Diagnostic challenges, management and outcomes of midline low-grade gliomas.

Introduction: Low-grade gliomas (LGGs) are slow-growing and diffusely infiltrating tumours constituting 25-30 % of adult gliomas. Rarely, these tumours may arise in the cerebral midline, including the thalamus, hypothalamus, tectum and brainstem. Here we present a contemporary experience with midline LGGs.

Methods: Midline LGGs were identified from a retrospective database of adult patients who received a histological diagnosis of WHO grade II glioma between 2006 and 2012 at a single institution. Location, radiological data and clinical outcomes were collected. IDH1 status was assessed by immunohistochemistry.

Results: Eighteen patients with midline LGGs were identified, with a median age of 45. Most received biopsy upon diagnosis, though asymptomatic patients with tectal tumours underwent active surveillance. Oligodendroglial tumours were much less common than in a comparable group of lobar tumours (6 vs. 38 %, Fisher's exact test, p = 0.007). Only one tumour was immunopositive for IDH1 (1/17). Radiological diagnosis correlated with histology in only 71 % of patients. Median survival of midline LGGs was 48 months (3-90 months) and radiological features such as contrast enhancement, size and radiological diagnosis did not predict survival in this cohort. Median overall survival of midline LGGs was less than lobar LGGs (log-rank, p = 0.006), though differences became insignificant when considering only biopsied astrocytomas in both locations (log-rank, p = 0.491).

Conclusions: Diagnosis of midline LGGs is complicated by both limitations of biopsy and imaging. Midline tumours have a poorer prognosis compared to lobar equivalents and survival differences are probably due to the absence of significant surgical intervention in midline locations.