Results

 
The following lesions can be differentiated with repeatability: cystic lesions, verrucous lesions, fibromatous lesions, and some variations of dermal proliferations. Criteria for differentiation are given in the following:
 
1. Cystic shape
 
A cystic lesion can be identified readily in a stained slide without a microscope because it consists of a space, usually lined, filled with a substance.
 
Without a microscope it cannot be determined with surety whether a cystic structure has a lining, but the shape of the cyst and the contents of the cyst can be assessed (Fig. 2A).
 
—A round cyst is one filled by a substance that gives stability to it, for example, an infundibular cyst and a tricholemmal cyst filled with keratin.
—A cyst with a jagged appearance is one that collapsed because it was filled with a soft substance that was resolved during processing, such as a steatocystoma filled with sebum.
 
Moreover, the type of content of a cyst can be assumed by its color (Fig. 2B and C).
 
—Blue content can be infundibular keratin in an infundibular cyst, and then it appears finely lamellar, or it can be structureless, such as in a mucoid cyst (Fig. 2B).
—Pink content can be tricholemmal keratin, such as in a tricholemmal cyst, shadow cells of a pilomatricoma, or apocrine secretion in an apocrine cyst or cystadenoma (Fig. 2C).
—Whereas pink keratin of tricholemmal cysts and pilomatricomas may calcify with blue granular material in the center, apocrine secretion is homogenous and never calcified.
—The pink keratin of a tricholemmal cyst is slightly different in color from the keratin in a pilomatricoma, which has an orange hue.
 
Sometimes, a cystic structure has a prominent lining, which is usually a hint that the cystic structure is a solid cystic neoplasm or hamartoma rather than a true cyst (Fig. 2C).
 
—In a pilomatricoma, the lining is variable in thickness and dark blue because it consists of matrical and supramatrical cells.
—In an apocrine cystadenoma, the lining is also variable in thickness but pink in color and sometimes shows papillations into the lumen.
 
Another hint to the type of a cyst is the surrounding dermis (Fig. 2A).
 
—If there are numerous terminal follicles, the specimen comes from the scalp and the diagnosis is tricholemmal (isthmus-catagen) cyst.
—If terminal follicles are absent, the lesion comes from elsewhere on the body and the diagnosis is more likely to be an infundibular cyst.
—If a cyst with blue content comes from the mucous membranes, however, it is a mucoid cyst, not an infundibular cyst.
 
Even variations of infundibular cysts can be differentiated at ultimate scanning magnification (Fig. 2D) :
 
—A small cyst coming from the face is a milium.
—A cyst with dense infiltration at one edge is a ruptured cyst with reactive foreign body reaction.

View Figure  		Fig. 2A  Cystic lesions in comparison. The first two examples are round cysts and the last one is a cyst with a jagged appearance. The first cyst with blue content is an infundibular cyst. The second cyst with pink content is an isthmus-catagen (tricholemmal) cyst. The third cyst with a jagged appearance is a steatocystoma; it collapsed because its soft contents had resolved completely during processing.

View Figure  		Fig. 2B  Cystic lesions with blue content. When a cyst has blue content with lamellar structure, it is an infundibular cyst (top). When the blue substance is devoid of structure, it is a "mucoid" cyst which, in actuality, is not a true cyst because it has no lining epithelium (bottom).

View Figure  		Fig. 2C  Cystic lesions with pink content. When a cyst has pink content that is compact and round with blue granular material in the center, it is an isthmic-catagen cyst with calcification (top). When the pink compact substance has an orange hue and is lined by variable thickness of blue proliferation, it is a pilomatricoma, which is a cystic neoplasm rather than a true cyst (middle). When the pink content is homogenous and lined by eosinophilic proliferation with papillation, it is a cystadenoma (bottom).

View Figure  		Fig. 2D  Infundibular cysts are always filled with blue lamellar keratin. When a nodular infiltrate is seen at one side, such as it is the case in the third example, it is a cyst that ruptured and induced a foreign body reaction. When the cyst is small and comes from a site rich in follicles, such as is the case with the fourth example, it is conventionally termed "milium."
 
2. Verrucous shape
 
A broad variety of lesions present themselves with verrucous shapes, the most common being seborrheic keratoses and warts (Fig. 3A). Those can be differentiated as follows:
 
—Seborrheic keratoses have a flat base and only slightly elevated broad and rounded digits and a smooth surface.
—Verrucae vulgares have a bulbous or endophytic base and an elongated digitated surface, the digits being oriented somewhat radially.
 
Moreover, verrucous lesions have different colors (Fig. 3A) :
 
—Seborrheic keratoses appear blue and have white spots, which represent infundibular cystic structures ("pseudohorncysts") (Fig. 3B).
—Verrucae vulgares appear pink, and on the top of digitations, pink cornification can be identified (Fig. 3C)
 
A challenging task is the differentiation of curettage material because size and shape of lesions is a consequence, at least in part, of the superficial operation technique (Fig. 3D) :
 
—Curettings of seborrheic keratoses often keep the flat shape, and white spots which represent infundibular cystic structures may be identified in them (Fig. 3C).
—Another lesion often curetted is molluscum contagiosum which, in contrast to seborrheic keratosis, consists of pieces relatively even in size, a round shape and blue color. Also in the center of each round lesion is a pale bluish spot, which are the molluscum bodies (Fig. 3E).
 
Malignant epidermal neoplasms may also be identified according to their silhouette.
 
—Keratoacanthoma is verrucous and exoendophytic but with a crateriform shape (Fig. 3F).
—Conventional squamous cell carcinoma is asymmetric, more endophytic than exophytic, and oriented in horizontal fashion (Fig. 3G).
 
Keratoacanthoma, as well as conventional squamous cell carcinoma, can be differentiated from basal cell carcinoma without a microscope in most instances because:
 
—Keratoacanthoma and conventional squamous cell carcinoma are eosinophilic and they consist largely of cells of spinous differentiation (Fig. 3G) whereas
—Basal cell carcinoma appears basophilic because it is made up of trichoblasts. Moreover, it is usually an exoendophytoc nodule rather than a verrucous lesion (Fig. 3H).
 
It may not be so easy at times to separate basal cell carcinoma from seborrheic keratosis without a microscope because both consist of blue basophilic cells (Fig. 3I). Hints to differentiating them are as follows:
 
—Basal cell carcinoma is asymmetric and endophytic or endoexophytic rather than only exophytic.
—Seborrheic keratosis is symmetric, has a flat base, and is typically exophytic.

View Figure  		Fig. 3A  Verrucous lesions in comparison. Whereas seborrheic keratosis (top) is blue with white spots that represent infundibular cystic structures ("pseudohorncysts"), verruca vulgaris (bottom) is pink, and on the top of digitations pink cornification can be identified.

View Figure  		Fig. 3B  Warts are pink verrucous lesions, and on the top of digitations pink cornification can be identified.

View Figure  		Fig. 3C  Seborrheic keratoses are blue verrucous lesions with a flat base and only slightly elevated broad and rounded digits at a smooth surface.

View Figure  		Fig. 3D  In curettage material, seborrheic keratoses can be easily differentiated from molluscum contagiosum because seborrheic keratoses appear flat and broad with white spots (top), whereas molluscum contagiosum are roundish with blue spots in the center (bottom).

View Figure  		Fig. 3E  Molluscum contagiosum consist of round lesions, rather even in size, shape, and color.

View Figure  		Fig. 3F  Comparison of a wart (top) with a keratoacanthoma (bottom) shows an impressive difference in the size of the lesions but also that the wart has a digitate surface, whereas the keratoacanthoma is a crateriform lesion.

View Figure  		Fig. 3G  Keratoacanthoma (top) in comparison with conventional squamous cell carcinoma (middle) and basal cell carcinoma (bottom). Keratoacantoma and conventional squamous cell carcinoma are both pink proliferations. Keratoacantoma is exoendophytic and crateriform, whereas conventional squamous cell carcinoma is more endophytic and asymmetric and less well circumscribed. Basal cell carcinoma, however, is an asymmetric blue proliferation, mostly endophytic.

View Figure  		Fig. 3H  Basal cell carcinomas are blue proliferations, often arranged horizontally, relatively well circumscribed, and asymmetric.

View Figure  		Fig. 3I  Seborrheic keratosis (top) in comparison with basal cell carcinoma (bottom). Both proliferations are blue, but seborrheic keratosis is verrucous and exophytic, symmetric, and with a flat base, whereas basal cell carcinoma is mostly endophytic, asymmetric, and with irregular circumscription and sometimes ulcerated at the surface.
 
3. Fibromatous shape
 
Many lesions may have a fibromatous shape at scanning magnification. Most frequently they are fibromas and Unna nevi, and less commonly neurofibromas or angiomas (Fig. 4A). The lesions can be differentiated with some degree of certainty without using the microscope when focusing on the content of the fibromatous process:
 
—Fibromas seem to have a dermis that contains "nothing" except dermal connective tissue. In contrast, Unna nevi and neurofibromas contain a proliferation of cells.
—Unna nevi have a blue content organized in a dotty fashion—those structures representing nests of melanocytes (Fig. 4B).
—Neurofibromas have a pink, loose material inside that never assumes arrangement in the form of nests (Fig. 4A).
—Angiomas are encircled often by a collarette of adnexal epithelium and they are filled with red dots—those representing dilated blood vessels filled with erythrocytes.

View Figure  		Fig. 4A  Fibromatous lesions in comparison. A fibroma shows pink dermis in the center (top); Unna nevus shows a blue nested proliferation in the center (middle); and neurofibroma shows a loose grey or pinkish proliferation in the center (bottom).

View Figure  		Fig. 4B  Unna nevi in comparison. All of them have in common the blue proliferation of cells in the center.
 
4. Dermal (and subcutaneous) proliferations
 
In a similar way, namely by concentrating on the structure and circumscription of a proliferation of cells, lesions can also be differentiated when they do not show a fibromatous shape, which may at times be the case for neurofibromas and angiomas. The following may serve as examples (Fig. 5A) :
 
—Dermatofibroma can be identified as a round but not sharply circumscribed pink or grey nodule in the dermis, sometimes retracting the epidermis in the form of a dell and sometimes elevating the subcutis in a focus.
—Neurofibromas have a pink, loose material inside that sometimes is separated from the surrounding dermis by a cleft.
—Lipoma can be diagnosed with ease without a microscope because it is a well-circumscribed lesion with a pale appearance, that color corresponding to proliferations of large adipocytes with a clear cytoplasm.
—Angiomas consist of red dots—those representing dilated blood vessels filled with erythrocytes.
 
With regard to melanocytic lesions, Unna nevi have been mentioned already in the paragraph on lesions with a fibromatous shape. Other types of congenital melanocytic nevi may also be identified with near certainty without a microscope. However:
 
—An umbrella-shaped arrangement of blue material in the dermis is indicative of a congenital nevus that shows marked adnexocentrism (Fig. 5B).
—If such a lesion is dome-shaped and appears in the context of prominent white lobules or of numerous follicles, it is a Miescher nevus, a congenital nevus on the face, the white lobules representing sebaceous glands associated with numerous follicles typical for that site (Fig. 5C).

View Figure  		Fig. 5A  Dermal (or subcutaneous) proliferations in comparison. In the first example, red spots are suggestive of an angioma; the pink loose content in dermis of the second example indicates a neurofibroma; a pale encapsulated lesion such as shown in the third example is a lipoma; and the last example shows a round but irregularly demarcated nodule of grey or pinkish color elevating in a focus the subcutis or at times retracting the acanthotic epidermis that is characteristic for a dermatofibroma.

View Figure  		Fig. 5B  Congenital melanocytic nevi can be identified by way of an umbrella-shaped blue proliferation in the dermis. Variations include fibromatous ones on the trunk (Unna nevi, third example) and dome-shaped ones on the face (Miescher nevi, fourth example), as can be seen from numerous sebaceous glands and follicles in the dermis around them.

View Figure  		Fig. 5C  Miescher nevi can be identified consistently because of their dome shape and a deep blue proliferation in a dermis that houses numerous follicles and sebaceous glands.