Psammoma bodies can be seen in the following except?
**Core Concept**
Psammoma bodies are concentric, lamellated calcifications found within certain types of tumors. They are a hallmark of papillary thyroid carcinoma and are also seen in other tumor types, including serous ovarian cystadenocarcinoma, meningioma, and papillary renal cell carcinoma.
**Why the Correct Answer is Right**
Psammoma bodies are formed through the deposition of calcium and phosphate ions within the tumor cells, leading to the formation of concentric layers. This process is thought to be mediated by the tumor's cellular metabolism and the presence of certain enzymes, such as alkaline phosphatase. The presence of psammoma bodies is often associated with a more favorable prognosis in papillary thyroid carcinoma.
**Why Each Wrong Option is Incorrect**
**Option A:** Psammoma bodies are indeed seen in papillary thyroid carcinoma, making this option incorrect.
**Option B:** Serous ovarian cystadenocarcinoma is another tumor type that can contain psammoma bodies, so this option is also incorrect.
**Option C:** Meningiomas, particularly those of the meningothelial subtype, can also exhibit psammoma bodies, ruling out this option as well.
**Option D:** Psammoma bodies are not typically seen in medullary thyroid carcinoma, which is a different subtype of thyroid cancer characterized by the absence of calcifications.
**Clinical Pearl / High-Yield Fact**
Psammoma bodies are a useful diagnostic feature in the histopathological examination of tumors, particularly in the context of papillary thyroid carcinoma. They can be identified as concentric, lamellated calcifications within the tumor cells, and their presence can help differentiate this tumor type from others.
**Correct Answer: D. Medullary thyroid carcinoma.**