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Published on: December 9, 2022
Imaging features of perinephric myxoid pseudotumors of fat
Stephen M Broski1, Jennifer A Knight2, Brandon T Larsen3
1Department of Radiology, Mayo Clinic, Charlton Building North, 1st Floor, 200 First Street SW, Rochester, MN, 55905, USA. Broski.stephen@mayo.edu.
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.
Insights
Perinephric myxoid pseudotumor of fat (PMPTF) is a rare, benign lesion that can mimic malignancy. Imaging features vary between native and transplanted kidneys, necessitating awareness to avoid misdiagnosis and unnecessary interventions.
Area of Science:
- Radiology
- Oncology
- Pathology
Background:
- Perinephric myxoid pseudotumor of fat (PMPTF) is an uncommon entity.
- PMPTF can be mistaken for malignant retroperitoneal tumors, such as well-differentiated liposarcoma.
- Understanding the imaging characteristics of PMPTF is crucial for accurate diagnosis.
Purpose of the Study:
- To retrospectively evaluate the multimodality imaging features of perinephric myxoid pseudotumor of fat (PMPTF).
- To differentiate PMPTF from malignant mimics based on imaging findings.
- To identify imaging characteristics specific to PMPTF in native versus transplanted kidneys.
Main Methods:
- Retrospective review of institutional cases of PMPTF with CT, MRI, and/or ultrasound evaluations between January 1, 2020, and September 1, 2023.
- Analysis of patient demographics, clinical history, and recorded imaging features.
- Pathological confirmation of PMPTF in most cases, with some diagnosed via imaging alone in specific contexts.
Main Results:
- 14 patients (11 male, 3 female; mean age 66.7 years) with 17 PMPTF lesions were analyzed.
- Lesions commonly contained macroscopic fat (82%) and showed T2 hyperintensity with signal dropout on opposed-phase MRI.
- Imaging features differed between native kidneys (multifocal or solitary masses) and transplanted kidneys (infiltrative masses).
Conclusions:
- PMPTF is a rare, benign lesion that can mimic malignancy, particularly liposarcoma.
- Distinct imaging features exist for PMPTF in native and transplanted kidneys.
- Increased awareness of PMPTF imaging characteristics can prevent misdiagnosis and unnecessary interventions.
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