Miliary brain metastasis presenting with dementia: progression pattern of cancer metastases in the cerebral cortex

We report an autopsy case of an 82-year-old woman with progressive dementia due to miliary brain metastasis from lung adenocarcinoma. The patient presented with dementia 5 months prior to death and suddenly died of pulmonary hemorrhage. Postmortem examination revealed normal appearance of the brain. However, there were numerous foci of cancer metastasis in all parts of the brain on light microscopic examination. The carcinoma cells were located in the perivascular (Virchow-Robin) space and did not invade to the brain parenchyma. The carcinoma cells were also found in the subpial space. In the cerebral cortex, foci of metastasis appeared to spread in the following way: tiny foci of metastasis initially occur in the middle cortical layer, then spread to all layers through the perivascular space, and finally reach the subpial space and subcortical white matter. Although the junction between gray and white matter is a preferred site for usual brain metastasis, middle cortical layer was considered to be the initial site for metastasis in our patient. The perivascular pial sheath plays an important role for the development of miliary brain metastasis.