++
KEY POINTS
One of the most common findings on sonographic evaluation of the fetal brain.
Easily detected due to its obvious anechoic appearance at places that should not be present.
Prognosis varies from a normal benign variant with minimal to no clinical significance that often regresses spontaneously, to poor, based on the specific type of cyst and associated structural and genetic anomalies.
Larger cysts may exert pressure on adjacent organs causing displacement of structures, or obstruct the flow of cerebrospinal fluid.
Although mostly isolated, they can be associated with other pathologies; therefore targeted neuroscan and detailed anatomy scan are warranted.
++
Intracranial cysts are relatively common findings encountered in the prenatal sonographic assessment of the fetal brain. The vast majority of these fluid collections (arachnoid and choroid plexus cysts) are of a benign nature, remain clinically silent, do not evolve, and regress spontaneously. When these lesions are not associated with other fetal anomalies, they are compatible with normal life regardless of whether they require postnatal treatment or not.1,2 Nevertheless, due to the numerous differential diagnostic entities as well as the associated parental anxiety, appropriate diagnosis and counseling of such cysts is clinically challenging.
++
The differential diagnoses of intracranial cysts encompass multiple etiologic and pathologic processes. Advancements in imaging techniques, especially in fetal sonography, have facilitated the workup of such cysts by depicting their exact location, size, relationship to the ventricular system, and midline structures. In addition, fetal sonography facilitates the detection of solid components seen in cases of brain tumors or blood clots as well as the use of Doppler studies to assess blood flow patterns in cases of vascular malformations, such as an aneurysm of the vein of Galen. Likewise, fetal MRI has been successfully utilized in prenatal imaging to further facilitate the morphological evaluation of such cysts and their relationship to the ventricular system and the brain cortex. It has particular importance as a supplement to ultrasound (US) evaluation, mostly in advanced gestational age when US evaluation may be impaired by the calcified fetal scull and relatively small fontanelle. Nevertheless, both imaging modalities may fall short of distinguishing between some of these lesions, which require histologic examination of the cyst wall to establish the correct diagnosis.3 In this chapter, we classify intracranial cysts based on the location of their origin into one of three groups: extra-axial, intraventricular, and intraparenchymal (Table 15–1).
++
+++
CLASSIFICATION OF INTRACRANIAL CYSTS