Different Approaches to the Overlapping Infratemporal Fossa and Parapharyngeal Spaces: a Case Series and Review of Literature

Abstract

Parapharyngeal space and infratemporal fossa are 2 overlapping spaces in head and neck which have complex anatomy with vital neurovascular structures passing through them. Tumors of this region are extremely rare but majority of them (80%) are benign. Benign tumors of this region can lead to swellings in facial region, neck and oropharynx. Dysphagia may be a complaint of the patient. Many of these tumors have malignant potential. Removal of these tumors requires a good understanding of the anatomy of this space so that correct surgical approach can be selected. The surgeon needs to be adept in using the most suitable surgical approach for excision of these tumors. There are various approaches which can be used to access these deeply seated tumors but the issue of prime importance is selecting the appropriate approach for the various tumors here based on their size and their exact location in this complex anatomical space. Inappropriate approach can lead to inadequate tumor excision and can lead to injuries to the neurovascular structures in this region which can cause significant disability. The case series reported here describes the various approaches to this region and highlights the importance of correct selection of the surgical approach.

Introduction

The terms ‘Parapharyngeal space’ (PPS) and ‘infratemporal fossa’ (ITF) define 2 intriguing spaces in head and neck which have been used interchangeably at times. Though the 2 spaces have been defined variably in literature with different boundaries they do have overlapping areas. Tumors in these spaces are rare and 80% of these tumors are benign [1, 2]. A sound knowledge of the anatomy of these 2 spaces is of paramount importance in deciding which approach to take while addressing the benign tumors in these spaces without giving significant morbidity.

The PPS is an inverted pyramid shaped potential neck space filled with areolar tissue. Its base lies superiorly at the skull base formed by the sphenoid and temporal bones. Its apex lies inferiorly at the greater cornu of the hyoid bone. Jugular fossa, hypoglossal canal and the foramen lacerum lie in its roof. It has 3 sides, medially the superior constrictor muscle, the buccopharyngeal membrane and the pharynx, laterally the medial pterygoid muscle, the ramus of the mandible, and the deep lobe of the parotid gland, and below the level of the mandible, the lateral side has the fascia of the posterior belly of the digastric muscle and posteriorly it is bounded by the prevertebral fascia where medially it communicates with the retropharyngeal space. It is divided by the fascia joining the styloid process and tensor veli palatini muscle into an anterior prestyloid and a posterior poststyloid space. The contents of prestyloid space include fat, lymphatics and ectopic salivary gland rests. The poststyloid compartment includes the internal carotid artery, internal jugular vein, lower cranial nerves (IX–XII), cervical sympathetic chain and glomus bodies. The stylomandibular ligament along with mandible forms stylomandibular tunnel through which the deep lobe parotid tumors can extend to parapharyngeal space. The sphenomandibular ligament continues as fascia upto skull base and it separates the parapharyngeal space from the inferior alveolar nerve and lateral pterygoid muscle (masticator space) [3, 4].

The ITF is a non-fascia lined irregular space on the side of the skull and its boundaries are as anteriorly, the posterior surface of the maxilla posteriorly, the mastoid and tympanic part of temporal bone, superiorly the inferior surfaces of the greater wing of the sphenoid and the squamous part of temporal bone. The ITF communicates with the temporal fossa in its lateral part superiorly. Lateral boundary of ITF includes the zygomatic arch and ascending ramus of the mandible. The medial boundary has been variously described in literature as the lateral pterygoid plate, the pharynx, the tensor and levator veli palatini. The medial boundary is the sphenoid pterygoid process, lateral portion of the clivus, first cervical vertebra and inferior surface of the petrous portion of the temporal bone [5]. The fossa is regarded as lacking an anatomical floor with the lateral lower limit at the insertion of the medial pterygoid to the mandible. Cummings describes the inferior boundary as the superior limit of the posterior belly of the digastric muscle. The contents of ITF include retroantral fat, medial and lateral pterygoid muscles and the inferior part of temporalis muscle, the maxillary artery and its branches, pterygoid venous plexus. Its roof formed by greater wing of sphenoid houses the foramen ovale and spinosum which form the highway for passage of neurovascular structures through them in and out of cranial cavity. These include the mandibular branch of trigeminal nerve and the middle meningeal artery.

The ITF and PPS overlap in the medial prestyloid compartment of PPS [6]. A good understanding of the relation of two spaces gives the edge to a surgeon to correctly approach the lesions in these spaces. Inadequate understanding of the intricate regional anatomic relationships can result in selection of an incorrect surgical approach. An incorrectly chosen approach can lead to suboptimal exposure leading to inadequate/difficult removal of tumor, tumor spillage and further recurrence. It can also lead to injuries to vital structures in these spaces.

This case series of benign tumors of PPS and ITF aims at highlighting the various approaches which can be used to access these tumors and also which approach is optimal where.

Case 1

Sixty four years old presented with left sided neck swelling of 18 years duration. He had undergone a surgical excision of the swelling 10 years back at another centre and final histopathology (HPE) was lipoma. He remained asymptomatic for 02 years following which he noticed a swelling in left side neck side. On examination there was a smooth non tender swelling on left side upper neck behind the angle of mandible extending into the submandibular region (Fig. 1a). Oropharyngeal examination revealed a smooth bulge in soft palate pushing the soft palate and lateral pharyngeal wall medially. Contrast enhanced computed tomogram (CECT) revealed a hypodense lesion occupying left parapharyngeal space. FNAC revealed presence of fat cells and the diagnosis of recurrent lipoma of left parapharyngeal space was made. In view of accessibility of the lesion through neck, a transcervical approach was used with incision 2 cm below angle of mandible (Fig. 1b). Blunt finger dissection was done around the lesion which was delivered into the neck and removed (Fig. 1c). There was no post op marginal mandibular nerve paresis. HPE was confirmatory of Lipoma. The patient is under regular follow up and shows no features of recurrence.

Fig. 1.

Cervical approach to PPS tumor, a bulge in left side upper neck, b horizontal neck skin crease incision

Case 2

Forty five years old female presented with history of insidious onset, painless, progressive swelling in right parotid region of 8 years duration. The swelling was non-tender, soft with normal overlying skin. There were no palpable neck nodes and ear-nose-throat (ENT) examination was normal. Sonography of neck revealed a cystic mass without internal vascularity. FNAC was suggestive of Lipoma. MRI of neck revealed a well-defined non enhancing homogenous smooth lobulated mass involving the right parapharyngeal space pushing the superficial lobe anterolaterally. There was preservation of fat planes around the lesion (Fig. 2a, b). Since the lesion involved the parotid region a transparotid approach was selected in this case. Modified Blair incision was given and the superficial lobe of parotid was partly dissected off the facial nerve to mobilise it without removing it. The lesion, which was deep to facial nerve, was then gently dissected out and removed in to with preservation of facial nerve and its branches (Fig. 2c). The final HPE of the specimen revealed it to be a dermoid cyst. Post-operatively patient had marginal mandibular paresis which recovered spontaneously within 02 months and currently the patient has good facial nerve functions and is asymptomatic on follow up.

Fig. 2.

Transparotid approach to PPS tumor, a coronal section of MRI neck—hypointense lesion on T1W seen in Right PPS extending to parotid region (Blue arrow), b Axial section of MRI neck—hyperintense lesion on T2W lesion in right PPS lesion extending to parotid region on T2W (blue arrow), c Intraoperative picture—superficial lobe of parotid (white arrow) dissected off facial nerve (Blue arrow) and the dermoid cyst (yellow arrow)

Case 3

A 38-year-old male reported with complaints of persistent dysphagia to solids and pain throat of 03 weeks duration. ENT examination revealed a bulge on right side of soft palate with medial displacement of tonsil. CECT scan showed well defined, soft tissue lesion with minimal heterogeneous post contrast enhancement in the right PPS measuring 42 mm in its greatest dimension with lesion extending superiorly up to skull base, inferiorly up to axial level of oropharynx, medially minimally displacing oropharynx contralaterally mildly compromising the aero- digestive tract, laterally up to mandibular condyle abutting both medial and lateral pterygoid muscles with preserved fat planes, anteriorly mildly indenting over right tonsillar fossa, posteriorly limited by styloid process. MRI scan concurred with CT scan findings and showed a well-defined oval shaped hypointense lesion on T1 WI (Fig. 3a) and hyperintense lesion on T2WI (Fig. 3b) in the right PPS with no signal suppression on fat saturated images but showed mild patchy post contrast enhancement. Transoral FNAC revealed a features suggestive of Pleomorphic Adenoma (PA). The lesion was approached by a combined transcervical and trans-parotid approach for excision. Consent for mandibulotomy had also been taken in case a necessity arose. A cervical incision, 02 finger breadth below angle of mandible was taken which was joined with the modified Blair parotid incision (Fig. 4a). Skin flap was raised in subplatysmal layer in the neck and in the plane of superficial musculoaponeurotic system (SMAS) in parotid region (Fig. 4b). Submandibular gland was dissected and retracted anteriorly after ligation of facial vessels. Posterior belly of digastric and stylohyoid were divided to create more space to deliver the tumour in the neck. The inferior part of tumour could be visualised after this. Facial nerve trunk was identified and preserved after mobilising the superficial lobe of parotid over it and partly along its branches. Stylomandibular ligament was divided. Superficial lobe of parotid was not excised. Deep lobe of parotid was dissected from facial nerve trunk and branches (Fig. 4c). By blunt finger dissection the tumour in anterior PPS and ITF was freed from its surrounding fascia. A 07 × 3.5 cm multilobulated tumor mass arising from the deep lobe of parotid was delivered into neck and excised in toto along with part of deep lobe (Fig. 4d). Final HPE of specimen confirmed it to be PA. Post-operatively he had immediate resolution of his symptoms but he had partial marginal mandibular nerve palsy which recovered over a period of 3 months.

Fig. 3.

MRI neck, a coronal T2W cut showing the lesion in right PPS (White arrow), b Axial cut T2W lesion in right PPS compromising the oropharyngeal airway (White arrow)

Fig. 4.

Combined Transparotid–Transcervical approach, a incision, b skin flap raised and submandibular gland retracted anteriorly (white arrow), c full exposure after mobilisation of superficial parotid (white arrow) dissected over facial nerve (Long black arrow), ECA (Short black arrow), angle of mandible (black star), mosquito artery forceps pointing to the tumor in PPS, d tumor (white arrow) being delivered into the neck with finger dissection

Case 4

Twenty one years old male was incidentally detected to have a left sided parapharyngeal mass in MRI during evaluation of syncope. Contrast enhanced MRI revealed a smooth heterogenous mass contiguous with left vagus nerve with displacement of internal carotid artery (ICA) and external carotid artery (ECA) anteriorly. Based on the MRI appearance, a differential diagnosis of Vagal schwannoma/vagal paraganglioma was made (Fig. 5a, b). Secretory paraganglioma work up was done which was normal. Radiological findings were suggestive of a benign lesion. As patient was asymptomatic he was kept on wait and scan follow up. On follow up CEMRI done 6 months later there was an increase in size by 2 mm in 2 dimension. Due to progressively increasing swelling and patient’s concerns regarding the swelling, surgical excision was offered. The lesion was at a distance of 2 cm from skull base hence a transmandibular, midline lip split incision was chosen for good exposure of the lesion and the great vessels anterior to it. Paramedian mandibulotomy was done and mandible segment on left side was retracted superolaterally to expose the lesion. The tumor was found to be arising from vagus nerve (Fig. 5c). There was a plane between the lesion and nerve and it could be peeled off easily from the nerve suggesting it to be a schwannoma. The ICA, ECA, vagus, glossopharyngeal and hypoglossal nerves were preserved. Even the lingual and inferior alveolar nerves were preserved. The histopathology was consistent with Ancient Schwannoma. Post operatively patient did not have any cranial nerve palsy and has good functional and cosmetic outcome. At one year follow up he has no recurrence.

Fig. 5.

Transmandibular approach, a MRI neck axial section T2W image shows lesion in left PPS (yellow arrow), b MRI neck sagittal section T2W image shows lesion in PPS 2 cm below skull base (yellow arrow), c Operative picture—mandible segment swung superolaterally (white arrow), digastric tendon (blue arrow), tumor seated deep in PPS (yellow arrow)

Case 5

Fifty year old male presented with insidious onset, painless and progressive swelling of left cheek of 10 years and proptosis left of 01 year duration. On examination the swelling was firm and non-tender, there was no oropharyngeal bulge or palpable neck nodes. The eye movements were also full and free with no diminution of vision. CECT scan base of skull to root of neck revealed a heterogenous enhancing lesion involving the left infratemporal fossa, extending into the maxillary antrum through its posterior wall, the pterygopalatine fossa and posteroinferior orbit causing proptosis. Superiorly the lesion extended upto skull base (Fig. 6a, b). FNAC of the lesion was suggestive of spindle cell neoplasm likely schwannoma. This lesion was approached for excision through maxillary swing approach due to its location in the infratemporal fossa posterior to maxilla and its extent upto skull base. Weber Fergusson incision with Dieffenbach extension (Fig. 6c) was used without raising the cheek flap. Maxillectomy cuts were given keeping the maxilla attached to the cheek for its blood supply. Maxilla along with the cheek flap was swung laterally giving good exposure to the lesion (Fig. 6d). Blunt dissection was done to free the lesion from its surrounding fat and fascia. Lesion was found to be arising from one of the branches of maxillary nerve. It was excised in toto, maxilla swung back and fixed with miniplates. Even orbital floor was reconstructed with Titanium orbital implant. Patient made uneventful recovery and HPE of the lesion confirmed schwannoma. At one year post op follow up he had good cosmetic and functional outcome.

Fig. 6.

CECT and Intraoperative pictures of the left ITF schwannoma, a schwannoma occupying left ITF (yellow arrow) extending to orbit and causing proptosis, b Left ITF schwannoma extending upto skull base and medially upto pterygopalatine fossa, c Weber Fergusson incision with Dieffenbach extension, d maxilla swung laterally attached to cheek flap (yellow arrow) and tumor exposed in ITF (blue arrow)

Case 6

Twelve year old male presented with Right sided recurrent epistaxis of 03 month duration and nasal obstruction since 01 month, on nasal endoscopy, a pink polypoidal mass was seen in right nasal cavity completely, CECT paranasal sinuses showed an enhancing mass filling right nasal cavity completely and displacing the nasal septum to left, it also caused widening of pterygomaxillary fissure and involvement of medial infratemporal fossa (Fig. 7a). A Digital Subtraction Angiography was also done which revealed multiple feeders from ascending pharyngeal and sphenopalatine arteries. A diagnosis of Juvenile nasopharyngeal angiofibroma was made and it was decided to approach the lesion through modified Denker’s endoscopic approach after pre op embolization. The ITF portion of the tumor was very well accessible through the endoscopic Denker’s approach (Fig. 7b). The tumor was excised completely HPE of specimen confirmed angiofibroma. The patient is currently on follow up and is asymptomatic at 1.5 years post-surgery.

Fig. 7.

CECT PNS and intraoperative picture of JNA, a CECT PNS axial cut showing the nasal and the ITF part (yellow arrow) of JNA, b endoscopic modified Denker’s approach to ITF showing posterior wall of maxilla (blue arrow) opened to expose the ITF part of JNA (Yellow star), open pterygopalatine fossa (green star), Nasal part of tumor (green arrow)

Discussion

This case series brings out the various surgical approaches possible to these complex areas of ITF and PPS from a ENT and Head-Neck surgeons’ perspective. A good clinical assessment and optimal imaging determines the extent of the lesion based on which the surgical approach is decided. The goals of surgery for benign tumors in this space include removal of the tumor without spillage/residual tumor with minimal morbidities. Morbidities due to surgery in this region are generally due to injury to the neurovascular structures here.

Tumors in parotid region/deep to parotid, can be accessed by transparotid approach. Superficial lobe is dissected above the facial nerve and its branches to expose the tumor. At times tumor in parotid region may not involve the superficial lobe. In such cases it is not necessary to remove the superficial lobe of the parotid. Its mobilisation over the facial nerve is enough to expose the tumor as can be seen in our transparotid and combined transparotid-transcervical approach cases. It is also emphasised here that a mandibulotomy can be prevented by using the transcervical approach or at times combining it with transparotid approach in most of the prestyloid space tumors [7, 8]. Division of the stylomandibular ligament, posterior belly of digastric and stylohyoid provides greater access to the deep and superior PPS [9, 10].

For poststyloid space tumors, close to skull base, a mandibulotomy approach provides excellent exposure giving good control over ICA, ECA and lower cranial nerves can be well visualised and preserved [11]. Due to this approach in our mandibulotomy case no morbidities related to any cranial nerve deficit occurred. Midline, paramedian and lateral mandibulotomy approaches have been described in literature. In most of PPS cases mandibulotomy can be avoided by a transcervical approach but in recurrent cases where there is lot of fibrosis mandibulotomy may be a necessity. Mandibulotomy can be associated with lot of morbidities like inferior alveolar nerve palsy, non-union, facial scars and longer hospital stay so wherever possible it should be avoided [12]. A temporary tracheostomy is also required to prevent any airway complication in postoperative period which is another morbidity for the patient.

Distance of the lesion from skull base and involvement of maxilla and orbit, guide us regarding which approach to take for the excision of tumor. A tumor which is reaching skull base and involving maxilla posteriorly and invading into orbit is best accessible through a maxilla swing approach [13]. Other approaches will not provide enough exposure to remove the maxillary and orbital part of the tumor as could be achieved in the above mentioned maxilla swing approach. Limitations of this approach include facial scar, palatal fistula, malocclusion and ectropion.

We have entered into an era of minimally invasive surgeries. ITF can be approached by this minimally invasive endoscopic Denker’s approach which provides excellent exposure to ITF with excellent close visualisation of the area and the lesion [14]. This approach helps to prevent any facial scars and is cosmetically more acceptable to the patients. The surgeon needs to have good endoscopic sinus surgery skills to use this approach.

Transoral approach to PPS has also been described in literature. This is an approach which is suited for well encapsulated prestyloid space tumors which are not attached to deep lobe of parotid, are away from the facial nerve and the ICA. Advantages of this approach include better cosmesis as there are no external scars. Surgery time is also less as one is directly onto the tumor once the incision is given on the anterior pillar and soft palate and even hospitalisation time is reduced. Limitations of this approach are that it provides limited exposure, capsular rupture of tumor with tumor spillage can occur. Severe haemorrhage can occur due to damage to vessels including ICA with limited space to take control of the bleeding vessel. Glossopharyngeal nerve and even facial nerve can get injured [15, 16].

There are situations where a single approach is not sufficient due to tumor size and site. In such cases combined approaches may be used such as combined transoral and transcervical [17], combined transparotid and transcervical as presented in this case series.

For ITF lesions involving skull-base, other neurotological approaches have been described [18] however they are beyond the scope of this article.

Conclusion

The concept of removal of benign lesions in any region is different from that of malignant lesions in the sense that aggressive surgery with adequate resection margins is not required. Patient expects to have minimal morbidity and hence the surgery needs to be tailored accordingly. It is challenging for a surgeon to have a balance between optimal removal of the benign tumors of this space without doing a debilitating surgery. A considered decision regarding the approach helps the surgeon in addressing the various tumors in different parts of these spaces optimally.

Compliance with Ethical Standards

Conflict of interest

The authors declare that they have no conflict of interest.

Informed Consent

Informed consent was obtained from the individuals participating in the study.