LGG-05. A Nine-month-old Boy with Regression of Milestones and Severe Constipation: An Unusual Case of a Spinal Pilocytic Astrocytoma

Pilocytic astrocytoma (PA), a World Health Organization Grade 1 tumor, is the most common brain tumor in children between 5 and 14 years of age and the second most common in children younger than 5 and older than 14. Although classical to the cerebellum and hypothalamic regions, it can also arise in the spinal cord. A nine-month-old boy with a history of torticollis and plagiocephaly presented with a four-month history of regression of milestones, irritability and severe constipation. He was noted to have flaccid paralysis of the lower extremities and decreased reflexes. Ophthalmologic exam was significant for papilledema and magnetic resonance imaging of the spine were notable for a large infiltrative heterogeneously enhancing lesion extending from T4 to the conus containing several loculated intratumoral cysts with abnormal enhancing margins from T4 to T8. He underwent embolization and complete tumor resection. Post-op MRI was notable for an oval shape non-enhancing soft tissue measuring 8 mm along the medial wall of the left lateral ventricle. Comprehensive tumor molecular profiling on the resected spinal tumor tissue (Caris MI), revealed an NTRK1 fusion, MEF2D-NTRK1, Exon 12. Larotrectinib was initiated at 100mg/m2 per dose oral twice daily to target this specific mutation. Follow up imaging 3 months later showed decrease in the size of intracranial lesions. To date, there is only one other case report demonstrating intracranial metastasis from a spinal PA. Due to the size of his spinal lesion, we believe this was his primary site; however, as described in the literature, there is no definitive way to determine the initiating lesion. The use of comprehensive molecular profiling facilitated the discovery of a targetable oncogenic mutation that changed initial management. To the best of our knowledge there has been only one other case report describing this specific fusion in a pediatric spinal CNS tumor.