Hidrocystomas, also known as eccrine hidrocystomas, are common benign skin tumors that are most frequently found along the eyelid margin. These benign tumors have a typical appearance and no malignant potential. Most often, they manifest as solitary, asymptomatic papules.
Clinical Findings: Eccrine hidrocystomas manifest as solitary, translucent, pale, clear to blue or light purple papules. They have a smooth surface and a dome shape. Eccrine hidrocystomas are soft; they feel as if pressure could easily rupture their cystic wall. Puncturing of the cyst wall with a 30-gauge needle causes drainage of a thin, watery fluid. These tumors are almost always asymptomatic. They can occur at any age but are far more common after the fourth decade of life. No difference in incidence has been observed based on race or gender. Lesions are typically small, 5 mm to 1 cm in diameter, and can fluctuate in size. It is not uncommon for a patient to relate that the tumor enlarges during physical exercise, only to shrink after a few days. If ruptured, these tumors drain a thin, watery liquid, and the cystic cavity deflates. Although they are almost always solitary, there are reports of hundreds of these tumors developing in some patients. Large eccrine hidrocystomas occurring in atypical locations have also been described.
The main differential diagnosis is between eccrine hidrocystoma and basal cell carcinoma. Cystic basal cell carcinomas can have an identical appearance; however, the patient history will be quite different. Basal cell carcinomas typically enlarge over time and ulcerate, causing bleeding of the ulcerated papule. Hidrocystomas rarely, if ever, ulcerate or bleed. If left alone, they only transiently increase in size and never get much larger than 1 cm in diameter, and usually they are much smaller. A biopsy for pathological evaluation is diagnostic.
Pathogenesis: Hidrocystomas develop from the eccrine apparatus. It is believed that a portion of the eccrine duct within the dermis becomes occluded. This occlusion causes a buildup of eccrine secretions proximal to the blockage. Once enough fluid collects, a translucent papule becomes evident on the surface of the skin. No genetic abnormalities of the involved eccrine duct have been discovered, and this cystic formation is most likely caused by damage from superficial trauma to the skin and the underlying eccrine ducts. Sun damage to the eccrine ducts has been theorized to play a role, although this theory has yet to be vigorously tested.
Histology: A lone cystic space is seen within the dermis. The cyst is well circumscribed, and the lining of the cyst contains two layers of cells. The cells are cuboidal and have an eosinophilic cytoplasm. The cell wall has no myoepithelial cell component. The cysts are found near eccrine gland structures. There is minimal to no inflammatory infiltrate surrounding the cyst. The central cavity of the cyst contains an small amount of lightly eosinophilic material that is consistent with eccrine gland secretions. There is no evidence for sebaceous gland or apocrine gland secretion or derivation.
Treatment: Most eccrine hidrocystomas are biopsied to make sure they are not actually basal cell carcinomas. They rarely recur after biopsy. If they do recur, no treatment is required. Surgical excision is the definitive treatment and is cur tive. Hidrocystomas almost never recur after excision.