Morphology and pathogenesis of Liesegang rings in cyst aspirates: report of two cases with ancillary studies.

Liesegang rings are laminated ring-like structures occasionally found in benign cysts and abscesses. They have been confused with parasites (especially eggs), algae, calcifications, and psammoma bodies. We examined Liesegang rings from fine-needle aspiration (FNA) biopsies of a benign cyst of the breast and a complex renal cyst. Liesegang rings were best observed with Papanicolaou, hematoxylin-eosin, Masson's trichrome, acid-fast (AFB), and Gram stains, which accentuate the concentrically laminated morphology. An amorphous electron-dense core and fibrillary lucent concentric rings were seen with transmission electron microscopy with no significant energy peaks by electron probe microanalysis or distinct diffraction patterns by X-ray diffraction. This investigation indicates that Liesegang rings are composed of organic substances most likely formed by periodic precipitation from a supersaturated solution within cystic fluid. Awareness of the Liesegang phenomenon within cystic lesions will decrease the possibility of erroneous misdiagnosis as another type of pathologic process.