A Case of Calcifying Pseudoneoplasms of the Neuraxis Coexisting with Interhemispheric Lipoma and Agenesis of the Corpus Callosum: Involvement of Infiltrating Macrophages: CAPNON and macrophage.

Calcifying pseudoneoplasm of the neuraxis (CAPNON) is a rare clinical entity. We report an unusual case of intraparenchymal bifrontal CAPNON coexisting with interhemispheric lipoma and agenesis of the corpus callosum.

A 64-year-old woman presented with slight weakness of her left leg. Computed tomography and magnetic resonance (MR) imaging showed massive nodular intraparenchymal calcifications at both sides of the interhemispheric lipoma associated with partial agenesis of the corpus callosum. Enhancement was observed at the periphery and within the calcification. Massive perifocal edema was also demonstrated. The enhanced lesion with calcification was partially resected. Histological analysis of the resected specimen disclosed nodular calcification with fibro-osseous components and histiocytic reaction, consistent with CAPNON. High ratio of M2 macrophages was observed among the infiltrating macrophages. ¹¹C-methionine positron emission tomography (PET) demonstrated high uptake of the tracer at the lesion corresponding to the calcified lesion on computed tomography. Postoperatively, massive perifocal edema was decreased and maintained without progression for a year.

The high M2 macrophage activity verified by histopathological analysis suggests that CAPNON is not a silent but a more active, tumefactive disease involving the immune response. This hypothesis may be supported by the high uptake of ¹¹C-methionine PET.