Head and Neck 02 (PPS and PMS)

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How can the parapharyngeal space be defined?: The central space of the deep face.
What are the spaces that directly surround (and thus lesions within can exert mass effect upon) the PPS?: Masticator

Parotid

Carotid

Lateral recess of retropharyngeal

Pharyngeal mucosal
What is the PPS primarily composed of?: Fat
Why is identification of the space that the mass is originating the most important factor in its evaluation?: Because each space has its own differential diagnosis for mass.
Why is that?: Because there are different types of tissue in each space.
What are the tissues from which the statistically common lesions of the pharyngeal mucosal space originate?: Mucosa

Lymphoid tissue

Minor salivary glands
What are the tissues from which the statistically common lesions of the masticator space originate?: Muscles of mastication

Mandible

CN V3
What are the tissues from which the statistically common lesions of the parotid space originate?: Salivary tissue

Lymph nodes
What are the tissues from which the statistically common lesions of the carotid space originate?: Carotid artery

Jugular vein

CN IX to XII
What are the tissues from which the statistically common lesions of the lateral recess of the retropharyngeal space originate?: Lymph nodes (of Rouvier)
What is special about the fascial margins of the PPS?: They are complex
What is its medial fascial margin made of?: The middle layer of deep cervical fascia as it curves around the lateral side of the pharyngeal mucosal space.
What is its lateral margin composed of?: The medial slip of superficial layer of deep cervical fascia as it curves around the deep border of the masticator and parotid spaces.
What is its posterior margin composed of?: The anterior part of the carotid sheath, which is made up of all three layers of the deep cervical fascia.
What are the only contents of the PPS?: Fat

Internal maxillary artery

Ascending pharyngeal artery

Pharyngeal venous plexus
Why is it so rare for a lesion to occur primarily within the PPS?: The PPS contains no mucosa, muscle, bone, nodes, or normal salivary tissue.
How is the PPS identified on axial images?: A a fatty triangle
When is the only time the PPS is totally obscured?: Only when the mass is very large.
When is a mass sometimes suspected in the PPS?: Prominent pharyngeal (pterygoid) venous plexus can mimic a vascular mass.
How is the PPS shaped in the CC dimension?: Crescentic
What is the inferior and superior extent of the PPS?: From the superior cornu of the hyoid bone to the skull base.
Because of this elongate orientation, what can PPS function as?: An "elevator shaft" helping infection and tumor in the spaces adjacent to it to spread down to the hyoid, and up to the skull base.
At its inferior aspect, what does the PPS contact?: The posterior aspect of the submandibular space.
What is special about this interaction?: There is no fascial separation between these structures.
What does this mean?: That lesions spreading through the PPS can easily seed, and may even first be recognized in the submandibular space.
What are the only lesions known to originate in the PPS?: Lipoma

Atypical 2nd branchial cleft cysts

Pleomorphic adenomas of minor salivary gland rests.
In order to state on imaging that a mass originates in the PPS, what must be true?: Fat must be identified to surround the entire circumference of the lesion.
What usually happens after an imager states he/she thinks a lesion is primary to the PPS?: On careful inspection of multiplanar images, a point of attachment to one of the other spaces of the deep face is found.
What structure is most commonly implicated in one of these confusing cases?: The deep lobe of the parotid.
When a lesion involving the PPS is discovered, what must be done.: 1) Ensure the entire PPS from skull base to hyoid bone is imaged.

2) Determine the real space of origin of the lesion.

3) If another space of origin is not found, ensure that the lesion is not a PPS pseudomass.
What is the only pseudomass of the PPS?: Asummetric pterygoid venous plexus
What is its appearance on CT?: A racemose-enhancing high density area
Where is it located?: along the medial border of the lateral pterygoid muscle.
What is its appearance of MRI?: A contrast enhancing area.
What is its significance?: Nothing. It is just a normal variant.
What are the classificatons of lesions that can occur within the PPS?: Congenital

Inflammatory

Neoplasm (benign and malignant)
What are congenital lesions that can occur within the PPS?: Atypical second branchial cleft cyst.
What is the clinical presentation of atypical second branchial cleft cyst? Age group?: Child or young adult with externally protruding parotid gland and internally bulging posterolateral pharyngeal wall.
When does this mass arise?: After URI.
How common is this lesion?: Rare
How does it differ from the typical 2nd branchial cleft cyst?: The cyst projects in the PPS toward the skull base?
How does this differ from typical second branchial cleft cyst?: Typically, they project downward toward the mandibular angle.
What is the imaging appearance?: A cystic mass

Projects from the oropharyngeal faucial tonsil deep margin, up the parapharyngeal space, toward the skull base.
How does it appear at its cephalad end on axial images?: It is surrounded by fat of the PPS.
How does it appear at its caudal end on axial images?: It anneals to the deep margin of the faucial tonsil.
What is the definition of fauces?: The narrow passage from the mouth to the pharynx situated between the soft palate and the base of the tongue.

(i.e. the lateral aspect of the ring separating the mouth from the oropharynx)
What is infection of the PPS?: Abscess
What is true of PPS abscess?: It will always arise from an adjacent space.
What is the one exception to this rule?: Direct penetrating trauma.

(infected 2nd branchial cleft cyst could probably mimic an abscess to the untrained eye)
What are typical sources of abscess of the PPS?: Pharyngitis that spreads from the PMS.

Dental infection or manipulation can cause masticator space infection with subsequent spread to the PPS.

Calculus disease may cause parotid space infection with subsequent involvement of the PPS.
How must case of PPS abscess be evaluated?: 1) Search for space of origin

2) Search for involvement of any additional spaces
What is a special situation for a PPS abscess?: When it abuts the skull base.
What must be done if PPS abuts the skull base?: One must carefully evaluate for the presence of osteomyelitis.
How are PPS and other deep facial space abscesses treated?: Drainage
What must be done to any space containing pus?: Drain placement.
What is radiologists role in this endeavor?: Decide how many drains need to be placed?

Help find most cosmetic surgical approach.
What modality must be performed when evaluating a suspected abscess of the head and neck?: CT
Why is CT better?: 1) Allows confident diagnosis of abscess pockets.

But also. . .

2) Permits identification of mandibular osteomyelitis.

3) Permits identification of calculus disease.

Both of which are important precipitating causes.
What types of tumors occur primary to the PPS? Benign? Malignant?: Benign
What are the benign tumors of the PPS?: Pleomorphic adenoma
What does pleomorphic adenoma arise from in the PPS?: Ectopic salivary gland rests
What is another name for pleomorphic adenoma?: Benign mixed tumor.

(makes sense, because it is benign, it is mixed (i.e. pleomorphic) and it is a tumor.
What is its appearance?: Same appearence as pleomorphic adenoma of the parotid, but ectopic.
What are imaging features? Shape?: Round to oval.
What are imaging features? Borders?: Well circumscribed
What are imaging features? What surrounds it?: A complete rim of PPS fat
What is caveat here?: Must make certain it is truly primary to the PPS, and not connected to the deep lobe of the parotid gland.
Why is this distiction important?: Different surgical approaches.
How is true PPS lesion approached?: True PPS lesion is approched from a submandibular (remember, posterior apect of SMS is apposed to inferior aspect of PPS, without fascial margin) or oral route.
How is deep parotid lesion approached?: Transparotid
Why?: So that facial nerve control can be achieved during the dissection.
What can occur if deep lobe of parotid lesion is approached from the oral or submandibular direction?: Facial nerve injury.
What is a rule about malignant tumors involving the PPS?: They didn't originate there.
What is the most common malignant lesion to invade the PPS?: SCCa from the PMS of the oropharynx or nasopharynx.
When there is invasive SCCa involving the parapharyngeal space, but no primary lesion is visible on imaging or scope, what is probably going on?: Situation is rare, but is likely secondary to mucosal tumor in nasopharyngeal adenoid crypts or crypts of the faucial tonsil.
Through what does the mucosal mass have to invade in order to get to the PPS?: 1) Basement membrane

2) Pharyngeal constrictor muscle

Middle layer of deep cervical fascia.
What if the tumor breaks into the PPS fat, and infiltrates it, obscuring its fatty PPS appearance?: The more lateral aspect of the PPS should not be involved, and can still be identified.
What are two other malignant tumors that can invade into the PPS?: Minor salivary gland malignancies

Non-Hodgkin lymphoma
Where do they usually arise from?: PMS
What is true about NHL in relation to the deep facial spaces.: It is in the differential diagnosis of malignant lesions primary to all of the deep facial spaces, except the PPS.
In what form does NHL occur in the deep facial spaces?: The extranodal, extralymphatic form.
What is the pharyngeal mucosal space?: It is the area of nasopharynx and oropharynx on the airway side of the middle layer of deep cervical fascia.
What are the contents of the pharyngeal mucosal space?: Mucosa
Lymphoid tissue
Minor salivary glands
Pharyngobasilar fascia
Superior and middle constrictor muscles
Salpingopharyngeus m.
Levator palatini m.
Torus tubarius (cartilaginous end of eustachian tube)
Which lymphoid tissue is present in the PMS?: Waldeyer's ring
What does Waldeyer's ring include?: Adenoids
Tonsils
Where does the superior constrictor muscle originate?: Skull base.
How does it attach?: Via the pharyngobasilar fascia.
What is the pharyngobasilar fascia?: Just the aponeurosis of the superior constrictor muscle.
Which two structures do not originate in the PMS?: Eustachian tube
Levator palatini m.
Where do they originate?: skull base
How do they get into the PMS?: Via the sinus of Morgagni
What is the sinus of Morgagni?: The defect in the superior portion of the pharyngobasilar fascia.
Why else is this structure important?: This is the site where SCCa of the PMS (typically nasopharyngeal carcinoma) gains access to the skull base.
What is the second most commn malignancy of the PMS?: NHL
Where do these neoplasms occur in the PMS?: Waldeyer's ring lymphatic tissues.
What space is directly posterior to the PMS?: Retropharyngeal space
What space is directly lateral to PMS?: Parapharyngeal space
How is a mass defined as being located within the PMS?: 1) Center is medial to the fat of the PPS.

2) It displaces the PPS fat laterally and/or invades the medial portion of the PPS fat.

3) It disrupts the normal architecture of the pharyngeal mucosa and submucosa.
What is the primary goal of the imager in neoplasia of the PMS?: The pathologic diagnosis has usually already been made endoscopically, since tumor is usually visible. However goal of imaging is to provide both a tumor stage and nodal stage.
What is the most common error made when interpreting images of the PMS?: Calling normal asymmetry a tumor.
What is the most common area of asymmetry?: Fossa of Rosenmuller (lateral pharyngeal recess)
What happens there?: This is a notoriously asymmetric area due to inflammatory debris and asummetry in the abount of lymphoid tissue.
What are the ways to overcome such errors?: 1) Look at the spaces adjacent to this area (PPS, retropharyngeal). If there is maintenance of soft tissue planes, the "mass" is doubtful.

2) Ask referring clinician how the mucosa looked.

3) Ask patient to do a modified Valsalva to blow open the recess, and repeat CT.
What is the next most common pseudomass?: Variability in amount of lymphoid tissue
Which patients are likely to have a lot of lymphoid tissue?: Young

Recent URI
How is this differentiated from mass?: Use CT or better yet MRI to look for preservation of soft tissue planes of the PPS and retropharyngeal space.
Visibility of what structures makes chance of a PMS lesion small?: Levator and tensor palatini muscles.
What is the appearance of lymphoid hypertrophy, i.e. that occurring after infection?: See filling of the nasopharynx with tissue, without invasion of tissue planes. Or see similar findings in the oropharynx done by the faucial tonsils.
What is appearance of tonsillar or peritonsillar abscess?: Fluid pocket confined by the pharyngeal constrictor muscle to the PMS.
In complicated cases, what occurs?: There is rupture of the abscess through the constrictor muscle into the parapharyngeal space. This is the most common cause of infection of the PPS.
What is a common incidental finding on CT or MRI?: Postinflammatory retention cyst (mucocele)
If they are symptomatic, how do they usually present?: If it occurs in the lateral pharyngeal recess, can cause mechanical obstruction of the eustachian tube, with resultant fluid accumulation in the middle ear cavity.
How big are they usually?: 1 to 2 cm.
How are they oriented when in Fossa of Rosenmuller?: Oblong, projecting along axis of the eustachian tube.
What is another incidental finding?: Postinflammatory calcification.
Where is it usually seen?: Multiple clumps of Ca.

Most common in faucial tonsil

Lingual tonsil and adenoids are other common locations.
What history goes along with this?: Remote history of severe pharyngitis.
What types of benign tumors occur in the PMS?: Benign mixed tumors
Imaging appearance?: These lesions are usually small, so best visualized on high resolution MRI. Seen as homogeneous well circumscribed soft tissue mass in the PMS. When large, oval to round well circumscribed mass which pedunculates into airway, and can easily be seen on MRI or CT.
What are malignant tumors that occur in the PMS?: SCCa

NHL

Minor salivary gland malignancy.
What do these tumors look like?: Infiltrating masses, with center medial to PPS, and invading PPS fat medial to lateral.
What else can they do?: When primary to nasopharynx, they can cause eustachian tube dysfunction.
When they occur in the oropharynx, where can they spread?: PPS and/or masticator space.
Where do they most commonly spread?: Cervical lymph nodes--spinal accessory or deep cervical chains.
What can help differentiate NHL from the other 2 malignancies?: Systemic manifestations, such as fever, distant adenopathy, hepatosplenomegaly. Also additional involvement of extranodal, extra lymphatic sites (i.e. salivary glands) is suggestive of NHL. (PMS is considered an extranodal lymphatic site).
What are miscellaneous PMS lesions?: Tornwaldt cyst
How are Tornwaldt cysts usually found?: Indicental finding on MRI of brain.
What is incidence of Tornwaldt cyst?: 4%
How can Tornwaldt cyst present?: If infected, presents with nasopharyngeal mass ans sepsis.
What is Tornwaldt cyst?: Midline congenital epithelial lined cyst found in nasopharyngeal portion of the pharyngeal mucosal space.
What is origin or Tornwaldt cyst?: Notochordal remnant (that's why its midline)
Where is Tornwaldt cyst?: Cystic mass in the upper nasopharynx, located between the prevertebral muscles in the pharyngeal raphe.
What is the pharyngeal raphe?: The midline aponeurosis of the pharyngeal muscles (the "linea alba" of the pharyngeal constrictors / prevertebral muscles).
Size of Tornwaldt cyst?: Few mm to several cm.
MRI characteristics of Tornwaldt cyst?: T1W imaging ranges from hypointense to hyperintense, depending on concentration of protein in cyst fluid.

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