Recurrence patterns in pediatric intracranial ependymal neoplasm: a systematic imaging work-up.

Purpose: Currently, the different types of ependymal neoplasm (EPN) are defined by anatomical localization and genetics. This retrospective multicenter study aimed to analyze the imaging patterns of both local and distant recurrences in supratentorial (ST) and posterior fossa (PF) EPN.

Methods: We exclusively evaluated patients with recurrent EPN. To form the basis for follow-up evaluations the imaging characteristics for ST-EPN and PF-EPN were assessed and compared to each other. Follow-up assessments included the idenTIFFication of local recurrent tumors, leptomeningeal dissemination, secondary intraparenchymal lesions, and extraneural metastases. MR-signal characteristics of local recurrent tumors were compared to the primary tumor.

Results: The imaging series included 73 patients (median age at diagnosis 4.6 years; 56 PF-EPN). Recurrences were observed at up to five time points, with a total of 145 recurrence events documented. At first recurrence most PF-EPN recurred locally (29/56), while ST-EPN relapsed by intracranial dissemination (9/17). Local recurrent tumor grew fast and differed in up to one-fifth from the primary (13.2% lower T2-signal, 14.6% brighter T1-signal, 19% less contrast-enhancement). Leptomeningeal dissemination in ST-EPN is mainly restricted to intracranial (90.5%) while PF-EPN more frequently present with spinal spread (45.7%). Transient post-radiogenic lesions (n = 2) and secondary malignancies (n = 2) were rare. Extraneural metastases (n = 3) were found mainly near the surgical access.

Conclusion: Recurrences can occur multiple times in EPN patients, and the recurrence patterns differ between ST-EPN and PF-EPN. Imaging characteristics of local recurrences can differ from the primary tumor which is crucial for accurate diagnosis and treatment planning.