Two Pilosebaceous Cysts with Apocrine Hidrocystoma in One Biopsy Site: DISCUSSION part 2
The review of correlation between pilosebaceous cyst and apocrine hidrocystoma is limited. But Anderson et al presented a combination of apocrine hidrocystoma and epidermal inclusion cyst. He reported four unusual cutaneous cysts in which apocrine epithelium is juxtaposed with keratinizing squamous epithelium and suggested that these cysts arise at the junction of glandular and keratinizing squamous epithelium, accounting for the mixture of lining cells seen histologically. It is also possible that squamous metaplasia within an apocrine hidrocys- toma accounts for the mixture of lining epithelium. Finally, he suggested these cysts represent collision lesions in which an apocrine hidrocystoma has fused with an epidermal inclusion cyst.
Takeda et al presented cases of hybrid cysts in Japan. The most frequent histological type was the combination of infundibular and trichilemmal cyst and one case was a combination of infundibular cyst and apocrine hidrocystoma. In our case, even though the cysts do not exactly correspond to hybrid cysts, the pilosebaceous cyst and apocrine hidrocystoma were close to each other and showed within one biopsy site.
Pilosebaceous cysts such as milia and EVHC and apocrine hidrocystoma are distinct entities. But these three conditions may show an overlap of histologic features and share many clinical similarities. As we know, most of the apocrine duct opens to the pilosebaceous orifice. At this point in time, we can make an assumption of the possibility of a correlation between pilosebaceous cysts and apocrine hidrocystoma. That is to say, these two entities are not distinct cysts but can be the same unit, namely “piloseboapocrine unit”.
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In summary, we report a rare case of multiple pilosebaceous cysts with apocrine hidrocystoma which occurred on the same biopsy site and that can be the same piloseboapocrine unit. Further studies, such as multiple biopsy specimens or serial sections from the patient with either milia, EVHC, or apocrine hidrocystoma and more similar cases are required to clarify the pathomechanism of these conditions.
