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

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. 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. 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. The differential diagnosis of a testicular mass in Klinefelter syndrome includes malignancy and nodular Leydig cell hyperplasia.Diagnosis can be challenging, both radiologically and histologically.Orchalgia is atypical in Leydig cell hyperplasia.