Karyolysis

thumb|right|350px|Morphological characteristics of karyolysis and other forms of nuclear destruction. Karyolysis (from Greek κάρυον karyon—"kernel, seed, or nucleus", and λύσις lysis from λύειν lyein, "to separate") is the complete dissolution of chromatin in a dying cell caused by enzymatic degradation through endonucleases. Following karyolysis, the entire cell typically stains uniformly with eosin. Karyolysis represents the final step in the process of necrosis, a form of cellular injury in which living tissue undergoes irreversible damage through premature cell death. Unlike apoptosis, which is a regulated and programmed process, necrosis is generally triggered by external factors. In apoptosis, after karyorrhexis, the nucleus usually fragments into apoptotic bodies, whereas in necrosis karyolysis leads to complete nuclear dissolution.

Disintegration of the cytoplasm, pyknosis of nuclei, and karyolysis of transitional cells may be observed in urine from both healthy individuals and from those with malignant cells. Cells with a partially preserved cytoplasmic tag were first described by Papanicolaou and are sometimes referred to as "comet" or "decoy" cells. Because these may exhibit features resembling malignancy, it is important that they be correctly identified.