Differential diagnosis in this case would include the following entities:
- anaplastic oligodendroglioma. The principal differential diagnosis, as this lesion can also manifest with multiple calcifications, bone remodeling, and lack of perilesional edema. On the other hand, this type of neoplasm tends to have coarse and larger calcifications and it is typically encountered in middle-aged adults.
- chondrosarcoma. The presence of rings and arcs calcifications and bone destruction raised the possibility of chondrosarcoma. Also, the T2 hyperintense regions resembling the cartilaginous matrix favored this option. However, chondrosarcoma does not usually appear as an intracranial mass and is rare in young patients.
- grade III meningioma. Cystic components are less frequent in this type of lesion, and enhancement is usually more significant and homogeneous.
- gangliocytoma / ganglioglioma. Ordinarily seen in children and young adults, these tumors can have a similar clinical presentation. Nevertheless, they have a more homogeneous radiological appearance and do not show bone resorption.
- anaplastic astrocytoma / GBM. These neoplasms rarely show calcifications and bone resorption, and frequently present with marked peripheral FLAIR hyperintensity.
- metastases. Although this diagnosis should always be considered, there was no oncological history in this patient.
The first diagnostic possibility was chondrosarcoma, especially due to the T1 and T2 hyperintense components and the rings and arcs calcifications. The patient went to have surgical resection of the lesion, and the pathological examination is shown above. No chondroid matrix was found, therefore chondrosarcoma was discarded. There were also no IDH mutations, 1p19q co-deletion, or glial cells to consider an oligodendroglioma. Finally, the histologic appearance together with the synaptophysin positivity was in keeping with an extraventricular neurocytoma. The T1 hyperintense components could be explained either by blood products, dense proteinaceous fluid, or areas of microcalcification.
Extraventricular neurocytomas are extremely rare WHO grade II primary CNS neoplasms, only described in a few case reports. They can have significant overlap in radiologic presentation with other primary brain tumors; consequently, it is difficult to make an accurate preoperative diagnosis.
Acknowledgments to Dra. Celia Lizi Oramas Requejo and Hospital de Palamós for providing the radiological images, to Dr. Pablo Benito Peña for sharing the macroscopic picture, to Dra. Laura Ferrazza Martín for contributing with the microscopic images, and to Dr. Nerses Nersesyan for his broad knowledge and incredible support.