Sonographic appearance of extra-axial fluid collections in the infant: further observations

Extra-axial fluid collections were identified in six infants by transfontanelle cranial sonography. Confirmatory computer tomography (CT) scans were performed following the sonograms in five of these patients. These extra-axial fluid collections were varied in appearance and could be divided into two types depending on their sonographic characteristics. The first group consisted of large, usually concave anechoic collections and the second of small extra-axial fluid collections best seen in the interhemispheric fissure. The large collections were easily identified using a routine 5 MHz transducer system. The smaller collections were not well visualized with a 5 MHz system and required a 7.5 MHz transducer to identify the fluid in the interhemispheric fissure. Additionally, the lateral extent of these small collections could not be visualized through the anterior fontanelle using either transducer and CT was required for definitive evaluation of their lateral extent.