Caso Clínico

Secondary functional veloplasty: a non-obstructive approach to valopharyngeal insufficiency
Schwannoma parafaringeo: a propósito de un caso

I. Doménech Juan¹, A. Monner Dieguez², E. Cisa Lluís³, A. Marí Roig³, B. de Frías¹, R. Jiménez⁴

1 Médico Residente del Servicio de Otorrinolaringología.
2 Jefe de Sección del Servicio de Cirugía Maxilofacial.
3 Médico Adjunto del Servicio de Cirugía Maxilofacial.
4 Jefe del Servicio de Otorrinolaringología.
Hospital Universitario de Belvitge. Barcelona.

Correspondencia:
Ivan Domenech Juan.
c/ Ibería nº 11 3-2ª
08014 Barcelona

Introduction

Tumors of the parapharyngeal space are a rare occurrence, representing around 0.5% of all of the oncological pathology relating to the head and neck. These tumors generally affect adults, they occur equally between the sexes, and the majority are benign.¹

Schwannomas are the second most common tumor in this space. Although the majority of the tumors are located in the head and neck, those having an extracranial location account for only 10% of the total, hence their rare occurrence.

Clinical case

A female patient, aged 45, was referred to the Service of Maxillofacial Surgery with a 6-month history of tumefaction in the right parotid area. On exploration, a tumor was observed in the right parotid region, which was hard, painless and which also protruded at the oropharyngeal level, displacing the tonsils and the pharyngeal wall medially.

As a process of parapharyngeal expansion was suspected, a Computed Tomography (CT) scan was carried out which showed the expansion process within the parapharyngeal space, with limited contrast and cystic component suggesting a neurogenic tumor extending to the pterygoid muscles on the right side which was displacing the light in the oropharynx medially and the parotid gland laterally. (Figs. 1,2,3).

Once a vascular source had been ruled out, a FNA was carried out which proved inconclusive, and a decision was made to perform a transoral incisional biopsy which suggested a schwannoma.

As the diagnosis was likely to be neurinoma of the parapharyngeal space, an excision using a cervicalparotid approach was decided upon, and a surgical specimen measuring 5 x 5.5 x 3.5 cm was obtained. It was encapsulated, of elastic consistency, and following histological examination proved to be a schwannoma of the parapharyngeal space.

Discussion

The parapharyngeal space can be described as an inverted pyramid with its floor on the small portion of temporal bone near the petrosphenoid suture, and its tip at the greater horn of the hyoid bone. The medial wall is formed cranially by the pharyngobasilar fascia and caudally by the constrictor muscle of the pharynx, while the lateral wall is made up of the fascia of the internal pterygoid muscle, deep lobe of the parotid [gland] and ascending branch of the inferior maxilla. Anteriorly the limit is the pterygomandibular raphe and the medial pterygoid fascia, the posterior limit being the paravertebral muscles and prevertebral fascia.² Within the parapharyngeal space there is the prestyloid compartment that contains fat and part of the deep lobe of the parotid [gland], and the retrostyloid [compartment] which contains the internal carotid artery, the internal jugular vein, cranial [nerve] pairs, and the cervical sympathetic [chain].

The tumors in the prestyloid compartment will therefore be lipomas and glandular tumors and those of the retrostyloid [compartment] will be schwannomas and paragangliomas.

Salivary tumors of the parotid gland are the most frequent in this area and account for approximately 50% of tumors, after neurogenic tumors that account for around 30%, the rest being miscellaneous. The most frequent neurogenic tumors are the schwannomas or neurilemomas, followed by chemodectomas and then the neurofibromas. They appear at any age, mostly between the 3rd and 5th decade, but more frequently in females with a 3:1 ratio. The majority originate in the vagus nerve, and the schwannoma of the vagus nerve represents the most frequent tumor in the retrostyloid space. They also exist in the cervical sympathetic chain, the glossopharyngeal*[ nerve], the hypoglossal [nerve] etc.^3,4 There are also cases of patients with multiple neurinomas in the parapharyngeal area, or neurinomas associated with other areas.^5,6 The most frequent clinical [manifestation] is the sensation of a foreign body in the pharynx, and the most frequent sign is a protrusion at the pharyngeal level, as this is the area with least resistance.^7,8 Dysphagia may also occur, sensation of a foreign body, and hot potato voice. Serous otitis may even occur if there is cranial expansion. The symptoms produced by the compression of the pairs of cranial nerves IX, X, XI, XII of the sympathetic [chain] appear in cases of large neurinomas, or in malignant tumors and chemodectomas. Pain, trismus and lesions in pairs of cranial [nerves] suggest malignancy.^9,10

The diagnosis depends on clinical [evaluation] and physical exploration. Bimanual palpation is important as it permits identifying the origin and continuity of the tumor.

Radiological studies by means of a Computed Tomography (CT) and Magnetic Resonance (MRI) is of vital importance, and should sometimes be backed-up with angioradiology in cases of hypervascular tumors. The tumors will appear on the CT scan to have a density similar to that of muscle. They have a more or less+ rounded contour, they are well defined, with a medial and lateral fat plane. As they commonly originate in the X pair [of nerves] or in the sympathetic chain, the internal carotid artery tends to be displaced anteromedially. RMI provides excellent information regarding soft tissue, and it is very useful for these types of tumors and for this region. The tumors have a low signal intensity on T1 and a high signal intensity on T2 and on T1 with gadolinium.⁴

Macroscopical examination tends to reveal whitish/yellowish tumor which is well defined with a firm, elastic consistency, and with cystic areas on occasions.⁴

From a microscopical point of view, there are two groups: Antoni A with an elongated, densely packed cellular composition, and Antoni B which is loosely structured with typical myxoid degeneration, although in most cases they appear together.¹¹

Treatment is surgical, although due to the infrequent presentation of theses tumors in this area, gaining surgical experience is difficult. There are various methods of approach, which depend on tumor size and localization. The cervical approach is the most common,^8,11 as it is adequate for most tumors. For larger tumors, or tumors of the prestyloid area, the cervical-parotid approach can be useful.¹² In tumors located in the deep lobe of the parotid [gland] a transparotid approach can be used, while the transmandibular approach should be reserved for large or malignant tumors. The transoral approach should be used only in specific cases as it carries the risk of vascular lesions, partial excision, infection, and for most authors it is not felt to be the most appropriate. ^8,12,13 Damage to the nerve itself, and the resulting deficit, is the most frequent complication in surgery. Recurrence is rare and is usually due to an incomplete excision and, in general, the postsurgical prognosis is good.

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