Testicular adrenal rests tumours in congenital adrenal hyperplasia: unraveling prevalence, risk factors and new therapeutic horizons in adolescents

Introduction

Congenital adrenal hyperplasia (CAH) is a group of autosomal recessive disorders of adrenal steroidogenesis. In more than 90%–95% of cases, CAH is caused by 21-hydroxylase deficiency, which reduces cortisol production and, in the most severe forms, aldosterone synthesis. Loss of cortisol-mediated negative feedback leads to chronically increased adrenocorticotropic hormone (ACTH), adrenal cortical stimulation, accumulation of steroid precursors such as 17-hydroxyprogesterone and progesterone and increased adrenal androgen synthesis. The clinical spectrum depends mainly on residual enzyme activity and includes classic salt-wasting, classic simple virilizing and nonclassic forms (1–3).

Testicular adrenal rest tumours (TARTs) are benign intratesticular lesions occurring in males with classic CAH. Although TARTs do not show malignant features and therefore do not usually require surgical removal, their typical central localization near the mediastinum testis may have important clinical consequences, ultimately leading to infertility (4).

Adolescence represents a critical window for the detection and prevention of TART, both due to the increasing prevalence of these lesions during puberty and because achieving an appropriate balance between over- and undertreatment can be particularly challenging during this period. Indeed, hormonal control is often suboptimal in adolescents, owing to reduced treatment adherence and puberty-related changes in glucocorticoid pharmacokinetics (5). Since poor hormonal control has been associated with gonadal dysfunction already during adolescence, early screening and regular follow-up may help prevent progression to irreversible testicular damage and subsequent infertility.

Embryology and pathophysiology

TARTs are thought to originate from ectopic adrenal-like cells derived from pluripotent embryonic tissue. During foetal development, the adrenal glands and gonads arise in close anatomical proximity, allowing adrenocortical precursor cells to migrate and persist within the rete testis (6, 7).

Among the factors implicated in tumour growth, chronic ACTH stimulation is considered the most important. Exposure to elevated ACTH levels, and possibly angiotensin II, beginning in utero and continuing postnatally, may stimulate the proliferation of these adrenal rest cells, which express ACTH and angiotensin II receptors (3). However, the observation that TARTs can occur in adequately treated patients, while remaining absent in some individuals with persistently suboptimal disease control, suggests that ACTH excess alone is insufficient to explain tumour development.

Epidemiology in childhood and adolescence

Reported TART prevalence varies widely, from 0% to 94%, depending on cohort selection, age, CAH phenotype, hormonal control and screening method (4), Table 1.

Table 1. Available studies on the prevalence and characteristics of TARTs in the paediatric population of patients with CAH of different aetiologies.

*Case report.

TARTs can already be detected during childhood, although prevalence appears to increase markedly with pubertal development (8). In a cohort of 51 males with CAH, TARTs were observed in 12.5% of children younger than 12 years, 29.4% of adolescents aged 12–17 years and 44.4% of adults (9). Similarly, other authors found a prevalence of 11% in children aged 5–12 years and 21% in patients older than 12 years (6). During adolescence, early detection may allow optimization of hormonal treatment before the development of irreversible testicular damage.

Clinical presentation

TARTs are bilateral in more than 80% of cases and are characteristically located near the mediastinum testis. Most lesions remain clinically silent and go often undetected on physical examination, particularly in the early stages. Due to their central location within the rete testis, TARTs generally become palpable only when they exceed 2 cm in diameter. Consequently, imaging plays a crucial role in diagnosis and surveillance, with scrotal ultrasound representing the preferred modality for early detection and follow-up (10).

Diagnosis and differential diagnosis

Ultrasound and MRI are both effective for detecting and monitoring TARTs; however, ultrasound is generally preferred due to its low cost, wide availability and ability to detect lesions as small as a few millimetres. Testicular ultrasound screening should begin in adolescence because it may help identify tumours at an initial stage and prevent irreversible gonadal damage. Evidence on proper timing is limited; expert opinions suggest screening yearly until puberty in asymptomatic males and more frequently in those with detectable lesions (8), Figure 1.

On ultrasound, TARTs are most commonly hypoechoic lesions, typically located near the mediastinum testis; some may show hyperechoic reflections, and hypervascularity is frequently detected with colour Doppler. MRI findings are less well characterized but generally show hypointensity on T1 and iso-/hyperintensity on T2 images (4).

The differential diagnosis of TARTs includes other testicular tumours, particularly Leydig cell tumour (LCT), because both entities share a steroidogenic origin and overlapping morphological features. In typical CAH patients, bilateral lesions near the mediastinum testis strongly suggest TART, whereas LCTs are more often unilateral and are generally removed because of malignant potential. Therefore, diagnosis relies on clinical context, bilateral involvement, localization, and hormonal profile; when available, absence of Reinke crystalloids helps distinguish TARTs from LCT (4, 11).

Risk factors for TART development during adolescence

Persistent ACTH excess is considered the main pathogenic driver of TART development, promoting hypertrophy and hyperplasia of adrenal rest cells and eventually leading to detectable testicular lesions (10). It is likely that not only the cumulative duration of ACTH exposure, but also persistent stimulation by ACTH (and also by angiotensin II, as previously discussed) from foetal life onwards, contributes significantly to TART development (12).

Consistent with this hypothesis, several studies have reported a higher prevalence of TARTs among patients with poor hormonal control, characterized by persistently elevated ACTH, 17-hydroxyprogesterone (17OHP) and androstenedione concentrations (13). However, the relationship is not always straightforward, as some patients develop TARTs despite apparently adequate biochemical control at the time of diagnosis (14).

Disease severity represents another important risk factor. TARTs occur predominantly in patients with classic salt-wasting CAH, whereas they are considerably less frequent in simple virilizing forms and rarely reported in non-classic disease. This observation supports the notion that cumulative exposure to ACTH excess, which is generally greater in severe genotypes with minimal residual CYP21A2 activity, contributes substantially to tumour development. Indeed, several studies have demonstrated higher TART prevalence among patients carrying severe CYP21A2 mutations, although genotype alone does not fully predict tumour occurrence (13, 15).

After adjustment for CAH phenotype, a diagnostic delay of more than one year after birth was associated with an increased risk of TART development. This association may reflect prolonged exposure of adrenal rest cells within the testes to elevated ACTH levels during early life. Consequently, neonatal screening programs, by enabling earlier diagnosis and treatment initiation, may contribute to improved disease control and potentially reduce the risk of subsequent TART development (15).

Adolescence appears to represent a particularly vulnerable period for TART progression. Pubertal maturation is associated with increased adrenal androgen production, accelerated growth and changes in glucocorticoid pharmacokinetics, all of which may complicate disease management. Furthermore, treatment adherence frequently declines during adolescence, resulting in periods of suboptimal ACTH suppression (16).

Therefore, ensuring care by specialists with expertise in these rare disorders is essential. A structured and timely transition from paediatric to adult care in specialized referral centres may help maintain treatment adherence, optimize disease control, and facilitate therapy simplification once final adult height has been attained.

The expression of luteinizing hormone (LH) receptors in TART, combined with the increased prevalence of TART during adolescence, suggests that the pubertal rise in LH may play a role in promoting the growth of adrenal rest cells. This could explain tumour expansion even in patients with relatively good hormonal control (17).

Moreover, a modulating role of inflammatory cells has been proposed, as lymphocytic aggregates have been identified in adrenal rest tumours, and transcriptional data revealed an increased expression of pro inflammatory cytokines (18).

Ultrasonographic screening studies have shown that TART prevalence increases progressively with age, becoming substantially more common during puberty and young adulthood than in prepubertal children (19, 20).

An emerging concept is that cumulative disease burden may be more relevant than isolated hormonal measurements. Long-standing exposure to elevated ACTH during childhood may initiate irreversible proliferative and fibrotic changes within adrenal rest tissue (21). This hypothesis is supported by observations that advanced TART lesions often demonstrate only partial regression despite subsequent optimization of glucocorticoid therapy (22). Consequently, the absence of biochemical evidence of poor control at a single clinic visit should not exclude the possibility of TART development.

As known, there is a significant gender-related difference in prevalence of adrenal remnants, with female patients presenting ovarian adrenal rest tumour (OART) only rarely; this is possibly related to the primary sex cord cells’ regression, during female embryogenesis, which includes also migrated adrenal cells (23, 24).

Taken together, these data indicate that puberty is not merely a period of higher TART detection, but a distinct biological and clinical window. Biologically, the pubertal rise in LH, accelerated adrenal androgen production and puberty-related changes in glucocorticoid pharmacokinetics converge to promote adrenal rest cell proliferation. Clinically, this period coincides with declining treatment adherence and the transition toward independent disease management, at a time when the underlying testicular damage-tubular obstruction and early fibrosis-remains at least partly reversible if treated promptly. Puberty therefore represents a key opportunity to intervene before damage becomes irreversible, rather than simply the age at which prevalence happens to be higher. Since infertility represents a significant consequence in patients with TART, appropriate counselling regarding this risk should be provided from an early age, also with the aim of improving treatment adherence, which in turn reduces the risk of further tumour growth. When appropriate, patients should be referred not only for semen analysis but also for cryopreservation (25).

It should also be noted that most of the evidence summarised above derives from cross-sectional cohorts combining children, adolescents and adults, or from adult series; studies specifically designed to compare prepubertal, pubertal and adult males as distinct groups remain comparatively scarce, which limits precise, age-specific screening and treatment recommendations for adolescents (19, 26).

Impact on gonadal function and fertility

Gonadal dysfunction is one of the most relevant long-term complications of CAH and a major cause of male infertility. Impaired gonadal function may indeed result from primary testicular damage, mainly related to TARTs and/or secondary gonadal failure caused by suppression of the hypothalamic–pituitary–gonadal axis. Signs of gonadal dysfunction may already appear during puberty, making careful monitoring essential in adolescent patients.

The main local mechanism is mechanical compression. Since TARTs typically develop near the mediastinum testis, progressive enlargement can obstruct the seminiferous tubules and impair sperm outflow, causing obstructive azoospermia. Long-standing obstruction may lead to hypospermatogenesis, peritubular fibrosis, tubular hyalinization, and ultimately complete loss of germ cells and Sertoli cells (27). A paracrine effect may also contribute to testicular damage, as steroids produced by TART cells may be toxic to Leydig cells and/or germ cells (28).

Biochemical evaluation of gonadal function in CAH is complex. LH and FSH may have limited value because adrenal androgens, partly aromatized to estrogens, could suppress gonadotropins. Testosterone may be normal or only slightly reduced despite impaired gonadal function. Inhibin B is a more useful marker of Sertoli cell activity and may also be informative in prepubertal boys, while semen analysis can be performed in post-pubertal and adult patients (29, 30).

Monitoring ACTH, renin, 17-hydroxyprogesterone, androstenedione and testosterone remains important, because tumour growth appears to be related to hormonal control. The androstenedione/testosterone ratio can help estimate the adrenal contribution to circulating testosterone; a ratio less than 0.5 is typically observed in eugonadal men, whereas values above 2 suggest inadequate disease control with a substantial adrenal contribution to testosterone levels (31).

Optimization or intensification of glucocorticoid therapy is generally considered the first therapeutic step, and tumour shrinkage after ACTH suppression has been described. However, response is variable and higher glucocorticoid doses may increase the risk of adverse effects, including weight gain, hypertension, and impaired final height. During puberty, increased glucocorticoid clearance may require dose adjustments, but treatment should aim for the lowest effective dose (32).

Testicular adrenal rest tumours in rare forms of congenital adrenal hyperplasia

Although TARTs have been most extensively investigated in 21-hydroxylase deficiency, they have also been reported in rarer forms of CAH, including 11β-hydroxylase deficiency, 3β-hydroxysteroid dehydrogenase type 2 deficiency, P450 oxidoreductase deficiency and steroidogenic acute regulatory protein deficiency, whereas they appear to be uncommon in nonclassic CAH (NCCAH). The available evidence is considerably more limited and consists predominantly of case reports and small case series (4).

TARTs in non-classic congenital adrenal hyperplasia

TARTs appear to be uncommon in men with NCCAH. In a recent review (33), four studies including a total of 124 males with NCCAH identified only two patients with TARTs (15, 34–36). This low prevalence likely reflects the milder degree of ACTH excess and generally preserved hormonal control observed in NCCAH compared with classic disease. Fertility is usually preserved in affected men. Based on the currently available evidence, routine testicular ultrasound screening is not recommended in asymptomatic NCCAH patients, although it may be considered in those with longstanding poor hormonal control or infertility (14).

11β-hydroxylase deficiency

Among rare CAH forms, 11β-hydroxylase deficiency (11OHD) provides the strongest evidence for clinically relevant TART development, with up to 40% of males affected (4).

Although 11OHD accounts for less than 10% of CAH cases worldwide, chronic ACTH excess remains a hallmark of inadequately treated disease despite the distinct steroid profile characterized by elevated 11-deoxycorticosterone and hypertension. Several reports have documented TARTs in affected males and available evidence suggests that these lesions may contribute significantly to infertility, similarly to what is observed in 21OHD (37–40).

A prospective study evaluating six young adult men with CAH, including two patients with 11OHD, detected TARTs in four individuals overall, with bilateral lesions in three cases. Impaired semen quality, including azoospermia in one subject, was observed in most patients. Although prevalence data are lacking, TART surveillance should be considered in poorly controlled male patients (41).

3β-hydroxysteroid dehydrogenase type 2 deficiency

Evidence for TARTs in 3β-hydroxysteroid dehydrogenase type 2 (3βHSD2) deficiency is limited but particularly noteworthy because tumours have been reported during childhood (42). The first biopsy-confirmed cases were described in two brothers carrying a novel HSD3B2 mutation who developed TARTs at 3 and 5 years of age. These observations demonstrated that adrenal rest tissue proliferation can occur early in life, even in rare forms of CAH (42).

Additional reports have described extensive bilateral and multifocal TARTs associated with severe gonadal involvement. Although the number of reported patients remains extremely small, available data suggest that TARTs in 3βHSD2 deficiency may exhibit a clinical behaviour comparable to that observed in classic 21OHD, including progressive impairment of spermatogenesis when diagnosis and treatment are delayed (43–45).

P450 oxidoreductase deficiency and STAR deficiency

TARTs have also been reported in non-classic forms of P450 oxidoreductase deficiency (PORD) and steroidogenic acute regulatory protein (STAR) deficiency. Despite major differences in the underlying molecular defects, both disorders share persistent ACTH stimulation as a consequence of impaired cortisol synthesis. Published cases describe primary testicular failure, oligospermia, elevated gonadotropins and sonographic evidence of adrenal rest tissue. Although patient numbers remain insufficient to establish prevalence or specific screening recommendations, these observations reinforce the concept that prolonged ACTH exposure can promote TART formation regardless of the specific steroidogenic defect (46).

17α-hydroxylase/17,20-lyase deficiency and other ultra-rare forms

In contrast to 21-hydroxylase and 11β-hydroxylase deficiencies, evidence supporting the occurrence of TARTs in 17α-hydroxylase/17,20-lyase deficiency is extremely limited. Although chronic ACTH excess is expected to promote adrenal rest cell proliferation, the virtual absence of adrenal and gonadal androgen production may reduce the trophic stimuli required for clinically detectable tumour growth. Consequently, it remains unclear whether TARTs are genuinely rare in 17OHD or simply under-recognized given the insufficient number of reported patients and lack of systematic screening; furthermore, severely affected testes may be atrophic, difficult to assess, or already surgically removed before TARTs are detected in 46XY patients. Future studies are needed to clarify whether factors beyond ACTH excess contribute to TART development in CAH (47).

Novel therapies and their potential impact on TARTs

The development of novel therapeutic approaches for CAH has generated considerable interest regarding their potential effects on TART development and progression. However, direct evidence that any of these therapies improve TART-specific outcomes remains scarce and largely speculative. With the partial exception of small exploratory analyses discussed below, TART prevalence, tumour volume, semen parameters and other gonadal endpoints have not been predefined outcomes of the available trials, which have instead focused primarily on biochemical control (17OHP, androstenedione, ACTH) and glucocorticoid dose reduction ⁽48).

Modified-release hydrocortisone (MR-HC; Efmody®) was designed to mimic the physiological circadian rhythm of cortisol secretion more closely than conventional glucocorticoid regimens. Clinical trials have demonstrated improved control of adrenal steroid excess, including significant reductions in morning 17OHP and androstenedione concentrations compared with standard treatment (48, 49). TART-related outcomes have not been included among the primary or secondary endpoints of the major MR-HC studies, however one male patient with a history of TARTs experienced an improved sperm count during therapy with hydrocortisone MR-HC in the phase 3 trial (48).

More specific targeting of the hypothalamic–pituitary–adrenal axis has been achieved through corticotropin-releasing factor type 1 (CRF1) receptor antagonists. Tildacerfont was among the first compounds in this class to be evaluated in adults with classic CAH. Phase 2 studies demonstrated significant reductions in ACTH, 17OHP, and androstenedione levels, particularly among patients with poor baseline disease control. Importantly, TART assessment was included as an exploratory outcome in a small subset of male participants. One patient experienced an approximately 23% reduction in TART volume after six weeks of treatment, accompanied by an 87% decrease in ACTH concentrations, while another patient showed disappearance of previously detected lesions on ultrasound (50). Although these findings are limited by the limited sample size and short follow-up duration, they provide the first clinical proof-of-concept that pharmacological ACTH suppression may influence TART biology.

Crinecerfont, a second-generation CRF1 receptor antagonist, has recently demonstrated efficacy in phase 3 clinical trials involving both adult and paediatric patients with classic CAH. Treatment resulted in significant reductions in adrenal androgen production and allowed substantial glucocorticoid dose reduction while maintaining disease control. Unfortunately, the phase 3 trials did not report TART prevalence, tumour volume, fertility parameters or ultrasound findings as predefined outcomes (51).

Emerging ACTH-targeted therapies

Additional ACTH-targeted therapies are currently under development and may further expand treatment options in CAH. Atumelnant (CRN04894), an oral melanocortin type 2 receptor antagonist and Lu AG13909, a monoclonal antibody directed against circulating ACTH, both aim to reduce ACTH-driven adrenal steroid excess. Given ACTH’s central role in TART pathogenesis, these compounds may theoretically have beneficial effects on adrenal rest tissue and gonadal outcomes. However, no data regarding TART prevalence, tumour volume, fertility parameters, or testicular function are available so far. A phase 3 trial evaluating atumelnant (CALM-CAH; NCT07144163) and a phase 2 study investigating Lu AG13909 in classic CAH (NCT06471829) are ongoing; results are awaited to clarify their potential role in preventing or modifying ACTH-related complications, including TARTs.

Conclusions

The development of TARTs represents a frequent complication in patients with classic CAH, with a potential future impact on gonadal function and fertility. Several factors, such as increased glucocorticoid therapy clearance, reduced compliance and rising LH levels, make the peripubertal period the most critical for managing this complication. Screening with testicular ultrasound should be initiated at the onset of puberty and is essential for all male patients, with earlier screening recommended in the first years of life if disease control is poor. Follow-up should therefore be performed annually at least until adulthood. Novel and promising treatments are emerging, but their real impact on this complication needs further investigation.

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Footnotes

Edited by: Tulay Guran, Marmara University, Türkiye

Reviewed by: Jan Idkowiak, University of Birmingham,United Kingdom