Dermatopathology Evaluation of Cysts

Excerpt

Dermatopathologists are frequently required to evaluate cysts, which are enclosed tissue sacs containing fluid or semisolid matter. An epithelium lines true cysts, and that epithelium may be native, originate from embryologic remnant tissue, or come from another part of the body entirely. Pseudocysts are the name for cystic structures that lack such an epithelium. While numerous subtypes exist, cutaneous cysts can be simplified into 3 groups:

1. Appendageal cysts or folliculosebaceous unit cysts, which are derived from dermal appendages (eg, hair follicles) as retention cysts

2. Developmental cysts, which are derived from vestigial structures (eg, embryonic remnants)

3. Miscellaneous cysts (some of which may be classified as pseudocysts) may be due to ectopic glandular tissue, lymphatic origin, infection, or deposition.

Cysts can also be histopathologically grouped with sinuses and pits, but these are not elucidated here. Occasionally, hybrid cysts with features suggestive of multiple lineages are encountered, such as an epidermal inclusion cyst that transitions to a trichilemmal cyst. Malignant transformation rarely occurs in otherwise typical cysts. A structured approach to the histopathologic diagnosis of cutaneous cysts involves the assessment of the following features:

1. Epithelial lining

2. Cyst contents

3. Ancillary histopathologic features

4. Clinical setting or clinical picture

Additional nuances include recognizing microscopic features or clinical settings where cysts may serve as cutaneous markers for an underlying genodermatosis or inflammatory disease. A practical approach to diagnosing true cysts involving the skin is provided.