Sonographic visualization of neonatal posterior fossa abnormalities through the posterolateral fontanelle.

Abstract

This study was performed to determine whether imaging through the posterolateral fontanelle in addition to the anterior fontanelle during neonatal cranial sonography improves diagnostic accuracy or examiner confidence in the diagnosis of neonatal posterior fossa abnormalities. In 1995 we changed our protocol of neonatal cranial sonography to include imaging through the posterolateral fontanelle in all patients. The reports of all sonography performed in the first 15 months of this protocol were reviewed, and two radiologists reviewed the images of all patients in whom a posterior fossa abnormality was diagnosed with posterolateral fontanelle images masked and then with posterolateral fontanelle images available. In total, 1292 sonograms were obtained in 462 patients. In 200 patients, the sonographic findings were abnormal; of these 200 patients, 24 (12%) had posterior fossa abnormalities (nine posterior fossa hemorrhages, four Arnold-Chiari malformations (type II), two posterior fossa arteriovenous malformations, and nine partial vermian defects). The posterolateral fontanelle images showed the posterior fossa abnormality better than the anterior fontanelle images did in 23 (96%) of the 24 patients, increased confidence in the diagnosis of 18 (75%) of the 24 patients, and was the only technique to reveal the posterior fossa abnormality in 11 (46%) of the 24 patients. Nearly all pathologic correlations with imaging confirmed the posterolateral fontanelle findings except for the diagnosis of inferior vermian agenesis, which was presumed to be a false-positive diagnosis in four patients in whom MR imaging showed no abnormalities. Additional imaging through the posterolateral fontanelle during routine neonatal cranial sonography added considerable benefit. False-positive diagnosis of vermian defects is a troubling problem but may be avoided with careful attention to the midline sagittal sonographic images of the vermis and fourth ventricle.