The parapharyngeal space is a potential space representing an inverted pyramidal shape with its base at skull base and apex at the greater cornu of hyoid bone. This space contains loose connective tissue, lymphatic vessels, lymph nodes and contents of the carotid sheath and is medially bound by the buccopharyngeal fascia covering the pharyngobasilar plane and the superior pharyngeal constrictor muscle and laterally by the ramus of the mandible and the medial pterygoid muscle.
This potential space is compartmentalized as prestyloid and poststyloid regions by thick fascial layers extending from the styloid process to the tensor veli palatine muscle, called as the tensor-vascular-styloid fascia, composed of the tensor veli palatine muscle itself, its fascia, the stylopharyngeal muscle and the styloglossus muscle. And, its these fascial layers that direct the tumor growth. [3
As the prestyloid compartment of this potential space consists of the retromandibular portion of the parotid gland, the lymph nodes of the parotid gland and adipose tissue, the poststyloid region consists of internal carotid artery, internal jugular vein, the 9th, 10th, 11th and 12th cranial nerves, the sympathic chain and the lymph nodes of the oral cavity, oropharynx, paranasal sinuses and the thyroid gland. While the most common lesion of the prestyloid space is the salivary gland neoplasms, especially pleomorphic adenoma of the parotid gland, the most common lesion of the poststyloid region is neurogenic lesions such as schwannomas and neurofibromas.
Primary tumors (benign or malignant), metastatic lymph nodes, lymph node involvement by lymphoproliferative diseases and tumors arising from adjacent sites that secondarily extend into the parapharyngeal space are the four different types of neoplastic lesions of the parapharyngeal space[2
The PPS tumors usually present as asymptomatic neck or parapharyngeal masses and they often discovered during routine physical examination. These tumors can also present with dysphia, dyspnea, obstructive sleep apnea syndrome, cranial nerve deficits, Horner syndrome (ptosis, miosis, anhydrosis), pain, hoarseness, dysarthria and trismus. Clinical detection of early PPS lesions is difficult since small tumors cause few symptoms. The tumors must reach to a size of at least 2,5 to 3,0 cm before a mass can be detected clinically [7
]. Also, when the PPS tumors cause a subtle fullness in the tonsillar region or in the soft palate they can be misdiagnosed as infections or tonsil tumors. In the presented case the neck mass was 4 × 4 cm in diameter, large enough to be noticed in the neck and in the oral cavity.
Initial evaluation of PPS masses should include a complete head and neck examination. Because the PPS lies deep to the muscle of mastication, the mandible, and the parotid glands, clinical examination remains difficult to assess accurately tumor presence and size. But a mass of considerable size -at least 3 cm- will cause a visible bulge or palpable abnormality of the lateral pharyngeal wall or external neck [8
]. For the evaluation of the parapharyngeal mass, CT scanning with contrast medium, MRI study with gadolinium, anjiography or MRI anjiography and laboratory studies for urinary vaniyll mandelic acid and metanephrine levels are useful diagnostic procedures and can give appropriate diagnosis up to 95% of the patients without tissue biopsy[1
]. And, for the first step diagnose, fine needle aspiration can be performed transorally, transservically or guided by CT or ultrasound.
Usually, the initial assessment of thyroid cancer is a palpable neck mass, an intrathyroidal tumor or a metastatic regional lymphadenopathy. However in some patients the tumor may be clinically occult and can be recognized at the time of surgery for benign thyroid disease. And, in approximately 5% to 14% of cases, the thyroid gland is clinically normal, and the first sign of disease is a solitary lateral neck mass [9
]. Less common presentations such as hoarseness, vocal cord paralysis, isolated cervical adenophaty, parapharyngeal masses, hemoptysis and pulmonary metastases, even in the face of clinically normal thyroid glands, have been reported and do engender diagnostic dilemmas [5
In this case presentation, although physical examination did not reveal the relation between the mass and the thyroid gland, the radiologic evaluations implicated that the tumor originated from the thyroid lobe and the superior thyroid artery was the main blood supply of this mass. Moreover follicular cells seen in the fine needle aspiration from the mass was highly suspicious for thyroid neoplasm.
As we mentioned above, tumors of the PPS are usually salivary gland in origin or derived from local neurogenous structures within the space [10
]. Other less common neoplasms include chordoma, lypoma, lymphoma, chemodectoma, rhabdomyoma, chondrosarcoma, desmoid tumor, dermois, ameloblastoma, amyloid tumor, ectomesenchyoma, fibrosarcoma and plasmocytoma [11
]. In this case the mass in the PPS was a primary follicular variant of thyroid papillary carcinoma. (The medline search did not reveal any cases with a primary tumor in PPS.) Although metastatic papillary carcinomas in the PPS were reported before, this case is the first as a primary thyroid neoplasm causing PPS mass symptoms, such as neck mass, hoarseness and dysphagia.
Surgery is the main treatment of the parapharyngeal space tumors. The surgent must be demiurge of the parapharyngeal space anatomy and must consider the size, the location of the mass, the relationship of the tumor to great vessels and the malignancy suspicion for determining the surgical approach for removing the mass[1
The surgical approaches can be classified as the transoral approach, the transcervical approach, the transparotid-transcervical approach, the transcervical-transmandibular approach and the infratemporal approach. [1
] The preferred approach for the removal of the tumor of this case presented here was transcervical approach because the surgent thought the mass originated from the thyroid gland, and this approach helped to remove the tumor easily. Moreover the elongation of the incision provided an extra exposure to remove the thyroid gland totally.
In this case report, thyroid tumor with the symptoms of parapharyngeal mass was presented to emphasize the importance of preoperative evaluation and selection of the appropriate approach for removal. Moreover, primary thyroid tumor should always be remembered in the differential diagnosis of parapharyngeal masses.