1. Keratocanthoma (see Figure 23.1)
• Benign tumor that behaves like a squamous cell carcinoma (SCC) and is difficult to differentiate histologically
• Characterized by rapid growth with a central crater/keratin plug
• Can spontaneously regress
• Treatment recommendation: Excision
2. Actinic keratosis (AK; also known as solar keratosis, senile keratosis; see Figure 23.2)
• Extremely common skin lesions reportedly affecting up to 12% of the population
• Benign, premalignant lesion that can progress to SCC
▪ Estimated rate of conversion to SCC is 13% to 20% over 10 years for lesions that are untreated.
• More than 80% occur on sun-exposed/sun-damaged areas such as the head, neck, and upper extremities (e.g., dorsal hand/forearm).
• Risk factors: Chronic sun exposure, increasing age, male gender, fair skin
• Characterized by a rough, erythematous papule with a white to yellowish scale or plaque
• Treatment: Cryosurgery, photodynamic therapy, medical treatment (e.g., topical or intralesional 5-fluorouracil [5FU], topical imiquimod)
3. Seborrheic keratosis (SK; also known as a senile wart) (see Figure 23.3)
• Benign skin growth originating from the basal and squamous cells of the epidermis
• Characterized by well-circumscribed, waxy lesions that are occasionally pigmented and have a “stuck-on” appearance
• Must be differentiated from AK, basal cell carcinoma (BCC), and melanoma
• Sudden appearance of multiple SKs can be a marker of internal malignancy.
• Treatment: Laser therapy, cryotherapy, electrosurgery, and excision
4. Nevus sebaceous (“nevus sebaceous of Jadassohn”) (see Figure 23.4)
• A benign hamartoma confined to the head and neck regions
• Can have malignant degeneration into BCC
• Characterized by a waxy, smooth or papillated, hairless, salmon-colored patch or thickening on the scalp that typically presents at birth
• Treatment: Excision
5. Juvenile melanoma (“Spitz nevus”; see Figure 23.5)
• Benign pigmented skin lesion typically found in children or young adults
• Difficult to distinguish from melanoma clinically and histologically
• Characterized by a red, pink, or brown papule or nodule with rapid growth
• Treatment: Complete excision with negative margins; if any concern for melanoma, obtain appropriate margins based on depth.
6. Nevus of Ota (see Figure 23.6)
• Benign blue nevus that is present within the dermatome of the first and second branches of the trigeminal nerve
• Most commonly affects Asian females
• Bimodal distribution: Early infancy and early adolescence
• Caused by dermal proliferation of melanocytes
• Treatment: Laser (e.g., Q-switched ruby, alexandrite); dermabrasion, peels, or cryotherapy have also been used.
7. Nevus of Ito
• Often considered a subtype of nevus of Ota
• Occurs in the acromiodeltoid region.
• Treatment: Similar to nevus of Ota
8. Mongolian spot (also known as congenital dermal melanocytosis; see Figure 23.7)
• A common benign proliferative disorder that affects the majority of Native American, Asian, and Hispanic infants
• Caused by entrapment of melanocytes within the dermis during development
• Characterized by multiple bluish-gray spots or a large patch covering the lumbosacral region
• Lesions typically disappear by 10 years of age.
• Treatment: Observation because most disappear without treatment; lasers for severe cases.
9. Blue nevus
• Also caused by dermal melanocytosis
• Characterized by a well-circumscribed, firm, blue-pigmented nodule/papule
• Three subtypes: Common, cellular (can invade the subcutaneous tissue), and combined (combined with a pigmented nevus or a Spitz nevus)
• Treatment: Biopsy for suspicious lesions; simple excision (see Figure 23.8)