Spindle Cell Rhabdomyosarcoma in a Cockatiel (Nymphicus Hollandicus)

A 2-year-old cockatiel (Nymphicus hollandicus) was presented with a large nodule on the ventral aspect of the right wing. Due to an accidental cutaneous trauma, the patient developed haemorrhage and subsequently died. The main necropsy finding was a pedunculated nodule that extended from the right pronator superficialis and biceps brachii muscles. Cytology of the nodule revealed neoplastic spindle cells with cytoplasmic cross-striations and multinucleate strap cells. Histologically, the nodule was composed of neoplastic spindle cells arranged in fascicles with a herringbone pattern. Neoplastic cells had multifocal cytoplasmic immunolabelling for vimentin and desmin, multifocal nuclear and cytoplasmic immunolabelling for myoblast determination protein 1 and rare cytoplasmic immunolabelling for α-smooth muscle actin. Neoplastic cells were negative for pancytokeratin. The final diagnosis was spindle cell rhabdomyosarcoma, a subtype rare in animals.