Fetal Intracranial Bright Reflectors and Echogenic Masses
· Choroid plexus- At around 17 weeks gestation the choroid plexus may fill most of the lateral ventricle. The fetal brain at this gestation is relatively sonolucent.
· Leptomeninges- The leptomeninges (pia mater outline the outer surface of the brain and are seen as highly reflectile. Surrounding the leptomeninges is CSF in the subarachnoid space. The echogenicity of this space depends upon the relative amounts of CSF/leptomeninges. The smaller cisterns may appear highly echogenic, while the larger cistern may have an echolucent appearance. Seen with particular clarity if an ossification abnormality of the skull vault occurs, e.g. osteogenesis imperfecta.
· Specular reflection from ventricular wall- This is an artifact which occurs when the ultrasound beam strikes the walls of the ventricles in a perpendicular/near perpendicular manner. The result is highly reflectile echoes emanating from the ventricular walls.
· Reflections of unknown causes- Deep within the brain tissue, mostly in the region of the white matter, occasional high amplitude echoes are noted. The way in which these are produced is unknown, but blood vessels, particularly penetrating veins, have been implicated.
· Echogenic sulci- Sulci may appear echogenic in one plane but a change in the scanning plane by about 90(degrees) reveals normal sulci.
· Reverberation artifact- A reverberation artifact in the near side of the fetal cranium is fairly common. This not only produces a pseudomass within the near side of the cranium but also prevents resolution of the proximal structures within the brain.
Reverberation artifact (White arrows)
· Pachymeninges- The falx and tentorium are components of the dura (pachymeninges), which also appear echogenic, making landmarks.
· Cerebellar vermis- The cerebellar vermis lying in the posterior fossa below the tentorium may cause high amplitude echoes. The fovea becomes visible as maturation occurs.
· Cerebroventricular hemorrhage- When recent, hemorrhage within the brain parenchyma or ventricles may appear as an echogenic mass. Blood in the ventricular system may show a fluid—fluid level or echogenic clot. Follow up sonography may show evolution of the hemorrhage progressing to liquefaction.
· Intracranial tumors teratoma- Teratomas account for 50% of all brain tumors in the neonate. Teratomatous lesions tend to have mixed solid and cystic areas and they usually have a great degree of disorganization. Calcification is common.
· Choroid plexus papilloma- There are small benign tumors which arise from the normal choroid plexus. They are echogenic masses and can be differentiated from blood clot on serial scanning when the appearances remain constant.
· Periventricular leukomalacia- This is caused by ischemia which may be hemorrhagic or non- hemorrhagic. The lesions affect the periventricular region, corona radiata and occipital area. The lesions change with time, becoming cystic.
· Calcification- Calcification within the brain of a fetus may be related to transplacental infection. Echogenicity is seen in the periventricular region. Calcification may be seen in tuberose sclerosis.
· Anteriorvenous malformation- AVMs usually present a cystic appearance but small compact AVMs may be highly reflectile because of the multiple interfaces. Diagnosis may be achieved by Doppler sonography.
· Sturge-Weber syndrome- SWS or trigeminal angiomatosis is associated with vascular malformations of the cerebral cortex and face. Even before the angiomatous malformation overlying the cortex calcifies, the leptomeninges show increased echogenicity.
· Lipomas - Most intracranial lipomas occur near the midline: the majority are sited in the corpus callosum, in or below the third ventricle in the cerebellum, the cerebellopontine angle, over the quadrigeminal plate or in the sylvian fissure. Sonographically they appear as hyperechoic, smoothly marginated masses. They do not normally cause acoustic shadowing.
· Glioblastoma- The only reported sonographic case of glioblastoma diagnosed prenatally presented with diffusely increased echoes throughout the tumor mass, causing a shift of the falx and hydrocephalus.
· Cranio-pharyngioma- A craniopharyngioma has been detected antenatally; this tumor replaced all the normal brain but had a different echo pattern. The mass was calcified and lobulated, and was surrounded by fluid.
· Dermoid or epidermoid cyst- Appear as well marginated echogenic masses.
· Cerebral neuroblastoma- This has been detected antenatally and diagnosed by a fetal brain biopsy. The lesion presented as a solid heterogeneous mass containing calcification, occupying the right cerebral hemisphere with a midline shift to the left. A large subdural fluid collection was also detected.