Objective: Our aim was to test the hypothesis that in neurofibromatosis type 1 (NF1), superficial plexiform neurofibromas have different MRI characteristics than deep plexiform neurofibromas.
Subjects and methods: Sixty-six patients (median age, 15 years) with superficial plexiform neurofibromas were compared with 56 patients with deep plexiform neurofibromas (median age, 12 years). All patients underwent axial STIR and coronal or sagittal STIR images.
Results: Superficial neurofibromas were more likely to be asymmetric (p = 0.004) and extend to the skin surface (p < 0.001). Lesion borders were poorly defined with similar frequency in both superficial and deep groups (77% vs 68%, p = 0.31). The morphology of superficial neurofibromas was more likely diffuse (64% vs 11%, p < 0.001), whereas deep neurofibromas were more likely nodular or fascicular. Of neurofibromas that were nodular or fascicular in morphology, superficial lesions had a smaller maximal fascicle-nodule diameter (mean, 10.3 mm) than deep lesions (mean, 13.4 mm) (p = 0.013). Signal characteristics of deep neurofibromas were more likely to be targetlike (75%) compared with superficial neurofibromas (21%) (p < 0.001). Superficial neurofibromas had a smaller mean volume than deep neurofibromas (180 vs 444 cm(3), p = 0.002).
Conclusion: Unlike the typical targetlike lesions along the course of major nerves seen in deep plexiform lesions, superficial plexiform neurofibromas in NF1 tend to be asymmetric, have nontargetlike signal intensity, lack nodular or fascicular morphology, and are likely to involve skin.