Summary

Testicular adrenal rest tumour (TART) due to CYP11B1 deficiency is a very rare clinical finding. Only seven cases have been reported previously. Here, the case of a 19-year-old boy with classic CYP11B1 deficiency and large testicles refractory to medical treatment that led to orchidectomy is reported. The clinical and laboratory manifestations of this patient are discussed and compared with that of the previously reported cases. The patient presented with rapid body growth, precocious puberty, hypertension, recurrent hypokalaemic paralysis and testicular enlargement. The most important differential diagnosis of his latter presentation is Leydig cell tumour (LCT). It was found that positive family history of congenital adrenal hyperplasia (CAH), hypertension, bilaterality, hypokalaemia and multiple hypoechoic masses on ultrasonography of the testes are in favour of a diagnosis of TART. Conversely, high titres of tumour markers and presence of Reinke crystalloids are supportive of a diagnosis of LCT.