Many benign pigmented lesions may be mistaken for melanoma. None should be ignored because melanoma can appear in a great variety of sizes, shapes and colors and can mimic benign lesions. Melanoma appears as a new mole or a pre-existing mole that changes. During self-examination at regular intervals, any new, changing or unusual mole should be examined by a physician.

Benign pigmented lesions can be diagnostically puzzling for physicians and a source of worry for patients. When a diagnosis of a suspect lesion is established to the physician’s satisfaction, the physician should explain the diagnosis in terms the patient can comprehend. The patient should ask questions until he/she feels the explanation is clear. If the lesion is equivocal or frankly suspicious, the physician should explain recommendations for additional diagnostic procedures and/or treatment.

Two topics suggested by site visitors for discussion are:

Halo nevi

Increased pigmentation of nevi during pregnancy

Halo Nevi

Halo nevi are relatively common acquired benign pigmented lesions that can occur in skin of all colors and in people of any racial or ethic background. Their underlying cause is not well understood. Vitiligo—patchy depigmentation of the skin—is often associated with halo nevi. Halo nevi can occur as an isolated event, is association with vitiligo, in association with prominent and/or atypical nevi, or rarely represent a new primary melanoma.

A patient’s alarm at discovering one or more halo nevi is understandable. (Click on Self-Examination for a description of identifying melanoma by changes in a mole’s size, shape or color). A halo nevus develops from an existing nevus. An area of depigmentation appears around the nevus over a period of days to weeks. The eventual typical appearance is a pink to brown central nevus surrounded by a "halo" of depigmentation. Patients need to be examined by a dermatologist for the presence of vitiligo, atypical nevi, and early melanoma.

These photos she characteristic halo nevi:

Halo nevi on the back of an adult female.

Halo nevi on a white-skinned person.

Halo nevi on a white-skinned person.

(Photos used with permission of the American Academy of Dermatology National Library of Dermatologic Teaching Slides and the Sulzberger Institute for Dermatologic Education)

The central nevus of the halo nevus may eventually regress and disappear, or it may remain unchanged for many years. New halo nevi may appear from time to time. No treatment is required for a typical halo nevus. However, a biopsy is often needed to verify the nevus is benign.

Acquired halo nevi, while benign, can occur in association with melanoma risk factors such as dysplastic nevi and personal or family history of melanoma. A dermatologist should be consulted to confirm a diagnosis of halo nevus. A dermatologist can recommend cosmetic measures to make a halo nevus less apparent. Halo nevi are common in childhood, adolescence, and early adulthood. The development of halo nevi in older adults should result in careful examination of the halo nevus and a total skin check for the presence of a melanoma elsewhere.

Increased Pigmentation of Nevi During Pregnancy

Hormonal changes are believed to be responsible for many changes in pigmentation that occur in the skin during pregnancy. Increased pigmentation is a frequent and often noticeable occurrence. Areas commonly affected are the face, nipples, external genitalia, armpits and thighs. Enlargement of an existing mole on the abdomen may occur with expansion of the affected body site.

The precise role of hormones in these changes in pigmentation during pregnancy is not well understood. The association between hormonal changes and other skin conditions of pregnancy are better understood—for example, the worsening of acne during pregnancy, and the appearance of skin tags. (Link to AcneNet for more information on the causes and treatment of acne).

A characteristic change in pigmentation of nevi during pregnancy is shown in this photo:

Melanocytic nevi in a 26-year-old woman darkened and became larger during the first trimester of pregnancy. New nevi and changing nevi are uncommon during pregnancy. A new or changing mole should be examined by a physician.

Changes in nevi should be monitored by self-examination and examined by a dermatologist as warranted. The next photos show melanoma that developed or was detected in pre-existing nevi during pregnancy:

A 28-year-old woman noticed enlargement and darkening of a pre-existing nevus on her left arm during the second trimester of pregnancy. The lesion was removed by excisional biopsy and was found to be a melanoma.

A 35-year-old woman noted enlargement and darkening of a pre-existing nevus on her back during the third trimester of pregnancy. Six months after delivery the lesion was removed by excisional biopsy and was diagnosed as a melanoma.

(Photos used with permission of the American Academy of Dermatology National Library of Dermatologic Teaching Slides and the Sulzberger Institute for Dermatologic Education)

Hormonal changes appear not to play a role in the malignant transformation of nevi during pregnancy. Pregnancy is not known to be a risk factor for melanoma, but melanoma may possibly escape early detection if it develops simultaneously with skin pigmentation changes during pregnancy and if the patient’s physician assumes that mole changes during pregnancy are a common occurrence. Melanoma risk factors such as dysplastic and atypical nevi, congenital nevi, and personal or family history of melanoma remain important considerations during pregnancy. The patient should inform her obstetrician/gynecologist regarding any risk factors for melanoma that should be taken into consideration during regular prenatal check-ups. Patients known to be at high risk for melanoma should be followed closely by a dermatologist during pregnancy.

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