Selected Pseudoneoplastic Lesions of the Skin
Mark R. Wick, MD; James W. Patterson, MD
● Context.—Pseudoneoplastic cutaneous lesions are di- cussion was drawn from the published literature on cuta-
verse, not only morphologically but also with respect to neous pseudoneoplasms, using an Internet-based search
their causes and cellular lineages. They include prolifera- engine. The authors’ collective experience was also used in
tions of epithelial, as well as mesenchymal, elements. writing this review.
Objective.—This review aims to consider selected le- Conclusions.—Sufﬁcient clinical and morphologic dif-
sions in the aforementioned groups, contrasting them with ferences exist in virtually all instances to separate pseu-
histologically similar neoplasms of the skin in a differential doneoplastic cutaneous proliferations from the tumors that
diagnostic setting. they imitate.
Data Sources.—Information used in assembling this dis- (Arch Pathol Lab Med. 2010;134:369–377)
P seudoneoplastic proliferations are commonly encoun-
tered in the skin because it is the largest organ of the
body and an easy one to sample surgically. Several cuta-
cell nests in BCC are horizontal. Moreover, der Wulst is
surrounded by normal dermis, as opposed to the ﬁbro-
myxoid stroma and stromal-epithelial clefts of BCC.11,12
neous lesions that may potentially be confused with neo- Also, prominent basement membranes are seen only
plasms include selected proliferations of the adnexae, mes- around the basaloid cellular aggregates of der Wulst.
enchymal dermal elements, ‘‘rests’’ or remnants of the Basal cell carcinoma tends to undermine the overlying
neuroectoderm, and inﬂammatory conditions. epidermis and to form an acute angle beneath it; in con-
Other cutaneous abnormalities that some may consider trast, der Wulst has a more rounded proﬁle with its wid-
as pseudotumors are, in our opinion, either true neo- est point at attachments to the follicle. It also lacks the
plasms or preneoplastic in nature. The latter include pro- mitotic activity, apoptosis, melanin, and keratotic micro-
liferations related to the human papillomaviruses,1 as cysts commonly seen in BCC.
well as Langerhans cell histiocytosis,2 ‘‘large plaque
parapsoriasis,’’3 selected cutaneous lymphoid ‘‘hyperpla- Pseudoepitheliomatous (Pseudocarcinomatous)
sias,’’4 lymphomatoid papulosis,5,6 the spectrum of ﬁbro- Epidermal Hyperplasia
matoses and melanocytic nevi,7,8 and spindle cell heman- It has long been recognized that reactive epidermal cells
gioendothelioma-hemangioma.9 They will not be consid- could proliferate with patterns simulating those of squa-
ered here. mous cell carcinoma or basal cell carcinoma. This process,
termed pseudoepitheliomatous hyperplasia (PEH; or pseudocar-
PSEUDONEOPLASTIC EPITHELIAL PROLIFERATIONS cinomatous hyperplasia), is potentially associated with or-
Hair Follicle ‘‘Bulges’’ (der Wulst) ganoid nevi, nonhealing ulcers, chronic dermatitides, re-
Der Wulst—also designated central facial folliculocentric actions to underlying neoplasms, and selected infections
basaloid proliferation—is problematic in the interpretation of the skin.13–16 Pseudoepitheliomatous hyperplasia may
of frozen sections or specimens from Mohs micrographic particularly be misdiagnosed as a carcinoma in very su-
surgical procedures. In those settings, the normal basa- perﬁcial biopsies because only the epidermal reaction to
loid expansions of paranasal hair follicles might be con- an underlying lesion is sampled.
fused with basal cell carcinomas (BCCs). Both of those PEH in Chronic Dermatitides. Pseudoepithelioma-
proliferations contain cytologically similar cell popula-