Cyst with a mural nodule: Unusual case of brain metastasis

A 34-year-old woman presented with history of headaches, vomit-ing and progressive left hemiparesis for the last 3 months. CECT showed right frontal juxtaventricular, cystic lesion with an enhanc-ing mural nodule and focal wall (Figure 1a). On MRI, the cyst was hypointense on T1WI (Figure 1b) and hyperintense onT2WI (Fig-ure 1c) and suppressed on FLAIR sequence (Figure 1d). Per-opera-tively, a cyst with yellowish clear fluid and a small grayish, solid part were removed. The cyst walls were not necrotic. HPE revealed a malignant tumor composed of cells with focal areas of glandular dif-ferentiation with marked pleomorphism. The tumor cells were im-munoreactive for cytokeratin and mucin. The wall of the cyst showed gliosis. A diagnosis of metastatic adenocarcinoma was made. No pri-mary could be localized. The radiological differential considerations for a cystic tumor with an enhancing mural nodule include pilocytic astrocytoma, hemangioblastoma, pleomorphic xanthoastryocytoma, menin-gioma and ganglioglioma.1,2 The radiological finding of a cystic tumor with a mural nodule had not been described previously in brain metastases. The presence of minimal edema relative to the size of the lesion in our case was also unusual for a metastatic deposit. FLAIR sequences have been reported to be useful in distinguishing between cystic neoplastic and non-neoplastic lesions.3 The cyst had suppression of signal inten-sity on FLAIR imaging, thereby suggesting non-mitotic pa-thology. This unusual appearance is possibly attributed to the lack of proteinaceous or myxoid material inside the cyst, which is rare in metastasis. Therefore, FLAIR images should be interpreted with caution