Testicular regression syndrome

Testicular regression syndrome (TRS), also known as vanishing testis syndrome, testicular agenesis, or anorchia, is a rare congenital condition in which one or both testes were present during early fetal development but subsequently degenerated or 'vanished' before birth. The condition is characterized by the absence of one (unilateral) or both (bilateral) testes in a phenotypically male individual (46,XY karyotype), with evidence that testicular tissue was functional at some point during embryonic development. This evidence includes the presence of male internal and external genitalia, indicating that the testes produced testosterone and anti-Müllerian hormone (AMH) during the critical period of sexual differentiation before regressing. The cause of testicular loss is thought to involve a vascular event such as torsion, thrombosis, or ischemia during fetal life, though genetic factors may also play a role in some cases. Clinical presentation varies depending on the timing of testicular regression during fetal development. If regression occurs early (before 8 weeks of gestation), the individual may present with ambiguous genitalia or a more female phenotype. If regression occurs later, after masculinization has been initiated, the individual typically has normal male external genitalia but with absent testes (empty scrotum). In bilateral cases, key features include absent testes on physical examination and imaging, micropenis in some cases, absent or rudimentary epididymis and vas deferens on the affected side, infertility, and absent puberty if both testes are lost. Unilateral cases may present as a nonpalpable undescended testis. Hormonal evaluation in bilateral cases typically reveals elevated gonadotropins (FSH and LH) and low or undetectable testosterone and AMH levels. Diagnosis involves physical examination, hormonal testing (including hCG stimulation test to assess for residual testicular tissue), imaging studies such as ultrasound or MRI, and sometimes surgical exploration (laparoscopy). Surgical exploration is often recommended to confirm the absence of testicular tissue and to remove any remnant tissue, which may carry a small risk of malignant transformation. Treatment for bilateral TRS includes testosterone replacement therapy initiated at the appropriate age to induce puberty and maintain secondary sexual characteristics, bone health, and overall well-being. Testicular prostheses may be offered for cosmetic and psychological reasons. Fertility is not possible in bilateral cases. Psychological support is an important component of management. There is currently no curative treatment to restore testicular function.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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