Non-enhancing T2 hyperintense mass of the dorsal midbrain is centred on the left superior and inferior colliculus, but with signal abnormality extending into the posteroinferior left thalamus as well as crossing the midline and surrounding the cerebral aqueduct. In addition, there is subtle FLAIR signal abnormality in the superior cerebellum, centred just right of midline, presumably due to contiguous spread along the right superior cerebellar peduncle. Although thin slice sagittal sequences centred on the lesion have not been performed, the mass does appear to arise from midbrain, separate from pineal gland.
The main portion of the mass measures 17 x 10 x 16 mm. It contains punctate foci of signal dropout, compatible with the coarse calcific foci identified within the lesion on CT. There is no diffusion restriction or cerebral blood volume (CBV) increase.
Lateral and third ventricles are mildly enlarged for age, consistent with some obstruction to CSF flow through the narrowed cerebral aqueduct.
Remainder of the brain is normal, with no further sites of signal abnormality.
Mass centred on the left dorsal midbrain has imaging morphology most consistent with a low-grade tumour of glial origin. Although these are most commonly astrocytomas, in the presence of coarse calcification oligodendroglioma or ganglioglioma are considerations.