A 75-year-old Taiwanese man presented with recurrent epistaxis, rhinorrhea, chronic cough with blood-tinged sputum. He was a heavy smoker with the consumption of 30 cigarettes per day for 50 years. Nasopharyngoscopic examination revealed several brown nodules near the opening of right Eustachian tube, which was tentatively diagnosed as nevus or melanoma. The overlying mucosa was intact (Figure 1). The lesion was biopsied for histological examination. Microscopically, nodules of oncocytic glands composed of plump epithelial cells with voluminous oncocytic cytoplasm were noted adjacent to seromucinous glands normally seen in the nasopharynx (Figure 2A and B). Dense lymphoplasmacytic infiltrates were present in the background (Figure 2C). Finely granular, brown pigments were evenly distributed in the cytoplasm of the oncocytic glandular cells (Figure 2D). The brown pigments were demonstrated to be melanin based on staining which was positive for Fontana-Masson (Figure 3A) and negative for Prussian blue. Immunohistochemically, the melanocytes and their dendritic processes were highlighted by S100 and Melan-A (Figure 3B) in the lesion, but negative for HMB-45. After diagnosis, the patient was followed by nasopharyngoscopic examination after 2 years and revealed no change in size of the lesion with uneventful clinical course.
Figure 1. Nasopharyngoscopic evaluation showing multiple brown discolorations near the opening of right Eustachian tube.
Figure 2. A, Low-power view showing nodular distribution of melanotic oncocytic metaplasia. Hematoxylin and eosin (H&E) staining, magnification ×40. B, Note melanotic oncocytic metaplasia near the seromucinous gland; H&E, magnification ×200. C, Numerous lymphocytes present in the background of metaplastic glands; H&E, magnification ×200. D, High-power view demonstrating many finely granular brown pigments in the cytoplasm of oncocytic cells; H&E, magnification ×400.
Figure 3. A, The melanin pigments positive for Fontana-Masson staining. Magnification ×400. B, Melanocytes and their dendritic processes highlighted by Melan-A; immunohistochemical staining, magnification ×400.
Melanotic oncocytic metaplasia (MOM) of the nasopharynx is an extremely rare lesion first described as a benign, brown nodular lesion near the Eustachian tube opening by Shek et al from Hong Kong in 1995.1 Later on, the lesion was reported in Japan, Korea, Taiwan, and China.1-15 The exceptional geographical distribution of MOM may link its occurrence to genetic predisposition in East and Southeast Asia. Of all the literatures, 7 (46.7%) reports were from Japan, followed by Taiwan (20.0%) and China (13.3%). Sakaki et al9 reported the largest case series, which included 7 patients. To date, only 27 cases have been reported in English literature. Patient age ranges from 51 to 80 years, with a mean of 67.5 ± 7.6 years. There is male predominance, with a male to female ratio of 8:1. All the patients are from East and Southeast Asia, including Japan, China, Taiwan, Korea, and Hong Kong.
Melanotic oncocytic metaplasias are dark brown or black, irregular in shape and pigmentation. Half of the clinicians (n = 14; 50.0%) had a tentative diagnosis of malignancy, either a melanoma or a carcinoma. Melanotic oncocytic metaplasia typically occurs in the nasopharynx or near the opening of Eustachian tube (n = 21; 75.0%), but may also found in torus tubarius (n = 7; 25.0%), nasal cavity (n = 2; 7.1%), and soft palate (n = 1; 3.6%). The majority of the lesions are multiple (n = 17; 60.7%) with unilateral distribution (n = 22; 78.6%). It is reported to be an incidental finding in 6 (21.4%) patients, and others reported symptoms of epistasis, nasal congestion or rhinorrhea (n = 8; 28.6%), hoarseness (n = 4; 14.3%), or discomfort of the throat (n = 3; 10.7%). Among those with known smoking histories, most patients (11 [91.7%] of 12) reported the duration of smoking more than 40 years. All these cases had stationary clinical course, without the evidence of progression or any concurrent melanoma.
The exact pathogenesis of MOM is unknown. Sakaki et al raised a hypothesis that tobacco use may be a predisposing factor.9 This hypothesis is supported by the fact that the majority of the patients reported a long-term tobacco use for more than 40 years. These morphologic appearances are similar to a miniature of Warthin tumor (adenolymphoma) of parotid glands, in which the tumor cells showed lymphocytic reaction to proliferating oncocytic cells.16 Oncocytic metaplasia of the nasopharynx and Warthin tumor of the parotid gland share several common features, including being circumscribed lesions, showing lymphocytic stroma intimately associated with oncocytic epithelium, occurring in the elderly population, following a benign course, and association with cigarette smoking.17
Microscopically, MOM is probably a metaplastic change of seromucinous glands lying directly under the unremarkable mucous membrane of the nasopharynx.1 The cells are characterized by basally located nuclei, voluminous oncocytic cytoplasm with coexisting granular melanin pigments. The melanocytes with their dendritic process could be highlighted by immunohistochemical staining of S-100 and melan-A.10 These melanocytes might be responsible for the production of melanin granules, which are passed to the adjacent seromucinous glands. The cytoplasmic brown pigments are proved to be melanin by positive Fontana-Masson staining and negative iron staining.
Since MOM is a benign pigmentation of nasopharynx, conservative management with periodic follow-up is suggested. The inflammatory process of nasopharynx may be alleviated through smoking cessation, although there is no tangible evidence to support the hypothesis. To date, concurrence or subsequent development of malignant neoplasms has not been reported in patients with MOM.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
The author(s) received no financial support for the research, authorship, and/or publication of this article.
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