Arnold Chiari malformation, type II
- Arnold chiari malformation, type ii
Heron Werner, MD
Clínica de Diagnóstico por Imagem (CDPI) & Instituto Fernandes Figueira (IFF) – FIOCRUZ – Rio de Janeiro – Brazil
Chiari II malformation is a congenital defect in the posterior fossa that is present in most fetuses with spina bifida. It results from herniation of the spinal cord. There is a reduction of intraspinal pressure allowing the hind brain to be displaced downwards. The posterior fossa compartment is too small because reduced intraspinal pressure in early pregnancy. The cerebellum grows into this small compartment and becomes compressed. This leads the observed abnormalities such as obliterated cisterna magna, banana sign (the cerebellum is compressed from a bi-lobed structure into the abnormal form) and lemon sign.
These are ultrasound images of a case from 17 to 37 week gestation.
Left image: The spine looks normal at 17 weeks (sagittal view).
Same case at 20 weeks showing the meningomyelocele (arrow). Note the ossification centers in the neural arch with a U-shaped configuration (axial view).
Axial view of a fetal head demonstrating ventricular dilatation, “lemon sign” and “banana sign” which derives from anterior curving of the cerebellar hemispheres with simultaneous obliteration of the cisterna magna (arrow).
The spine looks normal at 20 weeks (coronal view). Then, note the 3D coronal view showing the defect (arrow).
3D view of the meningomyelocele (arrow).
3D coronal view demonstrating widening of vertebral arches (left image) and the large sac (right image).
The newborn. Note the large sac and the intraoperative view of fetal surgical procedure to repair the meningomyelocele (Courtesy of Dr. Gabriel Mufarrej, Rio de Janeiro, Brazil).