The clinical appearance is that of a pedunculated or sessile nodular growth with a variably convoluted surface.

Microscopically a papilloma consists of benign squamous epithelium with variable acanthosis and hyperkeratosis overlying an expanded fibrovascular core, which creates the exophytic nodule (Fig. 3.1).

If symptomatic, surgical excision may be performed.

The clinical appearance varies considerably in terms of size (few millimeters to several centimeters) and degree of pigmentation making it sometimes difficult to differentiate clinically from nevi, pigmented basal cell carcinomas, and melanoma [1]. They are sharply demarcated warty plaques or dome-shaped growths with a greasy surface, which may become friable with inflamed eczema-like features (Fig. 3.2).

Seborrheic keratoses are divided into several histological types according to the predominant histologic features: acanthotic, hyperkeratotic, adenoid, clonal, and irritated (Fig. 3.2). The most common type is the acanthotic, in which there is a proliferation of squamous basaloid cells protruding above the skin surface, which is punctuated by horn pseudocysts. Hyperpigmentation can occur, which is due to transfer of melanin to the keratinocytes. When a patient experiences a sudden appearance of a seborrheic keratosis or an increase in the number or size of these lesions, this may be associated with an internal malignancy and is referred to as the Leser-Trelat sign [2].

Even in lesions that are large, the growth pattern is superficial with growth predominantly above the epidermal surface. Therefore, deep excision is unnecessary, and these lesions are often removed by shave biopsy.

Usually a solitary lesion of recent onset (less than 3 months), it may be nodular, papillomatous, or cystic in appearance. Inverted follicular keratosis can be easily mistaken for squamous cell carcinoma.

Histopathologically it consists of an endophytic proliferation of squamous epithelium with squamous eddies, variable pigmentation, and acantholysis and chronic inflammation. There may be increased mitoses and apoptosis (Fig. 3.3) [4].

Complete excision should be performed.

This entity occurs frequently in children but may also occur in adults anywhere on the body except the palms and soles. It appears as papules that are white or flesh colored measuring 2–5 mm, often with a central dimple or plug containing cheesy or waxy material (Fig. 3.4).

Molluscum contagiosum is characterized by downward growth of the epidermis forming multiple lobules. The keratinocytes contain large eosinophilic intracytoplasmic inclusion bodies (“molluscum bodies”) which are characteristic (Fig. 3.4). The central crater consists of disintegrating cells discharging the molluscum bodies and keratin.

These lesions usually resolve over months to years in patients with intact immune systems. However, removal of individual lesions can be done surgically or by scraping, de-coring, freezing, or electrosurgery. Medications used for warts may also be used, and cantharidin (“beetle juice”) is the most common solution used. Tretinoin cream is an alternative.

An elevated nodular or ulcerative lesion resembling basal or squamous cell carcinoma.

There is epidermal hyperplasia with elongated seemingly invasive tongues of epithelial cells which may anastomose and are frequently infiltrated by inflammatory cells (Fig. 3.5) [2]. The epithelium shows normal maturation without true dysplasia; however it is not always easy to separate this reactive process from squamous cell carcinoma because of the significant cytologic atypia that may occur.

Complete excision is recommended when clinically suspicious.

A protruding keratotic lesion is the presentation (Fig. 3.6). This lesion is associated with a variety of benign or malignant lesions. In a study of 48 cases involving the eyelids, the most common associated lesions were seborrheic keratosis, actinic keratosis, and basal cell carcinoma and squamous cell carcinoma [8].

There are no specific histopathologic features other than hyperkeratosis. The findings are solely dependent on the particular type of lesion present.

Treatment should be determined by the histopathology if possible. If the lesion is clinically suspicious for malignancy, excision is recommended.

There are a variety of clinical presentations, usually characterized by multiple, erythematous, excoriated, sessile plaques [11]. Although it is a precursor to squamous cell carcinoma, the mitotic activity is generally low [12]. In a study wherein histopathologic evaluation of the resected squamous cell carcinoma was undertaken, 82 % of cases had concomitant actinic keratosis close to the carcinoma [13]. However, population-based studies indicate a much lower annual rate of 0.01 % of malignant transformation of actinic keratosis [14]. Such discrepancy may exist because of differences in clinical and pathological nomenclature used to describe actinic keratosis and early squamous cell carcinoma. It is now believed that actinic keratosis is an incipient form of squamous cell carcinoma requiring treatment [15, 16]. Squamous cell carcinoma that arises from actinic keratosis is low grade and offers an excellent prognosis.

Histopathology generally shows hyperkeratosis and parakeratosis with varying degrees of squamous dysplasia, characterized by loss of epithelial cell polarity and dysmaturation. It involves the interfollicular epidermis, sparing the follicles and the intraepidermal portion of the sweat ducts, an important distinction from carcinoma in situ. Solar elastosis of varying degrees is present in the dermis (Fig. 3.7). Subtypes include hypertrophic (when the epithelium is acanthotic), atrophic (when the epithelium is atrophic or thin), acantholytic (when there is prominent dyscohesion of the basal cells), and lichenoid (when there is a dense mononuclear cell infiltrate in the upper dermis). When there is severe dysplasia, the differential is squamous carcinoma in situ or Bowen’s disease (Fig. 3.8).

Management is close observation and excision of more suspicious lesions. Multiple lesions can be treated with topical chemotherapeutic agents or cryotherapy [17]. A meta-analysis of published studies indicates that 3 % diclofenac in 2.5 % hyaluronan gel is effective in treatment of actinic kertatosis [18]. Topical gel must not be applied to the eyelids as it is not approved for ophthalmic use.

Congenital nevi may be single or multiple with sharp borders and are usually larger than acquired nevi. They tend to become darker and the surface undergoes papular or nodular change with age.

The congenital nevi are classified by their largest diameter as small (<1.5 cm), medium (1.5–19.9 cm), and large or giant congenital melanocytic nevi (>20 cm) [21].

The risk of malignant transformation varies significantly with the size of the lesion. The lifetime risk of about 6 % is highest with giant nevus [22]. In another study in which the authors did an analysis of several published studies with a total of 6,571 patients, the overall risk of melanoma was much less (0.7 %) [23]. In this same article, they found that by comparing the age-adjusted data from the SEER database, the relative risk of patients with congenital melanocytic nevi for developing melanoma during childhood and adolescence was 465-fold. Despite irrefutable evidence supporting origin of melanoma in small congenital nevi, the magnitude of risk associated with small- and medium-sized congenital nevi is probably much less although reliable data does not exist [20, 24]. The risk is particularly negligible in prepubertal years [20].