Diagnostic challenges of the neurofibroma-malignant peripheral nerve sheath tumor spectrum in neurofibromatosis type 1: illustrative case.

backgroundNeurofibromatosis type 1 (NF-1) is an autosomal dominant disorder characterized by neurofibroma development, with an increased risk of malignant peripheral nerve sheath tumor (MPNST) transformation. Diagnosis is challenging due to histopathological overlap with atypical neurofibroma and atypical neurofibromatous neoplasm of uncertain biological potential (ANNUBP). ANNUBP is a distinct, more aggressive entity than atypical neurofibroma and is considered an intermediate step in the progression from benign neurofibroma to high-grade MPNST. Early detection is critical, but biopsy sampling limitations may delay diagnosis and treatment. OBSERVATIONS: A 32-year-old male with NF-1 presented with intractable abdominal and arm pain and retroperitoneal, abdominal, and arm masses. Initial biopsies revealed ANNUBP. Following resection, the retroperitoneal mass was diagnosed as a high-grade MPNST, the arm mass as a low-grade MPNST, and the second abdominal mass as an atypical neurofibroma. Despite gross-total resection, the patient developed recurrent abdominal disease within 5 months, with biopsy confirming multifocal MPNST transformation. LESSONS: This case underscores the difficulty in distinguishing ANNUBP from MPNSTs. Accurate diagnosis is crucial for guiding appropriate treatment, improving patient survival, and reducing the risk of recurrence. Improved molecular and imaging techniques are needed to optimize early detection and treatment strategies for MPNSTs in NF-1 patients. https://thejns.org/doi/10.3171/CASE25580.