Computed tomographic signs of the Chiari II malformation. III: Ventricles and cisterns.

Abstract

In patients with Chiari II malformations, the fourth ventricle is usually not visualized or appears small; the third ventricle is relatively small, typically has a large massa intermedia, and only occasionally exhibits parasellar and/or posterior third ventricular diverticula. The lateral ventricles are usually asymmetrically dilated, show medial pointing of the floor of the body near the foramen of Monro, flattening of the superolateral angles, and frequent absence of the septum pellucidum. Prior to and after shunting, the interhemispheric fissure may be either obliterated, or widely open with serrations corresponding to the interdigitated gyri of the cerebral hemispheres. Prominent confluent cisterns at the hind end of the third ventricle in patients with ventricular collapse may represent the CT equivalent of the dilated pericallosal, ambient and retropulvinaric cisterns seen in patients with hydrocephalus and poor ventricular filling at pneumography.

Chiari II malformation: MR imaging evaluation

“…Most abnormalities previously described as seen by CT [2][3][4][5] were also seen by MR. In this article we review these abnormalities and report on other associated features of the Chiani malformation that either have a greater frequency than has previously been reported or that have not been described before.…”

“…Naidich et al [4] reported on the presence of a striking diamond-shaped cistern near the posterior end of the third ventricle in 26% of patients with the Chiani II malformation. They found that the cisterns, as in our cases, were largest in shunted cases.…”

Pathophysiology of Isolated Lateral Ventriculomegaly in Shunted Myelodysplastic Children

“…The massa intermedia, which is absent in only 17% of the general population [12], is typically enlarged in children with a myelomeningocele and Chiari II malfor mation 118-20], This finding, in addition to an eccentric bulge from the head of the caudate nucleus [21], promi nent commissural fibers extending across the anterior third ventricle [22], and anterior pointing of the frontal horns [22,23], results in an abnormally distorted and nar rowed foramen of Monro [24], Following shunt placement in children with a myelo meningocele, it has been noted that unilateral dilation of the contralateral, nonshunted ventricle may occur [2,3,25], Hubballah and Hoffman [26[, Babcock and Han 111 and Oi and Matsumoto [25] have postulated that a func tional obstruction takes place following ventricular drain age at the level of the ipsilateral foramen of Monro. An additional factor contributing to the isolated ventricles, namely the use of low pressure shunts, was also men tioned [ 14,25,26], After reviewing the MRI scans on our patients we noted that the dimensions of the foramen of Monro were greatly distorted giving the appearance of 'foraminal torsion', yet this was difficult to visualize in static, multiplanar images.…”

Metrizamide Cisternography and the Management of the Chiari II Malformation

“…Plain X-rays of the shunt system showed good placement of the system (in continuity) but CT scan of the head showed numerous findings characteristic of the Chiari II malforma tion [16][17][18]. The patient was then evaluated with a metrizamide cistemogram (contrast intro duced intrathecally via lumbar puncture) which demonstrated an enlarged upper cervical cord with a large posteriorly located cavity compatible with syringo-hydromyelia ( fig.…”