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Imaging features of perinephric myxoid pseudotumors of fat

  • Kidneys, Ureters, Bladder, Retroperitoneum
  • Published:
Abdominal Radiology Aims and scope Submit manuscript

Abstract

Objective

Retrospectively evaluate multimodality imaging features of perinephric myxoid pseudotumor of fat (PMPTF).

Methods

Institutional cases of PMPTF with CT, MRI and/or ultrasound evaluation from 1/1/2020 to 9/1/2023 were retrospectively reviewed. Patient demographics and clinical history were reviewed, and imaging features recorded.

Results

14 patients with pathologically-proven PMPTF were identified (11 M, 3 F; mean age 66.7 ± 17.0 years; range 40–87 years). Three patients (18%) had bilateral lesions; a total of 17 PMPTFs were reviewed. 15/17 (88%) were biopsy-proven; two cases were diagnosed by imaging only in patients with a contralateral biopsy-proven PMPTF. All evaluable specimens were negative for MDM2 amplification. 11/17 (65%) occurred in patients with renal disease, including 4/17 (24%) in patients with renal transplant. 100% (17/17) had CT, 11/17 (65%) MRI, and 6/17 (35%) ultrasound. The mean largest lesion dimension was 10.9 ± 4.6 cm (range 4.3–17.0 cm). Of cases involving native kidneys, 7/13 (54%) presented as multifocal perinephric masses and 5/13 (38%) as a solitary perinephric mass. All four transplant cases presented as infiltrative-appearing masses involving the renal sinus with lesser perinephric involvement. 14/17 (82%) lesions contained macroscopic fat on CT and MRI and 3/17 (18%) showed no macroscopic fat, all involving renal transplants. All cases with MRI demonstrated T2 hyperintensity with signal dropout on opposed-phase imaging. 11/13 (85%) PMPTF showed no or equivocal CT enhancement. Enhancement was better seen on MRI in all cases evaluated by both CT and MRI. Of the six PMPTFs imaged by ultrasound, four (67%) were heterogeneously hypoechoic and two (33%) had mixed regions of hypo-, iso- and hyperechogenicity relative to adjacent renal parenchyma.

Conclusions

PMPTF is a rare, benign, and underrecognized lesion that may mimic malignancy, particularly retroperitoneal well-differentiated liposarcoma. The imaging features of this unusual pseudosarcoma differ in native and transplanted kidneys. Improved awareness of this entity will facilitate appropriate patient management and avoid unnecessary intervention.

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Authors and Affiliations

  1. Department of Radiology, Mayo Clinic, Charlton Building North, 1st Floor, 200 First Street SW, Rochester, MN, 55905, USA

    Stephen M. Broski, Jennifer A. Knight & Doris E. Wenger

  2. Department of Laboratory Medicine and Pathology, Mayo Clinic, Phoenix, AZ, 85054, USA

    Brandon T. Larsen

  3. Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN, 55905, USA

    Andrew L. Folpe

  4. Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN, 55905, USA

    Doris E. Wenger

Authors
  1. Stephen M. Broski
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  2. Jennifer A. Knight
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  3. Brandon T. Larsen
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  4. Andrew L. Folpe
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  5. Doris E. Wenger
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Correspondence to Stephen M. Broski.

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Broski, S.M., Knight, J.A., Larsen, B.T. et al. Imaging features of perinephric myxoid pseudotumors of fat. Abdom Radiol (2024). https://doi.org/10.1007/s00261-024-04294-9

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  • DOI: https://doi.org/10.1007/s00261-024-04294-9

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