Question

Which of the following is the most characteristic ultrastructural feature of paraganglioma on electron microscopy?

• A. Shrunken mitochondria
• B. Large Golgi apparatus
• C. Frequent mitoses
• D. Dense core neuroendocrine granules

Hint:

Neuroendocrine cells store catecholamines in membrane-bound granules with a dark centre.

Answer 1

The Correct Option is D

Step 1: Paraganglioma is a tumour arising from the paraganglia, which are clusters of neuroendocrine cells. The phaeochromocytoma of the adrenal medulla is the best known example of this family.
Step 2: Neuroendocrine cells store catecholamines and peptide hormones inside membrane-bound secretory granules. These are called dense-core granules because their centre is electron dense on EM.
Step 3: So under the electron microscope the defining feature of a paraganglioma is the presence of numerous membrane-bound dense-core neuroendocrine (neurosecretory) granules in the cytoplasm.
Step 4: Why the others are wrong. Shrunken mitochondria and a large Golgi apparatus are nonspecific and are not a defining feature of any particular tumour. Frequent mitoses are a feature seen on light microscopy and indicate proliferation, not neuroendocrine differentiation, so they cannot be the characteristic ultrastructural marker.
Step 5: Hence the answer is dense-core neuroendocrine granules.
Answer: Option D (Dense core neuroendocrine granules).