Glossary of Head and Neck 04 (Parotid space)

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What contains the parotid space?
Like the case of the masticator space, the superficial layer of deep cervical fascia splits to encompass the PS.
What are the contents of the Parotid space?
1) Parotid gland

2) Facial Nerve (CN VII)

3) Retromandibular vein

4) External carotid artery

5) Intraparotid lymph nodes
What is important anatomically about the intraparotid facial nerve?
It creates a surgical plane that divides the parotid gland into superficial and deep lobes.
What is important about imaging of the intraparotid facial nerve?
It is not routinely identified on CT or MR, even with high resolution imaging.
Where does the facial nerve course?
About 2/3 of the way from the lateral to the medial part of the gland in the axial plane. So the superficial lobe of the parotid is larger.
What is the relationship between the retromandibular vein, external carotid artery, and facial nerve?
Carotid = most medial

Retromandibular = in middle

Facial nerve = immediately lateral to retromandibular vein
What does injury to the proximal intraparotid facial nerve cause?
Ipsilateral loss of motor function of the muscles of facial expression.
What is special about the retromandibular vein?
It joins with the sigmoid sinus to form the internal jugular vein. Makes sense, since it travels with the external carotid artery, which joins with the internal carotid artery to form the common carotid artery, which runs along with the internal jugular.
What is special about the lymph nodes associated with the parotid gland?
They are actually inside the gland (intraglandular)
Why are there intraglandular nodes in the parotid?
Because the parotid is encapsulated late in embryogenesis, allowing time for nodes to move in.
About how many nodes are in the parotid?
20 to 30!
What do these nodes drain?
They are FIRST ORDER drainage sites for

1) adjacent areas of scalp

2) external auditory canal

3) deep face
Which gland does not have intraglandular nodes?
The submandibular gland.
It undergoes early encapsulation, therefore the nodes associated with it are outside the capsule and extraglandular.
What is pseudonym for the parotid duct?
What is the course of the parotid duct?
1) emerges from the anterior aspect of the gland

2) Travels along the lateral surface of the masseter, superficial to the masticator space

3) After passing anterior to the masticator space into the buccal space, arches medially to pierce the buccinator muscle.

4) Opens into its orifice at the second maxillary (upper) molar.
How often is parotid duct visualized on imaging?
Routinely seen on 3mm CT sections.
At what axial level can the duct be seen?
Level of the hard palate
Describe the position of the parotid space?
Most lateral space in the deep face
What is the inferior portion of the parotid called, and how far does it extend inferiorly?
Parotid tail

Mandibular angle
How far does it extend superiorly?
External auditory canal
What is a normal variant of the parotid space?
Parotid tail dip inferiorly below the mandibular angle
What is significance of this clinically?
Mass of low-lying parotid tail can be mistaken for mandibular angle mass.
What is the problem with that?
Excisional biopsy is attempted, as the mass is not recognized as being within the parotid space, and the facial nerve is injured.
What forms the posteromedial border of the parotid space?
Posterior belly of digastric
What does the posterior belly of the digastric separate the parotid space from?
The carotid space
What is medial to the parotid space>
The parapharyngeal space
What is the first step when examining a CT or MRI examination with a mass suspected in the parotid space?
Determine whether the lesion in intraparotid or extraparotid
Why are non-parotid masses often mistook for parotid lesions by the clinician?
Because as the PS is the most lateral in the deep face, lesions in adjacent regions of the deep face push the PS even further laterally, making the parotid stick out and feel more prominent to palpation.
Why is the distinction between parotid and non-parotid mass so important?
Surgical approach is completely different for parotid and non-parotid lesions.
What are main differences?
Parotid lesions are approached transparotid, with control of facial nerve established before dissecting out the mass.

Extraparotid masses are approached via submandibular or oral approach usually.
When are lesions of the parotid easy to diagnose as such?
When they are small, and completely surrounded by glandular tisue.
When is parotid lesion most difficult to diagnose?
When involving the deep lobe of the parotid.
How is a mass confirmed primary to the PS on imaging?
Center: Lateral to parapharyngeal space

Displacement: Displaces parapharyngeal space fat medially.

Invasion: Invades the PPS fat from lateral to medial.
What is an additional feature of parotid space masses?
They widen the distance between the angle of the mandible and the styloid process.
What is this space called?
The stylomandibular notch/tunnel
Which parotid lesions need to be imaged?
The only ones that don't are those superficial parotid lesions that the surgeon can "get his fingers around" and do FNA on in office. If path reveals benign mixed tumor, they do superficial parotidectomy, and that is end of story.
What is the first question to ask when imaging a suspected lesion of the parotid space?
Which imaging method should be used?
What are the symptoms of parotid ductal disease?
Recurrent diffuse parotid swelling associated with eating.
What imaging modality should be used in these cases?
CT, with thin (3mm or less) sections.
If CT is not revealing, but parotid ductal disease is still suspected, what is next step?
What is imaging modality of choice when parotid space infection is suspected?
What are goals of CT in case of infection?
1) Abscess versus cellulitis

2) Presence or absence of calculus disease.
How good is CT at excluding parotid calculi?
60% sensitivity; therefore up to 40% will not be visible, and sialography is still a needed tool.
What is modality of choice for imaging a suspected tumor in the PS?
What are the goals of MRI in case of tumor?
1) Determine extent

2) Determine relationship of the tumor to the facial nerve

3) Assess for perineural spread of tumor along facial nerve into the temporal bone
What is the second question to ask when evaluating lesion of PS?
What is its relationship to the facial nerve?
How is facial nerve identified?
On MRI, the facial nerve is sometimes directly identified. If it is, great.

If it is not directly visualized, the nerve plane is extrapolated.
How is the facial nerve plane extrapolated?
A line connecting the stylomastoid foramen to a point just lateral to the retromandibular vein is drawn.
Why are these 2 points chosen?
Because the facial nerve emerges from the stylomastoid foramen upon exiting the temporal bone.

Because the course of the facial nerve is just lateral to the retromandibular vein.
Why is the relationship of the mass to the facial nerve important?
Because masses in the superficial lobe are removed by superficial parotidectomy.

Masses in the deep lobe require total parotidectomy, however, which carries greater risk of facial nerve injury.
What is the third question that must be answered in a lesion of the PS?
Is there perineural spread along the facial nerve?
How can the perineural spread occur, and thus what portions of the nerve must be imaged?
Can occur both antegrade (toward muscles of facial expression) or retrograde (back to mastoid segment in the temporal bone)
What is the fourth question that must be answered?
Is the lesion single or multiple?
Why is this distinction important?
The presence of a single lesion of the parotid does not exclude any diagnostic possibility, and all possibilities must be considered.

The presence of multiple lesions in the gland limits the differential possibilities greatly.
What are the categories of disease that occur within the parotid space?
1) Congenital

2) Inflammatory

3) Benign tumor

4) Malignant tumor, primary

5) Malignant tumor, metastatic
Where in the parotid space do metastatic lesions occur?
In the intraparotid nodes
Which congenital lesions of the parotid occur in the pediatric population only?

What is clinical history in hemangioma of the parotid?
Unilateral parotid swelling seen shortly after birth.
What are characteristics of parotid hemangioma?
Soft and compressible

Bluish discoloration over skin, especially when crying
What is pathologically unique about the lesion?
Involves entire parotd gland, thus facial nerve passes right through it.
What is imaging appearance?
Cystic mass superficial to, within, or deep to parotid gland.
What is treatment?
Many spontaneousy involute, so surgery is postponed if possible to avoid potential for facial nerve injury.
What is a congenital lesion of the parotid that does not typically occur in pediatric population.
First branchial cleft cyst
What age group gets symptomatic first brainchial cleft cyst?
Middle age
What can first branchial cleft cyst do?
Becomes infected and can drain out of body.
Where do the sinus tracts of first branchial cleft cyst end up?
1) External ear canal

2) Skin
Why can it end up at external ear canal?
Cyst may be congenitally connected to the bony-cartilaginous junction of the external ear canal
Where does the fistula occur when it occurs on skin?
Angle of mandible
How common is this lesion?
8% of all branchial complex abnormalities
How thick is the wall?
Varies with degree of inflammation
What imaging modality is best for this lesion?
CT--better demonstrates cyst and bony changes associated
What bony changes can occur?
Erosion into external auditory canal or adjacent temporal bone.
What are important parotid space inflammatory conditions?

Parotid abscess

Sjogren's syndroma

Benign lypmphoepithelial lesions

What etiologies for parotitis exist?
1) Bacterial

2) Calculus related

3) Viral
How does viral parotitis present?
75% bilateral involvement, but one side is affected 1-5 days earlier than the other.
How does bacterial parotitis present?
Unilateral cheek swelling with fever, chills, high white count.
What can bacterial or calculus related parotitis progress to?
Parotid abscess
What else can be involved in viral parotitis?
Both the submandibular and sublingual glands can also be involved
What is imaging appearance in viral parotitis?
Dense appearing glands. Enhance with contrast.
What is appearance of bacterial or calculus related parotitis?
Swollen, enhancing parotid, with adjacent soft tissue stranding.
What is appearnece of parotid abscess?
Same as parotitis, but with focal areas of rim-enhancing cysts.
What is Sjogren's syndrome?
Basically, they get sicca syndrome of dysfunctional salivary glands (lacrimal gland is essentially one also) that do not produce secretions properly, and become morphologically enlarged.

Triad of:

1) Enlarged salivary glands with xerostomia (dry mouth)

2) Enlarged lacrimal glands with keratoconjunctivitis sicca

3) Connective tissue disease
What is the most common connective tissue disease occurring with Sjogren's?
What is important to consider when interpreting a scan of patient with Sjogren's?
They get lymphomas. . .often with aggressive features.
What is CT appearance of SjS?
1) Bilateral enlargement

2) Increased density
What may be seen on unenhanced CT?
Diffuse punctate calcifications.
What may be seen on enhanced CT early in SjS?
Millimeter cystic collections

(probably stopped up ducts, with effaced acini)
What may be seen on enhanced CT late is SjS?
Cysts become larger and coalesce.
What else may be seen on enhanced CT in late SjS?
Soft tissue nodules or masses due to lymphocytic accumulation.
What are these soft tissue nodules?
They are benign, but can progress to lymphoma.
What is a sign that patient has progressed to lymphoma?
Mass that looks invasive

Presence of cervical adenopathy
What is most sensitive imaging method of diagnosing SjS.
MR sialography
What is seen on sialography or MR sialography?
There are four patterns
What are the 4 patterns?
1) Punctate type

2) Globular type

3) Cavitary type

4) Destructive type
What does end-stage gland look like in SjS
Honeycombed, with pseudotumors indistinguishable from NHL.
What is benign lymphoepithelial disease?
Occurs only in patients with HIV.
What is clinical presentation?
Bilateral parotid swelling in HIV+ patient.
What is appearance on CT?
Bilateral parotid enlargement with cystic and solid lesions.
What else is associated with it on imaging?
Reactive cervical adenopathy
What are some of the more common benign tumors of the partotid space?
1) Pleomorphic adenoma

2) Warthin's tumor

3) Oncocytoma
What is the now correct name for pleomorphic adenoma?
Benign mixed tumor
What is clinical presentation of benign mixed tumor?
Slow growing lump in the cheek
What is the typical age group for benign mixed tumor?
50 years old and up
What is special pathologically about benign mixed tumor?
Most common benign parotid tumor
What is the basic CT or MRI finding?
Sharply marginated mass. May be lobulated?
What is true of enhancement pattern?
What is true of calcification?
What is true of the CT imaging appearance when the lesion is large?
Internal pockets of low density.
What is this low density attributed to?
Mucoid matrix
Why is the mucoid nature of the matrix not surprising?
This is an ADENOMA
What is the salient MR feature of benign mixed tumor?
Very hyperintense on T2W images
What is the clinical presentation of Warthin's tumor?
Slow growing mass in parotid tail region
What is true epidemiologically about Warthin tumor?

(sex, age)
80% male

Like benign mixed, 50 years and up
What is true epidemiologically from a pathologic standpoint?
Second most common tumor of the parotid space
From where does the tumor arise?
Heterotopic salivary-gland tissue.
Where is this heterotopic salivary gland tissue within the parotid gland arising?
Intraparotid lymph nodes
What is the incidence of bilaterality?
What is the basic imaging appearance?
Well circumscribed.

Complex mixture of cystic and solid components.
What is the typical size?
3-4 cm
What else occurs besides bilaterality in some cases?
May be multiple lesions
What is true epidemiologically about oncocytoma?
Only occurs in patients over 50
What do these tumors arise from?
What are oncocytes?
Large grouped cells found normally within the parotid
What are the imaging features?
Nonspecific. Similar to benign mixed tumor.
What is the rule for odds of malignancy in salivary gland tumors?
Smaller the gland, higher the probablility that a given lesion is malignant
How often are parotid gland masses malignant?
How often are submandibular gland masses malignant?
How often are sublingual gland masses malignant?
How often are minor salivary gland masses malignant?
What are the common malignancies of the parotid space?
1) Mucoepidermoid carcinoma

2) Adenoid cystic carcinoma

3) Acinic cell carcinoma

4) Non-Hodgkin lymphoma

5) Metastatic disease
What is the clinical presentation of a malignant parotid mass?
Rock hard mass with associated pain or itching over the course of the facial nerve.
What is an ominous sign in parotid tumors?
Facial nerve paralysis
What is the most common malignant lesion of the parotid?
Mucoepidermoid carcinoma. True in both adult and pediatric populations.
From what does it arise?
Malignant transformation of the epithelium of the glandular ducts.
Why must benign appearing tumors of the parotid be biopsied?
Low grade malignancies appear and clinically feel the same: well circumscribed lesions.
When a malignant lesion of the parotid space is suspected, what must be done during the evaluation?
Search for perineural spread along the course of the facial nerve into the mastoid segment of the temporal bone.
What is another name for adenoid cystic carcinoma?
What part of the parotid does the adenoid cystic carcinoma sometimes affect?
Deep lobe of the parotid
How does a lesion of the deep lobe of the parotid present differently?
Neuropathy of both facial nerve and V3.
Where does this tumor arise?
Peripheral ducts of parotid gland
What is most important about the spread of this lesion?
Perineural spread is common
What must be included in MRI examination of potentially malignant parotid tumors?
Mastoid or descending portion of the facial nerve
What is the most common bilateral or multiple focus tumor of the parotid?
What is the second most common?
Acinic cell carcinoma
How comon is acinic cell CA?
Less than mucoepidermoid and adenoid cystic
How do most cases of NHL of the parotid space originate?
Within one of the intraglandular nodes, spreading eventually into the parenchyma
Where do metastatic lesions to the parotid space go?
To the intraglandular nodes first
What are the typical metastatic lesions to the parotid space?

When a biopsy reveals one of these lesions in the parotid, what must be done next?
Careful physical exam searching for the primary lesion.
Where are the primaries located?
Lateral head

External auditory canal
What is a pitfall in CT imaging of the parotid space in a child?
The parotid gland becomes progressively more fatty with age. So in pediatric populations, the gland appears as muscle density.

What is the adage about parotid tumors?
"All parotid masses must come out"
Why this adage?
Because low grade mucoepidermoid cardinomas can mimic benign tumors clinically and on imaging.
How common are low grade mucoepidermoid carcinomas?
What lesions overlap in appearance in the parotid space?
Inflammatory pathology may have indistinct margins, mimicking malignant tumor.

Tumor obstruction of the parotid ductal system may create a clinical appearance of parotid infection.
What is the diagnosis of an asymmetric mass overlying the masseter?
Accessory parotid gland
What percentage of people have these glands?
How is it diagnosed?
Same imaging appearance as the parotid gland.
What must be scanned to include the proper imaging of parotid space lesions?
From lower temporal bone (so to include descending facial nerve canal), to the hyoid bone.
Why go all the way to the hyoid?
Because this will include the parotid tail, and the first order drainage nodes.
What nodes are these?
High deep cervical nodes

When is MRI preferred over CT for parotid space?
Anytime tumor is being evaluated.
When is CT recommended over MRI?
CT is indicated over MRI when there is any suspicion of infection.
What is the protocol for evaluation of parotid masses?
1) If mass is palpable, needle aspiration is completed.
What is the next step if the pathology comes back benign?
If physical exam reveals that the lesion is definitely within the superficial lobe of the parotid, superfical parotidectomy is performed, without ever going to imaging.

If the lesion's margins are not clear by palpation, MRI to answer the quesions mentioned earlier.
What if pathology comes back malignant?
Do MRI to further evaluate lesion borders and spread.
What if the clinical complaint is diffuse swelling of the parotid?
CT (or MRI) used, but sialography is kept in reserve.
What if CT or MRI suggest parotid ductal disease? (calculi, stenosis)
Sialography is performed

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