A Ciliated Cyst with Müllerian Differentiation Arising in the Posterior Mediastinum

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Primary congenital mediastinal cysts are rare, have a broad range of etiologies, and can be bronchogenic, thymic, neuroen-teric, or esophageal in origin. 1 Recently, Hattori 2 described the first case of a ciliated cyst of probable Müllerian origin arising in the posterior mediastinum, a so-called Hattori's cyst. Since that time, several additional cases have been reported. 3,4 We found a posterior mediastinal cyst with Müllerian differentiation that was consistent with previous description of Hattori's cyst. To our knowledge, this is the first report of Hattori's cyst arising in the posterior mediastinum in Korea. An abnormal mass lesion in the posterior mediastinum of a 42-year-old woman was found incidentally during a routine medical checkup. Well-defined cystic lesion, measuring about 2.6 cm in diameter, and arising in the right paraspinal medias-tinum was noted on magnetic resonance imaging and computed tomography of the chest. The mass exhibited high signal intensity on T1-weighted imaging and low signal intensity on T2-weighted imaging, which suggested that the lesion was purely cystic (Fig. 1A). The differential diagnosis based on ra-diologic imaging included a bronchogenic cyst or neurogenic tumor with cystic change. She underwent video-assisted thora-coscopic surgery for the excision of the mass. The mass was a unilocular cyst with thin, lucent walls filled with clear serous fluid (Fig. 1B). It weighed 2.9 g with dimensions measuring 2.4×2.0×1.5 cm. We submitted the entire specimen for histo-logic examination. Microscopically, the cystic tumor had a papillary structure, reminiscent of a fallopian tube (Fig. 2A). The cystic wall was lined by a simple ciliated cuboidal to columnar epithelium supported by thin connective tissue. Some H-caldesmon positive bundles of smooth muscle cells were found (Fig. 2B). The epi-thelium of the papillary structure was composed of ciliated pseu-dostratified columnar and intercalated clear cells (Fig. 2C). We did not identify any atypia in the epithelial cells. We used im-munohistochemical assay for estrogen receptor (ER), progester-one receptor (PR), Wilms' tumor 1 (WT1), PAX-8, cytokeratin 7 (CK7), cytokeratin 5/6 (CK5/6), calretinin, and thyroid transcription factor-1 (TTF-1) to identify the character of the epi-thelium. The epithelial cells were positive for ER, PR, WT1, and CK7, but negative for TTF-1, CK5/6, and calretinin (Fig. 2D–G). This epithelium was histologically reminiscent of …