Chyluria

Chyluria is the finding of chyle in the urine, and is due to a pathological communication between the lymphatic system and the renal tract. It is most commonly found in South-Eastern Asia, where it is due to lymphatic filariasis, but in the non-tropical world it is most commonly encountered after trauma or surgery.

Epidemiology

In the tropics the commonest cause is lymphatic filariasis and other parasites, although it is still rare. In the Kinmen Islands in China, an area endemic with filariasis, only 0.7% population had chyluria ³.

It is a rare phenomenon outside the tropics. In the setting of renal surgery, it has been found in 3.2-5.4% patients post-partial nephrectomy. It was never found status post complete nephrectomy ^1,2. No correlation has been found between the stage of the renal cell carcinoma and the finding of chyluria post surgery ².

Clinical presentation

Most patients are asymptomatic. Patients sometimes complain of a milky appearance to the urine. If chyluria is chronic then hypoproteinaemia, hypolipidaemia, and immunodeficiency have been reported. Nephrotic syndrome may result.

Microscopic urinalysis shows microglobules of fat.

Pathology

After nephron-sparing surgery it is thought that the normally anatomically-separate perirenal lymphatics and pelvicalyceal system may be brought into contact and a fistulous communication can result.

In filariasis the Wuchereria bancrofti parasite obstructs the renal lymphatics leading to over-spill of chyle into the urinary tract.

Aetiology

• parasitic infection
  • lymphatic filariasis (especially Wuchereria bancrofti)
  • echinococcosis
  • cysticercosis 
• non-parasitic infections
  • tuberculosis
  • leprosy
  • fungi
• surgery
  • partial nephrectomy
• trauma
• malignancy
  • e.g. prostate carcinoma
• pregnancy
• aortic aneurysm

Radiographic features

Its appearance has only been described on cross-sectional imaging.  In view of its lower density, the fatty chyle forms a supernatant on top of the heavier urine in the bladder, forming a fat-urine layer. 

CT

If a CT is reviewed too hastily then the lower density fat lying superficial to the urine may be mistaken for iatrogenic gas, especially if there is a urinary catheter in situ. However on a lung window it will clearly be seen that the more superficial layer is not gas. A region of interest over the layer will demonstrate that the CT density is that of fat, and not of gas.

MRI

The typical MRI appearances of fat will be seen as a layer floating on top of the normal fluid signal urine.

Treatment and prognosis

Usually a conservative approach suffices. In 50% parasitic cases spontaneous remission of the chyluria occurs ³.

Occasionally however when patients experience the sequelae of chronic chyluria, such as hypoproteinaemia, surgical ligation and stripping of the renal lymphatics is required.

Differential diagnosis

Fat can also rarely be found in the bladder when there has been

• transurethral injection of lubricants/oils. Generally this can be differentiated: differentiated on the history.history
• bladder rupture⁴
• intramural bladder fat: differentiate on imaging appearance