10.03: Zone M1 – Masseter
YOUR ASSIGNMENT FOR THIS LESSON
✅ Step #1: Review all content below.
✅ Step #2: Image the M1 zone on your own with your ultrasond, and using the checklist provided on this page, check off all key structures to be identified in this location.
TRANSDUCER POSITION AT M1
STANDARD M1 ORIENTATION:
TRANSVERSE AND LONGITUDINAL
Palpate the masseter muscle and then scan over this muscle. Doing this fulfils scanning through all of M1.
Scan in the superior-inferior direction in transverse, and anterior-posterior direction in longitudinal.
- Start by increasing your depth until you can just see the mandible.
- The large hypoechoic structure with hyperechoic linear structures within is the masseter muscle.
- The hyperechoic linear structures are tendons associated with this muscle
- Superficial and posterior to the masseter muscle is a isoechoic triangular wedge shaped structure, this is the parotid gland.
- If this region looks dark, increase your gain. If this region is hard to differentiate from the masseter muscle, decrease your gain.
- Distinguishing the parotid gland from surrounding structures is a useful standardized technique for optimizing your gain setting when conducting ultrasound anywhere in the face!
- If this region looks dark, increase your gain. If this region is hard to differentiate from the masseter muscle, decrease your gain.
- As you scan superiorly over the masseter watch for a hypoechoic linear structure, lined with hyperechoic walls, superficial to the muscle and emerging from the parotid gland. This will be the parotid duct.
- There are few vascular structures in this zone and this is typically the only facial region where doppler is not performed as per the Learn the Face protocol. However, just anterior to the masseter muscle seen at M1 is the facial artery and vein as we will see at M2! You must be aware of this.
EXAMPLE OF TRANSVERSE SCAN OF M1
(Scan superior and inferior direction)
EXAMPLE OF LONGITUDINAL SCAN OF M1
(Scan anterior and posterior direction)
- Again, like you did in transverse start by increasing your depth until you can just see the mandible.
- The large hypoechoic structure with hyperechoic linear structures within is the masseter muscle.
- Glide to the anterior border of this muscle.
- A linear hypoechoic superficial band above the masseter muscle can be seen. This is the platysma muscle. As you scan posteriorly you will see this band continue.
- Superficial to the platysma is the risorius muscle, another hypoechoic band. This will only be seen in the most anterior portion of M1.
- A linear hypoechoic superficial band above the masseter muscle can be seen. This is the platysma muscle. As you scan posteriorly you will see this band continue.
- Glide to the anterior border of this muscle.
- As you scan posteriorly you will once again see the isoechoic wedge shaped parotid come into view superficial to the masseter muscle.
