A pathological approach to anomalies of the posterior fossa.

BACKGROUND: Both clinical and postmortem diagnoses of posterior fossa anomalies remain difficult to make and to corroborate. This is particularly true for Dandy-Walker malformation and variant. Difficulties arise for a variety of reasons, including technical and methodological ones, but also because the conditions may overlap anatomically with others, most notably mega cisterna magna, Blake's pouch cyst, and posterior fossa (arachnoid) cysts. Family counseling is difficult and complicated not only by diagnostic uncertainties but by the highly variable prognosis.
METHODS: In this study, a systematic pathologic approach to study of the posterior fossa is put forth. The benefits of postmortem imaging and in situ and ex situ examination of posterior fossa contents are demonstrated.
RESULTS: Normative data for cerebellar width (transverse cerebellar diameter) and height and vermian width and height are derived for the fetal period. These data will help workers recognize changes in these structures, particularly hypoplasia.
CONCLUSIONS: Basic morphologic definitions of posterior fossa anomalies are advanced, in the hopes that better agreement can be reached between clinical and pathologic diagnoses and that better patient and family care will result.