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The caruncle has a non-keratinised epithelial lining similar to the conjunctival epithelium. However, unlike the conjunctiva, the caruncle harbours skin elements such as hair follicles, sebaceous glands, sweat glands, and accessory lacrimal tissue. Consequently, the caruncle may develop a tumour or cyst similar to one found in the skin, conjunctiva, or lacrimal gland.
A 26 year old woman presented with a 2 mm, asymptomatic, pale yellow lesion of the right caruncle, present for 8 months (Fig 11).). It was excised intact under local anaesthetic and histological examination revealed a cyst lined by stratified squamous epithelium and containing sebaceous glands in its wall (Fig 22).). These communicated directly with the cyst lumen. No associated hair follicles were seen. An eosinophilic, crenulated cuticle was present on the inner aspect of the cyst wall in some areas. The patient had no other skin lesions of note. The nails, teeth and hair were normal. There was no family history of similar lesions. At the 6 month follow up there have been no signs of recurrence or development of other cysts.
The diagnosis was of steatocystoma simplex (SS) of the caruncle.
Steatocystoma simplex, the non-heritable solitary counterpart of steatocystoma multiplex (SM), was first described as a distinct entity by Brownstein in 1982.1 It is a benign adnexal tumour, thought to originate from a naevoid malformation of the pilosebaceous duct junction.2
Lesions are described on the forehead, nose, scalp, neck, axillae, chest, upper limbs, back, legs,1 and even intraorally.3 To our knowledge though, steatocystoma has not previously been reported in the caruncle.4,5
Thirty two cases of SS are reported in the literature, divided evenly between men and women and ranging in age from 15 to 70 years.1,3,6 Clinical and histological features in SS are usually identical to those seen in the individual lesions of SM. Lesions are described as asymptomatic, flesh coloured or yellowish, intracutaneous, well circumscribed, soft, mobile, and non-tender. On incision they are found to contain an oily substance composed of sebum.1
However, it is important to confirm the solitary nature of a steatocystoma. SM can be familial and autosomal dominantly inherited (steatocystoma multiplex congenita).7 Several familial cases have been linked to pachyonichia congenita and ectodermal dysplasia through a mutation in keratin 17.8 It has been associated with hypothyroidism, hypohidrosis, hypotrichosis and hypertrophic lichen planus, ichthyosis, and koilonychia.9 SM may be progressive with inflamed cysts, rupturing, and healing with scars.7
Steatocystoma is histologically characterised by a cystic structure with sebaceous glands within the cyst wall and epithelium that displays an eosinophilic cuticle. It is possible to make a diagnosis of steatocystoma if the characteristic hyaline luminal cuticle is present, even in the absence of sebaceous elements.1
The differential diagnosis included sebaceous gland hyperplasia, sebaceous gland adenoma, and lipogranuloma. Clinically they are also characterised by a yellow, nodular appearance.5 Rarely, sebaceous gland carcinoma of the caruncle may occur.5 Along with hidrocystoma and eruptive vellus hair cyst they can usually be excluded histologically. Oncocytomas are asymptomatic, slowly progressive, solid or cystic masses but usually described as reddish blue/tan.4,5
Most treatment regimens for steatocystoma reflect the multiplicity and widespread extent of lesions of SM. Oral isotretinoin has been used to reduce associated inflammation. Cryosurgery, carbon dioxide laser, and incision with removal of the cyst wall have been employed.7,10 We felt the best way to manage this solitary lesion arising in the caruncle was by simple excision with removal of the cyst wall intact, thereby reducing the risk of recurrence. We were able to confirm the unique nature of this lesion and rule out malignancy.