Histological examination of a calcified epidermal cyst reveals a dermal cystic structure. In addition to laminated layers of keratinous material, the cavity is filled with amorphous basophilic calcareous sediment (Fig. 1A). The cyst wall consists of thinned stratified squamous epithelium similar to the hair follicle infundibulum, which is surrounded by fibrosis (Fig. 1B). Active inflammation is sometimes seen around the cyst. The etiology and pathogenesis of these pathological findings are controversial. It remains unclear whether calcified epidermal cysts are the result of dystrophic calcification of preceding epidermal cysts that are affected by inflammation followed by cystic dilation, calcification, cyst wall rupture, and granulomatous reactions,1 or if they are truly idiopathic growths without any triggering factor such as foreign body infiltration, metabolic or hormonal disorder, or trauma.2 Calcified epidermal cysts reportedly have an eccrine origin.3 In some cases the cyst wall and keratinous material are absorbed, leaving only areas of calcification,4 suggesting that the pathological finding of the attenuated epithelial lining may ultimately disappear.
Calcified epidermal cysts are rare benign entities that were first described in 1947.5 There are reports of calcified epidermal cysts involving the intracalvarium, spinal cord, spleen, pancreas, kidney, testis, and several skin regions.6–9 Cutaneous calcified epidermal cysts have been reported on the scrotum, vulva, scalp, subungual area, breast, and heel, but are most commonly located on the scrotum.9 The typical clinical presentation is a rock-hard white nodule with associated pruritus that sometimes drains white chalky contents accompanied by secondary skin infection. The entity can also be clinically similar to a common epidermal cyst (Fig. 2).
The differential diagnoses for calcified epidermal cysts include: cutaneous tumors such as steatocystoma, lipoma, solitary neurofibroma, pilomatricoma, and cervical lymphangioma; inflammatory nodules, including cervical lymphadenitis and cervical lymph node tuberculosis; systemic diseases that cause cutaneous nodules, such as hyperparathyroidism, dermatomyositis, and systemic sclerosis. General diagnostic workup includes a detailed history, urinalysis, blood biochemical examination (calcium, phosphorus, and parathyroid hormone levels), and histopathologic study. The gold standard for the diagnosis of a calcified epidermal cyst is excisional biopsy and pathologic evaluation, which reveals an epidermal cyst with central irregular calcifications. Surgical management with complete excision achieves excellent results and reduces recurrence.
. Yuyucu KY, Kankaya D, Senel E, et al. Idiopathic scrotal calcinosis: the incorrect terminology of scrotal calcinosis. G Ital Dermatol Venereol 2015;150(5):495–499.
. Killedar MM, Shivani AA, Shinde U. Idiopathic scrotal calcinosis. Indian J Surg 2016;78(4):329–330.
. Ito A, Sakamoto F, Ito M. Dystrophic scrotal calcinosis originating from benign eccrine epithelial cysts. Br J Dermatol 2001;144(1):146–150.
. Song DH, Lee KH, Kang WH. Idiopathic calcinosis of the scrotum: histopathologic observations of fifty-one nodules. J Am Acad Dermatol 1988;19(6):1095–1101.
. Morley HV, Best JW. Multiple calcified cysts of the scrotum; case report. J Urol 1947;58(6):458–460.
. Agrawal M, Gour S, Borkar SA. Unusual calcification in intramedullary epidermoid cyst. World Neurosurg 2019;126:99–100.
. Ishigami K, Nishie A, Irie H, et al. Differential diagnosis of pancreatic epidermoid cyst without a solid component (residual splenic tissue) vs. mucinous cystic neoplasm. J Gastrointest Cancer 2019;50(1):91–97.
. Ravindran K, Rogers TW, Yuen T, et al. Intracranial white epidermoid cyst with dystrophic calcification – a case report and literature review. J Clin Neurosci 2017;42:43–47.
. Kalampalikis A, Scheungraber C, Goetze S, et al. Isolated epidermal cysts of the vulva. Hautarzt 2016;67(7):553–554.