Primary cauda equina neuroendocrine tumor mimicking myxopapillary ependymoma: illustrative case

BACKGROUND: Primary cauda equina neuroendocrine tumors (CENETs) are rare intradural extramedullary neoplasms that were historically termed cauda equina paragangliomas. They may resemble more common cauda equina lesions, including myxopapillary ependymoma and schwannoma, on preoperative imaging. Recent molecular and immunohistochemical studies support CENET as a distinct entity, creating a need for practical diagnostic frameworks that separate primary tumors from metastatic neuroendocrine disease and nonneuroendocrine mimics. OBSERVATIONS: A 42-year-old woman presented with progressive nocturnal low back pain, bilateral leg heaviness, lower extremity numbness, and urinary incontinence. MRI demonstrated a 5-cm L1-3 intradural extramedullary mass nearly occupying the spinal canal, with cauda equina compression and prominent surrounding vessels. She underwent urgent L1-3 laminoplasty and microsurgical resection. Intraoperatively, the tumor was extremely vascular, friable, and associated with the filum terminale. Gross-total resection was achieved. Pathology demonstrated a WHO grade 1 primary CENET with neuroendocrine marker expression, CK8/18 positivity, low proliferative index, and no evidence of systemic neuroendocrine malignancy on postoperative staging. LESSONS: Cauda equina neuroendocrine lesions should be approached as a diagnostic spectrum. Clinical tempo, lesion multiplicity, imaging clues, intraoperative vascularity, and immunohistochemical/molecular workup can help distinguish primary CENET from metastatic neuroendocrine disease and mimics. https://thejns.org/doi/10.3171/CASE26609.