What underlying conditions or hormones can cause a macropenis in infants or adults?
Executive summary
Excess penile size (macropenis/macrophallus) is rare and can be congenital or acquired; notable hormonal causes in infants include fetal or postnatal androgen excess such as congenital adrenal hyperplasia (CAH) and steroid 11β‑hydroxylase deficiency, while in toddlers and children cases have been linked to markedly elevated testosterone with suppressed gonadotropins [1] [2] [3]. Acquired increases in penile girth in adults have been reported after recurrent/priapistic episodes causing structural change in the tunica albuginea (a syndrome labeled “circumferential acquired macropenis”) in multiple case series [4] [5] [6].
1. Hormonal overexposure in utero and early life: congenital androgen excess drives many infant cases
When clinicians find an unusually large penis in a newborn or infant, they first consider excess androgen exposure during fetal life or early postnatal “mini‑puberty.” Reviews and clinical reports link excessive fetal androgens — for example from congenital adrenal hyperplasia (including 11β‑hydroxylase deficiency) — with virilized genitalia in females and macropenis in affected male infants, often alongside other signs (hypertension, acne, hyperpigmentation) that point to adrenal steroid abnormalities [1] [2].
2. Specific enzymatic defects: CAH (11β‑hydroxylase) is a documented trigger
Steroid 11β‑hydroxylase deficiency produces androgen excess and clinical pictures that include pseudoprecocious puberty and macropenis; case series emphasize that systemic features (high blood pressure, skin changes) should alert physicians because genital enlargement in that setting is part of a broader, treatable endocrine disorder [2].
3. Precocious puberty and testicular/adrenal tumors: autonomous androgen sources
Reports and clinical summaries note that precocious activation of androgen production — whether from central (hypothalamic/pituitary) causes or peripheral sources such as Leydig/interstitial cell hyperplasia or adrenal cortical tumors — can present with early penile enlargement, pubarche, acne and accelerated somatic features; pediatric case reports have documented toddlers with markedly increased testosterone and suppressed LH/FSH accompanying macropenis [3] [7] [8].
4. Structural vs hormonal — acquired adult macropenis often follows priapism and tissue changes
A distinct adult pattern described in surgical and urology literature is circumferential acquired macropenis: several case reports found that repeated priapism episodes lead to symmetric girth enlargement (both flaccid and erect) or idiopathic erection‑only girth increase with a thinned albuginea on surgery. In a small series, priapism was implicated in 5 of 7 acquired‑girth cases, and authors proposed the syndrome name and a geometrically based reduction corporoplasty as management [4] [5] [6].
5. Other medical conditions and case reports: sickle cell disease and vascular phenomena
Secondary enlargement has been described in the context of sickle cell disease (via priapism and vascular injury) and in isolated case reports where vascular or hematologic pathology led to problematic enlargement requiring surgical care [8] [9]. Popular and non‑peer reviewed sites echo these associations but vary in rigor; surgical/urology literature is more cautious and centers on structural sequelae of ischemic priapism [4] [6] [8].
6. Definitions, rarity, and measurement caveats — macropenis is not standardized
Unlike micropenis, which has formal cutoffs (SPL < −2.5 SD), the term “macropenis” lacks a universally accepted numerical definition; some neonatal series use >+2.5 SD or the 97th percentile as a practical threshold, but many authors stress that macropenis is uncommon and warrants investigation because it can reveal syndromic, endocrine or structural disease [10] [11] [12].
7. Diagnostic priorities and clinical workup according to the literature
Sources recommend evaluating hormonal status (testosterone, LH, FSH), screening for adrenal enzyme defects (CAH), imaging for adrenal or testicular tumors when indicated, and looking for systemic clues (hypertension, skin changes) that point to adrenal causes; in adults with rapid girth change, urological assessment for priapism sequelae and surgical planning is discussed in the literature [2] [3] [4].
Limitations and dissent: available sources are uneven — pediatric endocrine and surgical case reports are strong for CAH and priapism links [2] [4], but there is no consensus numeric cutoff for macropenis and some web sources and forums extrapolate tumor or testosterone links without robust citation [8] [9]. For items not covered in the provided reporting — for example long‑term adult outcomes after hormonal correction in macropenis or population prevalence — available sources do not mention those data.