The purpose of this study was to evaluate the usefulness of diffusion-weighted imaging (DWI) for the differential diagnosis of various intracranial cystic lesions.

This study included 19 patients (13 males, 6 females) with a mean age of 42.5 years. The final histopathological diagnoses for 14 patients were pyogenic brain abscess (n=3), glioblastoma (n=3), ependymoma (n=1), anaplastic astrocytoma (n=1), pilocytic astrocytoma (n=1), hemangioblastoma (n=2), arachnoid cyst (n=1), epidermoid (n=1) and schwannoma (n=1). The other cases of metastasis (n=4) and arachnoid cyst (n=2) were diagnosed on the basis of clinical, laboratory and imaging data. DWI imaging studies were performed with a 1.5 T MR system. A single shot spin echo EPI pulse sequence was applied. B values were set at 0 and 1000 sec/mm². The apparent diffusion coefficient (ADC) were calculated from the ADC map of 10 different cystic brain lesions. Conventional MR imaging included T2WI, T1WI, FLAIR and contrast enhanced T1WI. We analyzed the location, nature, signal intensity on DWI, and the enhancement pattern of the lesions.

All of the 3 cases of brain abscess, 1 of 4 cases of metastasis and 1 case of epidermoid showed hyperintensity on DWI. The mean ADC value of brain abscess (2 cases) was less than 1.15 (0.13x10-3 mm²/s). The mean ADC values of the other cystic lesions (8 cases) were variable, ranging from 2.840.66 to 3.100.16 (10-3 mm²/sec).

DWI and ADC values were useful in the differential diagnosis of various intracranial cystic lesions, but some metastatic tumors may mimic a brain abscess on DWI. Therefore, a clinical correlation is mandatory.