Disclaimer: The information contained within the Grand Rounds Archive is intended for use by doctors and other health care professionals. These documents were prepared by resident physicians for presentation and discussion at a conference held at Baylor College of Medicine in Houston, Texas. No guarantees are made with respect to accuracy or timeliness of this material. This material should not be used as a basis for treatment decisions, and is not a substitute for professional consultation and/or peer-reviewed medical literature.

The Introduction
Masses of the head and neck present a diagnostic challenge. The diagnostic tools available include history and physical examination, palpation, radiographic studies, and biopsy. Because the parapharyngeal space is located deep within the neck, clinical examination and palpation are limited and unreliable. One must depend upon other means of diagnosis. With the popularization of cross sectional imaging since the mid-1970's, a new approach to head and neck anatomy based on fascial spaces has been added to the traditional surgical compartmental descriptions. An interpretation of imaging data based on a combination of these systems can precisely locate a lesion. From this information an accurate differential diagnosis can be obtained, and an optimal surgical approach planned.

Anatomy
The neck can be divided into fascial spaces based upon fascial envelopes derived from layers of the superficial and deep cervical fascia. These spaces have functional significance because they serve as barriers to the growth and spread of inflammatory and neoplastic disease in the neck. The deep cervical fascia has three layers: the superficial or investing fascia, the middle or visceral fascia, and the deep or prevertebral fascia. This fascia divides the suprahyoid space into ten spaces: 1) Oral cavity (OC) 2) Pharyngeal mucosal space (PMS) 3) Sublingual space (SLS) 4) Parotid space (SMS) 5) Parapharyngeal space (PPS) 6) Masticator space (MS) 7) Parotid space (PS) 8) Retropharyngeal space (RPS) - which is also known as the danger space, 9) Carotid space (CS) and 10) Prevertebral space (PVS).

Of these spaces, the parapharyngeal space (PPS) plays a pivotal role in diagnosis because of its central location. This space is also referred to as the lateral pharyngeal spaces, and it serves as a contrasting marker space. When it is displaced by an adjacent mass, the direction of its displacement is an important diagnostic clue.

The parapharyngeal space extends from the skull base to the hyoid bone. It resembles an inverted triangular pyramid with concave faces. The medial border is the pharyngobasilar fascia superiorly and the superior pharyngeal constrictor and the fascia of the tensor and levator palatini muscles more inferiorly. Lateral to the PPS lies the infratemporal fossa which can be subdivided into the masticator and parotid spaces. Posteriorly it abuts the carotid space, retropharyngeal space, and prevertebral space.

Som, and other authors include the carotid sheath in their definition of the parapharyngeal space. Using this definition, the carotid artery, jugular vein, styloid muscles, lymphatics, sympathetic chain, and cranial nerves IX, X, XI, and XII are included within the space. Physicians using this definition of the parapharyngeal space refer to the pre- and post-styloid compartments to differentiate between the carotid sheath posteriorly and the fibrofatty area anteriorly.

The parapharyngeal lymph nodes, together with the retropharyngeal nodes drain the soft palate, lateral and posterior oropharynx and the base of the tongue. The most superior and lateral of these is the node of Rouviere. These nodes drain to the jugulodigastric and posterior cervical groups.

Signs and Symptoms
Parapharyngeal tumors generally present as a painless mass. They may present with hearing loss, dysphagia, a sensation of aural fullness, dysarthria, neck pain or even facial paresthesias.

Physical examination may reveal a mass palpable in the neck and transorally. Serous middle ear effusion caused by eustachian tube obstruction may be present. Nerve compression or infiltration may cause tongue hemiplegia, or Horner's syndrome. Involvement of the last four cranial nerves at the jugular foramen results in Vernet's syndrome with ipsilateral vocal cord paralysis, dysarthria and dysphagia from mass effect on the glossopharyngeal and vagus nerves. Trismus may occur due to irritation of the pterygoids or obstruction of mandible movement.

Differential Diagnosis
The differential diagnosis of PPS masses includes three broad categories: congenital, infectious or inflammatory, and neoplastic etiologies. The most common parapharyngeal tumors are salivary gland neoplasms, neurogenic tumors, and metastatic carcinoma. Most parapharyngeal masses are benign. Of these, salivary gland neoplasms are the most common lesions.

The enlargement of masses within the parapharyngeal space occurs in the plane of least resistance. The tonsillar fossa and lateral pharyngeal wall are easily displaced into the air-filled pharynx. The tumor may expand laterally between the tail of the parotid and the submandibular gland or posteriorly into the retromandibular area. Adenoid cystic carcinoma, squamous cell carcinoma and lymphoma are prone to perineural spread.

Some retromandibular masses expand medially through the stylomandibular tunnel to present as a mass displacing the lateral pharyngeal wall. Because the stylomandibular tunnel is rather narrow, it creates an isthmus in the tumor giving it the "dumbbell" shape described by Patey and Thackray in 1956. Virtually all of these dumbbell tumors are pleomorphic adenomas originating from the deep lobe of the parotid gland.

Salivary gland neoplasms
Fully 40-50% of all parapharyngeal tumors are of salivary gland origin. A mass in the prestyloid area which is predominantly medial and separate from the parotid gland is likely a minor salivary gland neoplasm. The most common salivary gland tumor is pleomorphic adenoma or "benign mixed tumor." This is also the most common tumor impinging on the PPS. These are slow growing and painless. They can occur at any age, but the incidence peaks between the ages of 20 and 40.

Neurogenic tumors
Neurogenic tumors account for 30% of primary PPS tumors. Neurogenic tumors are the most common postsyloid tumors and the second most common prestyloid tumors. Shoss, Donovan and Alford presented the combined data from four studies representing 213 patients and showed that neurogenic tumors may account for more PPS lesions than traditionally thought.

Schwannomas account for 20% of all PPS tumors, and are the most common enhancing extraparotid tumors. 25-40% of all schwannomas occur in the head and neck according to Park, Suh and Kim. Schwannomas are diagnosed most frequently in the third through fifth decades of life. Their histology was first described by Verocay in 1908, who called them neurinomas.

Neurofibromas arise from Schwann cells also. They are not encapsulated, and nerves can be incorporated in the tumor. Neurofibromas are often subcutaneous and multiple. Patients with von Recklinghausen's disease have multiple neurofibromas and cafe au lait spots. The disease is autosomal dominant, occurs in 1/3000 births, and in 50% there is no family history. These patients are at risk for malignant transformation of their lesions; 6-16% of these patients develop neurofibrosarcoma.

Paragangliomas
Paragangliomas arise from paraganglionic bodies of the autonomic nervous system. These cells are derived from the neuroectoderm rather than the neural tube. They are histologically similar to pheochromocytomas, but rarely secrete catecholamines. The most common symptoms are hoarseness and aspiration of fluids. Deep neck paragangliomas can be divided into three types: those which occur at the jugular foramen, those which arise from the nodose ganglion, and those originating in the carotid body.

Carotid paraganglioma can also be differentiated from cervical lymphadenopathy because these tumors are fixed to the carotid bifurcation and therefore are not mobile in the cephalocaudal dimension.

Metastatic carcinoma
The parapharyngeal space is the first site of metastases from the nasopharynx, nasal cavity, palate, and maxillary sinus. Enlarged parapharyngeal lymph nodes with central lucency and an enhancing rim on CT scan suggest metastatic carcinoma.

Biopsy
When lesions are palpable in the retromandibular area or submandibular area or transorally, fine needle biopsy may aid in surgical and postoperative planning. Open biopsy is reserved for lesions which are deemed unresectable that there is little danger of vascular injury.

Imaging
Of the five options available as imaging studies, computed tomography is inferior to plain films for evaluating the ductal system of major salivary glands. For most other applications however, the CT scan is a superior study to evaluate and localize suprahyoid neck lesions, according to Becker.

MRI has several advantages over CT. It uses non-ionizing radiation; it can image in multiple planes without changing the patient's position; it has superior soft tissue resolution; it is relatively artifact free, and images vessels well without contrast. According to Cross, Shapiro and Som, MRI is better able to differentiate tumors from normal salivary gland tissue than CT, especially using T2 weighted images in which most tumors have high signal intensity.

The use of gadopentetate dimeglumine (Gadolinium) as a paramagnetic contrast agent is useful in demonstrating involvement of the sinuses or perineural spread or intracranial extension, but it is of no additional value in demonstrating parotid tumors, schwannomas, or carotid body tumors according to Robinson et al.

Internal carotid artery displacement is the most reliable feature to distinguish neurogenic tumors from salivary gland lesions according to Tom et al. Glomus tumors prestyloid lesions displace the carotid posteriorly and carotid body tumors splay the internal and external carotid arteries.

Surgical Approaches
Historically, the transoral approach has been used to excise smaller PPS lesions, but this is no longer recommended due to the inadequate exposure afforded which led to a high rate of vascular injury, tumor spillage and local recurrence.

Therefore, according to Bass and Som there are four basic approaches to the parapharyngeal space including, (1) cervical or submandibular approach, (2) transparotid-cervical with or without angle mandibulotomy, (3) cervical-transpharyngeal with midline mandibulotomy, and (4) transmastoid-transcervical approach for jugular foramen lesions. The selection of approach is based on the need for exposure, the size of the lesion, and the nature of the lesion i.e. encapsulated vs. infiltrating, or benign vs. malignant.

The cervical or submandibular approach provides access to the parapharyngeal space through the submandibular space, and lesions arising from the minor salivary glands can be removed using this approach.

The transparotid-cervical approach provides exposure for facial nerve dissection. Performing a superficial parotidectomy and incising the stylomandibular ligament then allows for anterior dislocation of the mandible to provide adequate exposure to remove many parapharyngeal lesions, especially those originating from the deep lobe of the parotid. Access to large masses or lesions involving the carotid sheath near the skull base require mandibular osteotomy for greater exposure.

The cervical-transpharyngeal approach, also known as the "mandibular swing" utilizes midline mandibulotomy at the symphysis. Tracheotomy is mandatory in this procedure. With the hemimandible reflected laterally, wide exposure is afforded to approach extraparotid or post-styloid space lesions such as carotid space tumors. Although preoperative embolization has been advocated by some, but there are three reasons to question the efficacy or necessity of embolization for carotid body tumors. First, there are often multiple small feeding vessels; second, embolization precipitates an inflammatory response which makes subadventitial dissection more difficult; third, there is a risk of intracranial emboli.

The transmastoid-transcervical approach is used for proximal vagal lesions with both intracranial and extracranial components such as some glomus jugulare paragangliomas. Additional meddle cranial fossa or posterior fossa approaches may be required depending on the extent of intracranial disease.

Summary

In summary, the parapharyngeal space is best imaged with an MRI. Salivary gland tumors, schwannomas, paragangliomas, lymphomas, and metastatic SCCa may hide within the PPS. Angiography can be helpful in differentiating pre- from Post-styloid lesions. Open biopsy or excision through the mouth is not recommended. Choose your surgical approach based upon size and pre-post-styloid location, and not hesitate to divide the mandible if necessary.

A 49-year-old man presented with a sensation of fullness in the region of his left parotid gland and oropharynx. He was seen by a family physician one week prior to presentation and a mass was palpated near the tail of the parotid gland on the left. An MRI was obtained which demonstrated a dumbbell shaped tumor in the parapharyngeal space.

The patient denied any history of weight loss, fever, dysphagia, or chills and is a nonsmoker. His past medical history includes borderline glaucoma and nephrolithiasis. He had a tonsillectomy at age 12.

On physical examination the eyes, nose and ears appeared normal. There was a 4 cm x 6 cm submucosal mass protruding into the left oropharynx and a smaller mass near the parotid tail. The neck showed no lymphadenopathy or bruits. The remainder of the physical examination, including the cranial nerves, was unremarkable.

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