Nevus, lentigo, Seborrheic Keratosis, Pyogenic granuloma

Nevus (pl. Nevi)

Nevus (pl. Nevi) - Umbrella term for a group of benign, circumscribed overgrowth of cells composed of tissue elements normally present in the skin.  The most well known of the group is the melanocytic nevus (“mole”), composed of an increased proliferation of melanocytes, but multiple other types of nevi exist, such as vascular nevi, epidermal nevi, connective tissue nevi.

Melanocytic Nevus - These can be congenital, but most are acquired after birth.  They vary greatly in appearance.  They can be flat, elevated, smooth, rough, polyp-like, or sessile.  Nevi often come in a shade of brown, but some may be skin colored or occasionally blue in color.

It is important to distinguish a melanocytic nevus from malignant melanoma.  A symmetric shape, regular border, uniform color, small size (diameter <6 mm) are features that help distinguish the former from the latter.  Change in color, shape, or size, bleeding, pruritus, or other symptoms may be signs of suspicious lesions.

As nevi are normal skin findings, treatment is not necessary unless they are symptomatic or suspicious in nature.  Treatment consists of shave excision or elliptical excision.

The microscopic appearance of a benign melanocytic nevus depends on the type of nevus and what type of skin it may be located on. In general, melanocytic nevi are symmetrical, well delineated and circumscribed growths of melanocytes. This growth can be only in the epidermis (junctional nevi), only in the dermis (intradermal nevi) or in both (compound nevi). The melanocytes may have different cytologic appearances and arrangements depending on the type of benign nevus. A blue nevus is intradermal, roughly wedge-shaped and has thin, delicate melanocytes that may be in a dense fibrotic stroma with abundant melanin pigment. A common intradermal or junctional nevus has round and polygonal melanocytes which are nested or grouped. A Clark’s nevus has a more prominent proliferation of melanocytes, many of which are arranged as nests along rete ridges. The rete ridges are often “bridged” (connected at their bases). The papillary dermis is classically fibrotic in Clark’s nevi.

Clinical: nevi		Histology: melanocytic blue nevus, low power		Histology: melanocytic blue nevus, high power
Histology: melanocytic intradermal nevus, low power		Histology: melanocytic intradermal nevus, mid power		Histology: melanocytic junctional nevus
Histology: melanocytic clark's type compound nevus, high power Seborrheic Keratosis Seborrheic Keratosis - A superficial benign neoplasm of epidermal cells that presents as a papule or plaque with a characteristic “pasted-on” appearance.  These lesions are usually acquired later in life (middle age and beyond) and tend to grow slowly. Seborrheic keratoses vary in size, degree of elevation, and color.  Most commonly they come in a shade of brown and are round, greasy-appearing, well-circumscribed lesions.  The surface of the lesion is often rough and can have keratin-filled pits known as pseudo-horn cysts.  These lesions are usually found on the head, neck, trunk, and extremities, and are more common among the elderly.  It is the most common epithelial tumor.  Lesions can be hereditary. Microscopically there is an expansile plate-like growth of the epidermis with expanded and anastomosing rete ridges (the downward projections of epidermis that interdigitate with the dermis). There may be cysts that contain keratin and the lesions can show increased melanin pigmentation of the lesional keratinocytes. The histologic appearance is non-invasive with benign appearing cytologic characteristics. Clinical: seborrheic keratosis Histology: seborrheic keratosis, low power Histology: seborrheic keratosis, mid power unday, 20 July 2008 Solar lentigos Case 1: clinical image The clinical aspect of a solar lentigo* is a light brown macule. (* other denominations: lentigo actinica, senile lentigo) Case 1: dermoscopic image 2 types of patterns can be observed: reticular pattern with regular meshes and thin lines homogeneous pattern In all cases, the pattern has a sharp demarcation and a light brown to tan colour. Case 2: dermoscopic image In the 2nd case, the moth eaten borders are one of the typical aspects of solar lentigos. Another dermoscopic feature sometimes observed is fingerprint-like structures. Pyogenic Granuloma Pyogenic Granuloma - An acquired, erythematous round papule or nodule that projects from the skin or mucosa.  These lesions are made of friable granulation tissue and bleed easily.  Granulation tissue is comprised of connective tissue that forms during wound healing, ulceration, or inflammation.  Pyogenic granulomas are benign and usually occur at sites of prior trauma.  Commonly found on the fingers, toes, mouth, and trunk.  Proliferating capillaries and numerous neutrophils are present.  The surface is often smooth and may be ulcerated.  A collar of thickened stratum corneum may surround the papule or nodule.  Color can vary from red to violaceous or dark brown.  They can be readily excised and rarely recur.  Name is a misnomer.    Microscopically there is a lobulated circumscribed proliferation of capillary vessels within the dermis that creates a polypoid clinical lesion with a “collarette” of invaginated epidermis, likely due to its rapid growth. There is a variable inflammatory infiltrate that can simulate granulation (healing) tissue. Granulomas are not present and this part of the name is a misnomer. Clinical: pyogenic granuloma   Histology: pyogenic granuloma, low power   Histology: pyogenic granuloma, high power