Renal liposarcoma: case report and review of systemic treatment

Renal Parenchymal Defects Occasionally Observed in Non-Well-Differentiated Perirenal Liposarcomas Unlike in Well-Differentiated Types

OBJECTIVE

This study aims to clarify the frequency of renal parenchymal defects and deformations in each subtype of perirenal liposarcomas and to compare the differences between well-differentiated and non-well-differentiated types.

METHODS

Patients with perirenal liposarcomas seen between July 2004 and June 2024 were included. Two radiologists blinded to the subtypes retrospectively evaluated CT or MR images for renal parenchymal defects and deformations. Frequencies of these findings were compared between well-differentiated versus non-well-differentiated types using the Fisher test.

RESULTS

Forty-two patients (mean age: 66.3±11.5 y; 15 men) with perirenal liposarcomas were included. Renal parenchymal defects and deformations were observed in 0 (0%) and 1 (7.7%) of 13 well-differentiated, 5 (29.4%) and 6 (35.3%) of 17 dedifferentiated, 3 (37.5%) and 0 (0%) of 8 myxoid, and 1 (25.0%) and 1 (25.0%) of 4 pleomorphic types, respectively. Non-well-differentiated liposarcomas had higher frequencies of renal parenchymal defects and deformations compared with well-differentiated liposarcomas [9 of 29 (31.0%) vs. 0 of 13 (0%), P=0.038 and 7 of 29 (24.1%) vs. 1 of 13 (7.7%), P=0.398].

CONCLUSION

Renal parenchymal defects can be occasionally observed (31.0%) in non-well-differentiated perirenal liposarcomas unlike well-differentiated liposarcomas.

Perinephric myxoid pseudotumor of fat - histopathological and molecular characterization of 3 cases after renal transplantation

BACKGROUND

Perinephric myxoid pseudotumor of fat (PMPF) is a rare benign pseudo-neoplastic proliferation of the perinephric and renal sinus adipose tissue. Its pathogenesis is thought to be a reactive process typically associated with neoplastic and non-neoplastic end-stage kidney disease. The distinctive histopathological feature of PMPF is a myxoid process comprising bland, spindled stromal cells interspersed with mature adipose tissue. Macroscopically, it is characterized by tumorous lipomatous remodeling of the kidney, which may raise concerns of malignancy on imaging. To date, only seven cases of PMPF have been documented in the context of kidney transplantation.

CASE PRESENTATION

This report describes three cases of PMPF in patients following renal transplantation, involving both native and grafted kidneys. Macroscopically, all cases consisted of shrunken kidneys with thinned and atrophic renal parenchyma surrounded by massively hypertrophic perirenal fat with mass-forming nodules, which was in concordance with cross sectional imaging findings acquired before surgery. Histology of the remaining renal parenchyma showed end stage renal disease in all four surgically removed kidneys, with diffuse interstitial fibrosis, tubular atrophy and sclerosed glomeruli. Perirenal adipose tissue consisted of mature fat with areas of significant myxoid and collagenous stromal component, interspersed with bland spindle and stellate-shaped cells. Immunohistochemistry for S100, smooth muscle actin, desmin and IgG4 were negative. No MDM2 gene amplification was identified by fluorescence in situ hybridization. Broad molecular profiling using the FoundationOne®Heme assay revealed no evidence of pathogenic alterations on DNA and RNA levels.

CONCLUSION

PMPF is a rare benign condition typically associated with chronic kidney disease, occurring late in the course. The radiological findings may be mistaken for those of a malignant tumor, and histopathological examination is required to exclude a malignant neoplasm, in particular a well-differentiated or dedifferentiated liposarcoma of the retroperitoneum. Renal transplant recipients can be affected by PMPF, which can occur in both native and transplanted kidneys several years following renal transplantation.

Primary renal liposarcoma simulating angiomyolipoma

Liposarcomas are infrequent malignant tumors of mesenchymal origin most commonly seen in the extremities. Although infrequent, these can develop as primary lesions in the soft tissue of the kidney, making them difficult to diagnose through imaging modalities alone. Primary renal liposarcomas are associated with poor prognoses, increasing the importance of timely and accurate diagnosis. In extremely rare instances, the tumor can arise directly from the fat in the epicenter of the kidney, disguised as an angiomyolipoma. In this article, we report the case of a 54-year-old female who was diagnosed with a well-differentiated liposarcoma of the kidney and underwent radical nephrectomy. Our objective is to evaluate unique radiological imaging findings and correlate with histopathological analysis to optimize diagnosis.