Fig 5.

Patient 7. Sagittal postcontrast T1-weighted scan showing a large, well-delineated extra-axial mass (arrows) elevating and displacing the pons and medulla. The mass is slightly hyperintense compared with CSF. Slight rim enhancement is seen posteriorly, where the mass adheres to the brain parenchyma (open arrow). Cyst with watery, slightly cloudy fluid was found at surgery. Microscopic examination showed cyst lining composed of columnar epithelium with goblet cells, typical for NE cyst. Mild inflammatory changes in the cyst wall adjacent to the brain stem were present. Etiology of the rounded hyperintensity superior to the cyst is unexplained; the surgeons found nothing at the operation that clarified its nature. Postoperative changes of a prior occipital decompression for “Chiari 1” malformation are present (reproduced from Osborn AG, et al, Diagnostic Imaging: Brain, Amirsys/Elsevier, 2004).