Hydrocephalus: When the narrowing near the base of the spine prevents cerebrospinal fluid (CSF) from flowing freely around the brainstem or in and out of the skull, the CSF collects in ventricles (spaces in the child’s brain). The resulting condition is hydrocephalus. In babies, the most evident symptom of hydrocephalus is a quickly enlarging head circumference. Additional symptoms include:

• headaches
• irritability
• lethargy
• vomiting

Because an enlarged head is normal in achondroplastic children, pediatricians can use a special head circumference growth chart to distinguish between normal achondroplastic growth and possible hydrocephalus.