Case Summary
A 46-year-old woman presented to the surgical outpatient department with a 10-year
history of scalp swelling in the occipital region. The swelling was initially small
in size, which gradually increased to attain the size of a pebble ([Fig. 1]). There was no history of trauma preceding the onset of swelling. The patient did
not complain of any pain, itching, or discoloration. On examination, the skin overlying
the swelling was normal. The swelling was freely mobile in all directions and was
not adherent to overlying skin or underlying structures. The consistency was soft
to firm on palpation. The patient underwent surgical excision, and the specimen was
sent for histopathological examination.
Fig. 1 Swelling in occipital region of the scalp. The overlying skin appears normal.
Differential Diagnosis
The differential diagnoses considered on clinical examination in this case were lipoma,
epidermoid cyst, and sebaceous cyst.
Histopathological Workup
Gross Examination
A partially skin-covered globular tissue mass measuring 2.0 × 1.4 × 0.8 cm was observed.
It had a well-demarcated solid cystic swelling with a glossy white cyst wall ([Fig. 2]). The cut surface showed a firm whitish ovoid area measuring 1 × 0.6 × 0.6 cm with
other cystic area filled with yellowish material ([Fig. 3]).
Fig. 2 Excision biopsy of the scalp lesion. The outer surface is glossy white in appearance.
Fig. 3 The cut surface of the solid cystic lesion, which showed a firm whitish ovoid solid
area with other cystic area filled with yellowish material.
Microscopy
The cyst wall was lined by a keratinized stratified squamous epithelium with the absence
of a granular cell layer. Variable sized lobules of squamous epithelium were noted
undergoing abrupt change into eosinophilic amorphous keratin. The proliferating epithelium
showed pushing borders. The cyst cavity contained abundant keratin, cholesterol clefts,
and areas of calcification. No granuloma or giant cells were present. No dysplasia
existed ([Figs. 4],[5],[6],[7]).
Fig. 4 Cystic cavity lined by keratinized stratified squamous epithelium with the absence
of the granular layer. Cholesterol clefts are also evident (hematoxylin and eosin,
×40).
Fig. 5 Similar findings as in Fig. 4 but at a higher magnification. The keratin-filled cavity
is better appreciable at this magnification (hematoxylin and eosin, ×100).
Fig. 6 Variable sized lobules of squamous epithelium undergoing abrupt change into eosinophilic
amorphous keratin. The proliferating epithelium shows pushing borders. The lesion
is considered a mimic of squamous cell carcinoma (hematoxylin and eosin, ×40).
Fig. 7 Areas of calcification, which commonly occur in proliferating pilar tumors.
Diagnosis and Discussion
The low-power histomorphology of the lesion may mimic the appearance of a squamous
cell carcinoma. However, the important differentiating points that need to be considered
here are pilar-type keratinization, absence of a granular layer, presence of a well-defined
capsule, and the presence of the proliferating part only within the capsule, which
support the diagnosis of a proliferating pilar tumor.
This tumor was first described by E.W. Jones who referred to it as a proliferating
epidermoid cyst, which has also been called a proliferating pilar tumor.[1] Other terms that are used for the condition include proliferating trichilemmal cyst,
proliferating trichilemmal tumor, and pilar tumor of the scalp.[2] Although this has been considered a benign mimic of squamous cell carcinoma, there
are few reports describing the malignant behavior of these tumors.[3]
[4] Most cases are noted in women in the 43- to 66-year age range, with the most common
location being the scalp.[5] The incendiary appearance of this lesion may create a diagnostic dilemma, but a
thorough microscopic examination would lead to a definite diagnosis.
