Benign Skin Growths & Cysts

Epidermal and vascular papules

Seborrheic keratosis. The most common benign epidermal tumor of adults over 50: sharply demarcated, tan to black, waxy or verrucous papules that look "stuck on" the trunk, face, and limbs, sparing palms, soles, and mucosa. Dermoscopy shows keratin-filled horn (milia-like) cysts and comedo-like openings. No treatment is required; cryotherapy or curettage removes irritated lesions. An inflamed or dark keratosis can resemble melanoma, and doubt calls for biopsy rather than destruction. Variants include dermatosis papulosa nigra (small dark facial papules in darker skin) and stucco keratoses (gray-white papules on the lower legs).

Sign of Leser-Trélat: an abrupt eruption of many, often itchy, seborrheic keratoses can herald internal malignancy, most often gastric or other GI adenocarcinoma, frequently with malignant acanthosis nigricans. Perform an age-appropriate cancer evaluation, including upper endoscopy, colonoscopy, and CT.

Skin tags and cherry angiomas. Acrochordons are soft, pedunculated papules on the neck, axillae, groin, and eyelids that accompany obesity, insulin resistance, and pregnancy; snip excision, cryotherapy, or electrodesiccation is used only when they are irritated or unwanted. Cherry angiomas are bright red 1–5 mm capillary papules on the trunk that multiply with age and need no treatment. Spider angiomas differ: a central arteriole with blanching radiating branches, seen with liver disease, pregnancy, and estrogen excess.

Dermatofibroma. A firm, tan-pink to brown papule 0.5–1 cm across, most often on the legs of women, sometimes after an insect bite or minor trauma. Squeezing it from the sides makes the center dimple inward (dimple sign). It is a benign proliferation of fibroblasts and histiocytes, removed only for symptoms or diagnostic doubt.

Sebaceous hyperplasia. Soft, yellowish 2–4 mm papules with a central dell on the forehead, nose, and cheeks of middle-aged adults and of patients taking cyclosporine. The main mimic is basal cell carcinoma, which is pearly with a rolled border and arborizing telangiectasias; biopsy when unsure. Sebaceous adenomas or carcinomas, not hyperplasia, signal Muir-Torre syndrome, a Lynch syndrome variant.

Cysts and lipomas

Epidermal inclusion cyst. The most common skin cyst, often misnamed a "sebaceous cyst" although it contains keratin, not sebum. Rupture spills keratin into the dermis and provokes a brisk foreign-body reaction that looks infected but is often sterile.

Multiple epidermoid cysts in unusual sites with osteomas and desmoid tumors suggest Gardner syndrome, an APC-related form of familial adenomatous polyposis.

Lipoma. The most common soft-tissue tumor: a soft, rubbery, painless, freely mobile subcutaneous mass of mature fat on the trunk, neck, or proximal limbs, usually smaller than 5 cm and stable for years. Observation is appropriate, with excision for symptoms or cosmesis.

Never shell out a suspected sarcoma in the office. Obtain MRI first, then a core needle biopsy planned with the surgeon who will perform the definitive resection.

Pyogenic granuloma and scars

Pyogenic granuloma. Neither infectious nor granulomatous, this lobular capillary hemangioma is a bright red, often pedunculated papule that grows over weeks and bleeds profusely with minor trauma on the fingers, lips, face, or gingiva. Triggers include trauma, pregnancy (gingival lesions that often regress after delivery), isotretinoin, and EGFR inhibitors. Shave excision with curettage and electrocautery of the base lowers recurrence. Always send the tissue for pathology, because amelanotic melanoma and Kaposi sarcoma can look identical.

Treating keloids. Intralesional triamcinolone every 4–6 weeks is first-line; silicone gel sheeting and pressure (such as earlobe clips) help, and cryotherapy or intralesional 5-fluorouracil is used for resistant lesions. Any excision must be followed by adjuvant steroid injection or radiation, because excision alone usually recurs. In keloid-prone patients, avoid elective surgery and piercing at high-risk sites and close wounds with minimal tension.

Nevi and choosing a biopsy

Acquired nevi. Moles appear after infancy, increase through adolescence, peak in the third to fourth decade, and decline in older age. They mature from flat, uniformly brown junctional nevi to raised compound nevi and then soft, skin-colored intradermal nevi. Benign nevi are usually smaller than 6 mm, symmetric, and uniform; more than 50 nevi or atypical nevi increase melanoma risk.

Congenital nevi. Present at birth or appearing in infancy, they are classified by projected adult size: small (<1.5 cm), medium (1.5–20 cm), and large or giant (>20 cm). Small and medium nevi carry low melanoma risk. Large and giant nevi carry a lifetime risk of a few percent, often in childhood and deep in the lesion, and those on the posterior axis or with many satellites can signal neurocutaneous melanosis, so infants need MRI of the brain and spine and lifelong surveillance.

Biopsy any lesion that is changing, bleeding, ABCDE-positive, or an "ugly duckling." A suspected melanoma needs excisional biopsy with 1–3 mm margins so Breslow depth can be measured; superficial shaves that transect the base and cryotherapy or laser of undiagnosed pigmented lesions are errors.