OBJECTIVES: The goals were to identify and to classify causes and growth patterns of acquired (or progressive) microcephaly and to look for hypothesized correlations between causes, growth patterns, and developmental quotient/IQ.

METHODS: Fifty-one children (24 boys), 0.7 to 11.3 years of age, with early occipitofrontal circumference measurements above and later ones below the second percentile (SD: −2.03) were studied through retrospective note and growth chart review, with formal assessments of developmental quotient or IQ (n = 34).

RESULTS: Causes were classifiable into 5 groups as follows: idiopathic, familial, syndromic, symptomatic, and mixed. Four patterns of head growth were identified, as follows: type A, initial decrease from the normal range to below the second percentile, followed by growth below and parallel to the second percentile; type B, continued decrease away from the second percentile; type C, decrease below the normal range, with partial later recovery; type D, insufficient data. For 12 children, there were accompanying decreases in weight percentiles and for 5 of these in height percentiles as well. Infants with lower head circumference z scores at the end of the study also had lower z scores for final weight and final length. There was no correlation between causal group and growth pattern. Developmental quotient/IQ values were mostly <100 and did not correlate with head circumference z score, cause, or pattern.

CONCLUSIONS: The classification of causal groups and growth patterns should aid clinical management. Neither cause nor pattern predicted outcomes. The associations with poor weight gain and body growth deserve further study.

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