Dermoscopic
features of epidermoid cyst- IJDVL study1

Epidermoid cyst is the most common benign cutaneous cyst
encountered during dermatological practice. It usually presents as an
asymptomatic slow-growing, spherical, smooth, dome-shaped keratin-filled cyst. It
can be confused many a times with various benign adnexal and non-adnexal
tumours clinically due to its variable size, colour, and consistency. The
dermoscopic examination data in this lesion is primarily focused on
demonstrating the punctum, which facilitates the diagnosis. Recently a case series
describing the dermoscopic features of epidermoid cyst beyond the punctum was published
in the Indian Journal of Dermatology, Venereology and Leprology.

A total of 7 patients of skin phototypes IV and V presented
with lesion without any punctum being visible clinically or dermoscopically. All
the diagnoses were confirmed by histopathology. None of the patients showed any
features of rupture, secondary bacterial infection, or calcification at
presentation. All lesions were successfully excised without any recurrence.

A cystic consistency with central punctum is usually
diagnostic of epidermoid cyst. However, diagnostic dilemma arises when the consistency
of the cyst becomes firm or hard with or without tenderness which may be
secondary to bacterial infection, inflammation, and calcification.
Additionally, lack of punctum and colour variation, especially in darker skin
adds on to the dilemma leading to misdiagnosis.

The clinical differentials in these cases were diverse due
to morphological variations and heterogeneous colours. In epidermoid cysts,
demonstration of a punctum, called the pore sign, facilitates the diagnosis.
Other features include white, yellow, and blue homogeneous areas and
arborizing vessels. Dermoscopy revealed the punctum in almost 60% cases, even
when clinically invisible. In authors experience, the pore sign helps in
differentiating facial and scalp epidermoid cysts from trichilemmal cyst.
Likewise, in acral areas, the pore sign helps in ruling out phaeohyphomycosis
and myxoid cyst. A recent study reported that pore sign, blue-white veil and arborizing
vessels were associated with unruptured epidermoid cyst while red lacunae and
peripheral branched linear vessels indicated ruptured epidermoid cysts.

In the present series the white homogeneous areas represented
keratin, where the yellow colour results from mass effect of concentric layers
of laminated keratin, brown homogeneous areas occurred due to increase
epidermal melanin and the bluish colour may be attributed to Tyndall effect, as
described in apocrine hidrocystoma.

In conclusion, this case series describes some new and
diverse dermoscopic features of epidermoid cysts without punctum in skin of
colour. Additionally, grey homogeneous areas, pigment networks and rings may be
observed in such patients. Thus, an epidermoid cyst without dermoscopic pore
sign may mimic various appendageal tumours, and these dermoscopy features may
help in making a precise diagnosis.

References

Behera B, Kumari R, Thappa DM, Gochhait D.
Dermoscopic features of epidermoid cyst beyond punctum. Indian J Dermatol Venereol
Leprol 2022;88:404-8.

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