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).

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:

• lipoma

  • renal lipoma

  • perirenal lipoma

• retroperitoneal liposarcoma

• renal angiomyolipoma

• xanthogranulomatous pyelonephritis