Ganglionic eminence cavitations-these are not choroid plexus cysts!

Abstract

Choroid plexus cysts (CPC) are relatively common and innocuous, although, in rare instances, they can obstruct the foramen of Monro and cause unilateral ventriculomegaly. When isolated, they are usually not diagnosed before 16–17 weeks and disappear during the late second trimester. The identification of cysts bulging into the ventricle before 16–17 weeks should raise suspicion of a much more uncommon and severe condition, cavitation of the ganglionic eminence (GE). GE is a prominent transient fetal brain structure, characterized by highly active neuronal proliferation during the first and early second trimesters. GE cavitation has been reported previously in older fetuses on magnetic resonance imaging (MRI)1, 2 and in two fetuses on ultrasound3. In all cases, this condition was considered the cause of arrested brain development. In recent years, we evaluated three patients referred for second-trimester ultrasound following a very early diagnosis of suspected CPC which turned out to be GE cavitations. More recently, we diagnosed another fetus with GE cavitations at 15 + 3 weeks by transvaginal neurosonography. The first patient was examined at 20 weeks after identification of suspected bilateral large CPC during a routine scan at 14 + 3 weeks (Figure 1a,b). We found mild ventriculomegaly with irregular ventricular walls and bilateral cavitations, located within what we then assumed were the basal ganglia (Figure 1c). The parents opted for termination of pregnancy, which was performed by dilatation and evacuation. Two other cases, also referred for evaluation because of a similar diagnosis at 15 and 16 weeks, showed similar GE cystic formations, not related to the choroid plexus, and serious associated conditions, including callosal dysgenesis and abnormal cortical layering (Figure 2), as described previously by Righini et al. on MRI during the second half of pregnancy1, 2. In the most recent case evaluated by our team at 15 weeks, we observed clearly that the cysts were not located within the choroid plexus but rather within the GE and were associated with early anomalies involving the subplate and cortical rim (Figure 1d–f). Although GE cavitations are situated in the same place as periventricular pseudocysts, the latter are usually diagnosed during the late second or third trimester and may often be detected as an incidental finding in completely asymptomatic patients4. We believe that the timing of development of these two conditions is the cause of the striking differences in their effects on the germinal matrix and neuronal and axonal guidance. We conclude that early demonstration of cystic changes anterior to the choroid plexus should not be confused with the more common CPC but instead should be considered cavitations of the GE. Following their demonstration, a detailed neurosonographic examination would be useful to detect associated conditions such as callosal and cerebellar anomalies and malformations of cortical development. Data sharing not applicable to this article as no datasets were generated or analysed during the current study.