EPEN-29. Spatial transcriptomic analysis of ependymoma implicates unresolved wound healing as a driver of tumor progression

Ependymoma is a childhood brain tumor that remains incurable in approximately 50 percent of cases, most commonly in posterior fossa subgroup A (PFA). Uncovering how heterogeneous cell types within the tumor microenvironment (TME) interact is crucial to a complete understanding of PFA disease progression. The underlying cellular components of the PFA TME have been revealed by single-cell RNAseq (scRNAseq), identifying divergent epithelial differentiation and epithelial-mesenchymal transition (EMT) lineages. Here, we utilize spatial transcriptomics (Visium) of 14 PFA samples, integrated with scRNAseq, to chart neoplastic and immune cell architecture, with a higher resolution of cellular heterogeneity than scRNAseq alone. At a gross level, all PFA were primarily comprised of neoplastic epithelial and mesenchymal transcriptomic spatial zones, each containing a diversity of hierarchical cellular stages. In all samples we revealed spatially and transcriptomically-distinct mesenchymal zone-associated subclusters, including a quiescent undifferentiated progenitor-like subpopulation and clusters with characteristics of early and late stage EMT. Two early stage EMT clusters were distinguished by signatures of either myeloid cell interaction or hypoxia, and both were demonstrated to be EMT-initiating processes in in-vitro PFA experimental models. Myeloid cell interaction is the predominant initiating stage of EMT in PFA, occurring in zones that are spatially distinct from hypoxia induced EMT. Other mesenchymal clusters represent later EMT stages characterized by wound repair and tissue remodeling. Increased proliferation was a general characteristic of epithelial zone clusters, which included a second undifferentiated progenitor-like population that showed a particularly high mitotic rate and was associated with histologically hypercellular areas. Given the biological parallels with normal wound healing, we propose that mesenchymal and epithelial zones interact to create a cycle of persistent tissue damage response and mitogenic re-epithelialization signals. Unresolved wound repair is therefore a potential driver of PFA progression, a new concept that could provide novel targets for effective therapeutic intervention.

Modified prone position to dissect the popliteal fossa

Introduction

Traditionally, the prone position is used for dissecting the popliteal fossa, which requires endotracheal intubation. Access to the airway in this position is limited, hence the complications. It is not surprising that the prone position is not favoured by the anaesthetists, especially in patients with a high body mass index. We describe a safe and novel alternative to the prone position.

Methods

The modified prone position (MPP) is described as an alternative position that facilitates access to the airway.

Results

Between October 2007 and May 2010, 12 patients underwent popliteal fossa dissection using the MPP. All patients had general anaesthesia using a laryngeal mask airway with the exception of one, who had an epidural anaesthesia. There were no airway or haemodynamic complications. The surgical access to the popliteal fossa was as good as with the traditional prone position.

Conclusions

The MPP was satisfactory for both the surgeon and the anaesthetists. The authors now use this position routinely for dissecting the popliteal fossa.

Radiological classification of optic pathway gliomas: experience of a modified functional classification system

Optic pathway gliomas (OPGs) in childhood are associated with neurofibromatosis type 1 (NF1) and since 1958 have been classified anatomically using the Dodge classification (DC). MR scanning permits a more detailed anatomical description than can be classified by this historical system. A modified Dodge classification (MDC) has been applied to MRI scans from a cohort of 72 patients (36.1% NF1-positive) from 4 centres participating in an international clinical trial. The MDC was feasible, applicable and more detailed than the original DC. NF1-positive cases more commonly involved both optic nerves (p = 0.021) and other multiple locations (p = 0.001). NF1-negative tumours more commonly involved the central chiasm (p = 0.005) and hypothalamus (p = 0.003). Fewer hypothalamus-positive tumours were associated with optic nerve involvement (p = 0.009), whereas more were associated with central chiasm involvement (p<0.001). From diagnosis to follow-up, there was concordance between DC and MDC in 51/72 cases (70.8%). The MDC is therefore proposed for use in clinical trials of new treatments for OPGs.