Three cases of carcinoid in the equine nasal cavity and maxillary sinuses: histologic and immunohistochemical features.

The paper describes three cases of a rare type of tumor, carcinoid, identified in the nasal and sinus regions of horses, with specific focus on their histologic and immunohistochemical properties.

Summary of the Cases

• The researchers studied three instances of carcinoid tumors in horses, a type of cancer rarely seen in these animals.
• The tumors were discovered in the maxillary sinuses, the cavities within the cheekbone structures, as well as the area behind the eye ball, leading to exophthalmos, an abnormal protrusion of the eyeball.

Investigation of Tumors

• On the histological front, the tumors displayed an endocrine pattern, indicating that they originated from the hormone-producing endocrine cells and were argyrophilic. Being argyrophilic means that these cells stained positively with silver-based stains, a characteristic shared by some types of carcinoid tumors.
• The researchers used the Grimelius stain, a particular kind of silver stain, to confirm the argyrophilia of these tumors.

Immunohistochemical Analysis

• In order to prove the neuroendocrine nature of these tumors, the team performed immunohistochemical analyses. These tests revealed that all tumors exhibited markers for neuron-specific enolase and synaptophysin, proteins typically found in neurons and neuroendocrine cells.
• Furthermore, two out of the three tumors were reactive for both bovine and porcine chromogranin A, a protein connoting neuroendocrine differentiation.

Origins of the Tumors

• The researchers were unable to identify neuroendocrine cells within the nasal mucosa and maxillary sinuses of a normal horse, which usually determine the presence of carcinoid tumors.
• As a result, the exact origins of these carcinoid tumors remain unclear.