Is His Penis Too Small?

Patient Presentation
A pediatrician received a consultation about a 3-year-old male admitted for elective pressure equalizing tube surgery, who was noted to have a small penis during pre-operative evaluation. He had been followed by a local physician and according to his parents he was growing and developing properly and was current with his immunizations. He was obese and his parents had received dietary counseling and had made some changes to the family’s diet. The family said that he had no problems urinating or defecating and that he was toilet training. They said he had a normal urinary stream and did not seem to spray the toilet more than another child learning to urinate. The past medical history showed a full-term male infant who was circumcised at birth and was always “a big baby.” He had multiple episodes of otitis media. The family history was positive for coronary artery disease, dyslipidemia and diabetes. There were no congenital abnormalities, endocrinological or neurological problems in the family. The review of systems was negative.

The pertinent physical exam showed a healthy looking but obese male with normal vital signs. Weight was 22.1 kg (50% for a 6 year old), height was 101 cm (90% for 3 year old). BMI was 21.6 (50% for a 12 year old). Midparental height was 165 cm. HEENT shows scarred tympanic membranes with bilateral fluid. Genitourinary examination did not show a penis but a large suprapublic fat pad. His outstretched penis length was 5.2 cm when measured from the pubic symphysis to the tip of the glans. There was a normal meatal opening and no erythema, but urine in the surrounding fat pad was noted. His scrotum had rugations and both testicles were 2.3 cm in longest length. There were normal cremasteric reflexes, but it was difficult to check for inguinal hernias because of the fat pad. The anus was normally placed. The diagnosis of an inconspicuous but normal penis was made. The family was counseled about the importance of proper hygiene because the penis was buried. The family was also counseled again about the importance of proper nutrition and weight, particularly with the family history. They were offered nutrition counseling at the hospital and declined. They did say that they would return to his regular doctor and would talk with him about possible family lipid testing and obesity management.

Discussion
Examination of the genitalia in both genders is an important part of a complete physical examination. For males, a small penis is defined by normative data (see below). A micropenis “… is defined as a stretched penile length of less than 2.5 standard deviations below the mean for age.” Many people will use the terms micropenis and microphallus interchangeably, but others will use the term micropenis to be a short penis but normally formed, and a microphallus to be a short phallus with an associated anomaly such as hypospadias.

Causes of micropenis are usually genetic (i.e. Kleinfelter, Noonan, Prader-Willi syndromes, etc.) or endocrinological, particularly anywhere along the hypothalamic-pituitary-gonad axis. Testosterone biosynthesis (i.e. 17-beta hydrosysteroid dehydrogenase deficiency) or leutenizing hormone biosynthesis abnormalities can cause micropenis as well as end-organ problems (i.e. 5-alpha reductase deficiency). Hypopituitarism and hypoaldosteronism can cause micropenis, but infants with these abnormalities often also present with other problems including hypoglycemia and electrolyte problems which may lead to shock and even death. Other genital abnormalities may also present with micropenis including hypospadias and cryptorchidism.

Micropenis is part of the spectrum of ambiguous genitalia. It is also very important to distinguish micropenis from clitormegaly as part of appropriate evaluation and treatment. A child with ambiguous genitalia and their family need to be appropriately evaluated, treated and counseled. This usually requires an institution with an experienced multidisciplinary team including genetics, endocrinology, radiology, urology, surgery and social services.

It is also important to remember that if the penis size is borderline, meets the criteria for micropenis, has any anatomic abnormalities or there are any concerns about the genitalia not being completely normal, then a circumcision should not be done until a complete evaluation is made.

Inconspicuous penis is a term that notes a penis that appears small but is not. In the case above the penis was buried in the fat pad. Other reasons aninconspicuous penis include concealed penis, diminutive penis, poor penile suspension, trapped penis, and webbed penis.

Learning Point

Penis length should be measured from the base of the pubic symphysis to the tip of the glans. The penis should be stretched to the point of resistance before measuring. A healthy newborn male penis measures 3.5 cm with 2 standard deviations below the mean of < 2.0 cm. A 3 year old male should have a penile length of 5.5 cm with 2 standard deviations below the mean of 3.3 cm. Data for premature infants for gestational ages 24-36 weeks is 2.27 cm + 0.16 X (gestational age in weeks).

Testicular size can be estimated by volume using Prader models. Most people use long axis length as the standard.

Tables for penile length and testicular size can be found at Harriet Lane Handbook.

Questions for Further Discussion
1. What initial evaluation could be considered for a male with ambiguous genitalia?
2. What initial evaluation could be considered for a female with ambiguous genitalia?
3. What are the normal values for testicular size for a full term male infant?

Related Cases

Disease: Penis Disorders | Obesity | Obesity in Children

Symptom/Presentation: Growth Problems | Health Maintenance and Disease Prevention | Obesity

Specialty: General Pediatrics | Nephrology / Urology

Age: Preschooler

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com, the National Guideline Clearinghouse and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for this topic: Penis Disorders

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

Bergeson PS, Hopkin RJ, Bailey RB, McGill LC, Piatt JP. Inconspicuous Penis. Pediatrics. 1993;92(1):794-799.

Tuladhar R, Davis PG, Batch J. Establishment of a normal range of penile length in preterm infants. J Paediatr Child Health. Oct 1998;34(5):471-3.

Lee PA, Houk CP, Ahmed F, Hughes IA. Consensus Statement on Management of Intersex Disorders. Pediatrics 2006;118;e488.

Vogt KS, Kemp S. etc. al. Microphallus. Medscape Reference. Available from the Internet at http://emedicine.medscape.com/article/923178-overview (rev. 7/9/2008, cited 7/5/2011).

Custer JW, Rau RE. Harriet Lane Handbook. 18th edit. Mosby. Philadelphia, PA. 2009:296.

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