Blue-black mole with regular borders

The three clinically distinct forms of blue nevi are common blue nevi, cellular blue nevi and malignant blue nevi. The former was first described in 1906.1 The cellular blue nevus was first considered a variant of melanoma; however, it was...

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The three clinically distinct forms of blue nevi are common blue nevi, cellular blue nevi and malignant blue nevi. The former was first described in 1906.¹ The cellular blue nevus was first considered a variant of melanoma; however, it was later classified as a branch of blue nevi. Malignant blue nevi are the rarest form and often arise in conjunction with cellular blue nevi.

Asian populations seem to be affected by blue nevi the most, with 3%-5% of the adult population having the disorder.² About 1%-2% of white adults have the disorder, and blacks are rarely affected.² Approximately 75% of blue nevi cases arise during childhood and adolescence.² The other 25% may present with blue nevi during adulthood.² Although congenital blue nevi are rare, congenital common blue nevi account for one out of every four cases. Blue nevi are twice as common in females as in males.²

Although the etiology is not definitive, blue nevi are believed to be caused by dermal arrest in embryonic migration of neural-crest melanocytes. Genetic predisposition has been suspected due to variations in different populations. However, this notion has been dismissed since evidence of familial trends is lacking.³

Common blue nevi are well-circumscribed, dome-shaped papules. The papules are blue, blue-gray or blue-black in color and typically measure less than 1 cm in diameter.² The dorsal surfaces of the hands and feet are frequent locations for the lesions, accounting for 50% of all common blue nevi.^2,4 Other common sites include the face and scalp. The papules can occur in multiples, but this is rare. They may also arise with such other nevi as nevus spilus.²

Cellular blue nevi are blue to blue-gray or black nodules or plaques. They generally range from 1 cm to 3 cm in diameter; however, occasionally they will be larger than 3 cm.² The plaques can be found on various parts of the body, including the buttocks, scalp, face and feet. Their surface is usually smooth but can at times be irregular. This type of blue nevi is fairly uncommon, with the ratio of cellular blue nevi to common blue nevi being 1:5.² Congenital cellular blue nevi have been known to contain satellite lesions. A congenital melanocytic nevi may also develop a benign or malignant cellular blue nevus within it.^2,5

Malignant blue nevus is the rarest of all the variants. These nevi mostly arise in conjunction with cellular blue nevi. Unlike the other nevi, the malignant lesions progressively get larger until they are a few centimeters in diameter. They may also become multinodular and have a plaque-like resemblance.⁶ Malignant blue nevi are most commonly seen on the scalp and usually metastasize to the lymph nodes.⁷

Observations from a biopsy of cellular blue nevus will demonstrate deeply pigmented dendritic melanocytes, which are associated with nests and fascicles of spindle-shaped cells. The bundles of spindle cells intersect with one another and extend in all directions, giving it a storiform pattern. These cells often have abundant cytoplasm that appears pale in color with little or no melanin.⁸

For common blue nevi, a histologic examination will reveal wavy, elongated melanocytes with long branching dendrites. These melanocytes will bundle in the mid dermis, occasionally extending into the subcutaneous tissue. The nuclei of the melanocytes are rarely seen because the cells are filled with fine melanin granules that obscure their nuclei. This gives the papules their blue-gray to blue-black appearance. Also, the histologic fibrotic appearance is attributable to the high amount of collagen in the lesion.⁸

Malignant blue nevi will show various features of melanoma or other cancerous lesions, such as large size, asymmetry, ulceration, infiltration, cytologic atypia, mitoses and necrosis.²

A cellular blue nevus with satellitosis must be differentiated from a malignant blue nevus. If the lesion is located on the face, nevus of Ota should also be considered. The differential diagnosis of common blue nevus is broad and includes tattoo ink, combined nevus, vascular lesions, sclerosing hemangioma, primary and metastatic melanoma, atypical nevus, pigmented spindle cell nevus, dermatofibroma, papular basal cell carcinoma and glomus tumor.^2,9

If the blue nevi appear to be benign — meaning their diameter is less than 1 cm and they are clinically stable with no atypical features — no excision is necessary. In such other cases as the appearance of plaque-like lesions, multinodular lesions, evolving lesions, or de novo lesions, the blue nevi should be considered for excision. Because of the potential risk for malignant transformation, cellular blue nevi should be excised in most cases.^2,4

Patient prognosis for this condition is excellent. Once present, blue nevi tend to remain unchanged throughout the patient’s life. Depending on the age of the lesion, blue nevi tend to flatten and fade in color. Common blue nevi are clinically benign.

Cellular blue nevi are also benign but very rarely can undergo malignant transformation. If a patient has been diagnosed with a cellular blue nevus, discuss resection of the lesion to prevent recurrence and the misdiagnosis of malignant blue nevus and to lower the risk of malignant transformation. The blue nevi are not aesthetically pleasing, and patients may desire excision for cosmetic reasons.

Clinically, the lesion in this case was felt to be a common blue nevus, especially considering its small size and stable clinical appearance. After discussing the diagnosis with the patient and her mother — and given the patient’s concern for cosmesis — the area was biopsied with a 6-mm punch biopsy. The pathology was read as a common blue nevus.

Kerri Robbins, MD, is a resident in the Department of Dermatology at Baylor College of Medicine in Houston.

References

1. Tieche M. Uber benigne melanome (chromatophorome) der haut “blaue naevi.” Arch Pathol Anat. 1906;186:212-229.

2. Bolognia JL, Jorizzo JL, Rapini RP eds. Dermatology. 2nd ed. St. Louis, Mo.: Elsevier-Mosby; 2008:1722-1723.

3. Maize JC, Ackerman AB, eds. Pigmented Lesions of the Skin. Philadelphia, Pa.: Lea & Febiger; 1987:137.

4. Montgomery H, Kahler JE. The blue nevus (Jadassohn-Tieche): its distinction from ordinary moles and malignant melanomas. Am J Cancer. 1939;36:527-539.

5. Leopold JG, Richards DB. Cellular blue nevi. J Pathol Bacteriol. 1967;94:247-255.

6. Paller AS, Mancini AJ. Hurwitz Clinical Pediatric Dermatology. 3rd ed. Philadelphia, Pa.: Elsevier Saunders; 2006:298-299.

7. Fitzpatrick TB, Johnson RA, Wolff K, Suurmond R, eds. Color Atlas and Synopsis of Clinical Dermatology, 5th ed. New York, N.Y.: McGraw-Hill; 2005:171-172.

8. Elder DE, Elenitsas R, Johnson BL, et al, eds. Lever’s Histopathology of the Skin. 10th ed. Philadelphia, Pa.: Lippincott Williams & Wilkins; 2009:701-704.

9. Habif TP. Skin Disease: Diagnosis and Treatment. 2nd ed., Philadelphia, Pa.: Elsevier Mosby; 2005:464, 480-482.