Definition:

Cirrhosis-associated nodule with higher iron content than surrounding parenchyma. Histologically, iron-rich cirrhosis-associated nodules usually represent cirrhotic (regenerative) or dysplastic nodules. As imaging cannot reliably differentiate non-dysplastic from dysplastic iron-rich nodules, iron-rich nodules should be categorized LR-2 or greater as follows:

LI-RADS Categorization:

LR-2 Iron-Rich Cirrhosis-Associated Nodules

• Iron-rich cirrhosis-associated nodules with the imaging features below may be considered probably benign and so are categorized LR-2
• Imaging criteria (all of the following):
• Diameter < 20mm and
• Homogeneous and
• Iso-enhancement to background cirrhotic nodules in all phases and
• Homogeneous moderate or marked T2 or T2* hypointensity, or moderate or marked signal loss on the longer echo of a dual-echo imaging acquisition
• Such nodules are common in cirrhosis. They range in number from solitary to innumerable; in diffusely iron-overloaded cirrhotic liver, every nodule may be iron rich. They generally do not require LI-RADS reporting. Radiologists at their discretion may report them.

LR≥3 Iron-Rich Cirrhosis-Associated Nodules

• Iron-rich nodules that do not meet LR-2 criteria cannot be considered probably benign. These include nodules with imaging evidence of high iron concentration and any of the following:
• Diameter ≥ 20 mm or
• Heterogeneous in one or more sequences or phases or
• Enhancement that differs from liver in one or more phases or
• Any ancillary feature that favors HCC
• Such iron-rich nodules should be categorized LR-3, LR-4, or LR-5 depending on size and other imaging features.
• LR-3 iron-rich nodules should be reported if there are no LR-4, LR-5, or LR-M observations elsewhere in the liver. If there are LR-4, LR-5, or LR-M observations elsewhere in the liver, they may be reported at the radiologist’s discretion.
• LR-4 and LR-5 iron-rich nodules should be reported as per reporting guidelines. 

Synonyms:

• Synonym: siderotic nodule
• Preferred term: iron-rich nodule
• Rationale: term “siderotic nodule” may have a different meaning in pathology.

Comments:

• Iron-rich nodules can be identified with high specificity at MRI, due to T2/T2* shortening effects of iron. These nodules are moderately to markedly hypointense on T2w or T2*w images, and they show moderate or marked signal loss on the second echo of dual-echo imaging acquisitions. The degree of hypointensity relative to liver is accentuated with longer echo times and, if dual-echo imaging is performed, with greater inter-echo spacing.  
• The nodules may be hypo-, iso-, or hyperintense on T1w images, depending on the their iron content and imaging technique.
• Iron-rich nodules are more difficult to diagnose at CT; while iron causes hyperattenuation, the hyperattenuation may be subtle and, even if detected, is not specific for iron deposition.
• Rarely, a focus of HCC may develop within an iron-rich nodule. The development within an iron-rich nodule of an iron-poor component (i.e., nodule-in-nodule architecture) may indicate an incident HCC and should be categorized LR-3, LR-4, or LR-5 depending on other imaging features.