Leydig Cell Hyperplasia Mimicking a Testicular Tumour in a Patient with Klinefelter Syndrome

Background: Klinefelter syndrome (KS) is the most common sex-chromosomal disorder in males. Frequently under-recognized, it occurs in 1 in 500–600 male births. It is caused by the inheritance of at least one additional X chromosome from either parent. Patients often have uncommon or atypical malignancies. Patient: We describe the case of a 35-year-old man with 47XXY KS and previous cryptorchidism, presenting with a painful testicular mass. Histology confirmed Leydig cell hyperplasia. Discussion: Cryptorchidism is an established risk factor for testicular tumours and occurs six times more commonly in KS than in the general population. Despite this, large epidemiological studies have shown a reduced burden of testicular cancer in these patients. The presentation of a hypoechoic lesion on ultrasound will prompt consideration of testicular tumours, however orchalgia represents an atypical presentation. In patients with KS, Leydig cell hyperplasia is a much more common entity and should be considered early in the differential diagnosis.