Renal replacement lipomatosis is a rare condition characterized by fatty tissue proliferation in the renal sinus and perinephric space with marked destruction/atrophy of renal parenchyma (due to chronic inflammation).
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Epidemiology
Associations
Renal replacement lipomatosis has been associated with aging, calculus disease (nearly 70% of cases), renal tuberculosis, and post-transplantation. It may also be associated with fibrotic changes to a varying degree.
An advanced stage of xanthogranulomatous pyelonephritis is another common association. It is considered to be on the extreme end of a spectrum with renal sinus lipomatosis being the mildest form.
Clinical presentation
Patients usually present with non-specific complaints like flank pain, fever, and weight loss. Sometimes a patient may directly complain of a vague flank mass.
Pathology
The condition is usually unilateral but can occur bilaterally.
Radiographic features
Plain radiograph
Usually shows calculi and displacement of the bowel.
Ultrasound
It is usually difficult to come to a diagnosis on ultrasound alone but it may show an echogenic mass suggestive of fatty tissue and calculi in the atrophic renal tissue.
CT
It is diagnostic and shows typical features including:
renal parenchymal atrophy/destruction
perinephric and hilar lipomatosis
renal calculi
perinephric abscesses that may extend to the psoas muscle
Differential diagnosis
Possible differential considerations include:
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