Ipsilateral atrophy of the mammillary body and fornix after thalamic stroke: evaluation by MRI.

BACKGROUND: A focal brain lesion influences the function and morphology in the connected intact regions remote from it. However, it is not well documented that thalamic stroke may induce secondary degeneration of the mammillary body (MB) or the fornix (Fx).

PURPOSE: To investigate transneuronal degeneration (TND) in the MB and Fx following thalamic stroke on magnetic resonance imaging (MRI) and to assess the time course of these findings using serial MRI after stroke.

MATERIAL AND METHODS: Conventional T2-weighted axial MR images were retrospectively evaluated in 24 cases of thalamic infarction or hemorrhage involving the anterior thalamic nucleus and/or mammillothalamic tract (MTT). We recorded any change in size and/or shape of the MB and Fx after the infarction and the days on which those structural changes occurred.

RESULTS: Ipsilateral atrophy of the MB was shown in 9/20 patients (45.0%). MRI revealed MB atrophy as a small round shape in almost half of the patients and was too small to visualize in one-third of them on axial planes. Ipsilateral atrophy of the Fx was found in 2/23 patients (8.7%) and was observed as a thin lined shape on MRI. The atrophy was observed on follow-up MRI scans dated 356-1779 days (mean = 910 ± 516 days) after onset.

CONCLUSION: Damage to the anterior thalamic nucleus and/or MTT caused TND in the ipsilateral MB and/or Fx resulted in atrophy and asymmetry in less than half of patients studied, mostly within three years.