Melanocytic Nevus
Quick Summary Introduction References Photos		Clinical Features Histopathology Treatment Prognosis
Blue nevus of the hard palate (courtesy, Dr. Kabani, Boston University)

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Introduction

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The oral mucosa is a rare location for the presentation of the melanocytic nevus (pigmented nevus, nevocellular nevus; mole), the benign proliferation of nevus cells within subepithelial stroma. All cutaneous subtypes have been reported on the oral mucosa, including congenital nevus, blue nevus, Spitz nevus and halo nevus, but the great majority of identified cases are the intradermal nevus, usually referred to as intramucosal nevus. As with skin lesions, the oral nevus is considered to be a developmental anomaly or hamartoma of nevus cells (nevocytes) rather than a true neoplasm. Although rare in the mouth, the cutaneous melanocytic nevus is probably the most common of all human tumors, with white adults averaging 10-40 nevi each.  The nevus of the oral mucosa, however, is much less common, occurring in only 1/2,000 adults (Table 1).

Clinical Features

The cutaneous melanocytic nevus is first seen during childhood and most lesions are present before 35 years of age; most oral examples are biopsied during the young adult or middle-age years. While there is no gender bias for cutaneous lesions, 2/3 of oral nevi are found in females.

The intraoral nevus is usually an intramucosal (submucosal?) nevus. It has an appearance similar to its cutaneous counterpart but usually lacks the papillary surface change and has a greater tendency to be non-pigmented. The lesion is usually 4-6 mm. in greatest diameter and the most common sites of oral involvement are the hard palate, buccal mucosa, and gingiva.

Both types of blue nevus (dermal melanocytoma, Jadassohn-Tieche nevus) are found in the mouth. The common blue nevus is the second most common benign melanocytic proliferation encountered in the mouth, usually seen in females in their fourth decade of life. Typically found on the hard or soft palate, it presents as a macular or dome-shaped, blue or blue-black lesion less than 1 cm. in diameter (Figure 5). The cellular blue nevus is very rarely found on the oral mucosa but appears as a slow-growing blue-black papule or nodule which is typically less than 8 mm. in diameter and is seldom larger than 2 cm. This lesion is usually diagnosed in females between 10-30 years of age, but congenital examples have been reported.

The oral halo nevus appears as a central pigmented papule or macule with a surrounding zone of pallor which may be as much as 1.5 cm. in diameter. The oral Spitz nevus (benign juvenile melanoma, spindle and/or epithelioid cell nevus) occurs as a dome-shaped, pink to reddish-brown papule less than 6 mm. in diameter. It presents as a solitary mass and usually develops during childhood. The small lesional size and young age at diagnosis are useful in clinically distinguishing the Spitz nevus from a true melanoma.

Pathology and Differential Diagnosis

The oral intramucosal nevus presents as an unencapsulated proliferation of nevus cells within the subepithelial stroma. Lesional cells are often clustered together and are usually ovoid and uniform in size, but their appearance may vary in different parts of the nodule. More superficial cells are usually epithelioid and frequently contain intracellular melanin, while nevus cells of the mid-portion of the nodule have less cytoplasm, are seldom pigmented, and appear much like lymphocytes. Deeper nevus cells appear elongated and spindle-shaped, much like Schwann cells or fibroblasts. Some authorities classify these variations as type A (epithelioid), type B (lymphocyte-like), and type C (spindle-shaped) nevus cells.⁸ There may be a complete lack of melanin production within submucosal nevus cells and multinucleated giant nevus cells may be found with or without intracellular melanin deposits. A grenz zone of uninvolved connective tissue separates lesional cells from the overlying epithelium.

The junctional nevus is extremely rare on oral mucosa, but when present it demonstrates sharply-demarcated nests or thèques of type A nevus cells at the interface (junction) of the subepithelial stroma and the mucosal epithelium. Supposedly, nests of type A and type B nevus cells appear within subepithelial stroma with age, at which time the diagnostic term compound nevus is applied. Over time, the intraepithelial nests disappear, leaving nevus cells only in the subepithelial connective tissues, producing the intramucosal nevus described above.

The oral example of the common blue nevus presents as a submucosal aggregation of elongated, slender melanocytes with intracellular melanin deposition and branching dendritic extensions (Figure 6). These cells usually align themselves parallel to the surface epithelium and may be quite deep within the subepithelial stroma. The cellular blue nevus appears as a well-circumscribed, highly cellular aggregation of plump, melanin-producing spindle cells within the lamina propria or submucosa. Pigmented dendritic spindle cells are seen at the periphery of the lesion. A blue nevus may be found in conjunction with an overlying melanocytic nevus, in which case the term combined nevus is used.

The oral Spitz nevus has the same histopathology as its cutaneous counterpart, with the general appearance of a compound nevus with zonal differentiation from the superficial to deep portions of the nodule. Lesional cells are spindle-shaped or epithelioid, with the two types often intermixed . The epithelioid cells may be multinucleated, may appear somewhat bizarre and may lack cellular cohesiveness. Mitotic figures with a normal appearance may be seen in superficial areas of the lesion. Ectatic superficial blood vessels, which probably impart much of the reddish color of some lesions, are seen frequently.

Treatment and Prognosis

No treatment is required for any of the histologic subtypes of the oral mucosal nevus. However most adult-onset pigmented lesions are removed by excisional biopsy when encountered in order to rule our melanoma. The oral nevus is, therefore, routinely removed by default. Recurrence has not been reported, nor has spontaneous regression or malignant transformation into an oral mucosal melanoma.

References (Chronologic Order)

Note: For general references click on link to the left.

Specific references:

Buchner A, Hansen LS. Pigmented nevi of the oral mucosa: a clinicopathologic study of 36 new cases and review of 155 cases from the literature. Parts I & II. Oral Surg Oral Med Oral Pathol 1987; 63:566-572, 676-682.

Allen CM, et al. Probable congenital melanocytic nevus of the oral mucosa: case report. Pediatr Dermatol 1995; 12:145-148.

Pictures

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