Usefulness of 320-Row Area Detector Computed Tomography for the Diagnosis of Cystic Falx Meningioma
A 52-year-old male had gradually developing motor weakness in his left leg and focal seizures. He came to our outpatient service and CT showed a large cystic lesion of the right frontal lobe with a small nodule adjacent to the falx. On admission, he was alert but had left hemiparesis. Magnetic resonance imaging (MRI) showed a huge cyst in the left frontal lobe that was compressing the motor cortex (fig. ). A round mass with a diameter of 2 cm was located at the falx and appeared to be a mural module. It was highly enhanced together with its attached dura mater, but the cyst wall was not enhanced (fig. ). Cystic falx meningioma, cystic glioma or dural metastasis with cyst was suspected. Screening of the entire body showed no cancer. The results of MR spectroscopy (high choline peak, very low level of creatine and N-acetylaspartate) were consistent with an extra-axial tumor, such as a meningioma. Conventional cerebral angiography was not done. Additional imaging was performed using a 320-row CT scanner (Aquilion One, Toshiba Medical Systems, Nasu, Japan) that had a detector width of 160 mm and 320 detector rows. Time-resolved whole-head 4-dimensional CT angiography (4D-CTA) was performed instead of conventional digital subtraction angiography (DSA). The serial images showed the arterial supply feeding the tumor, and the tumor contrast became more pronounced at later time points, which indicated tumor staining commonly seen in meningioma (fig. ).\nAfter 4D-CTA, CT perfusion (CTP) imaging was performed and analyzed. The cerebral blood flow (CBF) in the tumor area (53.0 ml/min/100 g) was higher than that in the adjacent brain tissue (30.1 ml/min/100 g) (fig. ). The cerebral blood volume (CBV) in the tumor (6.4 ml/100 g) was also higher than that in the adjacent brain tissue (2.3 ml/100 g) (fig. ). Furthermore, the mean transit time (MTT) of the tumor (7.2 s) was longer than that of the adjacent brain tissue (4.9 s) (fig. ). The perfusion parameters of this tumor suggested that the tumor blood flow and capillary blood volume were 176 and 278% of the adjacent brain tissue, respectively. The possibility of congestion in the capillary bed of the tumor was suggested by the longer MTT. These findings were consistent with the data of meningioma obtained in our department [unpubl. observation].\nAs all of the preoperative imaging findings were consistent with meningioma, we made a definitive preoperative diagnosis of cystic falx meningioma. After the cyst fluid was aspirated during surgery, a reddish tumor showing the typical appearance of meningioma was found arising from the falx. The tumor was totally removed along with its attachment (Simpson grade 1). The histological diagnosis was meningothelial meningioma (WHO grade 1). Intraoperative frozen sections revealed no tumor cells in the cyst wall. According to the preoperative imaging and intraoperative findings, we regarded this case as an extratumoral cyst, classified as Nauta type 3 []. The cyst wall was left without excision except for the part attached to it. Postoperative MRI showed the absence of the tumor and collapse of the cyst. The patient's postoperative course was uneventful, and he was discharged from the hospital free of all symptoms.