Micropenis Evaluation and Management

Micropenis in Children
Evaluation and Management
Dr Shahjada Selim
Associate Professor
Department of Endocrinology, BSMMU
website: https://shahjadaselim.com

• Micropenis, or microphallus, is defined as a
stretched penile length of less than 2.5 standard
deviations (SDs) below the mean for age.
• Traditionally, the term micropenis refers to a penis
that is otherwise normally formed, and the term
microphallus has been used when associated
hypospadias is present [1].
1.Alsaleem M, Saadeh L. Micropenis. StatPearls. 2021 Jan.
Background and Definition

1. Tuladhar R et al. J Paediatr Child Health. 1998 Oct. 34(5):471-3.
The normal length of a newborn boy's penis is 2.5 to
3.5 cm. The measurement around a newborn boy's
penis (the circumference) is normally 0.9 to 1.25 cm.
The penis is measured by carefully stretching it.
The penis is measured from the tip to the base [1].
A penis length of less than 2.0 cm is
considered a micropenis.

• During embryonic development, following the
differentiation of bipotential gonadal ridge to testis,
placental human chorionic gonadotropin (hCG)-driven
testosterone synthesis begins in Leydig cells at 8-12
weeks, resulting in penile differentiation stimulated by
dihydrotestosterone (DHT), a product of the
transformation.
• Fetal androgen levels are high between the 8th and
24th weeks of gestation, with peak levels often observed
between the 14th and 16th weeks [1].
1. Johnson P et al. Ultrasound Obstet Gynecol 2000;15:308-310
Embryology

•Consequently, there is a marked increase in penile
length during the second and third trimesters, with an
increase of approximately 20 mm from weeks 16 to 38
[1,2].
•It can thus be deduced that a true micropenis is
caused by a hormonal abnormality that occurs after
the 12th week of gestation [3].
1. Johnson P et al. Ultrasound Obstet Gynecol 2000;15:308-310.
2. Zalel Y et al. Ultrasound Obstet Gynecol 2001;17:129-131.
3. Evans BA et al. Int J Androl 1983;6:143-156.
Embryology

Jeremy W et al. TheScientificWorldJOURNAL (2011) 11, 1462–1469 TSW Urology ISSN 1537-744X; DOI 10.1100/tsw.2011.135
Normal SPL (CM)

J. Endocr. Soc., Volume 6, Issue 2, February 2022, bvab172, https://doi.org/10.1210/jendso/bvab172
Figure 2. SPL in boys across childhood and adolescence in
different ethnic backgrounds. The numbers refer to the ...

Causes of
micropenis [1]
1. Ludwig G. Andrologia. 1999;31(Suppl 1):27–30.

Causes of micropenis [1]
2. Aaronson, I.A. (1994) .J. Urol. 152(1), 4–14
•Typically, when due to hypogonadotropic hypogonadism,
micropenis is associated with conditions such as Kallman’s
syndrome (hypogonadotropic hypogonadism and anosmia)
and Prader-Willi syndrome (hyperphagia, mental
retardation, short stature, hypotonia, and hypogonadism).
•Hypergonadotropic hypogonadism, or primary testicular
failure, can be due to gonadal dysgenesis, or may be
associated with Robinow’s syndrome [1] as well as poly-X
syndromes, such as XXY (Klinefelter’s syndrome), gene
translocations, and trisomies of chromosome 8, 13, and 18
[2].

Causes of micropenis [1]
1. Aaronson, I.A. (1994) .J. Urol. 152(1), 4–14
• Problems with testosterone action, such as 5-α
reductase deficiency, can present as micropenis in
its incomplete form, although hypospadias is a much
more common result [1].
• Finally, idiopathic causes of micropenis are
associated with an empirically normal hypothalamus-
pituitary-testicular axis [2].

Environment and Epidemiology
• The detrimental effect of environmental prenatal exposure
to endocrine disruptors on the androgenization of male
offspring has been described for more than 3 decades [1].
This has also been supported by other observations, such as
the reports of micropenis in cases of prenatal maternal use
of antifungals [2], as well as a reported association between
exposure to endocrine disruptor chemicals and micropenis
[3].
1. Main KM et al. Best Pract Res Clin Endocrinol Metab. 2010;24(2):279-289.
2. Skakkebæk NE et al. Hum Reprod. 2001;16(5):972-978.
3. Mogensen et al. Environ Health. 2017;16(1):68.
• However, the association between maternal exposure to
endocrine disruptors when assessed by measurement of
antenatal urinary concentrations of phthalates and related
chemicals has not shown this same relationship [3].

Environment and Epidemiology
In the USA, the incidence of micropenis was reported as 1.5
in 10 000 male children born between 1997 and 2000 [1].
1. Nelson CP et al. J Urol 2005;174:1573-1576.

To make an accurate diagnosis of micropenis, the examining clinician
must have a clear understanding of the definition of micropenis as
well as how to measure the penis.
DIAGNOSIS
• This is to exclude confounding diagnoses, such as webbed penis and
hidden penis.
• SPL is measured from the point where the penis meets the pubic bone
to the distal tip of the penis, which is put on maximal stretch.
• Care must be taken to compress any suprapubic fat pad, prevalent in
infants and most likely the major cause of misdiagnosis of micropenis
in this age group.
• The micropenis typically has a normal circumference-to-length ratio,
although, rarely, severely hypoplastic corpora cavernosa will be
seen[1].
• Frequently, micropenis is associated with cryptorchidism and small-
volume testicles, as well as a hypoplastic scrotum, most likely due to
the same causative factors that are responsible for the micropenis[1].
1.Ludwig, G. (1999) Andrologia 31(Suppl 1), 27.

DIAGNOSIS
• Other characteristics, such as delayed puberty in older
children, suggestive of hypogonadotropic hypogonadism,
should be noted to aid in diagnosis.
• Specifically, hypogonadotropic hypogonadism is commonly
associated with growth hormone (GH) deficiency and/or
adrenocorticotropic hormone (ACTH) deficiency, putting
the infant at high risk for death due to hypoglycemia or
cortisol deficiency.
• Plasma cortisol, serum electrolytes, and plasma glucose
may be obtained in this setting to rule out acute problems.

DIAGNOSIS
• Prolactin (PRL) levels help to isolate the defect to the
hypothalamus (high PRL) vs. the pituitary (low PRL).
• In addition, plasma GH, TSH, and ACTH can all be used to
isolate the location of dysfunction.
• Interestingly, it may be difficult to make the diagnosis of
hypogonadotrophic hypogonadism in the prepubertal
patient with micropenis if they are past infancy, as there is
a quiescent phase of the pituitary that sees levels of
follicle-stimulating hormone (FSH) and luteinizing
hormone (LH) drop precipitously [1].
1.Grumbach MM. J. Clin. Endocrinol. Metab. 90(5), 3122–3127.

DIAGNOSIS
• In parallel with an evaluation of central endocrine function,
testicular function may also be assessed through serum
testosterone levels before and after administration of hCG. No
rise in post-administration testosterone and rises in LH and FSH
are consistent with testicular failure or absence, although this can
also occasionally be seen in those patients with Kallman
syndrome and undescended testicles [1].
• Antimüllerian substance (AMH), and inhibin B, which are
produced by functioning Sertoli cells, can also be used to
determine the presence of functional testicular tissue[9,12]. Low
AMH coupled with a normal inhibin B is indicative of the rare,
persistent müllerian duct syndrome, which is the result of a
defect in the gene that encodes AMH [1].
1.Grumbach MM. J. Clin. Endocrinol. Metab. 90(5), 3122–3127.

DIAGNOSIS
1.Grumbach MM. J. Clin. Endocrinol. Metab. 90(5), 3122–3127. . 2. Elder J 2005. In Campbell-Walsh Urology. 9th ed. Elsevier, Amsterdam. pp. 3751–
3754. 3. Maghnine M et al. . J. Endocrinol. Invest. 27, 496–509.
• Magnetic resonance imaging (MRI) may be used to identify
midline structural defects, such as pituitary stalk dysplasia
syndrome, central diabetes insipidus (indicated by a lack
of a posterior pituitary bright spot), and pituitary
aplasia[1,2].
• Specifically, findings such as a small anterior pituitary
gland, attenuated or absent pituitary stalk, and ectopic
posterior pituitary are all suggestive of hypopituitarism
and thus can help to facilitate identification of the
etiology[1]. Finally, some authors advocate obtaining a
karyotype[3], although this recommendation is not
universal.

Correct technique for measuring penile length
Traditional methods utilize a ruler or caliper to measure penile length. Penile
length should be measured when the penis is fully stretched, not flaccid; the glans
penis should be held with the thumb and forefinger, and the measurement should
be taken from the pubic ramus to the distal tip of the glans penis over the dorsal
side. The suprapubic fat pad should be pressed inwards as much as possible, and if
present, the foreskin must be retracted during the measurement. While penile
diameter and its ratio to length are typically normal, the diameter may rarely be
smaller in cases with severe hypoplasia of the corpus cavernosum.

A modified syringe to be used for measuring penile length
A different approach involves the use of a 10 mL disposable syringe.
The needle-side tip of the syringe is cut off, and the piston is
inserted into the syringe on the cut side. The open side of the
syringe is placed on the penis. The piston is pulled back while
pressing the fat pads inwards, which causes the penis to be pulled
inside the syringe as a result of suction. Once the penis is stretched
inside the syringe, penile length is read from the scale added on the
modified syringe. This technique allows for the elimination of
measurement differences caused by the suprapubic fat pad.

• Treatment of micropenis should focus on penile size
sufficient for the patient to have an appropriate body
image, normal sexual function, and standing
micturition.
• Inability to bring the penis fully to the mean
measurement for age does not imply failure.
• Primary treatment of micropenis revolves around
exogenous testosterone administration to increase the
length of the penis so that it may be considered within
a range of normal.
TREATMENT

• Most authors endorse 25 mg of intramuscular
testosterone in infancy, typically in its ethanate
formulation to promote longer action, once a month for
3 months, followed by further courses at higher dosages
at the start of pubarche[1]. Good responses are typically
seen, with increases of over 100% in penile length over
the course of initial treatment to be expected.
• However, if the response is not deemed satisfactory,
repeat administrations over short time periods may be
performed without significant concern about early
maturation of bony growth plates and subsequent
reduction in stature.
TREATMENT

• Transdermal delivery of both testosterone and
dihydrotestosterone have also been reported, with the
application of dihydrotestosterone resulting in
increases in penile length of over 150% during the
treatment period[18], although others have found no
such results in head-to-head comparisons with respect
to testosterone[1].
TREATMENT

• There has also been two reports of administering LH and FSH to
an infant with hypogonadotrophic hypogonadism and
micropenis; however, although there was a significant increase
in testicular volume over the treatment period in both studies,
minimal increase in penile size was noted in one study[21] and
was seen in one out of two patients in another[22]. This is in
keeping with the gonadotropin releasing hormone (GnRH) surge
seen immediately after birth in normal infants[9], with
accompanying increases in Sertoli cell populations[23]
TREATMENT

• Typically, a good response is a 100% increase in penile
length in the course of the initial treatment (32,33).
Another author (26) considers a 3.5-cm increase in
penile length by testosterone injections as an adequate
response. In case of an inadequate response,
applications may be repeated within a short period of
time (9,33).
Testosterone Treatment: Dosning
Therefore, it can be said that long-term dermal application of testosterone
promotes skeletal growth, as well as penile growth (34).

• Topical testosterone application is effective during
infancy. Arisaka et al [1] demonstrated increases in
penile lengths in 50 infants and children aged between
5 months and 8 years, by administering 5%
testosterone cream for a duration of 30 days.
• Testosterone that is absorbed transdermally was
shown to stimulate growth hormone (GH) secretion
from the pituitary gland and promote bone growth by
increasing insulin-like growth factor-1 production [1].
Testosterone Treatment: Outcomes
Therefore, it can be said that long-term dermal application of
testosterone promotes skeletal growth, as well as penile
growth [1].
1.Arisaka O et al Pediatr Int. 2001;43:134–136.

There is no consensus on the dose,
method of administration, or duration
in testosterone therapy for
micropenis.

•In prepubertal patients with androgen insensitivity,
topical application of DHT gel to the periscrotal region
3 times daily for a total of 5 weeks has been shown to
increase serum DHT levels. In another study,
percutaneous 2.5% DHT gel was used in 6 children,
aged between 1.9 and 8.3 years, with micropenis of
different etiologies.
Topical 5-a Dihydrotestosterone (DHT) Gel
1. Bertelloni S Sex Dev. 2007;1:147–151.

• An increase in phallic growth was observed when one
daily dose of 0.2-0.3 mg/kg DHT was used for 3-4 months
[1]. Side effects were reported to be similar to that of
testosterone treatment, except for minimal effects such as
minor skin irritations (1).
Topical 5-a Dihydrotestosterone (DHT) Gel
1. Bertelloni S Sex Dev. 2007;1:147–151.
This treatment option might be a good alternative
for patients who do not respond to testosterone.

• Recombinant human FSH-LH treatment during the first
few years of life promotes an increase in testicular growth
and penile length in patients with hypogonadotropic
hypogonadism, although this effect is not very significant.
• An increase in penile length from 1.6 cm to 2.4 cm and a
170% increase in testicular volume evaluated by
ultrasonography in a patient with micropenis, when
testosterone treatment was added to subcutaneous
injections of 20 and 21.3 IU of recombinant LH and FSH
twice a week, for a duration of 6 months.
LH-FSH Applications
1. dan L et al J Pediatr Endocrinol Metab. 2004;17:149–155.,

• The treatment was tolerated well, even though certain
side effects, such as increased amount of body hair,
increased pigmentation, and intermittent vomiting, were
noted.
LH-FSH Applications
1. dan L et al J Pediatr Endocrinol Metab. 2004;17:149–155.,
Although exogenous hormone therapy in patients
with micropenis increases penile growth, the length
of the penis may still be below the mean length of
the normal adult population [1].

• If the micropenis does not reach an adequate length despite
medical interventions, surgical treatment options are
considered [1].
• Cosmetic and functional outcomes reached acceptable levels
particularly when an implant was used following reconstruction
with prosthesis. Even though the technique is utilized in select
patients, the chance of a complication is high even in the hands
of an experienced surgeon [2].
1. Babaei A et al Urol J. 2010;7:71–78. Wisniewski AB et al. Semin Reprod Med. 2002;20:297–304.
Surgical Treatment
In general, patients remain displeased with the appearance of
their genitals [1]. However, current evidence indicates that,
even if micropenis has remained as such, the majority of
patients who are raised as males have normal sexual
identities and functioning.

With early treatment the prognosis for boys with
micropenis due to hormone deficiency is good. They
usually respond well to testosterone therapy, gain
adequate penile length (though below average size) and
are able to function normally as adults.
The outlook is not as positive for those boys with
micropenis that are due to other disorders, such as
androgen insensitivity, who can’t be helped with
hormone treatment. In these cases, the penis remains
small.
What is the prognosis (outlook) for patients
with micropenis?

What are possible complications of micropenis in
a child?
In some cases, a man with micropenis may have a low
sperm count. This can lead to infertility or decreased
fertility.
When should I call my child’s healthcare provider?
Call the healthcare provider if your child has:
Symptoms that don’t get better, or get worse
New symptoms

Fate of the micropenis and constitutional small
penis: do they grow to normalcy in puberty?
The goals of treatment for micropenis are to provide
a body image that will not cause embarrassment for
the patient when seen by others, to enable the patient
to have normal sexual function, and also enable the
patient to urinate standing up. Not exactly reaching
the mean penile length of the healthy population
does not mean failure.

How do patients and their families cope with
micropenis?
If early treatment is unsuccessful for micropenis, coping
with the condition can be difficult for a boy and his
family.
In all cases, psychological counseling and social services
will probably be required to help the patient and his
family emotionally.
Micropenis is a rare condition and what to do about the
condition depends on many factors. Your doctors will
help you along with your decisions as a parent or as a
patient.

1. Bettocchi C et al. Int J Impot Res 34, 392–403 (2022).

Key points about micropenis in children
A micropenis is a penis that is smaller than normal. A penis length
of less than 0.75 inches for a newborn boy is considered
micropenis.
It can happen on its own. But it often happens along with other
disorders.
It can occur with a hormone disorder that causes an abnormal level
of the hormones involved in the growth of the sexual organs. This
can include problems with the pituitary gland or the hypothalamus.
Hormone therapy may be used to treat some children. This can
help to cause penile growth. Sometimes surgery may be an option.
In some cases, a man with micropenis may have low sperm count.
This can result in infertility or decreased fertility.

➢ Micropenis is part of a larger group of conditions broadly known
as inconspicuous penis; however, it is fundamentally different
from the other diagnoses in this group, such as webbed penis and
buried penis, in that the underlying problem is the size of the
penis itself, not with the surrounding and overlying skin.
SUMMARY
➢ This condition is usually the result of a defect in the hypothalamic-
pituitary-gonadal axis, although iatrogenic causes are identified
infrequently. Since micropenis can be the first manifestation
identified of a broader endocrinologic problem, a pediatric
endocrinologist should be consulted once the diagnosis of micropenis
is made.
➢A micropenis is a penis that is smaller than normal. A penis
length of less than 0.75 inches for a newborn boy is considered
micropenis. It can happen on its own. But it often happens along
with other disorders.

SUMMARY
➢ Treatment of micropenis revolves around testosterone, either
through direct administration or encouraging the patient’s body to
make its own, and long-term results in terms of increased penile
length are promising.
➢ Patients with micropenis in adulthood do report dissatisfaction
with the appearance of their penis, but the majority appears to
have adequate sexual function. It should be stated, however, that
long-term robust data are still lacking in this crucial area
➢ Reconstructive surgery comes with a variety of options, all
based on the principle of a vascular pedicle free flap, and is
reserved for those patients not responding to hormonal
treatment.
➢ Since micropenis can be the first manifestation identified of a
broader endocrinologic problem, a pediatric endocrinologist
should be consulted once the diagnosis of micropenis is made.

Micropenis Evaluation and Management

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