Perinephric myxoid pseudotumor of fat

Last revised by Bruno Di Muzio on 22 Jun 2024

Citation, DOI, disclosures and article data

Citation:

Botz B, Di Muzio B, Glick Y, et al. Perinephric myxoid pseudotumor of fat. Reference article, Radiopaedia.org (Accessed on 01 Jul 2024) https://doi.org/10.53347/rID-80779

DOI:

https://doi.org/10.53347/rID-80779

Permalink:

https://radiopaedia.org/articles/80779

rID:

80779

Article created:

4 Aug 2020, Bálint Botz ◉

Disclosures:

At the time the article was created Bálint Botz had no recorded disclosures.

View Bálint Botz's current disclosures

Last revised:

22 Jun 2024, Bruno Di Muzio ◉

Disclosures:

At the time the article was last revised Bruno Di Muzio had no financial relationships to ineligible companies to disclose.

View Bruno Di Muzio's current disclosures

Revisions:

5 times, by 5 contributors - see full revision history and disclosures

Systems:

Urogenital

Perinephric myxoid pseudotumor of fat is a very rare, benign, and slowly growing tumor, which can mimic renal cysts, retroperitoneal cystic tumors and liposarcomas alike. Due to its rarity and overlapping imaging appearance the diagnosis is almost always made by histopathological analysis.

Perinephric myxoid pseudotumor of fat is thought to be caused by irritation of the perinephric fat by pre-existing chronic kidney disease. It is most commonly encountered in elderly patients suffering from chronic kidney disease (end-stage renal failure, diabetes mellitus, chronic pyelonephritis) ^1,2.

Pathology

These tumors may involve one or both native kidneys or renal allograft. They predominantly comprise of normal adipocytes mixed with spindle cells and chronic inflammatory cells, with a small amount of fibromyxoid stroma. They lacks significant inflammation or necrosis, and cytologic atypia is notably absent ^1,2.

Radiographic appearance

These tumors present as masses involving the perinephric and renal sinus fat, and are largely composed of macroscopic fat. As such, imaging characteristics will reflect those of heterogenous fat tissue.

Ultrasound

heterogenous echogenicity with hypo and hyperechoic components
- smaller lesions may resemble an haemorragic cyst
CEUS may demonstrate irregular internal enhancement ¹

CT

low density on non-contrast CT
- may not be easily distinguished from a simple renal cortical cyst
- in larger lesions, irregular and more characteristically fat density areas can be encountered
low-grade postcontrast enhancement ¹

MRI

T1: heterogeneous intermediate to high signal
- T1 IP-OOP: macroscopic fat with signal loss on OOP
T2: hyperintense (myxoid component)
- the internal irregularity can be better depicted by applying fat suppression to the T2W sequence¹

Treatment and prognosis

These lesions typically demonstrate slow growth and are invariably benign. Due to their extreme rarity, surgical resection is the mainstay of therapy, whilst postoperative histology is typically needed for the final diagnosis ¹.