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Melanocytic neoplasms

Solar lentigo Key Features Thin rete with bulbous tips “dipped in chocolate” Differential Diagnosis Reticulated seborrheic keratosis looks similar to a lentigo but with anastomosis of rete and horn cysts. Melanotic macule Key Features Common on the lips and genitalia Rete are broad and squared-off with pigment at basal layer Melanotic macules are typically light brown and evenly pigmented, but those in the genitalia may sometimes…

Sweat gland neoplasms

Blue sweat gland tumors differentiate toward the secretory portion of the sweat gland. Red sweat gland tumors differentiate toward the sweat duct. Sweat duct tumors often demonstrate clear cell change. Most sweat gland tumors can show at least focal decapitation secretion, suggesting they are capable of apocrine differentiation. Cylindroma (turban tumor) Key Features Islands of blue cells with little cytoplasm Dark and pale blue nuclei present…

Pilar and sebaceous neoplasms

Pilar neoplasms Pilar neoplasms differentiate toward (resemble) various parts of the normal hair follicle. They are named according to what they resemble. Before reading this chapter, review the discussion of hair anatomy in Chapter 1 . Blue pilar tumors differentiate toward elements of the inferior segment of the hair follicle. Red pilar tumors differentiate toward the isthmus and infundibulum. Clear cell tumors differentiate toward the glycogenated…

Malignant tumors of the epidermis

Actinic keratosis Key Features Crowding, disorder, and atypia of epidermal keratinocytes Arises from the basal layer Solar elastosis typically present Atypical cells commonly surround the follicular infundibulum. In two-dimensional sections, they appear to form a shoulder zone peripheral to the benign follicular epithelium. The overlying stratum corneum may be normal or may have features of a “malignant horn.” A malignant horn is a compact, eosinophilic stratum…

Benign tumors and cysts of the epidermis

Benign acanthomas Acanthomas are benign cutaneous neoplasms characterized by an expansion of the epidermis. The acanthoma may be composed of clones of cells that displace or compress the preexisting epidermis. In contrast to the reactive acanthosis seen in inflammatory disorders, the rete ridge pattern is commonly ablated by the neoplastic tissue of an acanthoma. Seborrheic keratoses Seborrheic keratoses are acanthomas composed of small polygonal keratinocytes about…

The basics: Diagnostic terms, skin anatomy, and stains

Glossary of terms Acantholysis Loss of cell–cell adhesion Acanthosis Increase in thickness of the epidermis Regular (all rete pegs descend to the same level) or irregular (rete pegs descend to different levels in the papillary dermis) Anaplasia Atypical nuclei (abnormal size, shape, staining) and pleomorphism (variation in nuclear characteristics) Apoptosis (pronounced apohtosis) “Programmed cell death” “Dead red” keratinocytes with pyknotic nuclei Although the term is often…

Neoplastic and Non-neoplastic Disorders of the Conjunctiva and Eyelid

Non-neoplastic Disorders Inflammatory Lesions Conjunctivitis (Infectious and Non-Infectious) Conjunctivitis is an inflammation of the conjunctiva that can manifest in both an acute and chronic form (persisting for 4 weeks or more). The etiology of the inflammation can include allergic, infectious (bacterial, viral, protozoal, parasitic), autoimmune, or autoreactive. Clinical Findings Conjunctivitis typically involves erythematous changes to conjunctiva, which may be accompanied by chemosis, discharge or membranes. Depending…

Neoplastic and Non-neoplastic Disorders of the Nail Apparatus

Dermatopathology of the nail unit remains a somewhat esoteric and elusive subject for several reasons. Most dermatopathologists have little experience with material from this site, and little has been written comprehensively about this subject. Part of the difficulty stems from the fact that many dermatologic conditions affecting the nail unit are diagnosed on clinical grounds alone, in part owing to the reluctance of practitioners to perform…

Metastatic Tumors Involving the Skin

Tumors metastatic to skin are clinically important because they may represent the first manifestation of an unrecognized internal malignancy or the first evidence of recurrence of a previously treated primary tumor. It is critical to recognize that the tumor is in fact a secondary deposit and not to mistake it for an unusual primary tumor. Determining the site of the primary tumor, if unknown, is often…

Cutaneous Neuroendocrine (Merkel Cell) Carcinoma

Merkel cell carcinoma (MCC) is the eponymous term for primary neuroendocrine carcinoma of the skin, subcutis, or both. Merkel Cell Carcinoma Clinical Findings Merkel cell carcinoma is uncommon. Its annual age-adjusted incidence in the United States was 0.44 in 100,000 in 2001. MCC typically occurs on chronically sun-damaged skin of elderly white individuals but can also occur in younger patients on sun-protected sites and in individuals…

Histiocytic Proliferative Disorders

Definition of Terms The term histiocyte refers to a bone marrow–derived progenitor cell that differentiates, depending on the cytokine and growth factor milieu, into a dendritic antigen-presenting cell (Langerhans cell, dermal dendrocyte) or a phagocytic cell (tissue macrophage). Histologic subclassification of disorders of histiocytes can be performed based on the morphologic and immunophenotypic attributes of these differentiated descendent cells, but a diagnosis of disease entities often…

Hematopoietic Neoplasms

Cutaneous Lymphomas and Pseudolymphomas This chapter deals primarily with primary cutaneous B- and T-cell lymphomas, that is, lymphomas that initially or primarily affect the skin, and reactive lymphoid infiltrates, which may simulate a lymphoma (pseudolymphoma). Later sections of this chapter also address secondary cutaneous B- and T-cell lymphomas, that is, lymphomas that originate from an extracutaneous site and affect the skin, as well as leukemic infiltrates…

Soft Tissue Tumors and Tumor-like Reactions

Fibrous, Myofibroblastic, and Fibrohistiocytic Tumors Benign Tumors and Tumor-Like Reactions Dermal Scar and Keloid Clinical Findings The most frequently encountered soft tissue lesion is the dermal scar. It is commonly seen in a postsurgical setting (e.g., re-excision of a tumor) but may also reflect nonsurgical trauma or result from a ruptured cyst or hair follicle. A keloid is a distinct subtype of scar in which the…

Melanocytic Proliferations

The histologic interpretation of pigmented lesions represents one of the most common and at times most difficult challenges in dermatopathology. This chapter introduces readers to basic aspects in the histologic diagnosis of melanocytic lesions. Lentigines and Lentigo-Like Lesions Solar Lentigo Clinical Findings The solar lentigo is a usually circumscribed pigmented macule ranging in color from tan to dark brown. It typically occurs on sun-exposed skin of…

Adnexal Tumors

Adnexal tumors or tumorous proliferations are generally classified according to two principles, (1) benign versus malignant and (2) line of differentiation, that is, which normal cutaneous structure the lesion most resembles (hair follicle, apocrine or eccrine gland, or sebaceous gland). Although such a classification scheme seems simple at first glance, the reality is that there is still considerable controversy on how to catalog many lesions. The…

Tumors of the Epidermis

Benign Tumors and Tumorous Proliferations of the Epidermis The lesions described herein include noninfectious pseudoepitheliomatous epidermal hyperplasia, benign acanthomas and keratoses, and epidermal nevi. Epidermal proliferations associated with warts or deep fungal infections are described in the chapter on infectious diseases. Reactive Epidermal Hyperplasia with Emphasis on Pseudoepitheliomatous Hyperplasia Reactive epidermal hyperplasia is common. It may be associated with wound healing; infection; and miscellaneous inflammatory dermatoses,…

Cysts and Sinuses

A cyst is a dilated, saclike cavity lined by various types of epithelia. In the vast majority of cases, cutaneous cysts are lined by one type of epithelium, most commonly stratified squamous epithelium. Infrequently, cutaneous cysts may have significant portions of more than one type of epithelium and have been given the appellation hybrid cysts . A pseudocyst, on the other hand, is a cystic cavity…

Non-neoplastic Disorders of Hair

Non-neoplastic disorders of hair comprise mainly the alopecias and hair shaft abnormalities. In this chapter, only the alopecias are considered. Their diagnosis requires close clinicopathologic correlation. The hair shaft abnormalities are covered extensively in various textbooks and atlases, and readers are referred to them. Alopecias are traditionally classified into nonscarring and scarring (cicatricial) forms. This concept is controversial. In the clinical use of the terminology, a…

Non-neoplastic Disorders of Pigmentation

This chapter describes key clinical and histologic features of relatively common or well-known non-neoplastic disorders of pigmentation. Café-Au-Lait Macules Clinical Findings Café-au-lait macules are very common. Solitary lesions are seen in approximately 10% to 20% of the adult population. They are more common in the black population than in whites. Clinically, they appear as homogeneous light to dark brown completely macular lesions with well-defined borders that…

Mucinoses, Deposition Disorders, and Connective Tissue Alterations

This chapter includes cutaneous substances that may accumulate in abnormal amounts, such as mucin, as well as material deposits usually not present in the skin, either produced endogenously (e.g., porphyrins) or introduced as a foreign substance (e.g., tattoo pigment). Deposits in the skin may be divided into broad groups: (1) calcium, osseous, and cartilaginous deposits; (2) hyaline deposits characterized by an eosinophilic, homogeneous, glassy appearance in…