Hemosiderin deposition in papillary renal cell carcinoma and its potential to mask enhancement on MRI: analysis of 110 cases.

ABSTRACT

OBJECTIVES: To evaluate the relationship between imperceptible T1 enhancement of papillary renal cell carcinoma (pRCC) on MR and intratumoral hemosiderin deposition. METHODS: One hundred ten pRCCs (≤ 7 cm) were evaluated by MR with in- and opposed-phase spoiled gradient echo (GRE) and T1-weighted spoiled GRE with fat suppression before and after contrast. Hemosiderin deposition was assessed by SIindex and Dindex on in- and opposed-phase images. SIindex and Dindex are calculated as (SIin - SIopp)/(SIin) × 100, where SIin and SIopp are tumor signal intensities on in- and opposed-phase images and (Din)/(Dopp), where Din and Dopp are tumor diameters on in- and opposed-phase images, respectively. The degree of tumor enhancement was classified as grade 1 (no), grade 2 (subtle), or grade 3 (definite). Tumor enhancement on CT was assessed when available. RESULTS: Five (5%), 10 (9%), and 95 (86%) tumors were categorized as grades 1, 2, and 3 enhancement, respectively. The mean SIindex was - 33.9, - 25.3, and 1.00, whereas the mean Dindex was 1.26, 1.05, and 1.00 in tumors with grades 1, 2, and 3 enhancement, respectively. Tumors with grade 1 enhancement had significantly lower SIindex (p = 0.001) and higher Dindex (p = 0.005) than those with grade 3 enhancement. Among six tumors with grade 1 or 2 enhancement and available CT, four tumors showed > 20 HU enhancement. CONCLUSIONS: pRCC with no subjective enhancement on contrast-enhanced MR showed hemosiderin deposition evident by lower SIindex and higher Dindex. Hemosiderin deposition might mask the tumor enhancement on MR. KEY POINTS • 5% of papillary renal cell carcinoma showed imperceptible enhancement on contrast-enhanced MR. • Hemosiderin deposition in papillary renal cell carcinoma might mask the tumor enhancement on contrast-enhanced MR due to T2/T2*-shortening effects. • A renal lesion with extensive hemosiderin deposition but no perceptible enhancement on MR should be considered suspicious for papillary renal cell carcinoma.