Figure Legends:
Figure 1. Brain imaging. A) T1-weighted brain MRI without
intravenous contrast at 1-day of age showed a large extra-axial cystic
mass in the right convexity and temporal lobe signal alteration. Also
present was intraventricular hemorrhage with fluid-fluid levels in the
dilated lateral ventricles. B)-E) T1-weighted brain MRI images with
intravenous contrast. B) At 7-months of age, the previously noted
cystsic lesion demonstrated an extensive and avidly enhancing solid
component at the periphery. C) At 8-months of age, following surgical
resection, there is residual enhancing mass in the posterior aspect of
the tumor bed. D) At 13-months of age, 2 months after completion of
conventional chemotherapy, there is progressive residual mass. E) At
15-months of age, 2 months after starting larotrectinib, rapid reduction
of the residual tumor is seen.
Figure 2. Tumor histopathology. The desmoplastic portion of the
tumor is comprised of spindle cells (upper portion of panel A) with
abundant reticulin (B). Spindle cells are polyphenotypic. The expression
of S100 protein (C) and smooth muscle-specific actin (SMSA; D) are shown
here. Arrows in A-D mark the glia limitans border between abnormal
cerebral cortex and desmoplastic neoplasm. Away from the desmoplastic
components, the cerebral cortex contains nodular layer I clusters of
neurons (E-H; arrows in E-G) and cortical dysplasia (I-K), with
disorganized lower layers of the cortex (I) containing dysmorphic
neurons (J and K). Arrows in K point to neuronal cell bodies positive
for neurofilament. A minority of the tissue resection consisted of
high-grade neuroepithelial tumor. Malignant neuroepithelial neoplasm
(L-O) is hypercellular with foci of necrosis (M), vascular proliferation
(arrows in N and O), diffuse S100 protein expression (O), and high Ki67
proliferative index (P). There was no immunoreactivity for the mutant
proteins BRAF V600E or H3K27M. Clusters of malignant cells were present
in postoperative drain fluid, presumably CSF (Q).