²⁰¹Tl-SPECT and ¹H-MRS study of benign lateral ventricle tumors: Differential diagnosis of subependymoma

The introduction of computed tomography (CT) and magnetic resonance (MR) imaging has resulted in the detection of increasing numbers of asymptomatic intraventricular tumors. Establishing the correct preoperative diagnosis is important to prevent unnecessary surgical intervention. Our study includes nine cases of benign lateral ventricle tumors including two cases of central neurocytoma, two of subependymal giant cell astrocytoma, two of pilocytic astrocytoma and three of subependymoma treated surgically between 1996 and 2003. MR imaging, proton MR spectroscopy (¹H-MRS) and thallium-201 single photon emission computed tomography (²⁰¹Tl-SPECT) were performed in all patients. All three types of tumor demonstrated heterogeneous enhancement on MR imaging with gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) and increased choline (Cho) peak and decreased N-acetyl aspartate (NAA) and creatine (Cre) peaks on ¹H-MRS. ²⁰¹Tl-SPECT showed high uptake of ²⁰¹Tl without wash out in all cases of central neurocytoma, subependymal giant cell astrocytoma and pilocytic astrocytoma, but no uptake in cases of subependymoma. Absence of ²⁰¹Tl uptake in contrast with enhancement on MR imaging and the ¹H-MRS features of modest elevation of the Cho/Cre ratio, reduction of the NAA peak and presence of lactate/lipid peaks are characteristic features of subependymomas and useful to establish a preoperative diagnosis.