| Diagnostic Case 6 - Answer |
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Fig 2a. The mass is composed of epithelial cells arranged in cell packets separated by delicate fibrous connective tissue stroma. There is moderate anisocytosis, and a few "giant" nuclei are present (arrow). |
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Fig 2b. In some areas the stroma as highly vascular. Rare mitotic figures are present (arrow). |
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| Fig 3. Neoplastic cells are present within blood vessels. | Fig. 4. Grimelius silver stains reveal large numbers of black intrcytoplasmic granules. |
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| Fig 5. The granules were positive with neuron-specific enolase immunostaining. | Fig. 6. Granules were also positive with synaptophysin immunostaining. |
| Comment: Paragangliomas are tumors that are derived from neuroendocrine tissue present along the dorsal midline. Normally, this neuroendocrine tissue functions in chemo-and baroreception and includes the carotid and aortic bodies. Although most paragangliomas are considered benign, invasion into blood vessels has been reported in a few cases. Orbital paragangliomas are infrequently diagnosed both in humans and domestic animals. The main diagnostic features of orbital paragangliomas include an endocrine pattern, stromal vascularity, location along the dorsal midline, and presence of intracytoplasmic neurosecretory granules that stain black with Grimelius silver. Immunohistochemical staining of the granules is seen with antibodies to neuron-specific enolase, synaptophysin and chromogranin A. Of these, synaptophysin and chromogranin A are the most specific for paragangliomas, while neuron-specific enolase, the most sensitive, is non-specific and is best used as one of a battery of immunohistochemical stains. | |
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References: Bednar MM, Trainer TD , Aitken PA, Grenko R, Dorwart R, et al.:1992. Orbital paraganglioma: case report and review of the literature. Br J Ophthalmol 76: 183-5 van Maanen C , Klein WR, Dik KJ, van den Ingh TS: 1996. Three cases of carcinoid in the Equine Nasal Cavity and Maxillary sinuses: Histologic and Immunohistochemical features. Vet Pathol 33: 92-95 Vara Thorbeck R, Valentin OI, Ruiz Morales M:1986. Non-chromaffin paraganglioma of the orbit. Case report. Zentralbl Chir 111: 46-9 |
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| Diagnosis: Orbital Paraganglioma | |
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