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1 All authors: Department of Radiology, Division of Neuroradiology, University of Michigan Health Systems, 1500 E Medical Center Dr., Ann Arbor, MI 48109-0030.
Received October 16, 2007;
accepted after revision January 30, 2008.
Address correspondence to L. Ash
(lorash{at}umich.edu).
Keywords: laryngeal neoplasms • larynx • schwannoma
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Case History
A 65-year-old woman was referred from an outside hospital for
interarytenoid swelling seen on neck CT that was performed as part of a workup
for several years of hoarseness and dysphagia. On direct endoscopic
examination, a pale mucosal swelling was seen localized to the interarytenoid
area in the posterior glottis with telangiectatic vessels. Biopsy of the
lesion in the past had been negative for neoplasm and yielded only
inflammatory changes.
CT and MRI
MRI shows a T2 hyperintense, avidly enhancing polypoid submucosal mass in
the posterior interarytenoid region measuring 2.0 x 1.2 cm, with no
clear invasion of the posterior pharyngeal wall (Figs.
1A,
1B,
1C). CT of the neck performed
to define the relationship of the mass to adjacent bone and cartilaginous
structures (initial CT images from the outside institution were not available)
localizes the mass to the posterior commissure at the level of the arytenoids,
protruding into the posterior mucosal space. The mass shows avid,
heterogeneous enhancement and central low attenuation (Figs.
1D and
1E). No laryngeal cartilage
lysis or sclerosis is seen, nor any radiographically enlarged cervical lymph
nodes.
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In certain instances, it may be difficult to decide on initial imaging whether the lesion is mucosal or submucosal, especially when the lesion is large. In our case, two things helped us decide that the lesion was probably submucosal: Clinical examination showed only a pale mucosal swelling with overlying telangiectatic vessels, and the mass was in a posterior location with its epicenter between the arytenoid cartilages (mucosal lesions are typically anterior or paramedian).
Once a lesion is localized to the submucosal space, it should be kept in mind that submucosal lesions are most often malignant with SCC, constituting more than 50% of the lesions, as shown in two studies [1, 3]. Imaging alone cannot absolutely differentiate benign from malignant lesions. As a consequence, SCC should be kept in the differential diagnosis in this patient, although the mass has no imaging characteristics to suggest a malignant, aggressive process. Imaging findings favoring malignancy include lysis or sclerosis of the laryngeal cartilage, adenopathy, and the multifocality or infiltrating characteristics of the lesion [1, 2]. Other malignant considerations include adenoid cystic carcinoma (most commonly subglottic with cartilaginous lysis) and non-Hodgkin's lymphoma, which may be multifocal [4, 5]. Primary laryngeal lymphoma is extremely rare, likely developing in the lymphoid collections of the supraglottic lamina propria and laryngeal ventricles [5]. Fibrosarcoma, rhabdomyosarcoma, leiomyosarcoma, and angiosarcoma are rare in the head and neck and most often present as large, diffusely infiltrative supraglottic masses [1, 6–9]. Calcification in a mass or involvement of the laryngeal cartilage would also favor a chondrosarcoma or chondroma, although a single case of calcification in a degenerating laryngeal schwannoma has been reported [10, 11].
Benign submucosal laryngeal processes include laryngocele, amyloidosis, paraganglioma, papilloma, inflammation, certain myogenic tumors such as rhabdomyomas and leiomyomas, and nerve sheath tumors. Quite often, the imaging appearance of submucosal lesions is nonspecific; the radiologist should then carefully assess for the presence of air in the lesion, which can help narrow the differential diagnosis to a laryngocele. In one study, laryngocele was the most common benign submucosal entity, filled with either air or fluid [1]. In some cases, differentiating a small tumor from an inflamed laryngocele can be difficult; it should be kept in mind that laryngoceles can be associated with a malignant neoplasm [1, 6]. Interestingly, focal amyloid deposits can appear similar to high-density fluid-filled laryngoceles on CT [1, 12, 13]. In the present case, the lesion is posterior (in contrast to laryngoceles, which are paramedian) with no air showing within, suggesting a low likelihood of laryngocele.
Given the avid enhancement of the mass, one of the benign differential considerations is a paraganglioma. However, these typically have a supraglottic or paraglottic location, and in cases of diagnostic dilemma, a 111In pentetreotide nuclear medicine study can differentiate this from other benign laryngeal lesions [14–16]. A solitary polypoid mass of the airway in a middle-aged patient should also bring to mind a papilloma. However, when they involve the larynx, solitary papillomas are most often found along the anterior margins of the true vocal cords [17–19]. Because the patient had undergone prior biopsies revealing only inflammatory change, an inflammatory process such as relapsing polychondritis should also be considered, although this typically presents as diffuse mucosal thickening adjacent to cartilaginous structures rather than as a submucosal mass [20].
Rheumatoid arthritis is another inflammatory process that can involve the larynx; it is characterized infrequently by submucosal nodules of the true vocal cords as well as more commonly described erosive changes of the cricoarytenoid and cricothyroid joints [16, 21]. Cases of laryngeal tuberculosis involving the submucosa have also been reported, but those cases typically cause diffuse bilateral thickening of the vocal cords and diffuse thickening and increased density of the aryepiglottic folds and paralaryngeal tissues [1, 22, 23].
Schwannoma should always be considered in the case of a well-defined submucosal laryngeal mass to avoid nerve damage during surgical excision [1]. Typical imaging findings of laryngeal schwannomas include a well-defined margin with homogeneous or heterogeneous enhancement; larger lesions more often enhance heterogeneously. Areas of low attenuation on CT can be seen with corresponding T2 hyperintensity, which may appear cystic or even necrotic. It is theorized that these areas correlate to loose myxoid and edematous Antoni B areas in contradistinction to the compact spindle cells seen in Antoni A areas [24]. In our patient, the mass does show a small area of central low attenuation on CT (Fig. 1D). On MRI, schwannomas have low or isointense signal intensity on T1-weighted images compared with adjacent musculature and hyperintensity on T2-weighted images [24]. Avid gadolinium enhancement is common [24].
To summarize, this laryngeal mass is posterior, well-defined, submucosal, and avidly enhancing, and it does not invade adjacent structures. My differential diagnoses would be schwannoma, paraganglioma, and SCC.
Diagnosis and Patient Management
The patient underwent microdirect laryngoscopy with biopsy and laser
excision of the submucosal mass involving the posterior commissure. Although
initial frozen sections yielded only reactive fibrovascular stroma, the
permanent pathologic sections revealed the mass to be a schwannoma.
Commentary
Schwannomas of the head and neck are uncommon tumors that are typically
located in the parapharyngeal space
[25]. Those affecting the
laryngeal nerve are rare and most often arise in the supraglottic space along
the internal branch of the superior laryngeal nerve after penetrating the
thyrohyoid membrane [26]. The
aryepiglottic fold is the most common anatomic site for a schwannoma; the
arytenoids, ventricular folds, and true vocal cords are involved less
frequently [24,
27–29].
To our knowledge, this is the first report of a laryngeal schwannoma involving
the posterior commissure.
Symptomatic patients with laryngeal schwannomas may present clinically with odynophagia, dysphagia, stridor, dyspnea, globus sensation, and hoarseness of voice; the latter two are the most common [3, 25, 30]. Symptoms causing dyspnea may require urgent resection; at least one case of asphyxial death secondary to a laryngeal schwannoma has been reported [3].
Surgical excision is the treatment of choice for laryngeal schwannomas. For smaller tumors, an endoscopic technique is preferred to because of the lower incidence of postoperative nerve palsy. Complete removal can be difficult endoscopically, and tumor recurrence is a possibility [25, 29]. To avoid tumor recurrence, an external approach such as lateral thyrotomy is undertaken with large tumors, but places the recurrent laryngeal nerve at higher risk for injury [31]. Six weeks after endoscopic resection of the laryngeal schwannoma, the patient had improvement of her original symptoms. However, two 4-mm polypoid lesions were visualized on fiberoptic examination at the posterior interarytenoid space. She will require close follow-up in the future to determine whether those changes reflect residual areas of schwannoma, which might require further treatment orpostsurgical granulation material.
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