From the Research
To diagnose a sebaceous cyst on fine needle aspiration (FNA) smears, the presence of abundant amorphous, keratinous debris, anucleate squamous cells, and mature nucleated squamous epithelial cells is crucial, as noted in various studies 1, 2, 3, 4, 5. The smears typically show these key findings, which are essential for making an accurate diagnosis.
- Abundant amorphous, keratinous debris in the background, appearing as acellular, granular material
- Anucleate squamous cells (squames) present in large numbers, often appearing as flattened, plate-like structures
- Mature nucleated squamous epithelial cells, sometimes showing mild atypia but without significant nuclear abnormalities
- Multinucleated giant cells and inflammatory cells, particularly neutrophils and histiocytes, commonly observed, especially if the cyst is inflamed or ruptured
- Cholesterol crystals may occasionally be present, appearing as rhomboid clefts
- The absence of atypical cells, significant nuclear pleomorphism, or malignant features is important to note Sometimes, sebaceous cells with foamy cytoplasm might be identified, though they are often degenerated, as seen in studies such as 2. These findings collectively support the diagnosis of a sebaceous cyst, which is actually a misnomer as most are epidermoid cysts containing keratin rather than sebum, as discussed in 1, 3, 4, 5. The diagnosis is made more confidently when clinical information about a subcutaneous nodule is available, highlighting the importance of correlation between cytological and clinical findings 1, 2, 3, 4, 5.