AJR 2001; 177:1465-1470
© American Roentgen Ray Society
Imaging of Parapharyngeal Space Lesions
Focus on the Prestyloid Compartment
Ji Hoon Shin1,
Ho Kyu Lee1,
Sang Yoon Kim2,
Choong Gon Choi1 and
Dae Chul Suh1
1
Department of Radiology, University of Ulsan College of Medicine, Asan Medical
Center, 388-1 Poongnap-Dong, Songpa-Ku, Seoul 138-736, South Korea.
2
Department of Otolaryngology, University of Ulsan College of Medicine, Asan
Medical Center, Songpa-Ku, Seoul 138-736, South Korea.
Received February 5, 2001;
accepted after revision May 31, 2001.
Address correspondence to H. K. Lee.
Introduction
The parapharyngeal space is a deep potential neck space shaped as an
inverted pyramid extending from the base of the skull to the hyoid bone. The
differentiation of a prestyloid lesion from a poststyloid lesion is critical
for guiding the surgeon in both the differential diagnosis as well as the
potential surgical approach.
Normal Anatomy
The parapharyngeal space may be divided into two compartments on the basis
of its relationship to the styloid process or, more precisely, to the
tensor-vascular-styloid fascia (Fig.
1A,1B,1C,1D).
The importance of the parapharyngeal space also lies in its relationship with
the other spaces of the neck
[1]. The masticator and parotid
spaces are located laterally, the pharyngeal mucosal space is located
medially, and the retropharyngeal space is located posteromedially (Fig.
1A,1B,1C,1D).
The contents of the prestyloid compartment include the minor or ectopic
salivary gland, branches of the mandibular division of the trigeminal nerve,
internal maxillary artery, ascending pharyngeal artery, and pharyngeal venous
plexus, whereas those of the poststyloid compartment include the internal
carotid artery, internal jugular vein, cranial nerves IX-XII, cervical
sympathetic chain, and glomus bodies.
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Fig. 1A. —Normal anatomy of parapharyngeal space. BS = buccal space,
ICA = internal carotid artery, IJV = internal jugular vein, MS = masticator
space, PMS = pharyngeal mucosal space, PPS = parapharyngeal space, PS =
parotid space, PVS = prevertebral space, RPS = retropharyngeal space, SMS =
submandibular space, T = torus tubarius. Axial unenhanced T1-weighted
spin-echo MR image obtained at nasopharynx level shows fat-filled prestyloid
parapharyngeal space (asterisks) located between masticator space and
pharyngeal mucosal space. Torus tubarius represents pharyngeal mucosal space
at nasopharynx level. Poststyloid parapharyngeal space containing major
neurovascular bundle of internal carotid artery and internal jugular vein is
located posteriorly.
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Fig. 1B. —Normal anatomy of parapharyngeal space. BS = buccal space,
ICA = internal carotid artery, IJV = internal jugular vein, MS = masticator
space, PMS = pharyngeal mucosal space, PPS = parapharyngeal space, PS =
parotid space, PVS = prevertebral space, RPS = retropharyngeal space, SMS =
submandibular space, T = torus tubarius. Axial unenhanced T1-weighted
spin-echo MR image obtained at oropharynx level shows that parotid space
containing parotid gland forms posterolateral boundary of parapharyngeal space
(asterisks), and retropharyngeal space and prevertebral space form
posteromedial boundary of parapharyngeal space (asterisks).
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Fig. 1C. —Normal anatomy of parapharyngeal space. BS = buccal space,
ICA = internal carotid artery, IJV = internal jugular vein, MS = masticator
space, PMS = pharyngeal mucosal space, PPS = parapharyngeal space, PS =
parotid space, PVS = prevertebral space, RPS = retropharyngeal space, SMS =
submandibular space, T = torus tubarius. Coronal unenhanced T1-weighted
spin-echo MR image shows continuity of prestyloid parapharyngeal space
(asterisks) with submandibular space. Pharyngeal mucosal space is
located medially.
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Fig. 1D. —Normal anatomy of parapharyngeal space. BS = buccal space,
ICA = internal carotid artery, IJV = internal jugular vein, MS = masticator
space, PMS = pharyngeal mucosal space, PPS = parapharyngeal space, PS =
parotid space, PVS = prevertebral space, RPS = retropharyngeal space, SMS =
submandibular space, T = torus tubarius. Axial schematic at nasopharynx level
shows that parapharyngeal space is divided into prestyloid and poststyloid
compartments by tensor-vascular-styloid fascia connecting tensor veli palatini
muscle with styloid process.
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Congenital or Developmental Lesions
Branchial Cleft Cyst
The parapharyngeal space is a rare location for a branchial cleft cyst. The
pharyngeal attachment and lack of deformity of the derivatives of the first
branchial apparatus support the view that parapharyngeal space cysts originate
in the second branchial apparatus. A rapidly growing, infected branchial cleft
cyst can present with lower cranial nerve palsies
[2] (Fig.
2A,2B,2C).
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Fig. 2A. —Second branchial cleft cyst in 35-year-old woman with
multiple lower cranial palsies that subsided after removal of lesion. Axial
enhanced T1-weighted spin-echo MR image shows well-marginated, nonenhancing
mass that is slightly hyperintense to cerebrospinal fluid in right prestyloid
parapharyngeal space, displacing internal carotid artery and internal jugular
vein to its posterolateral side (arrow).
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Fig. 2B. —Second branchial cleft cyst in 35-year-old woman with
multiple lower cranial palsies that subsided after removal of lesion.
T2-weighted spin-echo MR image shows mass is slightly hypointense to
cerebrospinal fluid. Displacement of internal carotid artery and internal
jugular vein to its posterolateral side (arrow) can also be seen.
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Fig. 2C. —Second branchial cleft cyst in 35-year-old woman with
multiple lower cranial palsies that subsided after removal of lesion.
Unenhanced coronal T1-weighted spin-echo MR image shows mass
(arrowheads) occupying right parapharyngeal space from below skull
base to upper level of submandibular gland. On aspiration, contents contained
pus.
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Cystic Lymphangioma (Cystic Hygroma)
Lymphangiomas form from errors in the development of the lymphatic system
and can have variable vascularity
[3]. Most lymphangiomas occur
during early childhood because the greatest lymphatic development occurs
between birth and 2 years. MR imaging usually shows the signal intensity of a
multiloculated cystic lesion that does not displace adjacent soft-tissue
structures because of the lesion's compressibility (Fig.
3A,3B,3C).
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Fig. 3A. —Cystic lymphangioma in 2-year-old boy with left parotid area
swelling. Axial enhanced T1-weighted spin-echo MR image shows multiloculated,
nonenhancing cystic mass (arrows) in left prestyloid parapharyngeal
space and in left parotid space.
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Neoplastic Lesions
Tumors of the parapharyngeal space account for less than 0.5% of head and
neck neoplasms [4]. However,
various neoplastic lesions can involve the prestyloid parapharyngeal space.
Intrinsic tumors are minor or ectopic salivary gland tumors and neurogenic
tumors arising from the branches of the mandibular division of the trigeminal
nerve. On the other hand, extrinsic tumors are most commonly parotid tumors of
deep lobe origin, neurogenic tumors arising from the vagus nerve, or various
tumors originating from the other surrounding spaces.
Minor or Ectopic Salivary Gland Tumors
Pleomorphic adenomas comprise the majority of minor or ectopic salivary
gland tumors and are the most common neoplasms to originate in the prestyloid
parapharyngeal space [5].
Malignant tumors, such as mucoepidermoid carcinoma or adenoid cystic
carcinoma, are uncommon. Furthermore, several rare tumors, including basal
cell adenoma, can originate from the minor salivary gland (Fig.
4A,4B,4C).
Preservation of the fat plane between the mass and the parotid gland strongly
suggests an extraparotid origin.
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Fig. 4A. —Basal cell adenoma in 61-year-old woman with bulging mass on
left oral cavity. Axial unenhanced T1-weighted spin-echo MR image shows round,
solid and cystic (peripheral high-signal-intensity) (asterisk) mass
in left prestyloid parapharyngeal space. Cystic contents were hemorrhagic on
aspiration. Linear fat line between tumor and parotid gland (arrow)
suggests extraparotid origin of tumor.
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Fig. 4B. —Basal cell adenoma in 61-year-old woman with bulging mass on
left oral cavity. Axial T2-weighted spin-echo MR image shows signal intensity
of mass is slightly increased. Linear fat line between tumor and parotid gland
(arrow) can also be seen.
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Neurogenic Tumors
Neurogenic tumors are the second most common neoplasms originating from the
prestyloid parapharyngeal space and are the most common poststyloid
parapharyngeal space tumors. Most neurogenic tumors arise from the trigeminal
nerve in the prestyloid parapharyngeal space and arise from the vagus nerve in
the poststyloid parapharyngeal space. In tumors arising from the poststyloid
parapharyngeal space, anteromedial displacement of the carotid sheath
structures is frequent because the vagus nerve and sympathetic chain are
posterior to the internal carotid artery, whereas posterolateral displacement
of the carotid sheath structures is frequent in tumors arising from the
prestyloid parapharyngeal space
[5]. Malignant peripheral nerve
sheath tumors are rare, highly aggressive tumors capable of arising de novo or
from preexisting benign neurofibromas or schwannomas; 25-75% of this type of
tumor are associated with neurofibromatosis
[6] (Fig.
5A,5B,5C,5D).
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Fig. 5A. —Malignant peripheral nerve sheath tumor arising from
trigeminal nerve in 35-year-old man with right tinnitus and hearing
disturbance. Axial unenhanced T1-weighted spin-echo MR image shows ovoid
isointense mass (short arrows) in right prestyloid parapharyngeal
space. Laterally displaced parapharyngeal space fat suggests its origin in
prestyloid parapharyngeal space (long arrow).
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Fig. 5B. —Malignant peripheral nerve sheath tumor arising from
trigeminal nerve in 35-year-old man with right tinnitus and hearing
disturbance. Axial T2-weighted spin-echo MR image shows tumor
(arrows) is slightly hyperintense to muscle.
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Fig. 5C. —Malignant peripheral nerve sheath tumor arising from
trigeminal nerve in 35-year-old man with right tinnitus and hearing
disturbance. Axial T2-weighted spin-echo MR image shows tumor
(arrows) extends into eustachian tube (arrowheads).
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Fig. 5D. —Malignant peripheral nerve sheath tumor arising from
trigeminal nerve in 35-year-old man with right tinnitus and hearing
disturbance. Coronal enhanced T1-weighted spin-echo MR image shows strong
enhancement of mass (arrows). Foramen ovale is widened by tumor
(arrowhead), suggesting its perineural extension.
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Tumors from the Other Surrounding Spaces
Tumors of the skull base or tumors of the vertebrae, such as chordomas or
meningiomas, can extend into the parapharyngeal space. Pharyngeal mucosal
space lesions, such as nasopharynx carcinoma, may have extensive submucosal
and parapharyngeal space extension. The most common extrinsic tumors involving
the prestyloid parapharyngeal space are parotid tumors arising from the deep
lobe of the parotid gland [5].
Pleomorphic adenomas are the most commonly encountered parotid gland tumors.
Occasionally, a dumb-bell shape is seen with the waist formation by the narrow
stylomandibular tunnel in the deep lobe parotid tumors. The loss of the fat
line between the mass and the parotid gland suggests a deep lobe parotid
origin (Fig.
6A,6B,6C).
Schwannomas and paragangliomas may arise in the poststyloid parapharyngeal
space and extend into the prestyloid parapharyngeal space (Fig.
7A,7B,7C).
Infiltrative masses involving the parapharyngeal space are soft-tissue
sarcomas of fatty, muscular, or fibrous origin, arising mainly from the
adjacent spaces (Fig.
8A,8B).
Usually, associated bone destruction is also present (Fig.
8A,8B).
Rarely, Castleman's disease, arising from the lymph nodes in the adjacent
spaces, can involve the prestyloid parapharyngeal space
[7] (Fig.
9A,9B,9C).
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Fig. 6A. —Mucoepidermoid carcinoma of deep lobe parotid gland in
40-year-old man with left soft palate area swelling. Contrast-enhanced CT scan
shows inhomogeneously enhancing mass (asterisk) in left prestyloid
parapharyngeal space. Stylomandibular tunnel (arrows) is widened by
tumor, suggesting deep lobe parotid tumor. Medial fat line
(arrowhead) between mass and pharyngeal mucosa is displaced but
preserved.
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Fig. 6B. —Mucoepidermoid carcinoma of deep lobe parotid gland in
40-year-old man with left soft palate area swelling. Axial unenhanced
T1-weighted spin-echo MR image shows low-signal-intensity mass
(asterisk). Medial fat line (arrowhead) between mass and
pharyngeal mucosa is displaced but preserved, whereas lateral fat line between
mass and parotid gland is not seen, indicating parotid origin.
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Fig. 6C. —Mucoepidermoid carcinoma of deep lobe parotid gland in
40-year-old man with left soft palate area swelling. Axial enhanced
T1-weighted spin-echo MR image shows inhomogeneously enhancing mass
(asterisk). Preservation of medial fat line (arrowhead)
between mass and pharyngeal mucosa can also be seen.
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Fig. 7A. —Paraganglioma in 61-year-old woman with left submandibular
area swelling. Axial unenhanced T1-weighted spin-echo MR image shows slightly
inhomogeneous low-signal-intensity mass in left parapharyngeal space.
Anteromedial displacement of internal carotid artery (arrow)
indicates poststyloid parapharyngeal space origin of tumor.
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Fig. 7B. —Paraganglioma in 61-year-old woman with left submandibular
area swelling. Axial T2-weighted spin-echo MR image shows slightly
inhomogeneously hyperintense mass. Anteromedial displacement of internal
carotid artery (arrow) can also be seen.
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Fig. 7C. —Paraganglioma in 61-year-old woman with left submandibular
area swelling. Coronal enhanced T1-weighted spin-echo MR image shows location
of tumor on carotid bifurcation with clear splaying of internal and external
carotid arteries (arrowheads). These findings are highly specific for
carotid body tumor.
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Fig. 8A. —Rhabdomyosarcoma in 10-year-old boy with left infraauricular
area swelling. Axial unenhanced T1-weighted spin-echo MR image shows
lobulated, bulky low-signal-intensity mass involving left masticator, parotid,
prevertebral, and parapharyngeal spaces. Medial margin of mandible
(arrow) was partially destroyed by tumor.
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Fig. 8B. —Rhabdomyosarcoma in 10-year-old boy with left infraauricular
area swelling. Axial enhanced T1-weighted MR image shows inhomogeneous dense
enhancement. Partial destruction of medial margin of mandible (arrow)
is also seen.
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Fig. 9A. —Castleman's disease arising from retropharyngeal space in
34-year-old woman with painless swelling on right side of oropharynx. Axial
unenhanced T1-weighted spin-echo MR image shows well-marginated, isointense
mass in right parapharyngeal space. Parapharyngeal space fat is displaced
anteriorly (short arrow), and posterolateral displacement and
separation of internal and external carotid arteries are seen (long
arrows).
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Fig. 9B. —Castleman's disease arising from retropharyngeal space in
34-year-old woman with painless swelling on right side of oropharynx. Axial
T2-weighted spin-echo MR image also clearly shows posterolateral displacement
and separation of internal and external carotid arteries (arrows).
Linear hypointense signal is seen in mass (arrowheads), which was
revealed to be perivascular lamellar fibrosis on pathologic correlation.
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Fig. 9C. —Castleman's disease arising from retropharyngeal space in
34-year-old woman with painless swelling on right side of oropharynx. Coronal
enhanced T1-weighted spin-echo MR image shows moderate enhancement of
mass.
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Infectious or Inflammatory Lesions
Most commonly, infections of the masticator space involve the
parapharyngeal space and accompany medial displacement of the parapharyngeal
space fat. Obliteration of the parapharyngeal space fat plane is also
frequently associated with infections of the masticator space. Odontogenic
infection is most commonly the source of an inflammatory mass in the
masticator space and is frequently associated with facial swelling, pain, and
trismus [5]. The pharyngeal
tonsil and submandibular gland can be another source of infection involving
the parapharyngeal space. Cellulitis or abscess may form as a complication of
acute tonsillitis or sialoadenitis (Fig.
10A,10B).
On the contrary, infections may readily spread from the parapharyngeal space
into other areas of the neck or extend via the retropharyngeal space into the
upper mediastinum because of the parapharyngeal space's close attachment and
free communication with the other neck spaces
[8].
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Fig. 10A. —Abscess associated with sialoadenitis of submandibular gland
in 33-year-old woman with painful swelling of left submandibular area.
Contrast-enhanced CT scan shows abscess formation with air in left
parapharyngeal space (arrows).
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Fig. 10B. —Abscess associated with sialoadenitis of submandibular gland
in 33-year-old woman with painful swelling of left submandibular area.
Contrast-enhanced CT scan obtained from lower level clearly shows left
submandibular gland enlargement (arrowheads) with surrounding fluid
collection.
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Conclusion
The majority of lesions, mostly tumors, involving the prestyloid
parapharyngeal space are either neurogenic tumors or salivary gland tumors
from the deep lobe of the parotid gland or from the minor salivary gland. By
observing the direction of displacement or infiltration of the parapharyngeal
space, internal carotid artery displacement, and presence or absence of the
medial fat plane, it is possible to localize a lesion to one of several spaces
in the neck [1,
5].
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Introduction
Normal Anatomy
