A wide variety of congenital anomalies can affect the cerebellum. The antenatal findings overlap among different pathologies and normal variants. Consequently, a specific diagnosis is often not possible.
One of the most common abnormal findings that is encountered is the impression of a communication between the fourth ventricle and the posterior cisterna magna. When this is seen after 20 postmenstrual weeks' gestation, it identifies a group of conditions that are commonly referred to as the Dandy-Walker complex.
Within the Dandy-Walker complex, cases with a normal appearance of the vermis and cisterna magna most frequently have a normal outcome. Fetuses with an enlarged cisterna magna and/or an abnormal vermis frequently exhibit abnormal development, but a precise prognosis is difficult to predict.
A large cisterna magna (> 10 mm) when isolated, usually has a good outcome.
Other cerebellar anomalies can be encountered, but the diagnosis is often difficult or impossible and the prognosis difficult to predict.
Abnormal sonographic findings of the posterior fossa are among the most common reasons for referral in tertiary care centers for fetal neuroimaging. They represent a major diagnostic challenge, and inaccurate interpretation with significant implications for counseling and management has been reported.1,2 The problem is two fold: On the one hand, sonography is not an ideal tool for the visualization of the posterior fossa structures, particularly in the second trimester of gestation; on the other hand, many different entities, ranging from normal variants to severe anomalies, may have a similar sonographic appearance.1,2,3,4,5 Categorization of these entities is still controversial, and there is no uniform approach.2,6,7 In this chapter, we report our own vision of the problem and our own approach, which is summarized in Table 8–1.4
TABLE 8–1.DIFFERENTIAL DIAGNOSIS OF CEREBELLAR DISORDERS |Favorite Table|Download (.pdf) TABLE 8–1. DIFFERENTIAL DIAGNOSIS OF CEREBELLAR DISORDERS
|Diagnosis ||TCD ||Vermis Biometry ||Superior/Inferior Ratio ||Fastigium ||Fourth Ventricle ||Pons ||Prognosis |
|Delayed "closure" ||N ||N ||N ||N ||Open ||N ||Good |
|Vermian hypoplasia ||N ||Small ||N ||N ||Open/closed ||N ||Variable |
|Vermian agenesis ||N/S ||Small ||Abnormal ||Abnormal ||Abnormal ||N ||Malformations |
|Dandy-Walker malformation ||N ||–/Small ||Abnormal ||Abnormal ||Abnormal ||N ||Poor |
|Joubert and related syndromes ||N/S ||–/Small ||Abnormal ||Abnormal ||Abnormal ||? ||Poor |
|Pontocerebellar hypoplasia ||S ||S ||N ||No ||Normal ||Abnormal ||Poor |
|Rhombencephalosynapsis ||S ||– ||– ||Abnormal ||Abnormal ||N ||Poor |
We stress that many difficulties are encountered in assessing antenatally this area of the brain and that frequently an accurate diagnosis cannot be made in utero.
Dandy-Walker malformation, vermian agenesis, vermian hypoplasia, Blake's pouch cyst
Megacisterna magna, Joubert and related cerebellar syndromes (vermian agenesis/hypoplasia ...