Pseudosarcomatous fibroblastic/myofibroblastic proliferation in perinephric adipose tissue adjacent to renal cell carcinoma: a lesion mimicking well-differentiated liposarcoma

Abstract

Cytologically atypical stromal cells were found in the perinephric adipose tissue, mimicking well-differentiated liposarcoma in 12 of 59 (20%) consecutive nephrectomy specimens that were resected for renal cell carcinoma. Morphologically, the atypical cells included enlarged, hyperchromatic spindle cells and floret-type multinucleate cells. Of 59, 10 (17%) renal cell carcinomas invaded through the renal capsule into the perinephric adipose tissue. Of these cases, three (30%) contained the aforementioned atypical cells. In contrast, 9 of 49 cases without extrarenal invasion (18%) contained the atypical stromal cells. Of the 12 cases with atypical stromal cells, 3 (25%) were associated with extrarenal involvement. The atypical spindle cells exhibited focal to variable positivity for smooth muscle actin and desmin in 3 of the 14 cases (including two cases from our consultation files) each. Cytokeratin AE1/AE3, cytokeratin Cam 5.2, cytokeratin 7, epithelial membrane antigen, and S-100 were negative in all cases. Amplification of MDM2 gene region, which is commonly observed in welldifferentiated liposarcoma, was absent by fluorescence in situ hybridization (FISH) in the atypical stromal cells. Immunohistochemistry and FISH suggest that the atypical cells are most consistent with reactive fibroblasts/ myofibroblasts. Recognition of these atypical fibroblasts/myofibroblasts may help in avoiding the potential pitfall of misdiagnosing them as well-differentiated liposarcoma.

Perinephric myxoid pseudotumour of fat – first described case in allograft kidney, a mimicker of malignancy

“…Perinephric soft tissue mass lesions with adipose component are extremely rare, and encompass a large differential diagnosis ranging from benign to malignant. [1][2][3][4][5][6] These tumours are often discovered incidentally by radiological imaging techniques. Management of such lesions is clinically challenging.…”

Massive Localized Lymphedema in an Unreported Location (Retroperitoneum)

“…Bizarre polylobated hyperchromatic stromal cells of liposarcoma usually contrasts with multilobated reactive stromal fibroblasts in MLL that show open, relatively pale chromatin. Atypical reactive stromal cells in the perinephric soft tissue adjacent to the kidney have also been described in cases of renal cell carcinoma [ 11 ]. Kurt H, et al [ 2 ] have noted that dystrophic microcalcifications can mimic hyperchromatic nuclei in some MLL cases.…”

Renal cell carcinoma with sclerosing lipogranulomatous inflammation mimicking advanced disease

“…There have been a few reports of fibrosis in association with RCC requiring immunohistochemistry to distinguish from liposarcoma. 1,2 There has also been a report of fat necrosis in association with RCC in a transplant kidney which radiologically was suggestive of extracapsular extension. 3 Benign retroperitoneal fibrosis in association with RCC can occasionally simulate metastatic disease.…”