAL LEGEND FOR M4 LOCATION IN TRANSVERSE

*Standard image acquired at M4 labeled with key anatomical structures.
Deep Fat Compartments

KEY VESSELS IN THE REGION

DOPPLER IMAGES ACQUIRED AT M4 OF KEY VESSELS

At M4 the inferior labial artery and facial artery can be visualized
Play Video
QUICK TIP
  • At M4 you will be looking for the facial artery and inferior labial artery.
    • In this view the facial artery will often appear circular in crossection, whereas the inferior labial artery will appear liner as you are viewing it in the long axis.
    • The inferior labial artery will run just under the DAO muscle.
    • To confirm the vessel seen is the artery, track it back to M2,  There identify both the artery and vein at this location with the most anterior vessel (one furthest from the masseter muscle) being the facial artery.

DO IT YOURSELF CHECKLIST

Structures to Identify on Ultrasound for M4

Once you have completed this checklist, mark this part of the lesson as complete.