Intraparenchymal epidermoid cysts in the brain: diagnostic value of MR diffusion-weighted imaging

To evaluate the value of magnetic resonance (MR) diffusion-weighted imaging (DWI) and apparent diffusion coefficients (ADC) maps in the diagnosis of intraparenchymal epidermoid cysts (ECs).

Six cases of histopathologically proven intraparenchymal ECs were studied. All patients were examined with conventional MR (T1WI, T2WI, contrast-enhanced T1WI) and DWI sequences. Along with the mean ADC values (mADC) of the ECs, the cerebrospinal fluid (CSF) and grey matter (GM) were measured. Qualitative and quantitative assessments, as well as MRI findings, were retrospectively analysed using a double blind method by three radiologists in consensus.

Four lesions were located in the cerebellum, among them, one was accompanied by an arachnoid cyst; one huge lesion crossed the parenchyma of the frontal and temporal lobes; the other was located in the left temporal lobe. Two lesions had a homogeneous CSF-like intensity on both T1WI and T2WI. The other four were of mixed-intensity on both T1WI and T2WI. All lesions were strikingly hyperintense on DWI, and iso- or slightly hypointense on ADC (relative to the brain). The mADCs of the ECs were significantly higher than that of GM, but significantly lower than that of CSF. Three cases (3/6) were accurately diagnosed using conventional MR sequences without DWI, but in the remaining three cases, correct diagnosis could only be made with help of DWI.

DWI sequences can facilitate the diagnosis of intraparenchymal ECs, thus alerting surgeons of the risk of chemical meningitis at surgery. The MR findings of intraparenchymal ECs are basically as the same as those of extracerebral ECs, but the former is likely to have a mixed signal. The hyperintense signal of ECs on DWI is probably caused by the T2 shine-through effect in tumour tissue.