MRI appearance of massive renal replacement lipomatosis in the absence of renal calculus disease

Abstract

Renal replacement lipomatosis is a rare benign entity in which extensive fibrofatty proliferation of the renal sinus is associated with marked renal atrophy. In this report, we present a case of massive renal replacement lipomatosis demonstrated on MRI. The presentation was atypical given an absence of associated renal calculus disease, and an initial CT scan was interpreted as suspicious for a liposarcoma. The differential diagnosis and key MRI findings that served to establish this specific diagnosis are reviewed. Histopathological correlation is also presented, as the patient underwent nephroureterectomy.

Figure 1

Coronal single-shot half-Fourier turbo spin-echo image of the abdomen demonstrates a markedly enlarged left kidney with a prominent hyperintense structure expanding the renal sinus (RS) that proved to represent extensive fatty proliferation in the setting of renal replacement lipomatosis. There were additional ovoid hyperintense structures (*) more peripherally within the region of the atrophied renal parenchyma, corresponding with fluid-filled, significantly dilated renal calyces.

Figure 2

Axial in-phase (a) and out-of-phase (b) gradient-echo T₁ weighted images of the abdomen demonstrate T₁ hyperintensity of the tissue expanding the left renal sinus (RS). Although the T₁ hyperintensity by itself is non-specific, the peripheral etching along its margin with adjacent renal parenchyma indicates the fatty nature of this tissue. The dilated renal calyces peripherally are T₁ hypointense (*), consistent with their fluid content.

Figure 3

Axial chemically selective fat-saturation gradient-echo T₁ weighted images before (a) and after (b) the intravenous administration of gadolinium chelate demonstrate complete loss of signal of the structure expanding the left renal sinus (RS) that was hyperintense on the in- and out-of-phase T₁ weighted images, confirming the fatty nature of this tissue. The dilated renal calyces peripherally (*) fail to demonstrate excretion on the post-contrast images.

Figure 4

Low-power photomicrograph (a, haematoxylin and eosin stain (H&E), ×1) shows lobules of fatty tissue interspersed with fibrous bands that encroach on markedly thin atrophic renal parenchyma. High-power photomicrograph (b, H&E stain, ×200) of a lobule of fatty tissue shows mature adipocytes with interspersed chronic inflammation composed of lymphocytes and plasma cells.