Interstitial (Leydig) cell tumour in a cat

This is an aspirate from a middle aged to older male neutered cat that presented for a scrotal swelling.

Fig 1. Cytology image showing vacuolated polygonal epithelial cells frequently palisading branching capillary structures.
Fig 2. Higher magnification photomicrograph of figure 1.

Final Diagnosis

Interstitial (Leydig) cell tumour


Although this animal was reported to be neutered, the scrotal swelling is consistent with an interstitial (Leydig) cell tumour of the testis. It is presumed that this mass has arisen within a retained testicle. Testicular tumours are rare in cats and scattered case reports are described. Similar to this case, these reports largely concern development of tumours within retained testes. Growth of these neoplasms is often slow and expansile, features that are supportive of benign behaviour.