In this issue of Pathology Case Reviews the contributors shed light on the meaning behind those cutaneous neoplastic entities arising from adnexal structures. In the current literature, there is a striking lack of consensus for the exact nomenclature to apply to many of these entities, hence confusion lies not only in etiology, but terminology as well. After toiling with the terminology and ultimately arriving at a diagnosis of “benign adnexal neoplasm”, the pathologist herein learns that that diagnosis is not necessarily sufficient. Dr. Sharp, a dermatologist, reveals the significance of the benign adnexal neoplastic diagnosis from her side of the glass slide; that is, the clinical interpretation and follow up of the pathologic diagnosis. She discusses the contribution the pathologist makes in providing an opportunity for the clinician to explore the possibility of a patient's high risk for internal malignancies with a simple diagnosis of fibrofolliculoma, sebaceous adenoma or tricholemmoma. Her review of the most commonly encountered syndromes associated with internal malignancies that have, as one expression of their disease, a benign adnexal neoplasm, is emphatic with regard to the clinician's need for a diagnosis beyond “benign adnexal neoplasm”.
Clarifying the terminology mire is the focus of the approach of Drs. Mattoch and Cassarino. The notion of a folliculosebaceous apocrine unit provides a unifying concept for understanding patterns of differentiation that include sebaceous, follicular, apocrine and eccrine. Dr. Mattoch introduces this idea and elaborates on the significance, or lack of it, in attempting to differentiate an apocrine versus eccrine birthplace for these lesions whose ultimate diagnosis has no clinical significance as far as we know. The differentiation, at this point, is purely academic.
Due to significant histologic convergence, differentiating a metastatic lesion to the skin from a primary cutaneous lesion can be a challenging task, and in the absence of enlightening clinical history can be impossible. Even with an appropriate history, this differential can be elusive. With 5% of patients who have carcinoma developing cutaneous metastasis, and 10% of patients with metastatic disease having their metastasis in a cutaneous site, the chances of one such lesion crossing our microscope oculars in any given week, month or year is high. Although in women these cutaneous metastasis most often have a breast primary and in men a lung primary, many other sites are reported to be the nidus for the cutaneous metastases. Most commonly, these lesions present as a painless nodule resulting in low suspicion in both patient and physician, especially when the primary malignancy has not yet been discovered. This demands a high index of suspicion on the part of the pathologist. Dr. Perna and colleagues share with the reader the morphologic and immunohistochemical findings that are helpful in distinguishing a primary cutaneous adnexal neoplasm from its metastatic mimic.
An uncommon benign adnexal hamartoma and a not so uncommon malignant adnexal neoplasm are presented by Dr. Pashaei and Dr. Beyer respectively. Dr. Beyer presents a case of microcystic adnexal carcinoma, a mimic, at least superficially, of syringoma. In addition to the histologic differential diagnosis there is repeated caution in feeling obliged to place a definitive diagnosis on an inadequate specimen in which eccrine ducts extend to the deep margin.
Dr. Pashaei presents an unusual case of a vellus hair hamartoma presenting in an adult. Her discussion focuses on the histologic distinction of this entity from some of the more commonly encountered lesions with extensive follicular differentiation. She additionally builds support, through immunohistochemical interpretation of antigen expression, for the ontogenic nature of this lesion.
To conclude this issue, Drs. Schlauder and Morgan provide a review on lesions with a sebaceous etiology, from ectopias and hamartomas to benign and malignant sebaceous neoplasms. A thorough pictorial presentation is provided. In addition to these lesions of the sebaceous apparatus, other neoplasms, most frequently basal cell carcinoma but also other adnexal neoplasms, are known to undergo sebaceous differentiation, an important concept to remember in working through the differential diagnosis of a cutaneous nodule with sebocytes.
Internal malignancies have numerous opportunities to present themselves as cutaneous lesions: paraneoplastic pemphigus seen in non-Hodgkin's lymphomas, acrokeratosis paraneoplastica seen in upper aerodigestive tract malignancies, and explosive onset of seborrheic keratosis (sign of Leser Trelat) in visceral malignancies, most commonly gastric adenocarcinoma, to name a few. Two additional cutaneous manifestations are presented in this issue: the benign adnexal neoplasms that may be syndromic and indicative of an underlying malignancy and the cutaneous metastasis that can easily be mistaken for a primary cutaneous neoplasm. These articles, along with those discussing the folliculosebaceous apocrine unit and sebaceous neoplasms, intend to add a level of comfort to the pathologist providing the diagnosis as well as instilling a sense of importance for the ultimate care of the patient when rendering seemingly innocuous diagnoses such as trichofolliculoma.