Micropenis, or a penis that is less than 2.5 standard deviations below the average length for age, can be caused by several genetic factors or conditions that decrease testosterone production and signaling. Evaluation is needed if a newborn male's penis is less than 2-2.5 cm to determine the underlying cause and begin treatment. Testosterone therapy through injections can help increase penis size in infants and children with micropenis, while phalloplasty surgery is also an option for enlargement in some cases.

1. MICROPHALLUS
Dr. Zahoor Ahmad

2. MICROPHALLUS
Microphallus or micropenis, is
defined as a stretched penile length of
less than 2.5 standard deviations
(SDs) below the mean for age.

3. Traditionally, the term micropenis
refers to a penis that is otherwise
normally formed, and the term
microphallus has been used when
associated hypospadia is present.

4. The mean stretched penile length in a fullterm newborn male is 3.5 cm.
Measurements of less than 2-2.5 cm (2.5
SDs below the mean) in a full-term newborn
male meet the definition of micropenis and
warrant evaluation.

5. PENILE GROWTH IS ESSENTIALLY LINEAR
DURING MID-TO-LATE GESTATION
Penile length (cm) = -2.27 + 0.16 X (gest. weeks)

6. AMBIGUOUS GENETALIA?
Although micropenis can be considered a form of
ambiguous genitalia, the presence of a normal
scrotum and palpable testes indicates a high
probability of a normal male karyotype.

7. If the testes are not palpable and/or
the penile urethra is absent, the
examination is better described as
ambiguous, and an evaluation and
counseling for disorders of sex
development should be performed.

8. PATHOPHYSIOLOGY
Fetal production of testosterone and its
peripheral conversion to
dihydrotestosterone is necessary for
normal male development.

9. Early in gestation, placental human
chorionic gonadotropin stimulates
the developing testes to produce
testosterone by binding to the
luteinizing hormone (LH) receptor.

10. By approximately 14 weeks'
gestation, the fetal hypothalamicpituitary-gonadal axis is active, and
testosterone production falls under the
control of fetal LH.

11. Therefore, penile growth after the first trimester depends
on fetal testosterone production. Testosterone is
peripherally converted by the enzyme 5-alpha
reductase to the more potent androgen DHT, which is
responsible for virilization of the male external genitalia.
Finally, intact peripheral androgen receptors are
necessary for normal male development.

12. After age 6 months, the little subsequent
penile growth that occurs parallel to
general somatic growth. With the onset of
puberty penis growth resumes because of
increased testosterone production.

13. Growth hormone also plays a role in
penis growth as micropenis has been
observed in children with isolated growth
hormone deficiency.

14. Micropenis can also occur in children
with LH-receptor defects and
defects in testosterone
biosynthesis (e.g. 17-beta
hydroxysteroid dehydrogenase
deficiency).

15. Defects in peripheral androgen action include
5-alpha reductase deficiency (failure of conversion
of testosterone to DHT) and partial androgen
insensitivity syndrome due to an androgen receptor
defect. However, most children with these
conditions have varying degrees of incomplete
labioscrotal fusion, resulting in hypospadias and
genital ambiguity.

16. ASSOCIATED
SYNDROMES
Lastly, genetic syndromes in which
micropenis may be a feature include
Prader-Willi, Klinefelter, and CHARGE
syndromes, among others.

17. CAUSES
• Conditions associated with hypogonadotropic hypogonadism
• Conditions associated with decreased testosterone production and
hypergonadotropic hypogonadism
• Deficiency of 5-alpha reductase
• Partial androgen insensitivity syndrome
• Genetic syndromes (Klinefelter syndrome 47,XXY), Prader-Willi
syndrome, CHARGE syndrome

18. DIFFERENTIAL
DIAGNOSES
• 5-Alpha-Reductase Deficiency
• Adrenal Hypoplasia
• Ambiguous Genitalia and Intersexuality
• Androgen Insensitivity Syndrome
• CHARGE Syndrome
• Genital Anomalies

19. • Growth Hormone Deficiency
• Hypogonadism
• Hypopituitarism
• Hypopituitarism (Panhypopituitarism)
• Kallmann Syndrome and Idiopathic Hypogonadotropic
Hypogonadism
• Klinefelter Syndrome
• Noonan Syndrome
• Panhypopituitarism
• Prader-Willi Syndrome
• Smith-Lemli-Opitz Syndrome

20. TREATMENT
Testosterone therapy in the form of 3
monthly intramuscular (IM) injections
has been used to increase penis size
in infants and children.

21. PHALLOPLASTY
• Phalloplasty is a surgical technique that may be used for
penis enlargement. There are many micropenis cases
that were successfully treated with this kind of operation.
• Although in the past the procedure yielded poor
results, recent advances have made it a perfect option
for treating micropenis