Canti (1984) advocated the use of a double edge dissector, a lightweight instrument that can be used for removal of scrape samples and their spread on glass slides (Fig. 34-1). A variety of curettes, or even simple scalpel blades, may also be used for this purpose. In some cases, the layer of keratinized superficial cells must be removed from the surface of the lesion. Canti (1984) advocated the preparation of two smears, one fixed in alcohol for processing with Papanicolaou stain, and one unfixed, stained immediately with methylene blue or Diff-Quik stain (Dade Behring Inc., Deerfield, IL) for immediate microscopic diagnosis. In many instances, the rapidly stained smear is adequate for diagnosis and saves much time to the patient and the dermatologist who can initiate treatment without delay. Several examples of the latter techniques can be found in
this chapter, courtesy of Dr. G. Canti. The stain preparation techniques are discussed in Chapter 44.

For aspiration biopsies (FNA) of skin or subcutaneous nodules, a very small caliber needle (gauge 22 to 25), with or without syringe, can be used. For description of aspiration techniques of superficial skin nodules, see Chapter 28. Smear preparation may be the same, as outlined above for scrape smears. Nearly all of the recent reports are based on aspiration biopsies of palpable, nodular lesions of the skin and subcutaneous tissues (summaries in Koss et al, 1992; Layfield and Glasgow, 1993; Dey et al, 1996).

Direct smear preparations for infectious disorders of the skin, especially in scaly skin lesions, have been in use for many years. The diagnosis of fungus infections of the skin (dermatophytosis) is readily accomplished in direct smears using a few drops of potassium hydroxide (KOH) to clear the cornified cells (squames) scraped from the surface of a lesion. The smears may be inspected unstained or stained with methylene blue or another rapid stain. Fungal hyphae and yeast forms (such as cryptococcus or blastomyces) may be demonstrated.

Aspiration biopsies of nodular lesions of the skin caused by fungal organisms have been reported. Thus, blastomycosis was reported by Desai et al (1997) and histoplasmosis by Stong et al (1994). We observed a case of cryptococcosis of the skin in the form of a palpable nodule in a patient with AIDS (Fig. 34-2A). The morphologic features of these organsims are discussed in Chapter 19.

Some parasitic diseases of the skin, such as the mite Sarcoptes scabiei causing a severe skin itch known as scabies and Leishmania donovanii, may also be identified in scrape smears (Baez-Giangreco et al, 1989; Koss et al, 1992). Kapila and Verma (1989) and Koss et al (1992) described filariasis of the skin. African trypanosomiasis (sleeping sickness) can also be diagnosed by aspiration of lymph nodes as first reported by Graig and Gray in 1904. The disease produces ulcerated skin lesions (chancre). The diagnosis can be established on fluid from the chancre (Case Records of the Massachusetts General Hospital, Case 20-2002). The harmless small parasite, Demodex folliculorum, a common inhabitant of follicular infundibula of face, can also be recognized in scrape smears because of eight protrusions known as “sucker feet” and a striated abdomen (Canti, 1984). Kamal and Grover (1995) reported on several cases of cysticercosis diagnosed by aspiration of subcutaneous nodules. For a detailed discussion of leishmaniasis and cysticercosis, see Chapter 19.

Tuberculosis of the skin (known as lupus vulgaris) is now-a-days uncommon. Canti (1984) reported the presence of carrot-shaped epithelioid cells and occasional giant cells, accompanied by inflammatory exudate, in scrape smears. The same observer reported finding epithelioid cells in the uncommon skin manifestations of sarcoidosis. See Chapter 19 for a detailed discussion of these disorders.

The acid fast rods bacillus leprae (leprosy), which may
be very numerous in skin lesions of the lepromatous form, can also be recognized in aspiration smears (Singh et al, 1996). Other applications of this technique are to subcutaneous abscesses or infected cutaneous cysts that may also yield a diagnosis by this simple, rapid and inexpensive procedure. A case of intramuscular bacillary angiomatosis was diagnosed on thin needle aspiration of a subcutaneous mass in a patient with AIDS (Sanchez and Rorat, 1996). Besides inflammatory cells, the aspiration smears in this case contained clumps of amphophylic granular material containing small bacterial rods demonstrated by silver stain. The organisms belonging to the genus Rochalimacea (now Bartonella) are also involved in cat scratch disease (see Chap. 31).

These soft, brown, elevated benign lesions of the sun-exposed skin are usually recognized clinically and rarely need biopsy confirmation. Histologically, the lesions show a proliferation of basal squamous cells with formation of small cystic areas filled with keratin. Basal cell and, very rarely squamous cell carcinomas, may develop in seborrheic keratosis; such lesions may become ulcerated and indurated. The diagnostic procedures of these rare lesions are the same as for carcinomas, described below. Canti (1979) described the smears as composed of nucleated and anucleated squamous cells without specific features.

Benign and malignant tumors of the endocrine and apocrine sweat glands, hair or piliary apparatus are uncommon and show a wide spectrum of histologic patterns (Wick et al, 1985). The benign tumors are occasionally aspirated to rule out a primary or metastatic malignant tumor. Layfield and Mooney (1998) reported a case of a benign hydradenoma of the skin. We have seen a misleading case of clear cell hidradenoma in a young woman with a history of treated adenocarcinoma of the uterine cervix that was thought clinically
to be a metastasis. The aspirate contained small epithelial cells with hyperchromatic nuclei occurring singly and in clusters (Fig. 34-5A-C). The clear cytoplasm of some of the cells contributed to the erroneous diagnosis of metastatic adenocarcinoma. Excisional biopsy of the nodule disclosed a clear cell hidradenoma (Fig. 34-5D). Courtesy of Dr. G. Canti, we also examined a smear of an adenoma of a sebaceous gland. The smear contained a cluster of large cells with faintly granular, abundant cytoplasm, resembling fat cells (Fig. 34-6).

Fat-containing tumors, known as xanthogranulomas, and occurring mainly in infants and children, have been reported (Janney et al, 1991). Besides multiple macrophages, the lesions contained multinucleated giant cells (Grenko et al, 1996).

These tumors, which occur mainly but not exclusively in young people, form chalky-white subcutaneous nodules, usually located on the face, neck, or upper extremities, sometimes underneath pigmented skin. The cytology of this tumor was first described in needle aspirates by Woyke et al (1982). The aspirates of these tumors contain small basophilic cells, singly and in clusters, admixed with nucleated and anucleated squames, the latter forming clusters of yellowish “ghost” cells. Calcified material and foreign body giant cells round out the spectrum of features (Fig. 34-7). Numerous errors of diagnosis have been committed in the past mistaking pilomatrixoma for squamous carcinoma (Gomez-Aracil et al, 1990; Koss et al, 1992; Domanski and Domanski, 1997). In recent reports, the features of pilomatrixoma have been better recognized and no errors of identification were made (Viero et al, 1999).