Keywords
parapharyngeal space tumors - surgical approach - cranial nerve palsies - deep neck
space tumors - schwannoma
Introduction
Parapharyngeal space (PPS) tumors are rare, constituting approximately 0.5% of all
head and neck tumors with intriguing diverse histology.[1]
[2]
[3] It is also interesting to note that many of the tumors occurring in PPS are not
primary PPS pathology, but are metastatic or directly spreading tumors from adjacent
structures. The primary PPS tumor can originate in the prestyloid compartment or the
poststyloid compartment, which are separated by fascia between the styloid process
and the tensor veli palatini muscle.[4] The common tumors of the prestyloid origin are salivary gland tumors, lipomas, lymphomas,
and rarely neurogenic tumors. In contrast, most of the tumors of the poststyloid compartment
are neurogenic as this compartment contains the internal jugular vein, carotid artery,
vagus nerve, and sympathetic plexus.[5] Most of the PPS tumors are benign and only 10 to 20% of these are malignant.[6] The management of tumors of PPS is challenging. Presently, surgery with an appropriately
chosen approach is the primary modality for the treatment and radiotherapy is utilized
for the management of unresectable tumors, as an adjuvant treatment, or in patients
with a high risk of injury to cranial nerves during surgery.[7]
There is paucity of adequate literature on this disease entity. The rarity of the
diseases precluded conducting of prospective studies with high level of evidence.
The present study was done with an aim to present our experiences in various clinical
and pathological aspects of PPS tumors with a critical evaluation of management.
Subjects and Methods
The present study is a retrospective analysis of 60 cases of PPS tumors managed surgically
from 2007 to 2017. After obtaining ethical clearance from the institutional review
board, the complete medical records were obtained from the electronic medical record
system of the institute. The demographical, clinical, and pathological details and
management with surgical details were recorded. Any preoperative and postoperative
complications during follow-up were also recorded. Analysis of the collected data
was done using SPSS 22 software.
Results
A total of 60 patients who underwent surgical resection of PPS tumors from the year
2007 to 2017 were included in the study. The demographical details are given in [Table 1].
Table 1
Demographic details
|
Number
|
Percentage
|
|
Total number of cases
|
60
|
|
|
Gender
|
|
Male
|
38
|
63.33%
|
|
Female
|
22
|
36.67%
|
|
Male: Female ratio
|
1.7:1
|
|
|
Mean age in years (range)
|
45.22 (22–82)
|
|
|
Treatment naive
|
53
|
88.3%
|
|
Recurrent cases
|
7
|
11.66%
|
|
Location
|
|
Prestyloid
|
39
|
65%
|
|
Poststyloid
|
21
|
35%
|
|
Mean follow-up duration in months (range)
|
44 (4–161)
|
|
|
Deaths during follow-up
|
2
|
3.3%
|
The most common presentation was swelling/mass in the parotid or upper neck region
in 36 (60%) cases. Twenty-four (40%) patients presented with oropharyngeal (tonsillar)
or soft palate bulge. Dysphagia was the presenting symptom in 14 (23.3%) patients,
while 6 (10%) patients had a change in voice. Pain was the chief complaint in 5 (8.3%)
patients. Other rare presentations were trismus (2 cases), foreign body sensation,
and hearing loss (1 case each).
The primary imaging modality utilized for evaluation was magnetic resonance imaging
(MRI) with contrast in 42 (70%) cases, followed by contrast-enhanced computed tomography
(CECT) scan in 16 (26.7%) cases and positron emission tomography/CT (PET/CT) scan
in 2 (3.3%) cases. CT angiography was done for two patients along with MRI for suspected
vascular tumor.
A total of 42 patients underwent fine-needle aspiration cytology (FNAC) for histological
evaluation. The diagnostic accuracy of FNAC was 71% for benign lesions and 47% for
malignant lesions. FNAC was nondiagnostic in 13 (30.9%) patients, and the majority
of them were schwannomas (53.8%). On the final histopathological assessment, 43 (71.7%)
were benign and 17 (28.3%) were malignant. The histological distribution of various
tumors of PPS is given in [Table 2].
Table 2
Tumors of PPS: histological distribution
|
Type (number, percentage)
|
Benign (number)
|
Malignant (number)
|
|
Abbreviation: PPS, parapharyngeal space.
|
|
Neurogenic origin
(26, 43.3%)
|
Prestyloid
|
Nil
|
Nil
|
|
Poststyloid
|
Schwannoma (22)
Neurofibroma (1)
Vagal paraganglioma (2)
Meningothelial meningioma (1)
|
|
|
Salivary origin
(24, 40%)
|
Prestyloid
|
Pleomorphic adenoma (13)
|
Mucoepidermoid carcinoma (2)
Myoepithelial carcinoma (1)
Carcinoma ex pleomorphic (1)
Synovial sarcoma (1)
Adenoid cystic carcinoma (1)
|
|
Poststyloid
|
Pleomorphic adenoma (1)
|
Mammary analogue secretory carcinoma (1)
Myoepithelial carcinoma (2)
Salivary duct carcinoma (1)
|
|
Miscellaneous
(10, 16.7%)
|
Prestyloid
|
Fibromatosis (1) Lymphovascular malformations (1)
|
Metastasis from papillary carcinoma (3)
Metastasis from medullary thyroid carcinoma (1)
|
|
Poststyloid
|
Solitary fibrous tumor (1)
|
Metastasis from papillary carcinoma (1)
Metastasis from medullary thyroid carcinoma (1)
Metastatic squamous cell carcinoma (1)
|
|
Total
|
43 (71.7%)
|
17 (28.3%)
|
Among the tumors of neurogenic origin, schwannoma was the most common tumor. Pleomorphic
adenoma was the most common tumor of salivary gland origin and the majority was present
in the prestyloid compartment. Other histopathologies with their distribution are
given in [Table 2].
Surgery was the treatment modality in all the cases. The most common surgical approach
was transcervical, which was used in 43 patients. The combination of transcervical
and transparotid approach was used in eight patients, a combination of transmandibular
and cervical approach in six patients, and transoral robotic surgery (TORS) was performed
in three patients.
Adjuvant radiotherapy/concurrent chemoradiotherapy was advised to 11 patients out
of 16 patients having malignant tumors. A total of nine patients could complete the
treatment and two deaths were reported during the treatment. At the end of the follow-up
duration, seven patients were disease-free and two patients had developed nonsalvageable
recurrence after adjuvant therapy. None of the patients with the benign histology
had disease recurrence during follow-up period.
Cranial nerve palsies/paresis were the most dreaded complication of PPS tumors. A
total of 6 patients who presented with cranial nerve palsies in the preoperative period,
did not show any recovery during follow-up. Cranial nerve palsies were present in
16 patients in the postoperative period. The most commonly involved cranial nerves
were facial, lower cranial nerves (IX, X, XI, XII), and sympathetic chain. The most
common neurological complication was marginal mandibular nerve paresis, seen in eight
cases. One-half of these cases (4/8) improved with physiotherapy. A list of cranial
palsies in the preoperative and postoperative period in the present study is given
in [Table 3].
Table 3
Preoperative and postoperative nerve palsies
|
Serial no.
|
Histopathology
|
Cranial nerve palsy
|
Remarks
|
|
No. of patient
|
Preoperative
|
Postoperative
|
|
1
|
Carcinoma ex pleomorphic
|
1
|
VII
|
IX
|
Lower branches of VII nerve and IX nerve sacrificed
|
|
2
|
Metastasis from papillary carcinoma
|
1
|
X
|
XII
|
Left superior laryngeal nerve and left hypoglossal nerve sacrificed
|
|
3
|
Mucoepidermoid carcinoma
|
1
|
|
VII
|
Facial nerve - lower trunk sacrificed
|
|
4
|
Adenoid cystic carcinoma
|
1
|
|
VII
|
Marginal mandibular nerve paresis
|
|
5
|
Pleomorphic adenoma
|
4
|
|
VII
|
Marginal mandibular nerve paresis
|
|
7
|
Salivary duct carcinoma
|
1
|
VII
|
|
Facial nerve trunk involved by the tumor and sacrificed
|
|
8
|
Vagal paraganglioma
|
1
|
X
|
|
Left vocal cord palsy
|
|
9
|
Vagal paraganglioma
|
1
|
|
X, Horner’s syndrome, XII
|
X nerve palsy
|
|
10
|
Schwannoma
|
1
|
|
IX, Horner’s syndrome, VII
|
Originating from IX nerve and hence excised,
marginal mandibular nerve paresis
|
|
10
|
Schwannoma
|
1
|
Horner’s syndrome
|
|
Sympathetic trunk origin and engulfed by tumor and sacrificed
|
|
11
|
Schwannoma
|
1
|
|
Horner’s syndrome
|
Sympathetic trunk origin and engulfed by tumor and sacrificed
|
|
12
|
Schwannoma
|
1
|
|
X
|
Left vocal cord palsy
|
|
13
|
Schwannoma
|
1
|
Horner’s syndrome
|
X
|
Recurrent schwannoma
sympathetic trunk
|
|
14
|
Schwannoma
|
1
|
|
VII
|
Recurrent schwannoma
marginal mandibular nerve paresis
|
|
15
|
Schwannoma
|
1
|
|
VII
|
Marginal mandibular nerve paresis
|
|
16
|
Schwannoma
|
1
|
|
VII
|
Facial nerve sacrificed
|
|
Total patients
|
19
|
6
|
16
|
|
Discussion
The PPS is described as an inverted pyramid, with the base at the skull base and apex
oriented toward the hyoid bone. This anatomical space is seated deeply, surrounded
by other anatomically described spaces. The anatomy of PPS is complex and is neither
easily accessible for clinical assessment, nor a direct surgical approach is possible.
The tumors arising from PPS are most challenging for head and neck surgeons due to
their rare occurrence, late presentation, difficulty in establishing a diagnosis,
varied histopathology, and finally due to their complex surgical management.
The present retrospective analysis was done to share the clinical experience of these
rare tumors managed at Tata Memorial Hospital, Mumbai, Maharashtra, India. In our
experience, the mean age of presentation and sex distribution is comparable to preexisting
literature.[5]
PPS tumors have an indolent course and remain asymptomatic for long periods. Riffat
et al have given a comprehensive analysis of presenting symptoms in their systemic
review of PPS tumors. The most common presentation is the cervical or oropharyngeal
mass lesion.[5]
[6] In our study, the cervical mass was the most common presenting symptom followed
by the tonsil and soft palate submucosal bulge. Other presenting symptoms noticed
in our study were attributed to mass effect or cranial nerve deficits.
Imaging has an important role in diagnosis and guiding the management plan for the
PPS tumors. The various imaging modalities available for PPS tumors include MRI, CECT
scan, and angiography and these are complementary to each other. The origin of the
lesion can have an implication on the choice of surgical approach. Imaging can be
helpful in determining the origin of the tumor by assessing the displacement pattern
of fat in PPS.[7] There are few advantages of MRI, which is considered superior to CT scan in providing
better soft tissue contrast resolution between PPS masses and surrounding fat, while
the spatial resolution of CT scan delineates the vital structures well. The MRI enables
a better assessment of margins, stage of the disease, and fat infiltration. It is
also useful in cases with an equivocal CT scan and to assess skull base or perineural
spread.[8]
Angiography is particularly useful for vascular and enhancing lesions. The role of
PET/CT is limited as a diagnostic modality; however, it can be used to rule out distant
metastasis in malignant tumors.[9]
In our study, primary modality, MRI was done in 42 patients, while CECT was done in
16 patients. PET/CT was done in only two patients presenting with metastases.
FNAC may have an important role in guiding the surgeon especially in malignant cases
for complete extirpation of tumor and can aid in selecting the approach as well. This
can lead to preoperative and postoperative planning, prognostication, and counseling
of the patients. In our study, the diagnostic accuracy of FNAC was 71% for benign
PPS tumors and 47% for malignant PPS tumor. The diagnostic accuracy of FNAC for benign
PPS tumors was higher compared with diagnostic accuracy for malignant tumors. It is
to be noted that nondiagnostic cases were not included in statistical analysis for
measuring diagnostic accuracy. In our study, the higher nondiagnostic results for
benign pathologies can be attributed to the FNAC being hemorrhagic in paragangliomas
and hypocellular in schwannomas.
On the final histopathological assessment, 43 (71.7%) cases were benign and 17 (28.3%)
were malignant. In our series, schwannoma was the most common pathology (22 cases),
followed by pleomorphic adenoma (14 cases). In a systematic review, Riffat et al have
shown that among the 70 different histologies reported in 1,118 primary cases, 82%
were benign and 18% were malignant. The most common pathology reported was pleomorphic
adenoma.[6]
The proximity of PPS tumors to neurovascular structure often leads to menacing neurological
complications, which can be seen in the preoperative or postoperative period. It is
observed that preoperative nerve palsies are less symptomatic as compared with postoperative
nerve palsies, most probably due to slow onset and activation of rehabilitative mechanisms.
In malignant pathologies, usually, there is early involvement of nerve due to infiltration,
whereas in benign pathologies, tumor attains large size before palsy is even apparent.
In our series, patients presenting with preoperative cranial palsies did not improve
after surgery. A list of preoperative and postoperative cranial nerve palsies is given
in [Table 3].
Various surgical approaches that can be used for excision of the parapharyngeal tumors
are transcervical, combined transcervical-transparotid, transmandibular, transoral,
and transoral robotic approach. The choice of approach is guided by the location,
size, histology, and relationship with various anatomical structures.[1]
[3]
[10]
[11] Various facets of these approaches are described in the subsequent paragraphs.
In our study, the transcervical approach was used in the majority (72%) of the patients.
However, this approach can be used for tumors with limited cranial extension and not
involving the parotid gland. The combined transcervical-transparotid approach was
used in lesions arising from the parotid gland. This approach has the advantage of
better exposure of the facial nerve, but cannot be used for tumors greater than 4
cm in size.[6] The transcervical-transmandibular approach was used in cases where the tumor was
reaching up to the skull base in the region of the foramen ovale or was in close proximity
to the styloid process.
The transoral approach is minimally invasive but offers the least exposure and used
in none of the patients in the present study. The endoscopic-assisted transoral approach
can increase the visibility, provide better hemostatic control, and decrease complications.[12] The TORS has the advantage of being minimally invasive like the transoral approach
but provides better exposure with augmented reach.[11] Boyce et al have concluded that the TORS is safe and effective, but has the limitation
of reach in far lateral and superior areas of PPS.[13] In the present study, robotic approach was used for two cases of pleomorphic adenoma
that had submucosal palatal swellings and one case of schwannoma arising from the
posterior pharyngeal wall.
A treatment algorithm by Chu et al, suggest that the TORS can be an approach of choice
in a well circumscribed tumor with a clear plane of cleavage from neurovascular bundle
and has displaced internal carotid artery laterally. It can safely accomplish the
excision if uncontrolled bleeding or tumor spillage is not present. However, it should
not be utilized if preoperatively trismus, infiltration of surrounding tissue, or
medial displacement of the internal carotid artery is detected.[14]
In conclusion, PPS tumors arise from an anatomically complex area and have heterogeneous
histopathology. Most of these tumors are benign, indolent in nature, and usually become
symptomatic when they attain large dimensions. Multiple cranial nerve palsies are
often associated with tumors of neurogenic origin arising from the poststyloid space.
The MRI is the best imaging modality to assist in the diagnosis; however, the CT scan
and angiography are complementary. The FNAC has low accuracy for malignant lesions
in our series. Surgery is the primary modality of treatment and the majority of these
tumors are accessible through transcervical approach. The aim of surgery should be
complete resection of the tumor with minimum morbidity. Malignant tumors originating
from PPS when resected completely have a better prognosis but those with metastasis
to PPS have a poorer prognosis.
Key Messages
The parapharyngeal space (PPS) tumors are histologically diverse and rare tumors.
The article presents a single-institutional experience on clinical aspects and management
challenges of PPS tumor in one of the largest case series (60 cases).
