Fine-needle aspiration of squamous-lined cysts of the pancreas

Squamous-lined cysts (SLC) in the pancreas are rare and include lymphoepithelial cysts (LEC), dermoid cysts (DC), and epidermoid cysts in heterotopic spleen (EC). Previously only rare case reports and small case series have been published describing the FNA findings in these entities. The departmental archives were searched for surgically excised SLC from the pancreas. Twenty-five specimens were identified: 20 LEC, four EC, and one DC. Eight corresponding FNA specimens taken prior to resection were identified and available for review: seven LEC and one EC. A junior and senior pathologist reviewed the cases individually and then together for consensus. On morphological review, all lesions contained single nucleated and anucleated mature squamous cells, macrophages, and varying amounts of lymphocytes. Benign squamous fragments were found in half of all specimens. Amorphous debris was found in all cases. Keratin was found in all but two cases and its appearance varied among cases. Half of all cases contained cholesterol crystals. No nuclear atypia or necrosis was noted. Inspissated mucin, a potentially misleading finding, was seen in three cases. The most important goal in evaluating pancreatic cystic lesions is to exclude a mucin-producing neoplasm. If features of a SLC are present, the differential diagnosis should include LEC, DC, and EC. Only 38% (3/8) cases had the most specific features of an SLC present (squamous fragments, cholesterol crystals, keratin, and squamous cells), which suggests that most cases will not be specifically identified on FNA even by experienced cytopathologists.