When Should the Anterior Fontanelle Close?
A 1.5-month old male came to clinic with symptoms of an upper respiratory infection. He was noted to have a 3 millimeter anterior fontanelle opening.
The past medical history was negative.
The family history revealed no birth defect, congenital or neurological abnormalities.
The review of systems showed normal vision, hearing and development by his parents report.
The pertinent physical exam showed a well-developed, playful and appropriately interactive male with normal vital signs. His weight and length were 75%. His head circumference was 95% which was slightly increased from birth and his two week appointment when it was 90%.
The skull was normally shaped and there was no ridging of any suture line. His posterior fontanelle was closed. He had clear rhinorrhea. His neurological examination was normal. No other potential congenital anomalies were observed.
The radiologic evaluation of plain radiographs of the skull showed no craniosynostosis.
The diagnosis of upper respiratory infection with a small anterior fontanelle was made. He was to return for his regular health maintenance visits for follow-up.
Figure 36 -AP and lateral radiographs of the skull show the coronal, lambdoid and sagittal sutures to be patent. There is no evidence of craniosynostosis.
The skull is formed from 3 main bones.
The anterior frontal bone has two halves which are divided by the frontal or metopic suture. The medial parietal bone has its two halves divided by the sagittal suture.
The posterior occipital bone posteriorly has its two halves divided by the superior median suture.
Between the frontal and parietal bones lies the coronal suture. Between the parietal bone and the occipital bone lies the lamboid suture.
Anteriorly, at the confluence of the metopic, coronal and sagittal sutures is the anterior fontanelle. Posteriorly, at the confluence of the superior median, lamboid and sagittal sutures is the posterior fontanelle.
The sutures are palpated as slightly depressed linear concavities. The fontanelles are felt as soft circle-like concavities. The fontanelles should be assessed with the infant in the upright position, and in this baseline position they will be positioned slightly concave to the surrounding bones.
This baseline position will be elevated normally during vagal maneuvers such as coughing, crying or emesis.
A fontanelle position that is very concave may indicate dehydration. A fontanelle position that is even with, or elevated above, the surrounding bones may indicate a serious neurological problem such as meningitis or hemorrhage. Other causes of an elevated anterior fontanelle are Vitamin A or lead toxicity, sinus thrombosis or a brain tumor.
Pulsations felt in the fontanelles generally are normal and reflect the peripheral pulse.
The bones and suture lines may be overriding each other after birth because of molding of the skull through the birth process. This molding generally resolves in the first 2 days.
Suture lines felt to be prominently ridged may be an indication of craniosynostosis or premature closure of the sutures. This results in an abnormally shaped head as the skull grows perpendicular to the suture line. A variety of abnormally shaped heads may result.
Craniosynosis can be part of a genetic syndrome or it can be sporadic. Surgical treatment may be necessary to re-open the suture line and allow normal brain growth.
The posterior fontanelle generally measures 1-2 centimeters at its greatest diameter at birth and generally closes by 2 months of age.
The anterior fontanelle generally measures between 4-6 centimeters at its greatest diameter at birth and may be larger in the first 6-9 months of life. It generally closes between 4-26 months of age. A larger fontanelle may indicate hypothyroidism.
A small anterior fontanelle in a child with normal development and no evidence of craniosynostosis is most likely due to normal variation. As with all children, it is important to follow them over time.
Questions for Further Discussion
1. What the are the indications for plain radiographs versus computed tomography for the evaluation of craniosynostosis?
2. What are the possible treatments for positional plagiocephaly?
To Learn More
To view pediatric review articles on this topic from the past year check PubMed.
To view current news articles on this topic check Google News.
Bates B. A Guide to Physical Examination. J.B. Lippincott Company, Philadelpha, PA. Third Edit. 1983:465-67.
Barness L. Manual of Pediatric Physical Diagnosis. New York Medical Publishers, Chicago IL. 2nd Edit. 1961:47.
Adeyemo AA, Olowu JA, Omotade OO. Fontanelle sizes in term neonates in Ibadan, Nigeria. West Afr J. Med. 1999:18;55-9.
ACGME Competencies Highlighted by Case
2. Essential and accurate information about the patients is gathered.
3. Informed decisions about diagnostic and therapeutic interventions based on patient information and preferences, up-to-date scientific evidence, and clinical judgment is made.
4. Patient management plans are developed and carried out.
5. Patients and their families are counseled and educated.
8. Health care services aimed at preventing health problems or maintaining health are provided.
9. Patient-focused care is provided by working with health care professionals, including those from other disciplines.
10. An investigatory and analytic thinking approach to the clinical situation is demonstrated.
11. Basic and clinically supportive sciences appropriate to their discipline are known and applied.
24. Cost-effective health care and resource allocation that does not compromise quality of care is practiced.
Donna M. D’Alessandro, MD
Associate Professor of Pediatrics, Children’s Hospital of Iowa
April 17, 2006