Fontanelles - bulging

Alternative names:

bulging fontanels; soft spot - bulging

Definition:

Convex displacement of an infant's soft spot (fontanel).

Considerations:

The skull is made up of many bones (seven in the skull itself and 14 in the facial area). They join together to form a solid, bony cavity protecting the brain and supporting the structures of the head. The area where the bones join together are called the sutures.

The bones are not joined together firmly at birth (this allows the head to accommodate passage through the birth canal). The sutures gradually accumulate minerals and harden (this process is called ossification), firmly joining the skull bones together.

In an infant, the spaces where two sutures intersect form a membrane-covered "soft spot" called a fontanel (fontanel or fonticulus). The fontanels allows for growth of the skull during an infant's first year.

There are normally two fontanels that are present on a newborn's skull, the anterior and posterior fontanels. The anterior fontanel is midline on top of the head and slightly toward the front. The posterior fontanel is also midline but toward the back of the skull where it turns downward. Like the sutures, fontanels gradually ossify and become closed , solid bony areas. The posterior fontanel (in the back of the head) usually closes by the time an infant is 1 or 2 months old; the anterior fontanel at the top of the head usually closes sometime between 9 months and 2 years old with an average closure of 18 months.

The fontanels should feel firm and very slightly concave to the touch. In other words, the normal fontanel is usually sunken slightly below the level of the skull when the infant is upright and quite. A bulging fontanel means that the fontanel is pushed up above the level of the skull and appears ballooned outward. A bulging fontanel often feels tense and rubbery when pushed gently with the finger. A tense or bulging fontanel occurs when fluid accumulates in the skull cavity or when pressure increases in the brain (increased intracranial pressure).

Crying, lying down, vomiting, or straining with a bowel movement can make the fontanel momentarily look like it is bulging, but it will return to normal when the infant is in a calm, head-up position.

Common causes:

• hydrocephalus
• increased intracranial pressure (associated with brain tumor, subdural hematoma and multiple other disorders)
• meningitis
• intracranial hemorrhage
• shaken baby syndrome (usually results in intracranial hemorrhage)
• vitamin A toxicity (hypervitaminosis A)
• lead poisoning (not usually seen in an infant young enough to have open fontanels)
• brain tumors (space-occupying lesions)
• pseudotumor cerebri

Note: There may be other causes of bulging fontanels. This list is not all inclusive, and the causes are not presented in order of likelihood. The causes of this symptom can include unlikely diseases and medications. Furthermore, the causes may vary based on age and gender of the affected person, as well as on the specific characteristics of the symptom such as location, quality, time course, aggravating factors, relieving factors, and associated complaints. Use the Symptom Analysis option to explore the possible explanations for bulging fontanels, occurring alone or in combination with other problems.