MTC most likely results from the cystic transformation of medullary duct epithelium-derived structures (including Hassall's corpuscles) induced by an acquired inflammatory process. (#2006719#)

MTC would be pathogenetically analogous to a variety of cystic conditions of the head and neck region, for which the common denominator seems to be the induction of cystic transformation in ductular epithelial formations of branchial pouch or related derivation by an acquired inflammatory process. (#2006719#)

Synopsis (#2006719#)

 multiple cystic cavities partially lined by squamous, columnar, or cuboidal epithelium (some having features of Hassall's corpuscles)
 scattered nests and islands of non-neoplastic thymic tissue within the cyst walls, often continuous with the cyst lining
 severe acute and chronic inflammation accompanied by fibrovascular proliferation, necrosis, hemorrhage, and cholesterol granuloma formation
 reactive lymphoid hyperplasia with prominent germinal centers
 rarely, pseudoepitheliomatous hyperplasia (#1709608#)

References

 Suster S, Barbuto D, Carlson G, Rosai J. Multilocular thymic cysts with pseudoepitheliomatous hyperplasia. Hum Pathol. 1991 May;22(5):455-60. PMID: #1709608#

 Suster S, Rosai J. Multilocular thymic cyst: an acquired reactive process. Study of 18 cases. Am J Surg Pathol. 1991 Apr;15(4):388-98. PMID: #2006719#