Butterfly Lesion of the Corpus Callosum: An Unusual Case of Extramedullary Myeloid Sarcoma (Granulocytic Sarcoma)

A 49-year-old male patient presented with worsening forgetfulness for 2 months, without any focal neurologic signs. CT and MRI scans showed a small enhancing mass in the right frontal periventricular region and another larger characteristic “Butterfly” lesion within the splenium of the corpus callosum. Provisional diagnosis of lymphoma or glioblastoma multiforme was made. F-18 FDG PET/CT scan showed hypermetabolism of these lesions. The final histology revealed leukocytic large-cell neoplasm, compatible with extramedullary myeloid sarcoma (or granulocytic sarcoma). This case shows an unusual manifestation of myeloid sarcoma presenting as a lesion in the corpus callosum.