Location and Components
The parapharyngeal space is located in the neck below the skull and goes down to a small bone in the neck called the hyoid (Fig. 1 Parapharyngeal Space). It is well hidden behind the jaw on the side of the face. There are many important structures in this location including:
- Carotid artery
- Internal jugular vein
- Vagus nerve
- Sympathetic chain
- Glossopharyngeal nerve
- Parotid gland (Large salivary gland)
- Minor salivary glands
- Lymph nodes
- Other smaller nerves and blood vessels
Fig. 2 Parapharyngeal Space
Types of Tumors
Tumors of the parapharyngeal space are uncommon tumors as they are less than 1% of all tumors in the head and neck. Fortunately, 70-80% of these are benign while the remainders are malignant. Tumors arise from the structures that compose the parapharyngeal space as previously mentioned. In general, tumors are divided into tumors originating from the salivary glands or from nerves or neurologic structures.
Salivary gland tumors
The parotid gland is separated into a superficial and deep lobe. The deep lobe of the parotid gland presides in the parapharyngeal space and is the origin of the vast majority of salivary tumors in this location. 80% of these tumors are benign, and the most common is a pleomorphic adenoma. Other common benign tumors of the parotid gland are Warthins tumors and monomorphic adenomas. Common malignant tumors of the deep lobe of the parotid gland are mucoepidermiod carcinomas, acinic carcinimoas, adenocarcinomas, and adenoid cystic carcinomas. The behavior of the malignant lesions in the salivary glands are widely different thereby effecting their prognosis.
Treatment is usually surgical due to the fact that these tumors tend to continue to grow in this confined space and put pressure on the surrounding nerves. Additionally, the benign tumor pleomorphic adenoma has a potential of becoming cancerous, which is another reason to proceed with surgery.
There are a variety of benign neurogenic tumors in the parapharyngeal space. Most common is a neurilemomas, also called a schawnomma. These tumors arise from the cells that support, insulate and cover the nerves called schawn cells. These slowly growing surround the associate nerve but do not invade it or compromise its function. They can arise on any nerve in the parapharyngeal space but the vagus nerve followed by the sympathetic chain are commonly involved. Paragangliomas, another type of neurogenic tumor, arising from the specialized sensors. These tumors are benign in a majority of cases. These tumors can be hereditary or can happen at random. There is a slight chance that they may produce hormones or that there maybe several of these tumors in the body. Both of these possibilities must be explored.
Treatment for both types of tumor is surgical. However, the choice to proceed with surgery is based on size, location, state of health of the patient and rate of growth. Radiation has shown promise in terms of not allowing these tumors to grow but does not completely rid the patient of the tumor.
Diagnosis & Surgery
The diagnosis is usually made based on MRI studies, which are very good at distinguishing between the different tumor types (Fig. 3 CT Scan ). If imaging studies are not helpful, then an image guided (CT guided) needle biopsy is done.
At the Center, we routinely use the trans-cervical approach which is more then adequate in the majority of cases. This technique allows good visualization and identification of the important neck structures including nerves, vessels, throat muscles, glands, etc…. If this appraoch is not adequae, then a mandibular distraction or a mandibulotomy is perfomed to increase access (this is very rarely done).
Fig. 4 Neck Incision
Risks of Surgery
The risks of the surgery have to do with the extent of tumor and which structures the tumor involves. They can include:
- Swallowing Difficulty
- Facial Weakness
- Droopy Eye
- First Bite Syndrome
The recovery generally is very quick and patients tend to resume normal function within a week. The side effect profile is carefully investigated and discussed with the patient prior to surgery and can be understood by size and type of tumor present usually.