Dermatopathology is replete with illusions to colorful images that are designed to call specific diseases to mind. For example, “dilapidated brick walls” are supposed to suggest Hailey-Hailey disease, and “tombstones” are meant to indicate pemphigus vulgaris. “Corps ronds” and “grains” purportedly indicate Darier’s disease, and “shadow cells” reputedly mean pilomatricoma. “Cartwheel,” “pinwheel,” and “whirligig” pattern is claimed to signify dermatofibrosarcoma protuberans. Each of these flavorful designations lacks specificity. Acantholytic cells throughout the entire thickness of an epidermis may be seen not only in Hailey-Hailey disease but in Grover’s disease; suprabasal clefts above intact dermal papillae may be met with not only in pemphigus vulgaris but in Hailey-Hailey disease; foci of acantholytic dyskeratotic cells in the spinous and granular zones and acantholytic cells in the cornified layers occur not only in Darier’s disease but in Grover’s disease and in some expressions of epidermal nevus; “shadow cells” represent a flawed attempt at differentiation toward hair and may be found in conditions as disparate as mixed tumors with apocrine, sebaceous, and follicular differentiation and in desmoplastic trichoepitheliomas, as well as in pilomatricoma. The subject under discussion here, namely, so-called cartwheel, pinwheel, and whirligig patterns, not only is an attribute of dermatofibrosarcoma protuberans, but of several other conditions, as unalike as schwannoma and dermatofibroma.
Before addressing the lack of specificity of “cartwheel,” “pinwheel,” and “whirligig” patterns, it is reasonable to ask what, precisely, those words are meant to convey to a histopathologist. For most general pathologists, they are synonymous with a storiform pattern. In simple language morphologic, all of those images refer to oval and/or spindle cells arranged in fascicles that intersect one another, i.e., they “interweave.” That pattern is not diagnostic of any single disease. Although spindle cells in short fascicles of spindle cells that interweave are encountered commonly in dermatofibrosarcoma protuberans, many examples of that “low-grade” sarcoma are devoid completely of that pattern. In some lesions of dermatofibrosarcoma protuberans, deposits of mucin predominate over neoplastic cells. In some sections, there are no fascicles of spindle cells at all, and if a fascicle is present, it may not intersect with other fascicles.
Short fascicles of spindle cells that interweave may be seen in a benign neural neoplasm such as schwannomas. In addition to characteristic “Verocay bodies,” type A schwannomas may have a distinctive pattern of of spindle cells organized in short fascicles that interweave. As in the case of dermatofibrosarcoma protuberans, many, if not most, of the spindle cells in schwannomas may exhibit wavy nuclei, an indication of neural differentiation. One hypothesis in regard to dermatofibrosarcoma protuberans is that it is composed of perineural fibrocytes. In analogy to dermatofibrosarcoma protuberans, some schwannomas may lack a pattern of spindle cells in short fascicles that interweave. That is true of many schwannomas of Antoni type A and virtually all schwannomas of Antoni type B.
Dermatofibroma is a fibrosing inflammatory process, akin to scars and keloids. Longstanding lesions of it, prior to sclerosis, may be composed of oval or spindle cells in short fascicles that interweave. The cells in fascicles of dermatofibroma do not possess wavy nuclei, an attribute that enables them to be differentiated from the cells in fascicles of dermatofibrosarcoma protuberans and of schwannoma.
The three conditions mentioned here are very different from one another clinically, histopathologically, and biologically. Dermatofibroma is a fibrosing inflammatory process, schwannoma is a benign neoplasm, and dermatofibrosarcoma protuberans is a malignant neoplasm, to wit, a sarcoma that is notorious for persistence at the primary site despite numerous attempts at surgical extirpation of it, sometimes extending wider and deeper than surgery designed to root it out, and for metastasizing rarely.
Last, it should be noted that granuloma faciale/erythema elevatum diutinum, two names for a single condition on different sites anatomic, are examples of longstanding leukocytoclastic vasculitis that early in their course show fibrin in walls of venules in conjunction with abundant neutrophilic nuclear “dust” of neutrophils, years later display only hints of a mixture of inflammatory cells, but striking fibroplasia in which short fascicles of fibrocytes and accompanying wiry bundles of collagen interweave. The pattern then is reminiscent of that which is the basis for this chapter.
In conclusion, “cartwheel,” “pinwheel,” and “whirligig” pattern has become a clich? for dermatofibrosarcoma protuberans. Like all of the clich?s in dermatopathology, they are misleading because they are inaccurate.