Eruptive Vellus Hair Cysts Workup

Updated: Jul 29, 2019
  • Author: Stephanie Juliet Campbell, DO; Chief Editor: Dirk M Elston, MD  more...
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Punch biopsy of the skin is the diagnostic procedure of choice for eruptive vellus hair cysts (EVHCs).

Alternatively, the diagnosis can be confirmed with a potassium hydroxide wet mount of cyst contents extruded through a small incision. Microscopic examination of the cyst contents reveals vellus hairs. The cyst can be anesthetized with a local or topical anesthetic prior to incision with a sterile blade or 18-gauge needle.

In 2006, another extraction technique was described. Patients were treated with topical anesthetic prior to puncturing the surface of the cyst with a sharp-tipped electrocautery instrument. The cyst wall and contents were then dissected out with forceps and either sent to a pathology laboratory or examined microscopically with 10% potassium hydroxide to confirm the diagnosis of EVHC. [24]

A report indicated that dermoscopy can help to distinguish EVHC from acne and molluscum contagiosum. [25]


Histologic Findings

Histopathology of eruptive vellus hair cysts (EVHCs) shows a cystic structure in the mid dermis arising from the infundibulum of a hair follicle. [26] The cysts contain multiple cross-sections of vellus hairs and layered laminated keratinous material. They are lined by squamous epithelium 2- to 5-cells thick. Generally, no sebaceous glands are present in the cyst wall. A surrounding granulomatous reaction may be present, especially if the hairs disrupt the cyst wall.

The differential diagnosis of pilosebaceous cysts includes infundibular cysts, steatocystoma multiplex, and EVHCs. All 3 commonly affect the anterior chest and consist of asymptomatic papules or nodules. Obstructed or occluded follicles form the common infundibular cysts. These do not contain sebaceous glands or vellus hairs. The cysts of steatocystoma multiplex arise in the sebaceous duct and have a crenulated, eosinophilic, hyaline lining to the cyst wall where the granular layer is absent. Steatocystomas also contain sebaceous glands arising within the cyst wall.

Some authors believe that EVHC and steatocystoma multiplex are variants of the same disorder because both lesions have been reported in the same patient. [27] Other authors have defended their status as distinct entities based on different histologic patterns. One study showed EVHC lesions expresssed keratins 1 and 10, calretinin, and p63, but findings were negative for epithelial membrane antigen, filaggrin, and androgen receptors. [28] Another study demonstrated differential expression of keratins 10 and 17. [29] In 2 cases of EVHC, strong staining for keratin 17 was found but no staining for keratin 10 was evident. In 7 cases of steatocystoma, both keratin 10 and keratin 17 were expressed in the suprabasal cells of the cyst wall. In 5 epidermoid cysts, positive staining occurred only for keratin 10.

Several reports note patients having cysts containing elements of both EVHCs and steatocystoma multiplex. [30, 31, 32] The term hybrid cyst has been proposed to describe cysts containing combinations of EVHCs, steatocystoma multiplex, and epidermoid cysts. Some authorities argue that these cyst types all form from the pilosebaceous unit and are therefore all just a spectrum of the same disorder. Combinations of infundibular cysts, trichilemmal cysts, and pilomatricomas have also been described as hybrid cysts.

Note the images below.

Histopathology of an eruptive vellus hair cyst sho Histopathology of an eruptive vellus hair cyst showing a middermal cyst with squamous epithelium.
A close-up view of the contents of an eruptive vel A close-up view of the contents of an eruptive vellus hair cyst showing cross-sections of vellus hairs and laminated keratinous material.