Glossary of Head and Neck 03 (Masticator Space)

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What is the central structure in the masticator space?
The mandibular ramus.
Where is the masseter located?
Lateral to the mandibular ramus, at the inferior aspect of the masticator space.
Where are the pterygoid muscles located?
Medial to the mandibular ramus.
What pterygoid muscles are there?
Medial and lateral
How does the medial pterygoid appear?
It is elongated, and is thickest at the inferior aspect of the masticator space.
How does the lateral pterygoid appear?
It is rounded and located in the superior aspect of the masticator space.
What is the other muscle of mastication?
The temporalis
What space is it located in?
The suprazygomatic portion of the masticator space.
What other bone is part of the masticator space?
The zygomatic arch.
How far up does the suprazygomatic portion of the masticator space extend?
Way up the temporal bone to the origin of the temporalis m. on the floor of the temporal fossa.
What is the fascial anatomy of the masticator space?
The superficial layer of deep cervical fascia splits along the inferior aspect of the mandible, and creates a sling which encloses the masticator space. (Fig 3-2)
What is the deal with the lateral slip of superficial layer of deep cervical fascia?
After splitting from the medial layer on the bottom of the mandible,it travels up superficial to the masseter, and inserts on the zygomatic arch. Then continues upward on the surface of the temporalis m.
What is the deal with the medial slip of superficial layer of deep cervical fascia?
It travels up deep to the medial pterygoid muscle.
Where does the medial slip insert?
On the skull base, just MEDIAL to the foramen ovale (fig 3-2).
What is the significance of this relationship?
Lesions traveling cephalad within the masticator space will enter the skull base through the foramen ovale.
Contents of masticator space?
Muscles of mastication
Masticator nerve (V3 motor branch)
Inferior alveolar nerve (V3 sensory)
Inferior alveolar vein/artery
Ramus and posterior body of the mandible.
Which is the largest muscle of mastication?
What is another way tumor or infection in the MS can access the intracranial compartment?
Along the muscles of mastication.
What is the main clinical symptom resulting from tumor or infection involving the masticator space?
What is trismus?
Difficulty opening the mouth secondary to spasm of muscle(s) of mastication.
Masseter origin?
Zygomatic arch
Masseter insertion?
Lateral surface of manbible (ramus, angle, posterior body)
Lateral pterygoid origin?
There are 2 heads of the lateral pterygoid muscle. One originates on skull base contained by the masticator space. The other on the lateral pterygoid plate.
Lateral pterygoid insertion?
Medial aspect of mandibular condyle.
Medial pterygoid origin?
Fossa between medial and lateral pterygoid plates.
Medial pterygoid insertion?
Medial aspect of mandibular angle.
How many nerves enter the masticator space?
What nerves are they.
The senory and motor branches of V3.
What is the motor branch of V3 called?
Masticator nerve
What is the sensory branch of V3 called>
Inferior alveolar nerve.
What is the significance of this?
Lesions occurring in the infrazygomatic portion of the masticator space will commonly involve the suprazygomatic portion (temporal fossa) as well.

Therefore, careful examination of the suprazygomatic portion of the MS is the rule anytime a lesion of the infrazygomatic MS is found.
Where does the spread occur?
Back up the nerves, superiorly through the MS, passing through the foramen ovale. Spread can progress further into Meckel's cave, and then even further into the root entry zone of CN V at the lateral pons.
What is a syndrome you should be aware of related to perineural spread along V3?
Masticator muscle atrophy, mandibular dental pain, and serous otitis media.
Why is there serous accumulation in the middle ear?
The motor division of V3 also supplies the tensor veli palatini, resulting in dysfynction of the eustachian tube.
What is the most common source of abscess in the masticator space?
The mandibular ramus, angle, and posterior body form the central strut of the MS. The posterior body contains teeth, and odontogenic infection is the most common reason for masticator space abscess.
What is the relationship of the parotid duct to the MS?
It passes just superficial to it, coursing over the lateral surface of the masseter.
What must be recognized about the temporal fossa?
It is actually the superior extension of the masticator space (SZMS)
What is the infratemporal fossa?
The area between the pterygopalatine fossa (medially) and the zygomatic arch (laterally).
What is this region actually?
It is just the nasopharyngeal portion of the masticator space. There is no fascia separating it from any other part of the MS.
What is the more anatomically correct name for this region?
Nasopharyngeal masticator space
What is the anterior boundary of the MS?
Buccal space
What constitutes the posteromedial border of the masticator space?
Parapharyngeal space.
What constitutes the posterior border of the masticator space?
Parotid space.
What are the boundaries of the buccal space?
No fascial boundaries
What is its relationship to infection or malignancy in the MS?
Disease often spreads to it
What are contents of buccal space?
1) Buccal fat pad

2) Facial artery and vein

3) Distal portion of parotid duct

4) Buccinator muscle
What is the most important information to be gleaned from a CT or MRI examination of disease in the buccal space?
Its relationship to the distal parotid duct
When is a mass radiographically in the MS?
Center of mss is anterior to the parapharyngeal space, within muscles of mastication or the mandible.

The mass invades the PPS from A to P, posteriorly displacing the PPS fat.
When are these rules most helpful?
When mass is large. When small, easy to spot its location within the muscles or the bone.
After answering the question of what space the lesion is in, and coming up with answer MS, what is the next step?
Is there perineural spread along V3?
What patients need evaluation for perineural spread?
Any non-infectious mass in the masticator space
What are the ways tumor of the MS invades the skull base?
Within muscles of mastication

Along V3 (gains access to main trunk of V3 via masticator or inferior alveolar nerve)
What is most common clinical symptom related to perineural spread along V3?
Pain or numbness along ipsilaeral chin and jaw
What are the early imaging features of perineural spread during its early phases?
What about when spread is macroscopic?
Continuous or discontinuous perineural tumor.
What is important about this?
Must evaluate the ENTIRE V3, from mental foramen, through mandible, back out the mandibular foramen, as it ascends through the masticator space, through the foramen ovale, into Meckel's cave, and finally into its preganglionic segment to the dorsal entry zone at the lateral pons. All of this must be imaged every time, or else there will be areas that are improperly resected or irradiated, leading to "early recurrence" along V3.
How is perineural spread along V3 evaluated?
Why not CT?
Does not depict soft tissue differences well.

Lack of destruction at foramen ovale does not mean there is no perineural spread.

CT can't do jack shit for evaluating the intracranial portion of V3.
What is the third question that must be answered
What is the status of the skull base, and suprazygomatic masticator space.
What patients need evaluation of the skull base and suprazygomatic MS?
Any patient with infectious or neoplastic lesion
How does infection spread within the MS?
Superiorly (path of least resistance)
What can happen with infection in the MS?
Skull base osteomyelitis (pterygoid wing area)
How does malignancy spread usually?
Also cephalad. Involvement of skull base usually makes tumor unresectable, and radiation ports have to include this region.
What is the 4th question to be answered (1--where is lesion, 2--is there perineural spread, 3--what is status of skull base and SZMS)
What is status of the mandible?
Why is mandibular involvement important in infection?
Because a longer course of Abx and subperiosteal surgical drainage is necessary in mandibular osteomyelitis.
Why is mandibular involement important in the case of tumor.
Malignancy involving the mandible commonly results in perineural spread (distally, along the inferior alveolar canal, and/or proximally)
What is the 5th question that must be answered in the case of a lesion of the MS?
Is the parotid duct involved?
Why is this question important in infection involving the MS?
A calculus of the parotid duct may be causal. If the MS infection is drained without treating the cause (possibly a tiny stone of the parotid), then effect of treatment will not be lasting.
In case of suspected infection of the MS, what modality should be used?
Why is CT better?
Ease of identifying sialolith.

Ease of diagnosis of mandibular osteomyelitis.
When a lesion (mass) of the MS is encountered, what are the 3 technical questions that must be asked after Q#1 (what space is the lesion in)?
1) Is the entire course of CN V3 imaged?

2) Is the entire MS imaged, including the suprazygomatic masticator space?

3) Is the lesion a masticator space pseudomass?
What are the pseudomasses of the masticator space?
1) Asymmetric accessory parotid gland.

2) Benign masseteric hypertrophy

3) CN V3 motor atrophy
What is the incidence of accessory parotid gland?
Where is the accessory parotid gland?
Just lateral to the masseter, superficial to the masticator space.
What does imaging reveal?
Salivary gland tissue on the surface of the masseter muscle. May appear prominent.
How is the diagnosis made?
The tissue has the same density or signal intensity as the adjacent parotid gland.
What is benign masseteric hypertrophy?
Hypertrophy of masseters.
What is the cause?
Usually bruxism, thus usually bilateral process.
When is diagnosis pathognomonic?
Bilateral enlargement of the masseters, with discrete outer margins.
What makes diagnosis even more confident?
Concommitent hypertrophy of the pterygoids and temporalis.
When is diagnosis slightly less confident?
When hypertrophy is unilateral, but appearance is otherwise the same.
When should one be concerned about malignancy?
When there is unilateral masseteric mass, and the margins are not discrete.
What is crainial nerve V3 motor atrophy?
Occurs when there is compression (i.e. by tumor) or surgical cutting of V3.
What does V3 innervate?
Muscles of mastication


Anterior belly of digastric

Tensor tympani and palatini.
What happens when V3 is disrupted.
Atrophy and fatty replacement of the innervated muscles occurs within 6 weeks.
What is the imaging issue?
To not diagnose the normal contralateral masticator space as tumor.
Why is there a limited variety of pathology in the masticator space?
Because limited variety of normal tissues there:



What is the most common pathology encountered in the MS?
Odontogenic abscess
What is clinical presentation in odontogenic abscess?
Trismus. Also fever, swelling, etc.
What are the most common causes of odontogenic abscess.
There are two:

Poor dental hygeine

Recent dental manipulation
What is seen in odontogenic abscess?
Fluid collection within the masticator space, surrounded by swollen tissue.
What modatlity is best for suspected odontogenic abscess?
CT. Better defines osteomyelitis and calculus disease.
What should be examined in case of swelling after ORIF for facial fractures requiring wires around zygomatic arch, before or after wire removal?
The suprazygomatic masticator space.
What are the questions that must be answered during imaging for masticator space abscess?
1) In skull base or mandibular osteomyelitis present.

2) Is there evidence for parotid calculus disease?

3) Are there any other deep face spaces involved?

4) Is the suprazygomatic masticator space involved?
Why does infection tend to spread supriorly (towards skull base and SZMS) in masticator space infection?
Because of the firm attachment of the superficial layer of deep cervical fascia to the periosteum of the inferior mandible.
How does odontogenic abscess form?
1) Infection of tooth

2) Results in infection of tooth socket

3) Infected socket fistulizes into masticator space.
What does masticator space abscess do to nearby structures?
See bowing of soft palate and uvula medially, and the masseter muscle and cheek laterally.
What kind of benign tumors occur in the masticator space?
None really
What class of malignant tumors is most common in masticator space?
What are the tissue types that generate sarcomas in the masticator space, and the related tumors?
Muscle--sott tissue sarcomas

Mandibular bone--Chondrosarcoma and osteosarcoma
A tumor seen in the region of the TMJ?

--Arises there (where there is a cartilage-bearing joint)
Where in the mandible does osteosarcoma arise?
Anywhere in mandible
What distinguishes osteosarcoma and chondrosarcoma from other tumors in the MS?
Only the matrix. Usually some degree of mandibular destruction. But may just appear as infiltrating mass indistinguishable from other tumors, and destruction of bone does not imply that the tumor arises from bone.
What is tumor of V3 that occurs in the MS?
Malignant schwannoma
What are symptoms of malignant schwannoma?
Same as perineural spread of tumor along the nerve? Pain and numbness along distribution of the inferior alveolar nerve.
What is distribution of inferior alveolar nerve?
Chin and jaw
What parts of V3 can malignant schwannoma arise from?
Both masticator and inferior alveolar nerves
What is imaging appearance of malignant schwannoma?
Tubular mass along course of V3, usually involving inferior alveolar nerve in the inf alv canal.
What must be done in case of suspected malignant schwannoma?
Image full extent of V3, all the way through foramen ovale, gasserian gangion in Meckels cave, to main CN V in lateral pons.
Where does tumor commonly spread to?
Gasserian gangion
What is another malignancy of the masticator space?
What is unique about the appearance of NHL in the masticator space?
Nothing. Just appears as infiltrating lesion.
How can the diagnosis of NHL involving the MS be suggested on imaging?
If there is associated:

1) Nodal disease

2) Extranodal lymphatic disease

3) Extranodal extralymphatic disease
What are examples of extranodal lymphatic involvement?
Waldeyer's ring


(although both of these could also represent SCCa)
Wat are examples of extranodal extralymphatic involvement?


What is another tumor type that can occur in the masticator space?
When should SCCa be suspected in the masticator space?
Anytime there is history of oropharyngeal or oral cavity SCCa, even if primary lesion has already been treated.

SCCa does not occur primarily in the MS, as there is no squamous tissue normally there.
How does it get there?
Either by direct extension or perineural spread.
How does it get there in cases of direct extension?
Either via faucial tonsil or retromolar trigone.
What is clincal picture usually?
Usually known history of SCCa, usually already treated, presenting with Sx related to masticator space
What are those symptoms?

Pain/Numbness in inferior alvelolar nerve dist'n.

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