Renal peripelvic lymphangiectasia after bilateral renal vein thrombosis

Abstract

Renal peripelvic lymphangiectasia (RPL) is one of the rare conditions that mimic renal cysts. Its physiopathology remains unknown, but an association with renal vein thrombosis has been reported. We share the case of a male patient in his 20s suffering from antiphosphlipid syndrome. The patient was hospitalised for thrombosis of the inferior vena cava (IVC) extending from the iliac veins to the level of renal veins. Consecutive CT and clinical follow-up over the course of 14 years showed the development of numerous retroperitoneal venous collaterals and the apparition of several bilateral peripelvic cystic lesions after extensive thrombosis of the IVC and both renal veins. The renal function remained normal throughout the follow-up. We suggest that the development of RPL is secondary to bilateral renal vein thrombosis. The presumed mechanism would be an increased hydrostatic pressure in the kidney capillaries leading to a more important interstitial fluid drainage by the lymphatic system. To our knowledge, this is the first well-documented case of renal vein thrombosis followed by RPL, contrasting with the previous hypothesis that compression by the lymphangiectasia could cause the thrombosis.

Background

Renal peripelvic lymphangiectasia (RPL) is one of the rare conditions that often mimic renal cysts on imaging. It is a benign condition, almost always an incidental finding, and no special management is required. Few cases of complicated RPL were reported, two of them describing an association with bilateral renal vein thrombosis.^{1 2} We present the first case of RPL with 14 years of follow-up suggesting that bilateral renal vein thrombosis may be the primum movens of RPL.

Case presentation

We share the case of a male patient in his 20s suffering from a severe form of antiphospholipid syndrome and a history of recurrent thrombotic events.

The initial presentation was bilateral pain and oedema of the lower limbs for which a contrast-enhanced CT (CECT) was performed and demonstrated bilateral iliac veins thrombosis. CT showed acute thrombosis of the inferior vena cava (IVC), extending from the iliac confluence to the level of the renal veins ostia (figure 1). The kidneys, especially the pelvic regions, were normal. At that time, kidney function was normal (creatinine 78 µmol/L, glomerular filtration rate (GFR) >60 mL/min/1.73 m²). Urinalysis showed no microscopic proteinuria or haematuria. There were no other relevant laboratory findings. Because the clinical evolution was favourable after therapeutic intravenous anticoagulation, endovascular intervention was not considered. Long-term therapeutic anticoagulation with acenocoumarol was initiated.

Figure 1.

Initial CECT (40 s after the initiation of contrast injection): Axial plane (A) shows normal kidneys with patent right renal veins (arrow). Infrarenal IVC is thrombosed (arrowhead). Coronal plane (B) with maximum intensity projection shows the thrombosis extending from both iliac veins (arrowheads) to the infrarenal IVC at the level of renal veins (arrows).

Four years later, the patient was admitted for an acute postprandial abdominal pain, in the setting of anticoagulant discontinuity (because of poor treatment compliance). A new CECT showed acute thrombosis of the portal vein extending to the superior mesenteric and the splenic vein. In addition, it showed chronic thrombosis and atrophy of the IVC and renal veins, with the development of numerous retroperitoneal venous collaterals, along with important perirenal and pararenal fat stranding. Both kidneys were swollen with delayed enhancement (persistant corticulomedullary phase despite an acquisition 80 s after intravenous injection of contrast material). Bilateral small cystic peripelvic lesions had also appeared (figure 2). Laboratory findings showed that kidney function remained normal (creatinine 66 µmol/L, GFR >60 mL/min/1.73 m²). Intravenous therapeutic anticoagulation treatment was started and symptoms improved. Oral anticoagulation was then resumed with better compliance.

Figure 2.

CECT (40 s) 4 years after the initial presentation: Axial plane (A) and coronal reformat (B) reveal swollen and enlarged kidneys with parenchymal thinning. Note the development of retroperitoneal venous collaterals (arrowheads) and perirenal fat stranding due to bilateral renal vein thrombosis. Small cystic structures are seen around calices corresponding to lymphangiectasia (arrows). Acute portomesenteric thrombosis (asterisk) was accountable for the new onset abdominal pain.

Six years after the initial presentation, a follow-up CT showed increased size of these cystic peripelvic lesions with no filling with contrast material on late excretory phase acquisition (figure 3). Subsequent routine CT studies (9 and 10 years after the initial presentation) demonstrated subtle worsening of parenchymal atrophy of both kidneys but otherwise stability of the cystic peripelvic findings (figure 3). MR performed in 9 years after the initial presentation also confirmed that these cystic lesions contain multiple thin septa resulting in a cystic network around calices and pelvic structure (figure 4). Kidney function remained normal (creatinine 100 µmol/L, GFR 83 mL/min/1.73 m²). Blood pressure remained normal.

Figure 3.

CECT 6 years after the initial presentation. Corticomedullary-phase CECT (40 s after the initiation of contrast injection) (A) shows progressive enlargement of the cystic peripelvic lesions (arrows). Late excretory-phase CECT (5 min after contrast injection) (B) reveals the excretion of contrast material through non-dilated calices and pelvis (arrrowheads) surrounded by lymphangiectasia.

Figure 4.

CECT (40 s) and MRI 10 years after the initial presentation. Coronal reformat CECT (A) demonstrates the renal peripelvic lymphangiectasia as multiple, confluent cysts (asterisks) originating from the renal sinus. Axial (B) and coronal (C) T2-weighted images offer better delineation of the multiple thin septa (arrows) and connections between the cystic lesions.

Final diagnosis based on imaging characteristics was RPL after bilateral renal vein thrombosis.

Investigations

Because of the risk of complication (eg, bleeding or urinoma) along with the reassuring pathognomonic appearance at MR, no puncture or sampling were ordered.

Differential diagnosis

Differential diagnosis of hypodense lesions in the renal pelvis at CT includes cystic and non-fluid-containing lesions: hydronephrosis (contrast-filling on excretory phases imaging), simple parapelvic cysts (non-communicating cysts), urinoma (contrast-filling on excretory phases imaging), lymphocele (medical history of retroperitoneum surgery), multilocular cystic nephroma (often with contrast-enhancing septa), polycystic kidney disease (association of intra-parenchymal renal, liver and pancreatic cysts of varying size), lymphoma (soft tissue signal at MR) or nephroblastomatosis (in children).

The multiloculated communicating cystic MR aspect and the benign course over time are characteristic of RPL. Therefore, this diagnosis can be confidently achieved by imaging, as in our case.

Treatment

It is possible to treat symptomatic RPL with minimal invasive percutaneous aspiration and sclerotherapy [3]. In our case, the condition was asymptomatic and thus no intervention was required.

Outcome and follow-up

Subsequent follow-up showed no worsening of the renal function. RPL was stable overtime. Antiphospholipid syndrome is still in remission under specific therapies.

Discussion

Renal lymphangiectasia (RL) is a rare condition that often mimics renal cysts or hydronephrosis. This benign condition can affect children and adults. It accounts for about 1% of all lymphatic malformation.

These fluid-containing lesions correspond to the accumulation of lymph in the renal lymph ducts, which become ectatic and form simple or multiloculated cystic lesions around the kidney (perinephric lymphangiectasia), inside the kidney parenchyma (intrarenal and renal parapelvic lymphangiectasia) or around the calices and pelvis (RPL).³

RL is mostly asymptomatic and discovered as an incidental finding. Rarely, because of distension of the renal spaces and fascia, bleeding or fistulation in the peritoneal cavity, it may also present with pain, increased abdominal volume, hematuria, ascites, oedema of the lower limbs, arterial hypertension, renal vein thrombosis and chyluria.⁴

On ultrasound, RL appears as well-circumscribed anechoic unilocular or multilocular cystic lesions, centred on the renal sinus for the peripelvic subtype (RPL), that correspond to the enlarged lymphatic channels.⁵ CT appearance is similar to unilocular or multilocular fluid-filled masses, with thin or irregular and thick walls. MR findings confirm the cystic nature of the lesions (hyperintense on T2-weigthed sequences and hypointense on T1-weighted sequences). The better contrast resolution of MR enables the visualisation of pathognomonic thin multiple septa within the cysts. Percutaneous fluid aspiration is rarely performed in asymptomatic patients; it would show mostly lymphocytes, small amount of fat and protein and possibly high levels of renin.⁶ Lymphoscintigraphy may be useful to provide clear evidence of the abnormal lymphatic flow. In case of haemorrhagic complications, the cystic cavity content may become heterogenous with the typical density and signal of blood at CT and MR, respectively.^{4 7} Interventional radiology offers minimal invasive treatment (percutaneous drainage with sclerotherapy) in order to avoid the need for marsupialisation, which is associated with a risk of haemorrhage and may result in nephrectomy.^{8 9}

The association between renal vein thrombosis and RPL has only been reported in two published case reports.^{1 2} Riehl et al hypothesised that the renal vein thrombosis occurred as a consequence of the mass effect of the lymphangiectasia on the renal veins.²

In our case, the consecutive imaging studies showed that the renal vein thrombosis occurred before the development of lymphangiectasia. This hypothesis is upheld by anatomical and physiopathological considerations. Indeed, lymphatic vessels throughout the body serve a vital function in draining fluid and macromolecules from the interstitial space as well as returning them to the systemic circulation to avoid accumulation of interstitial fluid that could impair oxygen delivery to the tissues. This general concept also applies to the kidneys. Under physiological conditions, the interstitial fluid is absorbed by the lymphatic capillaries in the kidney, towards the hilum or the renal capsule. In the renal sinus, interconnected trunks drain the lymphatic fluid to the retroperitoneal lymph nodes and finally to the thoracic duct.¹⁰ Interestingly, a few cases of RL have been described in kidney graft after transplantation, presumably because of defective lymphatic connections.¹¹ According to the Starling equation, transendothelial filtration increases with the hydrostatic intravascular pressure. It has been demonstrated that the rise of venous pressure upstream to lower limb deep venous thrombosis causes an elevation of transendothelial filtration and leads to higher lymphatic transport and leg swelling.^{12 13} A similar phenomenon surely occurs after renal vein thrombosis. Based on this, we suggest that the rise of hydrostatic pressure in renal capillaries secondary to renal venous thrombosis is responsible for an increase of lymphatic drainage, leading to the development of lymphatic ectatic channels depicted as lymphangiectasia such as in our case.

Interestingly, Meredith et al reported a case of RL growth during pregnancy. They postulated that the physiological increase of glomerular filtration during pregnancy causes a more important lymphatic flow and leads to the increase of the cystic lesion, in keeping with our theory.¹⁴ Finally, our hypothesis is also supported by the development of intestinal lymphangiectasia after cardiac Fontan shunting. This palliative surgical procedure used in children with univentricular hearts involves diverting the venous blood from the inferior vena cava and superior vena cava to the pulmonary arteries without passing through the morphological right ventricle causing a rise of systemic venous pressure.¹⁵

Although we report an association of renal vein thrombosis with RPL and shed a new light on the physiopathological mechanism, no conclusion can be made based on this single case report. Raised attention about this association will enhance further research.

Learning points.

• Renal peripelvic lymphangiectasia (RPL) is a rare condition that often mimics renal cysts.

• This cystic lesion corresponds to the accumulation of lymph in the renal lymph ducts, forming simple or multilocular cysts around the kidney (perinephric lymphangiectasia), inside the kidney parenchyma (intrarenal and renal parapelvic lymphangiectasia) or around the calices and pelvis (RPL).

• This condition is benign and most of the time asymptomatic. In rare cases, interventional radiology may offer minimal invasive treatment (percutaneous drainage with sclerotherapy).

• Renal vein thrombosis can be associated with RPL. Further research is needed to determine the exact physiopathological mechanism.

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