Mystery myxoid mass: diagnostic uncertainty of a myxoid plexiform spindle cell mass in a 13-month-old infant

We present the case of a myxoid plexiform spindle cell mass in 13-month-old infant without definitive diagnosis. The firm lumbosacral was first identified at age 6 months and biopsied 13 after continued growth. lesion localised to subcutis showed intense heterogeneous enhancement on MRI, raising suspicion neoplastic process. At surgical excision well circumscribed not adherent surrounding structures. pink yellow fleshy lobulated measuring 55 mm. A triage frozen section subsequent formal histopathology revealed lobulated, with areas stroma. cellularity variable but cytology bland low mitotic rate. edges concerning ‘budding’ nodules extension resection margin. microscopic morphology suggestive benign nerve sheath tumour. However, wide immunohistochemical work-up did support this diagnosis or suggest any alternative An RNA sequencing panel found no pathogenic variants gene fusions. Multiple expert opinions were sought, unfortunately specific able be reached. is being managed as monitored for risk local recurrence.