Asymptomatic pontine lesions found by magnetic resonance imaging: are they central pontine myelinolysis?

Clinicians occasionally receive radiographic reports noting pontine lesions in their patients who have undergone magnetic resonance imaging (MRI) for symptoms not referable to the pons. Based on these relatively isolated lesions, patients may receive the presumptive radiographic diagnosis of central pontine myelinolysis (CPM). Review of our MRI database from the last five years identified twelve such patients with hyperintense pontine lesions on T2-weighted scans which were out of proportion to supratentorial white matter disease processes and unexplained by the remainder of their radiographic studies. In an attempt to further clarify whether these findings were more consistent with CPM or some other process, we reviewed these patients' clinical records with particular attention to electrolyte disturbances, alcoholism, liver disease and hypertension. We also compared the MRI studies from these twelve patients with four MRI scans from patients with clinically diagnosed CPM and with eight post-mortem MRI scans on autopsy-proven asymptomatic CPM. By comparing pre- and post-mortem scans, five of the twelve unknown pontine lesions were felt to be too large to represent asymptomatic CPM. Five were thought to be incompatible with CPM based on shape and/or discohesiveness; one of these came to autopsy and showed cerebral and pontine ischemic rarefaction, not CPM. Only two of these twelve cases were felt to be asymptomatic or mildly symptomatic CPM, but have not come to autopsy. We conclude that pontine lesions found incidentally on MRI scans are a heterogeneous group, many of which are more consistent with pontine ischemic rarefaction than with asymptomatic CPM.