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FIG 3. 44-year-old man with left-sided tinnitus and hearing loss, paraesthesia, and respiratory distress.
A, T1-weighted transverse image (500/12/2) of the posterior fossa shows a paramedullary, space-occupying lesion with signal intensity similar to CSF, compressing the left ventrolateral portion of the medulla oblongata (arrow).
B, T2-weighted SE image (2000/80/1) of the same section as in A. Different compartments are not visible; the lesion has the same signal intensity as the surrounding CSF spaces, and margins of the cyst are not reliably detectable, making the diagnosis of an arachnoidal cyst highly probable.
C, Corresponding preoperative SSFP image (20/25/1) shows a circumscribed, hyperintense, premedullary lesion (large arrow), indicating stationary CSF of a noncommunicating arachnoid cyst in contrast to the significantly reduced signal of moving CSF in neighboring compartments (small arrows) and in the fourth ventricle (arrowhead). This finding strongly supports the decision for neurosurgical intervention.
D, SSFP image (20/25/1) after membranectomy shows signal attenuation in most parts of the formerly hyperintense cyst (arrow), indicating communication with neighboring CSF spaces. The patient experienced relief of his symptoms.
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