|Vol. 2, Issue 2, Article 3||Edelstein, et al.|
The supraglottic submucosal lesions can be categorized into lesions that arise in the submucosal layers, lesions that arise within the pre-epiglottic and paraglottic spaces, and lesions that arise in, or primarily involve, the outer cartilage skeleton.
These lesions arise from the mesenchymal elements present within the pre-epiglottic and paraglottic regions.
Neurogenic tumors of the larynx are rare and either occur as an isolated schwannoma, neurofibroma, or plexiform neurofibroma. Virtually all benign neurogenic laryngeal tumors arise in the supraglottic larynx, with the true vocal cord being a rare site. Regardless of site, they are all submucosal in location (11). Despite a 22% rate of head and neck involvement in NF1, the larynx is rarely involved. However, most laryngeal neurofibromas occur in NF1 patients. These non-plexiform types are well-localised and encapsulated (Fig.5), in contrast to the plexiform lesions which are diffuse, poorly demarcated, infiltrative, and almost impossible to completely excise (10, 12). They can be multiple and involve the adjacent cervical esophagus (10, 12, 13). The diagnosis of a malignant neurosarcoma is almost always histologic, as these tumors usually have similar imaging findings to their benign counterparts (Fig.6).
Characteristically neurofibromas do not enhance as strongly as schwannomas, which have a denser stroma. Compared to schwannomas, neurofibromas tend to have fewer areas of cystic degeneration, but greater regions of fatty degeneration (10, 11). If occurring in an NF2 patient, onset is usually earlier than in solitary lesions (14).
Hemangiomas of the larynx occur in one of two types: an infantile type that affects the subglottic airway, presenting as airway obstruction within 6 months of birth, and an adult type (now referred to as a vascular malformation) which most commonly occurs in the supraglottic larynx, although an occasional glottic lesion has been reported (15). On imaging, these lesions may have rapid intense, delayed, or minimal contrast enhancement (Fig.7), as they may have very slow flow despite their highly vascular nature. They tend to be well delineated, submucosal masses. If the endoscopic diagnosis of an hemangioma is suspected and the CT or MR imaging findings are not specific, a 99mTc-labelled red blood cell SPECT scan can be performed. This shows delayed pooling of labelled RBC's over 1-3 hours.
The larynx normally contains two matched sets of paraganglia, which are presumably the site of origin for true laryngeal paragangliomas. Laryngeal paragangliomas tend to occur in the lower, ventral supraglottic larynx and although infrequent, these lesions tend to be more often malignant than those paragangliomas occurring elsewhere (16). They are submucosal soft tissue lesions that usually have significant enhancement, although this may be variable depending on scan delay time (Fig.8). On MR imaging, paragangliomas have high signal intensity on T2-weighted images and may show a characteristic "salt and pepper" appearance and flow voids.
Primary laryngeal lymphoma is extremely uncommon, comprising less than 1.5% of all laryngeal tumors. Almost all are of the non-Hodgkins type and mostly of B-cell origin. They are radiosensitive and have a relatively good prognosis. The vast majority arise in the supraglottic larynx, especially the epiglottis and aryepiglottic folds, presumably deriving from the mucosa-associated lymphoid tissues (MALT) of the lamina propria (17).
On CT, they have a soft tissue density, are submucosal, and homogeneously enhance (Fig.9). On MR imaging, they have tend to have a homogeneous appearance, an intermediate T1-weighted signal intensity and a lower T2-weighted signal intensity. The lesions show moderate enhancement (17). These lesions are indistinguishable on imaging from the rare inflammatory pseudotumor that can occur within the larynx (Fig.10).
Of the numerous granulomatous diseases that affect the larynx, sarcoidosis is one of the more common found in North America. Sarcoidosis affecting the head and neck occurs in approximately 10% of patients with systemic disease, but only 6% of those patients with head and neck disease develop laryngeal sarcoidosis. There are non-specific presenting symptoms and upper airway sarcoidosis is asymptomatic in about 20% of cases (18). Notably, a significant percentage of patients presenting with laryngeal sarcoidosis show no evidence of generalized disease (19). The supraglottic larynx is mainly affected, with epiglottic and aryepiglottic fold enlargement (Fig.11). Disease affecting the true vocal cords and subglottic larynx, with resultant laryngeal and tracheal stenosis, is far less common. As opposed to this "edematous type" of supraglottic involvement, a rarer "polypoid type" has also been described, where the lesion is pedunculated (Fig.11C)(19). On imaging, these are homogeneous, submucosal infiltrative lesions, that are similar in appearance to lymphomas.
Wegener's granulomatosis is a necrotizing granulomatous vasculitis that usually affects the upper and lower respiratory tracts and causes a renal glomerulonephritis. The larynx is rarely the only affected site, however, when the larynx is involved, submucosal granulomas cause a diffuse or nodular submucosal mass that is indistinguishable from sarcoidosis or amyloidosis (Fig.12).
Amyloid comprises a family of different types of extracellular, fibrillar protein deposits. Although amyloidosis usually affects the larynx as a solitary (primary) lesion, it may be part of a generalized systemic disease, derived from either familial amyloidosis, a primary disorder, or secondary amyloidosis, which is secondary to another underlying disease or tumor proliferation (6). Approximately 9-15% of amyloidosis cases are localized, with the larynx being the most commonly affected site in the respiratory tract (20). Nevertheless, laryngeal amyloid deposits are rare, accounting for only 0.2% - 1.2% of benign tumors of the larynx . The deposits are usually of the localized type, but may be diffusely infiltrative, involving any level of the larynx (Fig.13) (20). When laryngeal amyloid, particularly the nodular type, occurs in the ventricle, it has been associated with laryngocele (20).
On MR imaging, the amyloid deposits characteristically have signal intensities similar to those of skeletal muscle (Fig.14). Thus, they have low-to-intermediate T1-weighted and low T2-weighted signal intensities (6). The CT findings can be mistaken for a submucosal tumor, with amyloid deposits producing submucosal nodules or thickened areas that may occasionally calcify (10).
Obstruction of the minor salivary glands just deep to the mucosa of the upper airway may cause a cyst to form. These cysts have a tendency to arise in the hypopharynx (especially the valleculae) and the supraglottic larynx. Being near the surface, they usually can be clinically distinguished from other submucosal lesions (Fig.15).
A laryngocele is one of the most frequently found submucosal, supraglottic laryngeal lesions (6). A simple internal laryngocele is an uncomplicated air filled dilation of the normal laryngeal appendix such that it causes a submucosal supraglottic mass. As the normal ventricular appendix may be routinely seen on axial imaging, it should only be termed a laryngocele if it causes a deformity of the supraglottic airway (10). If this laryngocele enlarges sufficiently, it can prolapse laterally through the thyrohyoid membrane to present clinically as a mass in the lateral neck. Once in the lateral neck, the paraglottic component may collapse. Such a laryngocele is often referred to as an external laryngocele, although a more proper term is a mixed or combined laryngocele (10, 21). A laryngeal mucocele or saccular cyst refers to a laryngocele that is filled with secretions secondary to an obstruction of the normal outlet of the laryngeal appendix in the laryngeal ventricle. Although this obstruction is usually secondary to local inflammation, a tumor in the laryngeal ventricle may present clinically as a saccular cyst (6, 7). If this cyst becomes infected, it is referred to as a laryngopyocele which due to its size and inflammation may cause airway compromise.
A saccular cyst may also occur following laryngeal surgery, presumably related to scarring at the saccular orifice. The risk of developing such an iatrogenic laryngocele is approximately 2% and thus a submucosal mass arising after a partial laryngectomy does not necessarily indicate disease recurrence (22).
On imaging, an internal laryngolcele is seen as a submucosal, paraglottic space, air-filled sac that causes an inward bulge of the supraglottic mucosa towards the airway. An external laryngocele extends through the thyrohyoid membrane into the lateral neck (Fig.16A). If this lesion is filled with "mucoid" attenuation material, it is a saccular cyst (Fig. 16B) and if there is contrast enhancement of the wall of the cyst, it is a laryngopyocele.
|Fig. 16A||Fig. 16B|
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