Suprahyoid and Infrahyoid
4
Parapharyngeal Space Lesion
DIFFERENTIAL DIAGNOSIS
Common
•Direct extension into parapharyngeal space from neoplasm
from adjacent space
○Pharyngeal mucosal space/surface → parapharyngeal
space
–Nasopharyngeal Carcinoma
–Squamous Cell Carcinoma, Palatine Tonsil
–Non-Hodgkin Lymphoma, Pharyngeal Mucosal Space
○Masticator space → parapharyngeal space
–Sarcoma, Masticator Space
–Rhabdomyosarcoma, Masticator Space
○Parotid space → parapharyngeal space
–Benign Mixed Tumor, Parotid Space
–Adenoid Cystic Carcinoma, Parotid Space
–Mucoepidermoid Carcinoma, Parotid Space
•Direct extension into parapharyngeal space from abscess
from adjacent space
○Abscess, Masticator Space
○Tonsillar Abscess, Pharyngeal Mucosal Space
○Parotitis, Acute, Parotid Space
Less Common
•Primary parapharyngeal space lesion
○Pterygoid Venous Plexus Asymmetry
○Venolymphatic Malformation
○Lipoma
Rare but Important
•Benign Mixed Tumor, Parapharyngeal Space
•2nd Branchial Cleft Cyst, Variant
•Ranula, Diving
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
•Parapharyngeal space (PPS) lesion is suprahyoid only
○Some literature separates PPS into pre- & poststyloid
compartments
○Using this scheme, functional differential considerations
by space can be sorted as
–Prestyloid PPS = PPS (differential considerations here)
–Poststyloid PPS = carotid space (not addressed here)
–Carotid space masses are uncommon but displace PPS
fat anteriorly
□Considerations include vascular lesions, neurogenic
tumors, & paragangliomas (not addressed here)
•Primary PPS lesions are rare
○Intact fat plan separates mass from adjacent spaces
•Displacement of PPS fat is useful to determine origin of
masses arising from adjacent suprahyoid head & neck
spaces
•PPS most commonly affected secondarily by direct spread
of local malignancy or infection
Helpful Clues for Common Diagnoses
•Pharyngeal mucosal space/surface (PMS) → PPS
○PPS fat displaced laterally if mass located in PMS
○Most common etiologies are infection or malignancy
•Nasopharyngeal Carcinoma
○CT/MR: Lateral pharyngeal recess tumor bulges into
medial PPS
○PPS fat displaced anteriorly & medially
○Direct invasion of carotid space or bony skull base
possible
•Squamous Cell Carcinoma, Palatine Tonsil
○Induration of PPS fat & irregular margin between fat &
tumor are key findings
○CT/MR: Tumor arises in tonsillar fossa, extends laterally
with either mass effect or direct invasion of PPS
○Tumor staged as T4 if PPS invaded
•Non-Hodgkin Lymphoma, Pharyngeal Mucosal Space
○CT/MR: Bulky PMS tumor bulges medial wall of PPS,
without direct invasion
○Homogeneous density, usually without necrosis
•Masticator space (MS) → PPS
○PPS fat displaced posteromedially for mass in MS
•Sarcoma, Masticator Space
○CT/MR: Aggressive MS tumor ± calcific matrix
•Rhabdomyosarcoma, Masticator Space
○CT/MR: Aggressive noncalcified MS tumor in child
•Parotid space (PS) → PPS
○PPS fat displaced medially
–Most deep lobe parotid tumors compress &/or involve
PPS
–Fascia less adherent along medial aspect of deep lobe
parotid
○When tumor is large, may be difficult to determine if site
of origin is PS or PPS
○Lesion of parotid gland can arise in, or spread to, deep
lobe of parotid & extend medially
–Widening of stylomandibular tunnel characterizes
primary parotid masses extending into (prestyloid)
PPS
•Benign Mixed Tumor, Parotid Space
○Benign deep lobe tumor often asymptomatic until large
○May be hard to determine if tumor is from deep lobe of
parotid or primary PPS
○CT/MR: Large, well-circumscribed mass flattening lateral
aspect of PPS
•Adenoid Cystic Carcinoma, Parotid Space
○CT/MR: Invasive parotid mass with propensity for
perineural spread (CNVII)
•Mucoepidermoid Carcinoma, Parotid Space
○CT/MR: Invasive parotid mass; enhances, "feathery"
margins
•Abscess, Masticator Space
○Odontogenic origins; recent tooth extraction or lucency
around molar
○CT/MR: Pus pocket in MS; edematous muscles;
induration of PPS from lateral aspect
•Direct extension into PPS from abscess from adjacent space
•Tonsillar Abscess, Pharyngeal Mucosal Space
○CT/MR: Palatine tonsil pus with surrounding edema &
induration
○Displaces PPS fat laterally if intratonsillar; abscess may
rupture laterally into PPS
•Parotitis, Acute, Parotid Space
○CT/MR: Edematous parotid gland with increased
density/enhancement
