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Siderotic Nodules at MR Imaging: Regenerative or Dysplastic?

Objective To determine if iron containing “siderotic” nodules detected at magnetic resonance (MR) imaging are regenerative (RN) or dysplastic (DN) and to attempt to identify features that may distinguish them. Material and Methods MR imaging (1.5 T) was performed on 77 cirrhotic patients who underwent orthotopic liver transplantation within 0–117 days (mean 30 days) of MR imaging. Two readers retrospectively evaluated breath-hold gradient-echo pulse sequences (echo time ≥9.0 ms, flip angle ≤45°) for the presence of hypointense nodules, which were classified as micronodular (≤3 mm), macronodular (>3 mm), or mixed. Nodule distribution was classified as focal (<5), scattered (5–20), or diffuse (>20) per slice. Thin section pathologic correlation was available in all cases, and Prussian blue iron stains were performed. Results Of 35 patients with pathologically proven siderotic nodules, 10 (29%) had at least 2 siderotic DN. MR detected siderotic nodules in 10 of 10 (100%) patients with siderotic DN and RN, and in 18 of 25 patients (72%) with siderotic RN only. Conclusion Siderotic RN cannot be reliably distinguished from siderotic DN with MR imaging, and therefore the widely used term “siderotic regenerative nodule” should be avoided and replaced by “siderotic nodule.”