DESMOPLASTIC/NODULAR MEDULLOBLASTOMA IN A 2-YEAR-OLD CHILD WITH A FAVORABLE OUTCOME: A CASE REPORT AND LITERATURE REVIEW

Abstract

Desmoplastic/nodular medulloblastoma (DNMB) is a histologically and molecularly distinct variant of a common pediatric embryonal brain tumor. DNMB is disproportionately represented among Sonic Hedgehog (SHH)-activated tumors in infants and very young children. When it is TP53-wildtype, a comparatively favorable prognosis is expected. We report on a 2-year-old boy who presented with a four-week history of morning headaches, vomiting, lethargy, developmental regression, head tilt, and diplopia. Examination revealed papilledema, a setting-sun sign, and truncal ataxia; magnetic resonance imaging (MRI) demonstrated a heterogeneously enhancing vermian mass with fourth-ventricular extension and obstructive hydrocephalus. Following multidisciplinary tumor board discussion, the patient underwent suboccipital craniectomy with gross total resection. Histopathology confirmed DNMB, WHO grade 4, with immunohistochemistry (IHC) showing GAB1 and YAP1 positivity and absent nuclear beta-catenin, confirming SHH pathway activation; p53 was wildtype, and downstream testing identified Patched homolog 1 (PTCH1) pathway alterations. Staging studies were negative for metastatic disease. Given his age, the patient received intensive, radiation-sparing chemotherapy rather than craniospinal irradiation. At 18-month follow-up, he remained in complete remission with only mild residual ataxia and age-appropriate neurocognitive function.