Psammoma body

A psammoma body is a round collection of calcium, seen microscopically. The term is derived from the Greek word psammos meaning "sand."

Psammoma bodies are commonly seen in certain tumors such as:
 * papillary thyroid carcinoma
 * papillary renal cell carcinoma
 * serous papillary ovarian adenocarcinoma (cystadenocarcinoma)
 * endometrial adenocarcinomas(Papillary serous carcinoma ~3%-4%)
 * meningioma
 * mesothelioma

Psammoma bodies have a laminar appearance.

The origin of psammoma bodies is controversial, but one theory is that the nidus for their formation is a single necrotic tumor cell, upon which layers upon layers of calcium salt deposits are added.