Cystic/solid mass located posteriorly at the craniocervical junction. Larger non-enhancing cystic component which is present anterosuperiorly with a small and intensely enhancing nodule located posteroinferiorly. Cystic component appears intra-axial and separate from the fourth ventricle. The location of the solid nodule is less clear and may be intra-axial with a large eccentric component, or alternatively extra-axial in location posterior to the medulla. No prominent T2 flow voids, susceptibility artefact or diffusion restriction. Medulla is compressed anteriorly with effacement of the premedullary cistern. Abnormal T2 signal throughout the medulla extending into the pons and middle cerebellar peduncles bilaterally.