Leydig cell tumour

A non-painful mass was detected in the left testicle of a 12-year-old male Labrador during a routine examination at the time of vaccination. The mass was aspirated and following the cytology results, castration was performed and the affected testicle submitted for histopathology.

Fig 1. Cytology preparation: neoplastic cells can be seen palisading capillary vessels.
Fig 2. Cytology preparation: the neoplastic cells contain a moderate amount of pale blue cytoplasm that frequently contains small, clear punctate vacuoles.
Fig 3. On gross examination, the testis contains a discrete yellow-tan mass. The yellow colour of the tumour is related to the lipid-rich steroid production and is characteristic of a Leydig cell tumour. Areas of cystic cavitation (arrow) and haemorrhage are common additional features.
Fig 4. Histopathology: the neoplastic cells resemble normal interstitial cells with abundant, finely granular eosinophilic cytoplasm.

Final Diagnosis

Leydig (interstitial) cell tumour


Leydig cell tumours are common tumours of the testis and may be solitary or multiple. These tumours arise from the interstitial cells of the testis which under normal conditions are responsible for androgen production. The vast majority of Leydig cell tumours are behaviourally benign and metastatic spread is exceptionally rare. Occasionally Leydig cell tumours may be hormonally active which can result in concurrent prostatic and/or perianal gland hyperplasia. These changes usually regress following castration