Bronchial carcinoid tumor with crystalloid cytoplasmic inclusions

We report a bronchial carcinoid tumor with distinctive, cytoplasmic, rod-shaped crystalloid inclusions that were visible by light microscopy. These cytoplasmic structures were immunoreactive with antibodies against chromogranin A and synaptophysin in paraffin-embedded tissue. Ultrastructural studies showed them to be paracrystalline in nature and located within lysosomes. This case highlights an interesting, and potentially confusing, histologic manifestation in an otherwise typical bronchial carcinoid tumor.