Teaching Case

The patient had undergone left-sided partial nephrectomy due to renal cell carcinoma (RCC). There was no metastatic disease, and the operation was considered radical. CT was performed as part of the post-operative control program 18 months after the operation. At this time the patient was without symptoms.

Contrast-enhanced CT of the chest, abdomen and pelvis was performed. There were no signs of relapse of RCC, but normal post-operative findings after partial nephrectomy in the left kidney were observed (Figure 1). No metastases were present.
As an incidental finding floating fat was observed within the urinary bladder with a distinct fluid-fluid level (Figure 2), in keeping with chyluria. The diagnosis of fat was established by measurement of the HU value (Figure 2c). Furthermore, the observed structure in the bladder was not dark enough to represent air.

Chyle is a lymphatic fluid rich in chylomicrons that normally flows from the lymphatic capillaries to the larger lymphatic vessels and eventually drains into the left subclavian vein through the thoracic duct. When an abnormal connection between the lymphatic vessels and the urinary tract develops, chyluria can occur [1, 2].

Worldwide the most common cause of chyluria is parasitic infestation with filariasis which cause obstruction and stasis in the lymphatic system [3]. Other causes of chyluria are trauma and surgery. It is believed that chyluria is more common after partial than complete nephrectomy. The proposed mechanism is that a fistulous connection between the lymphatics and urinary collecting system occurs at the site of operation [3, 4]. In the present case chyluria was also detected in a patient with previous partial nephrectomy.

Chyluria is most often asymptomatic and an incidental finding on follow-up CT after surgery [3]. If symptomatic patients will report that they observe a milky and fatty looking urine. Proteinuria will be present and if this is severe hypoalbuminemia, weight loss and malnutrition develops [1, 5]. Treatment of the chyluria with surgery or sclerotherapy should be reserved for such severe cases [2]. In asymptomatic patients an observational approach should be applied. In the litterature most cases of non-parasitic chyluria have shown spontaneous remission during a period of 6 – 12 months [4, 5]. The patient in the present case was asymptomatic and no further investigations or interventions were deemed necessary.
The purpose of this case is to raise focus on chyluria as a rare complication to partial nephrectomy. As the number of partial nephrectomies increase these years, it can be expected to see more patients with chyluria, and radiologists should be aware of this entity. It is especially important that the fat-fluid level in the bladder is not mistaken for an air-fluid level, and the patient undergoes investigations for bladder fistulas.

In conclusion, chyluria is a rare finding after renal surgery.