27/04/2024
Differentiating Fetal Brain Anomalies Part One:
1. Encephalocele: Cystic mass with or without herniated brain tissue. Encephalo(brain), Cele(Herniation) essentially means a herniation of the brain.
2. Meningoencephalocele specifically indicates that both brain tissue (encephalo-) and meninges (meningo-) are involved in the protrusion, whereas encephalocele merely indicates the presence of brain tissue in the protrusion without specifying the involvement of meninges, and thus can include brain tissue alone or brain tissue with meninges.
3. Meningocele: Meninges and CSF herniating through a defect in the occipital cranium. No brain tissue is seen within the lesion, which helps differentiate it from an encephalocele.
4. Myelomeningocele: Develops in a fetus during the first four weeks of pregnancy. It is characterized by incomplete neural tube closure and results in a fluid-filled sac that protrudes from the baby’s back. The sac contains Part of the spinal cord, Meninges (tissues covering the spinal cord), Nerves, and Cerebrospinal fluid (CSF). (Adding this so this is not confused with Meningocele.)
5. Chiari I Malformation: Cerebellar tonsils are shifted downwards through the foramen magnum.
6. Chiari II malformation: Part of the cerebellum (a region of the brain affecting motor control) is shifted downward into the upper spinal column, causing compression of the brain or spinal cord. Obliteration of the cisterna magna resulting in a banana-shaped cerebellum (the banana sign) and flattening of the frontal calvarium known as the lemon sign. There may also be evidence of fetal ventriculomegaly due to obstructive effects as a result of downward cerebellar herniation. Chiari I malformation does not have Myelomeningocele.
7. Dandy-Walker Malformation: Dilated cisterna magna communicating with the fourth ventricle (≥10 mm), Complete aplasia of the vermis, which is the part of the cerebellum that connects the two hemispheres, and a trapezoid-shaped gap between the cerebellar hemispheres.
8. Aqueductal Stenosis: Causes obstructive Hydrocephalus. Narrowing of the aqueduct of Sylvius, a narrow channel connecting the third and fourth ventricles, causing a noncommunicating hydrocephalus. Features will show a dilated third ventricle, a nondilated fourth ventricle and a normal posterior fossa.
9. Agenesis of the corpus callosum: The corpus callosum, which connects the two cerebral hemispheres, fails to develop fully or is absent. Absence of the CSP between the frontal horns of the lateral ventricles.
10. Vein of Galen malformation: An anechoic cystic mass is seen in the midline, superior and posterior to the third ventricle and thalamus. Color and spectral Doppler imaging demonstrate the presence of low-resistance flow and a turbulent waveform. Blood flow may be seen draining posteriorly into the venous sinuses.
