Please note that this list is not intended to substitute for a medical dictionary. Terms are described with respect to their common usage in dermatopathology reports and do not necessarily constitute exact definitions.

Acantholysis: loss of intercellular connections between squamous cells. This can be seen under the microscope as cells appear to fall apart from each other. Acantholysis can be focal or extensive and may or may not be clinically significant.

Acanthosis: increased thickness of the epidermis.

Acral: pertaining to peripheral parts of extremities.

Acute: something that is new/young in age or develops rapidly.

Adipose: fat tissue or cells.

Adnexa: hair follicles, sebaceous glands, eccrine glands, and apocrine glands are all considered adnexal structures.

AFB: “acid fast bacilli”, the AFB stain is a special (histochemical) stain to detect mycobacteria. Mycobacteria are small and generally very scarce, therefore difficult to detect in a biopsy specimen, even with the aid of a special stain. Furthermore, the species of mycobacteria can not be determined. Therefore pathology results are supplemented with the results of microbiology culture which, although having a longer waiting period, have the advantage of increased sensitivity and the opportunity for speciation.

Alcian blue: a special (histochemical) stain used to detect mucin in the dermis. Mucin may be increased in entities such as granuloma annulare, mucinoses, and connective tissue diseases, among others.

Alopecia: hair loss. There are many different causes of alopecia, and it may sometimes be difficult to determine the exact cause. Helpful clues include the pattern and timing of hair loss as well as presence or absence of scarring. A biopsy may also provide additional information.

Apocrine gland: a type of sweat gland with less extensive distribution than the more common eccrine type of sweat gland, apocrine glands are found primarily in the axilla, perianal and genital area, nipple/areola and certain parts of the head/neck.

Apoptosis: a form of programmed cellular death, apoptosis is a mechanism by which the body purposefully eliminates particular cells that are no longer useful or potentially harmful to the body. Many tumors also induce apoptosis.

Atrophic: diminution or decrease in size of a structure.

Atypia: cellular abnormalities that can be observed under the microscope but are not of clear significance. Atypia may be neoplastic (pre cancerous) or reactive (in the setting of inflammation, infection, irritation etc) in origin. Interpretation of atypia depends on many factors including cellular context, sampling, and clinical history.

Bacteria: single-cell organisms that are numerous and diverse in nature. Some species of bacteria are associated with human disease, while others simply colonize tissue without causing disease or may even be symbiotic (providing a mutually beneficial relationship) with humans. Bacteria can be seen under the microscope, however microbiology culture provides a more sensitive means of detection and allows for speciation.

Basal cell: keratinocytes in the lower most layer of the epidermis, basal cells anchor the epidermis to the basement membrane and dermis below. Furthermore, the basal layer provides a cellular reserve, with the ability to divide and to replace dying cells in the epidermis.

Basaloid: a descriptive term applied when a cell population shows characteristics reminiscent of basal cells, such as dark blue color. Of note, squamous cells can take on a marked basaloid appearance, sometimes making distinction between squamous cell carcinoma and basal cell carcinoma impossible.

Basement membrane: a thin connective tissue matrix upon which the basal layer of the epidermis sits, providing anchorage between the epidermis and dermis below. Increased basement membrane thickness is not specific for any one disease, but is part of a characteristic constellation of findings seen in discoid lupus erythematosus.

Benign: lacking the ability to metastasize, the term benign usually implies that a lesion does not pose a significant health threat. It should be noted that benign tumors may recur and grow, causing problems if they becomes too large or are situated in key anatomic locations.

Cancer: an abnormal growth of a population of cells that form a malignant neoplasm. Because these cells form a mass, cancer in considered a neoplasm or tumor, and when that neoplasm or tumor has the ability to metastasize, it is considered malignant.

Carcinoma: a malignancy derived from epithelial cells, there are many different kinds of carcinoma that can involve different organs of the body. In the skin, most commonly encountered are squamous cell carcinoma and basal cell carcinoma.

Chronic: something that is persistent with time.

Civatte bodies: dyskeratotic cells (dying keratinocytes) often seen in dermatitis that has a prominent interface pattern. Examples of interface dermatitis that may show Civatte bodies include (but are not limited to) lichen planus, lupus erythematosus, drug reaction, graft versus host disease, and erythema multiforme.

Colloid bodies: dyskeratotic cells. Often used interchangeably with the term Civatte bodies.

Colonization: when agents of infectious disease (bacteria and fungi) are present in human tissue but do not evoke symptoms or disease.

Congo red: a special (histochemical) stain used to aid in visualization of amyloid. Amyloid will appear pink/orange under normal light microscopy, and will fluoresce apple green under polarized light.

Crust: if the epidermis has been irritated (often by intentional or un intentional mechanical forces such as picking or rubbing), crust will form. Crust consists of serum that may be colonized by bacteria and debris. While crust generally sits on top of the epidermis, in cases of forceful mechanical disruption the epidermis may ulcerate and be absent altogether.

Cytologic atypia: changes that are seen in individual cells, in either the nuclear and/or cytoplasmic component that are abnormal but of unclear significance. Atypia may be pre cancerous but can also be reactive in nature.

Dermatitis: inflammation of the skin, dermatitis has many causes and most commonly presents as an itchy rash.

Dermis: the dermis lies below the epidermis and stratum corneum but above subcutaneous fat. Relative to the epidermis, the dermis is rather thick, however thickness varies with body site. The dermis consists primarily of collagen and elastic fibers, and other extracellular materials. The dermis houses sweat glands, hair follicles, blood vessels and nerves.

Desmoplasia: a specific type of stromal reaction that can be seen under the microscope and is usually associated with an invasive malignancy.

Differential diagnosis: a certain constellation of findings (be it clinical signs and symptoms or microscopic observations) does not usually correlate to just one disease. Additionally, one disease will not always have the same signs and symptoms or microscopic findings in every individual. The differential diagnosis is a list of the most reasonable diagnostic possibilities for a given patient’s ailments at a given point in time. Additional tests, such as blood tests, radiology, or special staining of slides are all aimed to narrow down the differential diagnosis by providing additional information. Sometimes the diagnosis in unclear despite all these additional studies. In such cases, the most helpful information comes from observation of disease evolution and response to treatment over time.

Duct: a tubular structure that conveys substances such as sweat, milk or sebum from their point of origin to the point of exit from the body.

Dyskeratosis: abnormal keratinization of cells, usually seen in the squamous epithelium of the epidermis. Dyskeratotic cells may be observed in processes such as interface dermatitis (i.e. lichen planus, erythema multiforme, drug reaction etc) as well as squamous cell carcinoma.

Eccrine gland: the primary type of sweat gland found in the human body. Apocrine glands are a second type of sweat gland, present in smaller numbers.

Ectasia: dilation of a tubular structure such as a duct.

Edema: accumulation of fluid, usually in the dermis. The finding of dermal edema is non specific meaning that it can have many causes. Edema is often seen in spongiotic dermatitis or as a result of structural/architectural changes of dermal structures that obstruct flow of body fluids.

Elastic: material found in the dermis that gives skin its ability to recoil. Elastic tissue degenerates with age and with sun exposure (solar elastosis). While solar elastosis may be seen on regular H&E stained slides, visualization of elastic fibers requires a special histochemical stain.

Eosinophils: a cell of the immune system, eosinophils are a type of white blood cell (leukocyte) that belong specifically to the granulocyte series (other granulocytes include neutrophils and basophils). Eosinophils play many different roles in the human body, and are important mediators of allergic/hypersensitivity reactions. In the field of dermatopathology, eosinophils are commonly found in skin biopsies of drug reactions, insect bite reactions, accompanying mast cells, T cells or Langerhans cells, and in various other disease states.

Epidermis: being the outer or uppermost layer of skin, the epidermis sits on top of the dermis, which in turn sits on top of the subcutaneous tissue below. The epidermis consists of an acellular stratum corneum that overlies several layers of squamous cells ranging from the granular layer on top to the basal layer on bottom. The basal layer connects to the basement membrane and dermis below. The epidermis plays critical protective roles such as minimizing water loss and serving as a barrier to infection.

Epidermotropism: a term commonly used in the setting of suspected mycosis fungicides to describe the migration of T cells, which normally reside in the dermis, upwards into the epidermis above. The term “epidermotropism” is conceptually similar to “exocytosis”, with the main difference being that “epidermotropism” is used specifically in this setting, while the term “exocytosis” is more broadly applied.

Epithelium: cellular tissue that lines body surfaces and cavities, forming a membranous coating. Along with connective tissue, muscle and nerve, epithelium is one of the major classes of tissue in the human body. In the field of dermatopathology, epithelial tissue forms the epidermis (superficial layer of skin made of squamous epithelium) and dermal glands (such as sweat glands and sebaceous glands).

Erythrocytes: also known as red blood cells, erythrocytes are the major component of blood. Their main function is to transport oxygen throughout the body.

Exocytosis: a descriptive term used when cells that normally reside in the dermis begin to migrate upwards, and infiltrate into the epidermis above.

Fibrin: a protein product of the coagulation cascade, fibrin is key to thrombosis (formation of blood clots) and is also generated in inflammatory states. In a skin biopsy, fibrin may be seen in ulcer beds, in vessel walls (as a component of vasculitis) or within vessels themselves (vasculopathy).

Fibrosis: deposition or development of increased connective tissue, often seen in chronic inflammatory states.

Fite: a special (histochemical) stain used to detect mycobacteria. Mycobacteria are small and generally very scarce, therefore difficult to detect in a biopsy specimen, even with the aid of a special stain. Furthermore, the species of mycobacteria can not be determined. Therefore pathology results are supplemented with the results of microbiology culture which, although having a longer waiting period, have the advantage of increased sensitivity and the opportunity for speciation.

Fontana-Masson: a special (histochemical) stain used to detect melanin.

Full thickness: when evaluating changes in the epidermis, the number of cell layers involved is often an important clue. “Full thickness” refers to all cell layers, from the basal layer on bottom to the granular layer on top.

Fungus: eukaryotic organisms that include both yeast (unicellular) and mold (multicellular). Like bacteria, fungi are numerous and diverse in nature. While some may cause disease, others may be present in human tissue without causing symptoms (colonization). Detection of fungi in tissue is aided by special stains such as GMS and PAS. Ultimately, pathology results are supplement with the results of microbiology culture, which take longer but are more accurate and are able to yield information as to the genus and species of the fungus in question.

GMS: “Gomori/Grocott Methenamine Silver” is a special (histochemical) stain used to aid in the visualization of fungus. Due to sampling issues, even in cases of true fungal infection the fungi may not be seen under the microscope. Furthermore, the species of fungus can not be determined. Therefore pathology results are supplemented with the results of microbiology culture which, although having a longer waiting period, have the advantage of increased sensitivity and the opportunity for speciation.

Gram stain: a special (histochemical) stain commonly used to detect bacteria and separate them into one of two large groups: gram positive (have a thick peptidoglycan layer and appear blue/purple) and gram negative (lacks this layer and appear red). Microbiology culture is a supplementary test used for more sensitive detection of organisms and for determination of the genus and species of bacteria.

Granular cell layer: the uppermost cellular layer of the epidermis, the granular cell layer consists of keratinocytes that have prominent keratohyalin granules in their cytoplasm. These granules can be seen on an H&E stained slide. Alterations of the granules/granular cell layer can be seen in states such as viral infection (verruca) and psoriasis.

Granulocyte: neutrophils, eosinophils, basophils and mast cells are all examples of granulocytes. Granulocytes and lymphocytes (B and T cells) are leukocytes, or white blood cells, which are part of the cellular immune system.

Granuloma: a discrete collection of immune cells, primarily histiocytes. Granulomas can be seen in many disease states, including sarcoidosis, Crohn’s disease, and infection, among others.

Grenz zone: a superficial strip of dermis that is spared by a process that otherwise infiltrates throughout the dermis. The Grenz zone usually appears on H&E stained slides as a pink band just below the epidermis. This finding may be seen in a number of different inflammatory or neoplastic processes.

H&E: “hematoxylin and eosin”, the routine (histochemical) stain used to visualize tissue on a slide in pathology. Hematoxylin imparts a blue color that is taken up primarily by nuclei (and occasionally by other structures such as keratohyalin granules), while the eosin counterstain colors other structures with shades of pink and purple. Not all elements stain with H&E; after initial review of H&E slides, the pathologist may need to request additional special stains to visualize entities such as elastic, mucin, bacteria and fungi..

Hemosiderin: a protein-iron storage complex found within cells, particularly erythrocytes (red blood cells). Hemosiderin is present in areas of stasis and erythrocyte degeneration and is sometimes apparent a brown pigment. Sometimes, special staining (Prussian Blue) may be required to visualize hemosiderin or to differentiate it from other sources of brown pigment such as melanin.

Histiocyte: a white blood cell of the immune system that represents macrophages in tissue. The primary job of histiocytes is phagocytosis (uptake of foreign material) and antigen presentation (presentation of parts of that material to other immune cells, thereby initiating immune response when necessary).

Histochemical stain: a stain applied to tissue in the pathology lab whereby it takes up pigment based on various histocehmical properties of the tissue. Examples include H&E, Gram, Fite, Prussian blue, PAS, GMS and many others.

HMB-45: a special (immunohistochemical) stain commonly used in evaluation of melanocytic lesions. In benign lesions, HMB-45 tends to be expressed by melanocytes at the dermal/epidermal junction and expression is lost as melanocytes mature into the dermis. In contrast, melanomas, which lack maturation, tend to retain HMB-45 expression throughout. Exceptions include spindle cell melanoma, which is usually HMB-45 negative, and blue nevi which although benign tend to retain strong and diffuse expression of HMB-45.

Hyperchromasia: overly dark or intense in color, nuclear hyperhcromasia is an abnormal finding that may signify increased DNA content.

Hypergranulosis: when the granular layer of the epidermis is increased in thickness. This may be seen in many different settings, most commonly in chronic inflammatory/irritative disorders that show acanthosis and hyperkeratosis such as lichen simplex chronicus.

Hyperkeratosis: a term used to describe increased thickness of the stratum corneum (the top layer of skin consisting of dead keratinocytes).

Hyperplasia: increased numbers of cells resulting in enlargement of a structure or organ.

Immunohistochemical stain: a special stain that uses antibodies to detect specific proteins in tissue. Antibodies are coupled to a detection system that then allows for visualization on the slide. The pattern and extent of protein expression gives clues as to the cell of origin and nature of the lesion.

Impetiginized: when bacteria are seen superficially in an area where there has been prior damage, such as bacteria within serum crust on a excoriated epidermis. Impetiginization does not necessarily indicate significant infection.

In situ: malignant (cancerous) growths that are restricted to their microscopic site of origin. For example, squamous cell carcinoma and malignant melanoma both originate from cells in the epidermis. If the melanoma or squamous cell carcinoma involves only the epidermis, it is considered an “in situ” malignancy (squamous cell carcinoma in situ or melanoma in situ). If it breaks through the basement membrane into the dermis below (“invasion”), then it can no longer be considered in situ (squamous cell carcinoma or melanoma).

Inflammation: the body’s response to an insult or injury, there are many components to an inflammatory response. When looking at a slide of a skin biopsy, we can see inflammatory cells (lymphocytes and granulocytes), fibrin, and evidence of wound healing such as granulation tissue. Inflammation is often subdivided into acute inflammation (neutrophil predominant) and chronic inflammation (lymphocyte predominant).

Infundibulum: The portion of the hair follicle that lies within the superficial half of the dermis and ultimately connects with the overlying epithelium. This region gives rise to infundibular or epidermal inclusion cysts.

Interface: the interface region lies at the dermal/epidermal junction. If certain changes are seen in this region, most notably basal vacuolar change and/or dyskeratosis, the process may be classified as an interface dermatitis. There are many different dermatoses that present with an interface pattern, for example: erythema multiforme and graft versus host disease. Ultimately, diagnosis depends on correlation of the biopsy findings with clinical observations. A variable amount of inflammatory infiltrate may also be present; when intense and band like in distribution, the term “lichenoid” may be applied. While some may attempt to separate interface and lichenoid dermatoses, the two often overlap and so others consider these as forming one group” “interface/lichenoid”.

Isthmus: the portion of the hair follicle that runs through the lower half of the dermis, this is also the region that gives rise to pilar or isthmic cysts.

Keratinization: a process of differentiation through which keratinocytes acquire keratin filaments in their cytoplasm and ultimately die.

Keratinocyte: the primary cell of the epidermis, keratinocytes play an essential role in imparting protective function to the epidermis. The epidermis consists of several layers of keratinocytes, that migrate from the basal layer on bottom to the granular layer on top. These keratinocytes have strong cell-cell junctions with their neighbors, and as such form a solid sheet that constitutes the epidermis. Keratinocytes also produce protective substances such as keratin, filaggrin, enzymes, and lipids that counteract water loss and infection.

Lentiginous: term used to describe a pattern of growth as single cells along the dermal-epidermal junction.

Lentigo maligna: a form of melanoma in situ occurring on sun damaged skin. Because this is a form of melanoma in situ, the cancerous cells are seen only in the epidermis, and do not invade down into the dermis below.

Lentigo maligna melanoma: invasive melanoma that involves the dermis, and derives from lentigo maligna type of melanoma in situ.

Lesion: term used generically to refer to an observable area of abnormality.

Lichenoid: a term used to describe a band like inflammatory infiltrate in the superficial dermis. This finding is seen in dermatoses such as lichen planus and others within the lichenoid/interface group.

Lymphocyte: B and T cells. Lymphocytes are cells of the immune system belonging to the larger class of white blood cells (leukocytes). White blood cells are subclassified as lymphocytes (B cells and T cells) or granulocytes (neutrophils, eosinophils, basophils, mast cells etc). Lymphocytes are primarily responsible for the adaptive immune response which involves antigen presentation and antibody formation.

Lymphohistiocytic: term used to describe the nature of an inflammatory infiltrate when it is composed primarily of lymphocytes and histiocytes.

Macrophage: a cell of the immune system responsible for phagocytosis (uptake of foreign material) and antigen presentation (presentation of that material to other cells of the immune system, thereby initiating an immune response).

Malignant: having the ability to metastasize, the term malignant generally implies that a lesion may pose a health risk. It should be noted however, that there is a large amount of variability in terms of the behavior of different malignancies and of different malignancies in different patients. While some can be quite aggressive, other malignancies are indolent and quite slow to grow or metastasize.

MART-1: a special (immunohistochemical) stain used to detect melanocytes.

Mast cells: a cell of the immune system that belongs to the class of white blood cells known as granulocytes. Mast cells store and release inflammatory mediators and play diverse roles particularly in the allergic response.

Maturation: the process by which a cell progresses from its primitive state to become more terminally differentiated. In dermatopathology, this is a feature often used in evaluation of melanocytic neoplasms. The presence of maturation in the deeper aspects of a melanocytic lesion is a reassuring feature that suggests a benign nature.

MELAN-A: a special (immunohistochemical) stain used to detect melanocytes.

Melanin: the pigment produced by melanocytes. This can sometimes be seen as golden-brown pigment on H&E stain, but in some cases may require use of Fontana-Masson stain to see.

Melanocyte: a cell of the epidermis that produces melanin pigment. Melanocytes are present in lesser numbers than keratinocytes (one melanocyte for every 4-10 keratinocytes) and tend to be limited to the basal layer. While melanocytes produce melanin, the pigment is then transferred to and stored in neighboring keratinocytes. Melanocytes are the cell of origin of nevi (moles) and melanoma.

Metastasis: a term used to describe spread of a cancer beyond its site of origin. Most commonly this term is used to describe a cancer which has spread another location in the body. The term metastatic calcification however, is unrelated to cancer and describes abnormal calcium deposition in otherwise normal tissue due to elevated serum calcium levels.

Mole: also known as a nevus, moles are growths of melanocytes. Although benign, moles or nevi commonly show “atypical” features under the microscope. If the atypia is particularly concerning, further procedures may be warranted to make sure the entire lesion is removed. Removal of the entire lesion allows the pathologist to have a good look at all areas of the nevus, from the least atypical to the most atypical, and ensure that we are not dealing with something worse. While the frequency with which an atypical mole turns into melanoma is extremely low, the presence of atypical moles may be a marker for someone who is at higher risk for development of melanoma.

Mucin: heavily glycosylated proteins often found in the extracellular matrix of the dermis. Mucin may be increased in entities such as granuloma annulare, mucinoses, and connective tissue diseases. Difficult to see on H&E stained slides, dermal mucin is commonly visualized with a colloidal iron stain.

Mycobacteria: a large group of pathogens containing, among may others, the causative agents of tuberculosis (Mycobacterium tuberculosis) and leprosy (Mycobacterium leprae). Not all mycobacteria are human pathogens. For example Mycobacterium gordonae is a common contaminant of tap water and soil that is not a major disease causing agent. Special stains such as AFB, TBC, or Fite must be employed to see mycobacteria on slides. Even then, the organisms are characteristically small and sparse in number, making identification quite difficult. A second sample or biopsy is often taken and sent to the microbiology laboratory. Microbiology culture should be used to provide more definitive identification as well as speciation.

Necrosis: a type of cell death that differs from apoptosis in that is does not follow a programmed course but rather generally results from unplanned trauma or injury. Necrosis is commonly seen in areas of ischemia (as in large tumors that have outgrown their blood supply), in areas of infection, and in areas of trauma such (as in fat necrosis).

Neoplasm: an abnormal growth of cells that results in a mass of tissue or a tumor. While some neoplasms are malignant with the capacity to metastasize throughout the body (cancer), many tumors or neoplasms are benign. For example, melanocytic neoplasms include malignant melanoma as well as benign nevi.

Nested: term that refers to a type of cellular growth pattern whereby cells form groups of nests. This pattern is commonly seen in melanocytic neoplasms.

Neutrophil: a cell of the immune system, neutrophils are classified within the category of granulocytes, which are a type of white blood cell. Neutrophils play an important role in the acute inflammatory response.

Nevus: also known as a mole, a nevus is a lesion created by increased numbers of melanocytes. Although benign, moles or nevi commonly show “atypical” features under the microscope. If the atypia is particularly concerning, further procedures may be warranted to make sure the entire lesion is removed. Removal of the entire lesion allows the pathologist to have a good look at all areas of the nevus, from the least atypical to the most atypical, and ensure that we are not dealing with something worse. While the frequency with which an atypical nevus turns into melanoma is extremely low, the presence of atypical nevi may be a marker for someone who is at higher risk for development of melanoma.

Pagetoid spread: term used to describe a pattern of cellular growth that may be seen under the microscope whereby cells spread upwards within the epidermis as single cells or small groups of cells. Pagetoid spread may be seen in many different disease states, including Paget’s disease, melanoma, and squamous cell carcinoma, among others.

Panniculitis: inflammation of the subcutaneous adipose tissue (fat). There are many different diseases which can be classified as panniculitis, such as erythema nodosum, erythem induratum, pancreatic panniculitis, lupus panniculitis, cold panniculitis and traumatic panniculitis. Many factors are evaluated under the microscope in attempting to determine the precise disease causing panniculitis. These include the distribution of inflammation (lobular or septal centered), presence or absence of vasculitis and presence and nature of an inflammatory infiltrate. Ultimately, definitive diagnosis may not be possible just based on microscopic findings, and requires correlation with clinical factors.

Papillary dermis: the superficial portion of the dermis that spans the region from the dermal/epidermal junction to the superficial vascular plexus.

Parakeratosis: retention of nuclei within the stratum corneum of the epidermis. Parakeratosis is an abnormal finding that is often seen in states of squamous proliferation, such as acintinc keratosis and squamous cell carcinoma.

PAS: periodic acid schiff, a special (histochemical) stain used in dermatopathology to primarily to highlight basement membrane as well as fungus. PAS stains molecules with a large amounts of carbohydrate. Due to sampling issues, even in cases of true fungal infection the fungi may not be seen under the microscope. Furthermore, the species of fungus can not be determined. Therefore pathology results are supplemented with the results of microbiology culture which, although having a longer waiting period, have the advantage of increased sensitivity and the opportunity for speciation.

Pigment incontinence: melanin pigment is made by melanocytes and stored in keratinocytes, but can be found free in the dermis (pigment incontinence). This is often seen in post inflammatory states, such as in chronic stages of interface dermatitis.

Pleomorphic: a term used to describe variability in the appearance (size, shape, hyperchromasia) of cells. In general, pleomorphism is a feature of malignant cells, however there are exceptions.

Pseudoepitheliomatous hyperplasia: term used to describe a growth pattern of squamous epithelium whereby it closely mimics squamous cell carcinoma. Pseudoepitheliomatous hyperplasia may be seen as a result of chronic irritation/injury, overlying other tumors (granular cell tumor is a classic example), or overlying infection. The presence of pseudoepitheliomatous hyperplasia can cause a diagnostic pitfall, particularly in superficially sampled lesions or in cases of unknown infection.

Psoriasiform: term used to describe a pattern of growth whereby the epidermis is acanthotic (thickened) in a pattern that bears resemblance to psoriasis.

 

Reticular dermis: the portion of the dermis that lies below the papillary dermis and above the subcutaneous tissue. The reticular dermis accounts for the majority of the dermis.

Sebaceous gland: gland located in the dermis that produces sebum and secretes it into the hair follicle. Sebaceous gland are most numerous in the head/neck area but can be found in almost all body sites except the palms and soles.

Sensitivity: also known as the true positive rate, sensitivity is a measure of how often a test “gets it right” in identifying a disorder when one is present. A very sensitive test detects a disorder and gives a positive result whenever the disorder it is looking for is present. A less sensitive test will erroneously give a negative result even though the disorder it is designed to detect is present (false negative). In dermatopathology, sensitivity is often linked to sample size; the more tissue available for examination, the higher the chances of arriving at the correct diagnosis.

Solar elastosis: a degenerative change of elastic fibers within the dermis in response to sun damage. Although intact elastic fibers require special stains to see, solar elastosis can be seen on H&E stained slides as pools of gray material within the dermis. The degree of solar elastosis present increases with age and with amount of exposure to the sun.

Speciation: identification of the genus and species of an organism. Typically this is done through microbiology culture of a separate sample (often another biopsy) that is sent to a microbiology lab. Examination of slides by a pathologist can yield information as to whether there is evidence of infection and if that infection is due to bacteria, fungus or mycobacteria. However, microbiology culture is more sensitive (can be positive even if nothing is seen on the slide) and can yield information as to which bacteria, fungus, or mycobacteria is present; for example, the disease causing Mycobacterium tuberculosis, or the contaminant Mycobacterium gordonae.

Spindle cell: a term used to describe cells that appear elongated and spindle shaped on microscopic examination. This spindled appearance can be seen in a number of different settings: subtypes of melanoma and squamous cell carcinoma as well as various mesenchymal tumors such as leiomysarcoma and neural tumors may have spindled morphology. As most spindle cells appear very similar to each other, a number of different immunohistochemical stains are generally required to identify the cell type of origin.

Spirochete: a unique phylum of bacteria characterized by a double membrane with flagellar structures that allow for movement. Not all spirochetes are associated with human disease, but those that do are the causative agents of syphilis, Lyme disease, and leptospirosis, among others.

Spongiosis: accumulation of edema fluid between keratinocytes. This can be visualized under the microscope as small white spaces surrounding cells of the squamous epithelium. Spongiosis has many causes but is the hallmark of eczematous dermatitis.

Stratum corneum: the uppermost layer of the epidermis, consisting primarily of keratin in the form of corneocytes or dead keratinocytes. The stratum corneum plays an important protective role, minimizing water loss through the epidermis and protecting against infection.

Squamous: a type of epithelial cell, squamous cells comprise the bulk of the epidermis (as keratinocytes) and are the origin of actinic keratoses and squamous cell carcinoma.

Subcutaneous tissue: underneath the epidermis and dermis lies the subcutaneous tissue, which is composed of adipose (fat), connective tissue, nerves and blood vessels.

Telangiectasia: dilated blood vessels in the superficial dermis. These are generally of little significance, but may impart a red appearance to skin or take the form of “spider veins”.

Tumor: an abnormal growth of cells that results in a mass of tissue or a tumor. While some tumors are malignant with the capacity to metastasize throughout the body (cancer), many tumors are benign.

Vacuolar change: a change that appears as vacuoles or holes in basal keratinocytes, vacuolar change is a component of interface dermatitis (see above).

Vasculitis: inflammation of a blood vessel. Vasculitis may be primary (blood vessel inflammation is the main disease) or secondary (some other disease leads to blood vessel inflammation). There are many different causes of vasculitis. Leukocytoclastic vasculitis is a common pattern of vasculitis seen in dermatopathology, but has a myriad of different causes and microscopic observation does not allow for determination of the cause. In general for cases of suspected vasculitis, microscopic examination is helpful to confirm or refute the presence of vasculitis and describe the caliber and location of vessels involved. However, ultimately diagnosis requires on integration of pathology findings with many other clinical findings.

Viral cytopathic effect: a unique set of nuclear changes in virally infected cells that can be seen under the microscope. The type and extent of changes depends on the virus in question. Viral cytopathic effects are most commonly seen in cases of herpes simplex, varicella zoster, and cytomegalovirus infection. The finding of viral cytopathic effect alone should not be relied on for definitive diagnosis of viral infection. Immunohistochemical stains can be helpful and have the ability to identify specific viruses (for example herpes simplex versus varicella zoster). Correlation with serology or microbiology is also important in cases of suspected viral infection.

Von Kossa: a special (histochemical) stain used to detect calcium.

Yeast: a unicellular fungus that may be associated with disease or may be seen simply to colonize human tissue as part of the normal flora.