What Causes a Bulging Anterior Fontanelle?

Patient Presentation

A 6-month-old female was admitted with fever, fussiness and a bulging anterior fontanelle. The symptoms began approximately 8 hours before coming to the emergency room. The experienced mother noted the bulging fontanelle and said that “I just can’t get her to calm down.” The past medical history showed a healthy term female with current immunization status. The last set of immunizations had occurred two weeks previously. The review of systems showed no emesis, diarrhea, rash, localized pain, or strange movements. She had been drinking and was making wet diapers.

The pertinent physical exam on admission to the floor after the emergency medicine evaluation revealed a tired and very fussy infant with temperature of 38.4 degrees C, with other vital signs normal and growth parameters of 75-90%. She had a bulging but balottable anterior fontanelle when in a seated position. There was no head bruit. The rest of the examination was normal including her neurological examination. The work-up in the emergency room included complete blood count with a white blood cell count of 8.8 x 1000/mm2, C-reactive protein of 1.4 mg/dl and a lumbar puncture with 3 red blood cells, no white blood cells, glucose of 62 mg/dl and protein of 14 mg/dl with a negative gram stain. Electrolytes including phosphorous, urinanalysis, and a respiratory viral panel including influenza and respiratory syncytial virus were normal. The radiologic evaluation included a normal chest radiograph and head computer tomography.

The diagnosis of possible meningitis was made. The patient’s clinical course showed that she was given meningitic doses of ceftriaxone and over the next 36 hours her temperature became normal and her anterior fontanelle returned to normal. She had become happy and playful by 24 hours after admission. All cultures were eventually negative including testing for herpes simplex virus. Because she had bulging fontanelle and laboratory testing was negative and also not consistent with aseptic meningitis, a small workup for causes of benign intracranial pressure was performed during admission including Vitamin A and D levels and thyroid levels. The mother denied any medications, soaps, lotions or other products which may have contained Vitamin A or steroids. Her neonatal metabolic screening was also rechecked and was negative including galactosemia. She was discharged home to follow with her regular care provider but her workup had not identified a specific cause of the bulging fontanelle.

Included in the physical examination of the young child is palpation of the head. The posterior fontanelle is usually 1-2 cm at birth and closes around 1-2 months of age. The anterior fontanelle is usually 4-6 cm in size at birth and closes at 4-26 months of age. The fontanelle should be palpated in the upright position, and usually it is slightly depressed relative to the bony rim. Therefore a fontanelle that is level with the rim, or bulging above the rim, are both considered abnormal. A child in a recumbent position will normally have a fontanelle that is level or above the bony rim because of differences in pressure recumbent. A sunken or depressed fontanelle is usually caused by dehydration.

A more extensive discussion about fontanelles can be found here.

Learning Point
The differential diagnosis of bulging fontanelle in infancy includes:

  • Infectious
    • Meningitis
    • Encephalitis
    • Otitis Media
  • Cerebrospinal Fluid or Pressure Problem
    • Hydrocephalus
    • Benign intracranial hypertension
    • Crying
    • Emesis
  • Space Occupying Lesion
    • Cerebral hemorrhage
    • Intracranial abscess
    • Subdural hematoma
    • Tumor
  • Vascular
    • Sinus thrombus
  • Miscellaneous
    • Recumbent position
    • Lead poisoning
    • Transient bulging fontanelle associated with (not caused by) vaccination

Causes of benign intracranial hypertension that would be important to consider in infancy include:

  • Drugs
    • Hypervitaminosis A
    • Steroid therapy withdrawal
  • Metabolic/Nutritional
    • Galactosemia
    • Hypoparathyroidism
    • Hypophosphatasia
    • Hypothyroidism
    • Hypovitaminosis A
    • Rapid brain growth after starvation
  • Infections
    • Roseola infantum
    • Otitis media
  • Miscellaneous
    • Allergic disease
    • Anemia
    • Carbon dioxide retention
    • Heart disease
    • Migraine
    • Polycythemia vera
    • Systemic Lupus Erythematosus
    • Wiskott-Aldrich syndrome

Questions for Further Discussion
1. What is the differential diagnosis of a large anterior or posterior fontanelle?
2. Why is it called a fontanelle?

Related Cases

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: Brain Malformations

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

To view images related to this topic check Google Images.

Stockman JA, Corden TE, Kim JJ. The Pediatric Book of Lists. Mosby Year Book, Philadelphia, PA. 1991;225-226.

Bates B. A Guide to Physical Examiation. 3rd edition, J.B. Lippincott, and Company. Philadelphia, PA. 1983;465.

Robertson WC. Pseudotumor Cerebri, Pediatric Perspective. eMedicine.
Available from the Internet at http://emedicine.medscape.com/article/1179733-overview (rev. 11/30/2009, cited 1/28/11).

ACGME Competencies Highlighted by Case

  • Patient Care
    1. When interacting with patients and their families, the health care professional communicates effectively and demonstrates caring and respectful behaviors.
    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.
    7. All medical and invasive procedures considered essential for the area of practice are competently performed.
    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.

  • Medical Knowledge
    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.

  • Practice Based Learning and Improvement
    13. Information about other populations of patients, especially the larger population from which this patient is drawn, is obtained and used.

  • Systems Based Practice
    23. Differing types of medical practice and delivery systems including methods of controlling health care costs and allocating resources are known.
    24. Cost-effective health care and resource allocation that does not compromise quality of care is practiced.


    Donna M. D’Alessandro, MD
    Professor of Pediatrics, University of Iowa Children’s Hospital