Psammoma Bodies · What Are They, Where They Are Found, and More

Psammoma bodies are round calcifications (i.e., collections of calcium salts) seen under the microscope in certain types of tumors and pathological conditions. Their name is derived from the Greek word for sand because they resemble grains of sand. They also have a concentric laminated, or onion-like, appearance.  

Psammoma bodies are generally found in damaged tissues and are commonly associated with malignant cancers as well as some benign, non-cancerous conditions. Their main function is to halt the growth of cancer and serve as a barrier against the spread of malignant cancer cells. Although psammoma bodies are typically seen microscopically, some can be big enough to be detected through computerized tomography (CT) imaging. 

Psammoma bodies can be found in organs such as the thyroid, ovaries, endometrium, and the lining of the central nervous system. They are involved in both cancerous and benign tumors and can also be a sign of chronic inflammation.  

Some of the non-cancerous conditions in which psammoma bodies can be found include benign ovarian tumors, cervical polyps, or growths on the cervical canal connecting the uterus and vagina. They may also be found with endometriosis, in which the tissue lining the uterus grows outside of the uterus. Additionally, psammoma bodies can be found in meningiomas, or tumors that form on the meninges, the membranes that cover the brain and spinal cord inside the skull. As many as 90% of meningiomas are benign and non-cancerous. Similarly, prolactinoma and glucagonoma are non-cancerous, hormone-related tumors that often show psammoma bodies.  

Psammoma bodies—from both non-cancerous and cancerous conditions—can be detected after a biopsy of the mass is taken and stained with hematoxylin and eosin, a common tissue stain used in histology. Ultrasound may also be used to detect calcifications of thyroid nodules. 

Psammoma bodies are found in a variety of cancers. They are commonly a diagnostic feature of papillary thyroid carcinoma (PTC), the most common form of thyroid cancer. In individuals with PTC, detection of psammoma bodies usually means that the individual is more likely to have lymph node metastasis (i.e., spread of cancerous growth) and high-stage cancer when compared to those without psammoma bodies. PTC and other thyroid cancers are often diagnosed using fine-needle aspiration (FNA), in which a small hollow needle is used to remove a sample of cells from the thyroid gland at the front of the neck. Psammoma bodies are also commonly detected in papillary serous cystadenocarcinoma of the ovary, the most prevalent form of malignant ovarian cancer.  

Other, less common, cancers in which psammoma bodies can be found include papillary serous carcinoma of the endometrium, a rare form of cancer in the lining of the uterus; melanotic schwannoma, a rare tumor that forms in the nerve sheath lining the nerves that extend from the spinal cord into the body; as well as with some lung cancers.  

Little is known about the exact mechanisms responsible for the formation of psammoma bodies, but it’s believed that they are caused by the thickening of the basal lamina, a layer of the extracellular matrix that underlies epithelial cells which often occurs in some early stages of cancer. This unusual process is followed by thrombosis (i.e., blood clotting), calcification, and then tumor cell death. When cells in a tumor or in other tissues die, especially in a slow and controlled way, the remnants can become a scaffold for calcium deposition. Calcium builds up in layers around a central core, which gives psammoma bodies their characteristic onion-skin appearance. Additionally, many tumors that form psammoma bodies have a papillary structure, meaning finger-like projections with a fibrovascular core. 

These fragile papillae can outgrow their blood supply, leading to necrosis and calcification, which encourages psammoma body formation. 

It is hypothesized that rather than being an outcome of calcification of dead tissue, psammoma bodies may represent an active process that leads to the degeneration and death of tumor cells. In the case of papillary thyroid carcinoma, psammoma bodies may be a result of thyroid tumor thrombi, which refers to a part of the tumor having migrated into the vascular system and calcified there.