Two different types of neurogenic tumors of the larynx have been described: Schwannomas and neurofibromas. Both entities are rare and comprise only about 0.1% to 1.5% of all benign laryngeal tumors [4]. Neurofibromas are encountered more frequently in Neurofibromatosis. Malignant transformation is reported in 10% of neurofibromas while in schwannoma it is very uncommon [2]. Neurogenic tumors of the larynx are most frequently located in the aryepiglottic fold or in the true or false vocal cords [5–7].
The clinical symptoms of the disease are those usually associated with a slow growing lesion of the larynx: Over a period of years the patient gradually develops hoarseness, globus sensation, dysphagia, dyspnoea on exertion with inspiratory, sometimes biphasic stridor [2, 6]. Some patients complain about dyspnoea in the supine position which seems to be associated with the location of the lesion [6, 10]. One case of asphyxial death due to laryngeal schwannoma is reported [10].
The true vocal cord on the affected side is usually immobile or hypomobile [6, 11, 12], although some authors report normal mobility [9, 13]. In many cases, such as in our reported case, the bulgy supraglottic tumor obstructs the view of the true vocal cord [14, 15]. Also, the mass effect of a large tumor can mimic fixation of the cricoaritenoid joint ("pseudo-fixation") [6].
The diagnostic workup should include indirect and fiberoptic laryngoscopy which usually reveals a submucosal mass in the described location. Such a lesion coupled with impaired vocal cord mobility should draw attention towards a neurogenic tumor.
In CT scans of the disease, most authors describe a well defined, hypodense submucosal mass without signs of infiltrative or destructive growth [11, 16–19]. Many authors describe a heterogeneous contrast enhancement [6, 9, 12, 14, 17, 19, 20].
On MRI scanning, the lesion is expected isointense to slightly hyperintense in T1-weighted images with strong, inhomogeneous enhancement of Gadolinium, in T2 the lesion is hyperintense [11, 12, 17, 18, 21].
The differential diagnoses of neurogenic tumors of the larynx include chondroma and adenoma [21]. Also laryngeal cyst and internal laryngocele should be taken into consideration [6].
A definite diagnosis can only be made histologically. Schwannomas almost exclusively are comprised of spindle cells with long, oval nuclei and indistinct cell membranes. These Schwann cells either form cellular regions with compact cell bundles with nuclei lining up in palisades (Antoni A regions) or edematous regions with loosely arranged cells in a myxoid matrix prone to degeneration (Antoni B regions) [2, 6]. Two compact rows of well aligned nuclei separated by fibrillary cell processes are called Verocay bodies. Axons are usually not found in Schwannomas [6]. A clear capsule, the presence of Antoni A and/or Antoni B areas, and intense immunoreactivity for S-100 protein are criteria for the histologic diagnosis of Schwannoma [2, 6].
Neurofibromas like Schwannomas exhibit an abnormal proliferation of Schwann cells. However, while Schwannomas emanate from Schwann cells, neurofibromas emanate from perineural fibrocytes. They are not encapsulated and comprise a variety of cell types: elongated spindled Schwann cells interwoven with axons and collagen fibers [4, 6, 22]. Thus an important feature of neurofibroma is entwining of the tumor with the parental nerve fascicles while Schwannoma grows extrinsic to the nerve fibers [6].
The surgical separation of the tumor from the nerve is theoretically possible in Schwannoma, whilst in neurofibroma it is impossible [4].
The only effective therapeutic option in benign neurogenic laryngeal tumors is complete resection. Since the diagnosis can only be made histologically, direct laryngoscopy with biopsy of the lesion will usually be the first step in treatment [6, 13, 18, 23]. However, in Schwannoma biopsy can be difficult due to the solid capsule of the tumor [6, 23]. Complete surgical excision of the tumor should be planned according to the individual requirements of each case. Most authors favor external approaches with alternative airway provisions such as a preliminary tracheotomy in larger tumors. Median or lateral thyrotomy or median or lateral pharyngotomy are recommended [2, 9, 11, 12, 14, 16, 24]. In smaller tumors, endoscopic (laser-assisted) resection of the tumor can be a reasonable treatment option [2, 13, 18]. Independent of the approach, restoration of the vocal cord mobility is possible even if it was immobile prior to surgery [12, 13, 17].
In some cases including ours, rapid regrowth after incomplete resection of laryngeal schwannomas has been described [6].
At least one case has been reported where histologically verified laryngeal schwannoma revealed an unknown Neurofibromatosis type II [17]. Thus, if histology points towards neurofibroma but also in Schwannoma, neurofibromatosis should be considered and physical examination should rule out café au lait spots and further neurinomas. Also, MRI should rule out neurinomas of the cranial nerves and spinal cord [17–19].
An association of benign solitary schwannomas with malignant tumors (especially skin and breast cancer) has been reported [25]. Dermatological and when appropriate gynecologic consultations should be considered.
