Pilar Simón

Solitary keratoacanthoma : A self-healing proliferation that frequently becomes malignant

To discuss the relation between solitary keratoacanthoma (KA) and crateriform squamous cell carcinoma (cSCC), the clinical and histologic features of cutaneous crateriform squamous cell proliferations were studied. Two hundred twenty cases of wholly excised crateriform squamous cell proliferations were studied both clinically (age, sex, location, and duration) and histologically (hematoxylin-eosin–stained sections). For comparison, we studied 100 consecutive cases of wholly excised noncrateriform squamous cell carcinoma (ncSCC). One hundred forty-four of the 220 cases of crateriform squamous cell proliferations were histologically classified as KA. In 47 other cases, a relatively large area of the KA showed frank histologic and cytologic malignant transformation (mKA); this event could happen during every stage of the KA. Twenty-nine lesions were cSCCs without remnants of KA. The patients in the KA group were significantly younger (p = 0.000) than those in the other three groups. The ages of the patients in these three groups were not significantly different (p = 1.0). More KAs (16%) were located in areas that are not usually exposed to the sun than was the case with the other groups of neoplasms considered (2%, 3%, and 3%, respectively), and this difference was statistically significant (p = 0.001). Regarding the duration of the lesion, only the differences between KA and cSCC, KA and ncSCC, and mKA and ncSCC were statistically significant. Not every cutaneous crateriform squamous cell proliferation is a KA; in KA, the crater must be multilocular, the “lips” must be perforated, and the cornified contents do not usually project out of the “mouth.” At least a quarter of KAs undergo malignant transformation, which occurs more frequently in older patients and photoexposed areas. This transformation is a focal event and may happen at any stage of KA development. Consequently, a suspected KA must be wholly excised and studied in serial paraffin blocks so as to disclose any focus of malignant transformation.

Sebomatricoma: a unifying term that encompasses all benign neoplasms with sebaceous differentiation.

Literature regarding neoplasms with sebaceous differentiation is confusing, particularly concerning the concept of sebaceous epithelioma, accepted by some observers as a specific neoplasm but defined by others as basal cell carcinoma with sebaceous differentiation and still others as sebaceous adenoma in which undifferentiated basaloid cells predominate. From our study of 19 benign sebaceous neoplasms within this spectrum and a critical review of the literature, we conclude that (a) “sebaceous epithelioma” is a nonuseful term; (b) the term “basal cell carcinoma with sebaceous differentiation” should be used only for an otherwise conventional basal cell carcinoma with histological evidence of sebaceous differentiation; (c) “sebaceous adenoma,” as described by Rulon and Helwig, and “sebaceoma,” as described by Troy and Ackerman, represent polar ends of the spectrum of a benign neoplasm with varying degrees of sebaceous differentiation, for which we propose the term “sebomatricoma” and (d) sebomatricoma, so defined, embraces such diverse benign neoplasms with sebaceous differentiation as superficial epithelioma with sebaceous differentiation and previously “unclassifiable” sebaceous neoplasms, often found in patients with Muir–Torre syndrome or within nevus sebaceus of Jadassohn.

Striated muscle: a normal component of the dermis and subcutis in many areas of the face.

Striated muscle is typically not mentioned in histology chapters of most dermatology and dermatopathology books. In others, authors only speak of its presence in the dermis or subcutis but do not provide any details about its quantity, distribution, or orientation. In the course of an investigation concerning regional histologic variations of the skin, the presence of striated muscle fibers (StrMFs) has been a noteworthy feature of many areas of the face. Striated muscle fibers are a normal constituent of the dermis of the eyebrow (few and deep fibers); eyelid and nose (excluding the nasal tip) (numerous and deep fibers); and lips and chin (numerous, vertical, and more superficial fibers). They are also found in the subcutis of all these areas with some differences in density and distribution among them. Striated muscle fibers form a compact layer beneath the subcutaneous fat on the forehead and cheek, but because of their deep location, they are rarely included in cutaneous biopsy specimens of the latter area. Mainly based on the presence of StrMFs in the dermis, an algorithm to accurately determine the location of biopsy specimens from the face has been elaborated. With the aid of other features such as the type of hair follicles and the presence and degree of solar elastosis, the sex and approximate age of the patient can be established in many cases. Some practical and scientific consequences of these findings are discussed.

Stimulation of folliculo‐sebaceous proliferations by neurofibromas: a report of two cases

Two unrelated patients, a woman aged 44 and a man aged 56, with a type I neurofibromatosis, showed comedo‐like formations at the top of some neurofibromas. One of them was excised in each case and they were studied histopathologically. The comedo‐like formation of the first case mimicked the epithelial component of a fibrofolliculoma, and that of the second case had the structure of a primary late microcomedo and showed also anagen hair differentiation in the form of a follicular bulb and papilla. Both events are considered to be the result of a stimulation phenomenon and to reflect the essential role of the stroma in many cutaneous epithelial hyperplasias, hamartomas and possibly in some neoplasms.