PMC4310131_01
(a) Axial section of preoperative magnetic resonance imaging (MRI) on T2-weighted image (WI) reveals a cyst with isointensity to cerebrospinal fluid (CSF) located behind the medulla oblongata along the midline. (b) Sagittal section of preoperative MRI on fast imaging with steady state acquisition (FIESTA) shows the cyst to be composed of two portions, attached to the choroid plexus, and compressing both cerebellar hemispheres
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F1
Magnetic resonance imaging (MRI) of the head showed a cystic lesion in the foramen of Magendie, which was compressing the inferior part of the vermis and the medial part of the cerebellar hemisphere without causing hydrocephalus [Figure 1].
Intraoperative microscopic view after the removal of the small cyst at the outer membrane reveals that the cyst is located between the two hemispheres (a), and the part of the cyst wall was attached to the choroid plexus (b)
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F2
The retromedullary cistern was open, but the cyst had not shrunk, and the cyst was found not to communicate with the surrounding cistern [Figure 2a]. A small part of the cyst that was still attached to the choroid plexus at the foramen of the Magendie was allowed to remain [Figure 2b], and the fourth ventricle was not opened via the obex.
Photomicrograph demonstrating the cyst wall to be composed of a collagenous membrane lined by a single layer of arachnoid cells (hematoxylin and eosin; original magnification x200)
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F3
Pathohistological examination demonstrated that the cyst wall was composed of a collagenous membrane lined by multiple layers of arachnoid cells [Figure 3].
(a) Axial section of postoperative MRI on T2-WI reveals that the cyst cavity has markedly reduced such that the CSF flow artifact can be seen clearly. (b) Sagittal section of postoperative MRI on FIESTA shows the residual CSF space in the foramen of Magendie
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F4
MRI performed 2 weeks after the operation revealed that the cyst had diminished and clearly demonstrated a flow artifact entering into the foramen of Magendie [Figure 4].