Anaplastic Meningioma Arising From a Radiologically Diagnosed Arachnoid Cyst

Abstract

We report the first example of an anaplastic meningioma arising from an intracranial arachnoid cyst and discuss the diagnostic challenges of this case, including the useful role of genetic markers. A 72-year-old man presented with transient episodes of expressive dysphasia and focal motor seizures, superimposed on a 6-month history of worsening headaches and dizziness. His past history was significant for a previously drained left-sided chronic subdural hematoma and a radiologically diagnosed left middle fossa arachnoid cyst. Magnetic resonance imaging on admission showed variable wall thickening of the arachnoid cyst with mild mass effect on the left frontotemporal lobes. The patient underwent decompression of the arachnoid cyst and biopsy of the cyst wall. Histologic and immunohistochemical studies of the thickened portion initially suggested a metastatic carcinosarcoma, but fluorescence in situ hybridization (FISH) studies confirmed the diagnosis of anaplastic meningioma based on characteristic chromosomal deletions. The patient returned 2 months later with progressive disease, leading to his death 6 weeks later despite repeat surgery for tumor debulking. Malignant transformation of meningothelial elements in arachnoid cysts is an exceptionally rare complication that poses considerable diagnostic challenges. Genetic markers may be particularly helpful in such cases.