Renal vein thrombosis with pulmonary embolism

Case Discussion

Renal vein thrombosis (RVT) is defined as a thrombus causing an occlusion in the renal vein. RVT can present acutely or develop over time, causing an acute kidney injury. They can be due to infection, trauma, nephrotic syndrome, primary hyper-coagulability disorders, malignant renal tumours, external compression of the renal vein, or post-transplant complications ¹. Bilateral renal vein involvement is seen in two-thirds of cases, and the left renal vein is most likely to be involved ². Due to the occlusion in the renal vein, this results in a swollen and enlarged kidney, which can result in nephron damage. Patients present with symptoms of flank pain, haematuria, and reduced urine output.

RVT is a complication that is seen in patients with nephrotic syndrome, and it’s especially prevalent in patients who have membranous neuropathy, ranging from 5–60% ³. Other systemic causes for RVT include renal vasculitis, systemic lupus erythematosus, diabetic nephropathy, pregnancy, and oestrogen therapy. Local causes include malignant renal tumours such as renal cell carcinoma, which has the potential to spread into the renal vein; thrombus formation is seen in 4%–25% of cases ⁴.

There is an observed male predominance and an age-related factor, usually affecting people in their forties through their sixties. The pathogenesis of an RVT is based on Virchow’s triad, which is due to a combination of factors including stasis of blood flow, being in a hyper-coagulable state, and vascular endothelial damage. Narrowing or occlusion of the renal vein can be caused by a malignant (tumour thrombus) or bland (non-malignant) thrombus.

Chronic RVT develops slowly and does not have obvious symptoms at first. Acute renal vein thrombosis will present with symptoms of flank pain, gradually worsening proteinuria, haematuria, and worsening renal function ⁵. Various imaging modalities have advantages over others. For instance, ultrasonography (US) delivers both qualitative and quantitative information in real time. Doppler US, in particular, offers the added benefit of providing real-time renal vascular flow information ⁶. Computed tomographic angiography (CTA) and magnetic angiography (MRA) provide anatomical information, which could be beneficial for identifying anatomical variants. Specific CTA imaging protocols can be used to assess venous structures. Computed tomography (CT) offers advantages by providing rapid image acquisition, high spatial resolution, and postprocessing capabilities that can yield additional information about renal vasculature ⁶. On the axial CT, there is a filling defect that points to a total occlusion of the right renal vein and an enlarged right kidney with perinephric fat stranding and oedema. Depending on the imaging modality, the renal vasculature can be difficult to assess.

Non-invasive treatment options for RVT include anticoagulation therapy; early initiation in symptomatic patients can prevent propagation and additional complications. In certain cases, invasive treatments such as thrombectomy and/or thrombolysis are employed to preserve kidney function.

In this case, the thrombus had extended into the inferior vena cava (IVC). The leading cause of IVC obstruction is bland thrombus, which can increase the risk of pulmonary embolism. IVC thrombi can be malignant or non-malignant in origin. Imaging plays an important role in detection and differentiation. Bland thrombus is differentiated from tumour thrombus by a lack of enhancement, continuity with adjacent structures, and uptake of fluorodeoxyglucose on positron emission tomography (¹⁸F-FDG-PET) ⁷. A tumour thrombus is more likely to be seen with vessel expansion. Abnormalities in Virchow’s triad are the mechanisms that can lead to the development of a bland thrombus. CT with contrast is the most common imaging modality for identifying IVC pathology and anatomical variation ⁸. Specific MR imaging techniques have been shown to be more reliable than CT for evaluating tumour thrombus ⁹.

A deadly complication of venous thromboembolic disease is acute pulmonary embolism (PE). This patient had pulmonary emboli in the lower lobe segmental pulmonary arteries and a left lower lobe pulmonary infarction.