Purpose or Case Report: The posterior fossa houses the brainstem and cerebellum. These vital and complex parenchymal structures contain many important white matter tracts, nuclei, and neurons responsible for both basic fundamental and higher-level functions. A number of disease processes can interfere with rhombencephalic development, including genetic malformations and disruption such as hypoxia, toxins, infections, trauma, and vascular disorders. Structural changes associated with fetal imaging pathology that deviate from the normal gestational-age specific developmental patterns can define the etiology, improve our understanding of the disease, and help with prognostication. A comprehension of basic embryology and developmental anatomy is necessary to achieve a true understanding of posterior fossa anomalies and normal variants. In this exhibit, we aim to illustrate common and rare anomalies of the brainstem, cerebellum, meninges, and meningeal spaces visible on fetal MRI, presented in a temporal manner based on the embryologic development of the posterior fossa.
Methods & Materials: Fetal MRI and correlative fetal ultrasound and post-natal images with didactic value will be procured from the teaching file of a pediatric medical center in order to demonstrate developmental anatomy and posterior fossa pathology.
Results: Normal anatomy of the posterior fossa in various stages of developement will be shown and contrasted against the following entiites:
1. Cysts:
a. Blake pouch
b. Arachnoid duplication
c. Fibrous arachnoid
2. Insutls:
a. hemorrhage/infarction
b. Sinus thrombosis
c. Infection
3. Malformations:
a. Chiari II
b. Walker-Warburg syndrome
c. Diencephalic-mesencephalic junction malformation
d. Rhombencephalosynapsis
e. Dandy-Walker malformation
f. Joubert syndrome
g. Pontocerebellar hypoplasia
4. Tumor
Conclusions: Posterior fossa anomalies are common indications for fetal MRI. Most can be diagnosed and classified by appearance. Prognosis ultimately depends on type and presence or absence of additional abnormalities.