Psammoma bodies are microscopic, layered spheres of calcium found in various tissues. Their name is derived from the Greek word “psammos,” meaning sand, due to their granular appearance. While they can occur in different organs, their presence within the thyroid gland carries specific clinical implications. This article explores their formation, diagnostic relevance, and what they may indicate for a patient’s outlook.
Formation and Microscopic Appearance
Psammoma bodies form through dystrophic calcification, a process occurring in dying or degenerating tissues. The process begins with a small, central point of decay called a nidus. In the thyroid, this nidus is often composed of dying cells at the tip of a papillary structure, a small, finger-like projection of tissue. Formation can start from the necrosis of tumor cells or the blockage of small blood vessels within the tissue.
Once this central point is established, layers of calcium and proteins deposit around it in an organized manner. This results in the microscopic appearance of round or oval structures with distinct, concentric rings. This layered pattern is often compared to the rings of a tree trunk or an onion, making them visually unique for pathologists.
Association with Papillary Thyroid Carcinoma
The discovery of psammoma bodies in a thyroid sample has a strong connection to Papillary Thyroid Carcinoma (PTC), the most prevalent form of thyroid cancer. These calcified structures are found in up to 50% of PTC cases. Their appearance in tissue is a highly specific marker, meaning that when psammoma bodies are identified, a diagnosis of PTC is highly probable.
The link is so well-established that finding psammoma bodies, even without obvious tumor cells in a sample, prompts a thorough search for an underlying PTC. In fact, most patients with psammoma bodies found outside of a tumor are discovered to have a PTC elsewhere in the thyroid. While psammoma bodies can occasionally be found in benign thyroid conditions like Hashimoto’s thyroiditis, this is an uncommon event.
Diagnostic Procedures and Identification
The initial step to identify psammoma bodies is often a Fine-Needle Aspiration (FNA) biopsy. During an FNA, a thin needle withdraws fluid and cells from a suspicious thyroid nodule for microscopic examination. A pathologist can identify the distinct, layered appearance of psammoma bodies among the thyroid cells.
The other primary method is histopathology, which involves the microscopic examination of surgically removed thyroid tissue. Pathologists analyze thin slices of the tissue to look for these calcified structures. They are often found within the fibrovascular cores of papillary projections.
Prognostic Significance
The identification of psammoma bodies extends beyond diagnosis and can provide information about a patient’s prognosis. The presence of these calcifications is linked to more aggressive features of Papillary Thyroid Carcinoma. Specifically, finding psammoma bodies is correlated with a higher likelihood of the cancer spreading to nearby lymph nodes, a condition known as lymph node metastasis.
This association with lymph node involvement can influence clinical decision-making. A surgeon may be more inclined to perform a more extensive surgery, such as removing a larger portion of the thyroid or adjacent lymph nodes, if psammoma bodies are identified. Their presence may also point towards a higher risk for tumor recurrence, which helps determine the appropriate course of treatment and follow-up care.