Expanding Porencephalic Cysts: Prenatal Imaging and Differential Diagnosis.

OBJECTIVES: The aim of this study was to report the prenatal imaging findings of expanding porencephalic cyst, which have not been previously described in the prenatal period, and to underline that these lesions can involve the cerebellum and not exclusively the supratentorial structures. MATERIALS AND METHODS: This is a retrospective observational study of five cases with a prenatal diagnosis of expanding porencephalic cyst. RESULTS: The cystic lesion was located in the supra- and infratentorial space in 2 cases, respectively, or in both in one case. The lesion expanded into the pericerebral space or communicated with the ventricular system in 4 and 1 cases, respectively. Differential diagnosis included tumoural lesion in 2 cases because of internal echogenic components related to haemorrhagic changes, which were identified using foetal MRI, and arachnoid cyst in 2 cases because of expansion into the pericerebral space. In the last case, communication within the ventricular system mimicked a unilateral ventriculomegaly. CONCLUSION: Differential diagnosis of any cystic lesion with extra-axial component should include expanding porencephalic cyst. Foetal MRI is helpful to differentiate this entity from extra-axial lesions such as arachnoid cysts but also from rare tumours.

Evaluation of image quality of DWIBS versus DWI sequences in thoracic MRI at 3T.

PURPOSE: To compare diffusion weighted imaging with background suppression (DWIBS) sequence with classic spectral diffusion sequence (DWI) with and without respiratory gating in mediastinal lymph node analysis at 3T. MATERIALS AND METHODS: 26 patients scheduled for mediastinoscopic lymph node analysis, prospectively undergone a thoracic 3T MRI with DWIBS (FatSat=STIR; TR/TE=6674.1/44.7ms; IR=260 ms) and DWI sequences (FatSat=SPIR; TR/TE=1291/59.6 ms) (b=0-400-800 s/mm2) with and without (free breathing) respiratory gating. Images at b=800 were analyzed by two radiologists. They performed qualitative analysis of fat-sat homogeneity and motion artifacts, rated from 0 to 4, and quantitative evaluation by studying signal to background (STB) of lymph nodes. RESULTS: Quality of fat suppression was significantly higher for DWIBS than for DWI both for free-breathing (score 3.48±0.65 vs. 1.76±0.96, p<0.0001) and respiratory-gated scans (3.17±0.77 vs. 1.72±0.73, p=0.0001). Similarly, artifacts were reduced with DWIBS (3.16±0.47 vs. 1.76±0.59, p<0.0001; 3.0±0.73 vs. 2.04±0.53, p=0.0001). Quantitative analysis showed higher STB with DWIBS (3.26±1.83 vs. 0.98±0.44, p<0.0001; 3.56±, 2.09 vs. 0.92±0.59, p<0.0001). Gating did not improve image quality and STB on DWIBS (p>0.05). CONCLUSION: In thoracic MRI, ungated DWIBS sequence improves fat-sat homogeneity, reduces motion artifacts and increases STB of lymph nodes. Respiratory gating does not improve DWIBS image quality.