Encyclopedia of Pathology

Living Edition
| Editors: J.H.J.M. van Krieken

Anorchism, Testicular Regression Syndrome

  • Manuel NistalEmail author
  • Pilar González-Peramato
Living reference work entry
DOI: https://doi.org/10.1007/978-3-319-28845-1_4781-1



Anorchidism is defined as the absence of one (monorchidism) or both testes (testicular regression syndrome) in males with 46, XY karyotype. The monorchidism may be due to a congenital absence of testis or a loss of it (vanishing testis).

Clinical Features

Patients with absence of one testis show no other symptoms than an empty scrotum. The diagnosis is confirmed by laparoscopy when observing blind-ended vas deferens and presence of spermatic vessels. In some patients compensatory hypertrophy of the contralateral testis is observed (more than 2 cm3) (Grinspon et al. 2016).

Testicular regression syndrome (TRS) refers to different situations in which patients show from a female phenotype (congenital bilateral absence of testis) to male phenotype (some microorchies and involutions of both testes). Depending on the moment of fetal life in which the testis disappeared, the following syndromes develop: rudimentary testis syndrome, bilateral congenital anorchidism, vanishing testis syndrome, and Leydig cell-only syndrome.

Patients with rudimentary testes syndrome have a male phenotype with micropenis, but no ambiguous genitalia, testes less than 0.5 cm, both cryptorchid. Wolffian derivatives are present most of the time and there is absence of Müllerian derivatives. It is estimated that testicular disappearance occurred between weeks 14 and 20 of fetal life. Some cases have been related to a primary defect in testicular vascularization (Dangle et al. 2017), others with a genetic disorder that has not been clearly demonstrated.

Patients with bilateral congenital anorchidism show male external genitalia with penile and scrotal hypoplasia. Wolffian derivatives are present while there is absence of Müllerian derivatives, suggesting that the testes have been present until 20 weeks of gestation. The causes of the disappearance are probably multiple: genetic (mutations isolated from the SF1 gene), intrauterine torsion of both testes, and immune disorder. Patients with bilateral absence of both testes are characterized by gonadotropin elevation, absence of response to stimulation with hCG, and undetectable AMH values (Hunter et al. 2016).

Vanishing testis syndrome refers to the disappearance of one or both testes in a period estimated from the last months of pregnancy until the beginning of puberty. Patients show hypoplasia of external genitalia and gynecomastia. The loss of the testes in most cases is considered secondary to twisting of the spermatic cord in a period that extends from the last months of gestation to adulthood.

Leydig cell-only syndrome is a condition known as agonadism without eunuchoidism. These patients have well-developed external genitalia but lack testes. Testosterone would be produced by clusters of Leydig cells located along the spermatic cord. The amount of testosterone would be sufficient to produce a male phenotype but insufficient to develop all male secondary sexual characteristics.
  • Incidence

    The absence of a testis is estimated at 4.5% of all undescended testes, representing 40% of the nonpalpable testes, or one per 5,000 males. Bilateral anorchia is rare (1 per 20,000 males).

  • Age

    Newborn to adolescence

  • Sex


  • Site

    Unilateral anorchia is more frequent on the left side (68%). The structures of the spermatic cord and testicular remnants, when present, are located in the inguinal canal (59%), abdomen (21%), superficial inguinal ring (18%), and scrotum (2%).

  • Treatment

    There is no consensus in the literature about the need for excision of testicular remnants in the context of surgery for an impalpable testis and testicular regression syndrome (Nataraja et al. 2018). In clinical practice, most are inclined by resection for histological study.

  • Outcome

    Most patients develop a hypergonadotropic hypogonadism in adulthood that can benefit from a treatment with testosterone (Vandewalle et al. 2018).


It is related to the fact that there is congenital absence or disappearance of a preexisting testis. In the first case, laparoscopic study does not prove the existence of either epididymis or deferent. In the second case, not only these structures but also spermatic vessels ending in a fibrous tissue are described. The percentage in which these structures can be identified is very variable being the vas deferens the most constantly found followed by the epididymis.


In the histological sections of the removed remnants, apart from vas deferens, hypoplastic epididymides and vascular plexus, dystrophic calcification (35.5–60%) with hemosiderin macrophages (30–48%) (Fig. 1) and variable number of giant cells are observed. A not infrequent finding is the presence of groups of seminiferous tubules in 5.3–20% of these remnants. These seminiferous tubules rarely contain germ cells and are the basis for the controversy of whether their extirpation is worthwhile or not because, despite extra-scrotal localization, the possibility of a tumor is exceptional.
Fig. 1

Monorchidism. Connective tissue with fibrosis, macrophages with hemosiderin, and dystrophic calcification at the end of the spermatic cord. All these findings are suggestive of perinatal testicular torsion

Differential Diagnosis

The differential diagnosis of monorchies should be done with undescended testes of patients with cryptorchidism, and in some cases of bilateral congenital anorchia with 46, XY gonadal dysgenesis.

References and Further Reading

  1. Dangle, P., Salgado, C., Reyes-Mugica, M., Schneck, F., Ost, M., & Sims-Lucas, S. (2017). Testicular hypoplasia is driven by defective vascular formation. Urology, 101, 94–98.CrossRefGoogle Scholar
  2. Grinspon, R. P., Habib, C., Bedecarrás, P., Gottlieb, S., & Rey, R. A. (2016). Compensatory function of the remaining testis is dissociated in boys and adolescents with monorchidism. European Journal of Endocrinology, 174, 399–407.CrossRefGoogle Scholar
  3. Hunter, J. D., Pierce, S. R., Calikoglu, A. S., & Howell, J. O. (2016). Embryonic testicular regression syndrome presenting as primary amenorrhea: A case report and review of disorders of sexual development. Journal of Pediatric and Adolescent Gynecology, 29, e59–e62.CrossRefGoogle Scholar
  4. Nataraja, R. M., Yeap, E., Healy, C. J., Nandhra, I. S., Murphy, F. L., Hutson, J. M., & Kimber, C. (2018). Presence of viable germ cells in testicular regression syndrome remnants: Is routine excision indicated? A systematic review. Pediatric Surgery International, 34, 353–361.CrossRefGoogle Scholar
  5. Vandewalle, S., Van Caenegem, E., Craen, M., Taes, Y., Kaufman, J. M., & T’Sjoen, G. (2018). Growth, sexual and bone development in a boy with bilateral anorchia under testosterone treatment guided by the development of his monozygotic twin. Journal of Pediatric Endocrinology & Metabolism, 31, 361–367.CrossRefGoogle Scholar

Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.Department of Anatomy, Histology and NeuroscienceUniversidad Autónoma de MadridMadridSpain
  2. 2.Department of PathologyUniversidad Autónoma de MadridMadridSpain
  3. 3.Department of PathologyUniversity Hospital La PazMadridSpain