Background <p>Plexiform neurofibromas are benign peripheral nerve sheath tumors that typically present in childhood and are most often associated with neurofibromatosis type 1. They usually manifest as diffuse, infiltrative masses involving a single nerve distribution. Adult-onset, multifocal, discrete retroperitoneal plexiform neurofibromas are rare and sparsely reported. This case is presented to expand the known phenotypic spectrum and to emphasize the diagnostic challenges posed by atypical presentations.</p> Case presentation <p>A 37-year-old Iranian woman presented with a 3-month history of vague, intermittent abdominal pain without bowel or urinary symptoms. Her medical history was notable for long-standing refractory iron deficiency anemia of unknown cause. Physical examination revealed mild bilateral lower abdominal tenderness with no palpable masses or neurological deficits. Laboratory investigations confirmed microcytic anemia. Although anemia has occasionally been reported in patients with neurofibromatosis type 1 due to associated gastrointestinal lesions or chronic disease, no evidence of such an association was identified in our patient, and the anemia was considered an incidental comorbidity. Abdominal ultrasonography demonstrated bilateral hydronephrosis, prompting further imaging. Computed tomography revealed multiple well-defined soft tissue masses along the bilateral paraspinal and psoas muscles, causing ureteral compression. Magnetic resonance imaging showed lesions that were isointense to muscle on T1-weighted sequences and hyperintense on T2-weighted sequences, with persistent signal on fat-suppressed images and contrast enhancement. No osseous involvement or intra-abdominal organ invasion was identified. The imaging findings were highly suggestive of plexiform neurofibromas, and the diagnosis is therefore radiologically favored in the absence of histopathological confirmation. Genetic testing and further management were recommended; however, the patient did not return for follow-up.</p> Conclusions <p>This case illustrates an unusual adult-onset, multifocal, discrete presentation of plexiform neurofibromas in the retroperitoneum without a prior diagnosis of neurofibromatosis type 1. Recognition of such atypical imaging and clinical features is important to avoid misdiagnosis and unnecessary intervention. The case underscores the value of multimodality imaging in identifying rare variants and highlights the need for heightened clinical awareness of phenotypic variability in plexiform neurofibromas.</p>