We describe a 20-year-old patient with chronic transtentorial herniation of the diencephalon and midbrain [1] (Fig. 1a–c) due to a large middle cerebral artery infarct that occurred 16 years earlier, which developed into severe progressive headaches. Neurological examination disclosed a slight left hemiparesis with associated pyramidal signs. Besides the baseline abnormalities of a kinked and apparently enlarged brainstem and mild lateral ventricular dilatation, follow-up MRI (Fig. 1d–i), performed to investigate this new symptom, showed a ‘‘mass-like’’ nonenhancing lesion in the dorsal midbrain, adjacent to the subependymal surface of the left lateral ventricle. The mass was initially considered a neoplasm due to morphology and evolution pattern, although the normal spectrum on MR-spectroscopy (Fig. 1i) was compatible with interstitial edema in normal neural tissue [2]. Due to the lesion location, no biopsy or surgical procedure was performed, and further follow-up imaging was ordered. Headache spontaneously resolved 9 months later and follow-up MRI (Fig. 1l–n) demonstrated complete spontaneous resolution of the midbrain lesion. There was no longer evidence of the focal abnormality, with resolution of mass effect, and of T2-prolongation. The aqueduct appeared less distorted. There was also a reduction in the size of the lateral ventricles, most likely as a consequence of ameliorated CSF-flow dynamics. We hypothesize that the mass consisted of a focal area of parenchymal edema, representing a ‘‘pre-syrinx’’ state, which was most likely due to abnormal CSF dynamics through a distorted and compressed third ventricle and aqueduct. Other causes of T2and T1-prolongation, such as demyelination, tumor, and infarct are not compatible with the spectroscopic findings and the spontaneous resolution. Pathophysiology of syrinx formation is not well understood, but most of the literature points to CSF-flow abnormalities as the main cause [2]. The lesion we describe never showed true cavitation. The most likely explanation is that the pre-syrinx state represented a progressive but transient focal accumulation of CSF in the extracellular space of the midbrain, probably originating from a fissuration of the ependyma lining the left lateral ventricle that did not progress to a true syrinx cavity. Spontaneous resolution of syringes of the spinal cord can occur following resolution of altered CSF-flow dynamics, or parenchymal dissection and rupture of the syrinx cavity into the subarachnoid space [3]. This is, to our knowledge, the first report of such a condition in an intracranial location [4]. A. Cianfoni Neuroradiology Section, Radiology Department Medical University of South Carolina (MUSC), Charleston, USA