replacement lipomatosis (RRL)

Renal replacement lipomatosis (RRL)

RRL is a more aggressive form of RSL usually occurring unilaterally.

Aetiology

There is marked proliferation of fatty tissue within the renal sinus and hilum extending to the perirenal space. This occurs usually secondary to destruction or atrophy of renal parenchyma due to longstanding inflammation. This condition most commonly follows calculus disease and also has been associated with aging, renal TB and postrenal transplantation.

As in RSL compensatory or inflammatory fatty proliferation secondary to renal loss are postulated as mechanisms of injury.

It has been postulated that renal calculi trigger a process of hydronephrosis and chronic inflammation which in turn results in parenchymal atrophy and fibrofatty replacement in the sinus.

Clinical signs and symptoms

Unlike RSL patients with RRL are usually symptomatic and present with recurrent flank pain, fever, and weight loss and mass per abdomen.

Ultrasound

RRL appears as a hyperechoic mass in the renal fossa often extending into the perinephric space.

The kidney is often enlarged with atrophic parenchyma with or without visualization of a calculus.

Computed tomography

Helps make accurate diagnoses. It confirms the fatty nature of the pelvic lesion and differentiates it from nonfatty lesions of the pelvis (Fig. 10.12.2.6.2). CT scan defines the extent of the fatty proliferation in the renal fossa and in perinephric area, detects associated conditions such as hydronephrosis, renal/ureteric calculi and helps assessing the degree of parenchymal atrophy. Perirenal fat stranding and dilated, thick-walled and enhancing ureters have also been described.