On ultrastructural examination, the cytoplasm may contain dense-core granules
measuring 100 to 200 nm and abundant filaments of an intermediate size.
Astrocytes, similar to specialized secretory cells, contain three types of secretory organelles, the glutamate containing synaptic-like microvesicles (SLMVs) [9, 29, 30], the peptide containing large dense-core granules
(LDCGs; [31, 32]), and the lysosomes [11-13].
The abundance of dense-core granules
does not necessarily correlate with the type of neuroendocrine tumor diagnosed by light microscopy.
Ultrastructurally, these tumors are composed of cells with high nuclear-cytoplasmic ratios, conspicuous nucleoli, and rare, single, small membrane-bound dense-core granules
, compatible with neurosecretory-type vesicles.
A neural origin is supported by expression of neuron-specific enolase and CD57 with ultrastructural findings of occasional dendritic processes and dense-core granules
. Factors that argue against a neural origin include negative staining for synaptophysin, chromogranin, and neurofilament protein.