Added value of diffusion weighted imaging in pediatric central nervous system embryonal tumors surveillance

Abstract

Diffusion weighted imaging (DWI) has an established role in primary CNS embryonal tumor (ET) characterization; however, its diagnostic utility in detecting relapse has never been determined. We aimed to compare DWI and conventional MRI sensitivity in CNS ET recurrence detection, and to evaluate the DWI properties of contrast-enhancing radiation induced lesions (RIL).Fifty-six patients with CNS ET (25 with disease relapse, 6 with RIL and 25 with neither disease relapse nor RIL) were retrospectively evaluated with DWI, conventional MRI (including both T2/FLAIR and post-contrast images), or contrast-enhanced MR imaging (CE-MRI) alone. MRI studies were independently reviewed by two neuroradiologists for detection and localization of potential brain relapses. Sensitivity for focal relapse detection was calculated for each image set on a lesion-by-lesion basis. A descriptive per subject analysis was also performed. Evaluation of follow-up MRI studies served as standard of reference.Focal recurrence detection sensitivity of DWI (96%) was significantly higher than conventional MRI (77%) and CE-MRI alone (51%) (p=0.0003 and p<0.0001). On per subject analysis there were not missed diagnoses for DWI. At the time of DWI relapse detection, conventional MRI missed 2 diagnoses, and CE-MRI 8. Analysis of medulloblastoma relapses revealed that DWI identified a higher number of focal lesions than CE-MRI in subjects with classic variant. All but one RIL did not show restricted diffusion.In conclusion, DWI is a valuable complementary technique allowing for improved detection of focal relapse in CNS ET patients, particularly in children with classic medulloblastoma, and may assist in differentiating recurrence from RIL.

Clinical applications of diffusion weighted imaging in neuroradiology

“…An even greater accuracy can be achieved by combining DWI and MRS to obtain more information about the tumour proliferative potential [ 48 ]. DWI has also been reported to be useful in detecting relapse of embryonal tumours such as medulloblastoma, being more sensitive than contrast-enhanced MRI in subjects with the classic variant [ 49 ].…”

European Society for Paediatric Oncology (SIOPE) MRI guidelines for imaging patients with central nervous system tumours

“…Diffusion-weighted imaging (DWI) has become established as a standard sequence in neuroradiology. It is extremely valuable in the assessment of tumour cellularity, differential diagnosis and treatment response and in identifying metastases [24][25][26][27]. We recommend 2D echo planar DWI sequence with at least 2 bvalues (b = 0 s/mm 2 and b = 1000 s /mm 2 ).…”

Detection of recurrent brain tumors in children: No significant difference in sensitivity between unenhanced and contrast-enhanced MRI

“…Whereas the majority of primary embryonic tumors have shown enhancement, the degree of enhancement may be variable, and sometimes absent, with, for example, 11% to 25% of medulloblastomas that do not enhance 24,25 and are variable depending on the molecular subgroup 26 (absence in the subset of group IV 27 ), or some ATRTs. On the other hand, previous studies have shown that medulloblastoma metastases tend to have a lower enhancement than their initial primary lesions, 28 and cancer recurrence was totally unenhanced in 36% of cases, 24 with up to 20% of secondary leptomeningeal diseases missed by conventional MRI but detected by cerebrospinal fluid cytology.…”

“…29 This may support the hypothesis of the abstention from GBCA injection during the follow-up of embryonic tumors, which has been developed in a study aiming to reinforce the role of diffusion-weighted imaging for this purpose. 25 However, the embryonic tumors that belong to WHO grade IV are more at risk of recurrence, with worse prognosis, and thus require increased follow-up.…”