Renal malformation tumor, a relatively common benign tumor of the kidney, resembles renal cancer in its clinical presentation and is therefore easily misdiagnosed as renal cancer. However, it also has its characteristic features to differentiate, and there are many differences in the treatment of the two.
What is renal malformation tumor?
Renal malformation tumors, also known as “renal vascular smooth muscle lipomas,” are composed of abnormal growths of blood vessels, smooth muscle, and adipose tissue in varying proportions and have the following characteristics:
Benign, but fatal!
Renal malformation tumor is a benign tumor of the kidney, but if left unattended, larger renal malformation tumors can lead to rupture and bleeding, which is an emergency and equally life-threatening. The number of reports of malignant epithelioid renal malformations has increased in recent years and needs to be well recognized.
The incidence is significantly higher in women than in men
Renal malformation tumor is a benign genetic disease that may be associated with inactivation of the X chromosome and mutations or heterozygous deletions, which may explain the significantly higher incidence in women than in men. A single-center study in China reported a male-to-female ratio of 1:7 in patients with renal malformation tumors.
Patients tend to present with low back and abdominal pain and hematuria
Renal malformation tumors are benign growing tumors that are slow-growing and non-destructive, and their clinical presentation is related to the size and location of the tumor and the presence or absence of ruptured bleeding.
A high percentage of patients present with pain or discomfort in the lower back and abdomen, and less frequently with hematuria. When the tumor is large and compresses the stomach and duodenum, etc., symptoms of compression such as nausea and vomiting may also occur.
How to diagnose renal malformation tumor?
Due to the availability of CT and MRI, the majority of renal malformations are found incidentally during physical exams or tests for other diseases, and only a minority of patients are seen for symptoms such as hematuria. Therefore, the clinical presentation has limited diagnostic value for renal malformations.
The majority of renal malformations are diagnosed by imaging, such as B ultrasound, CT, and MRI, because they generally contain a fatty component.
The majority of renal malformations are diagnosed by imaging, such as B ultrasound, CT, and MRI.
B ultrasound often shows moderately strong echogenic areas within the mass due to the presence of a fat component in a typical malformation tumor, whereas in renal cancer, fat is rarely present and therefore appears as moderate to low echogenicity. The most important thing is that the patient’s body is not only a good example, but also a good example of how to make sure that the patient’s body is not too weak.
CT has been the first choice for renal malformations because of its excellent sensitivity and specificity, as well as its efficiency and speed. Even in masses smaller than 2 cm, the presence of fat can be distinguished from the image.
Magnetic resonance imaging (MRI) has a unique diagnostic value for renal malformations with low fat content. In addition, compared with CT, MRI is free of the risk of ionizing radiation and does not require enhanced scanning, making it particularly suitable for patients with renal insufficiency.
How to treat renal malformation tumors?
Conservative or surgical treatment may be used, depending on the patient:
Close observation
Some patients with small masses and high surgical risk may be treated conservatively without surgery. Because conservative treatment does not fundamentally remove the lesion, the incidence of complications such as rupture and bleeding secondary to infection and the rate of late surgery are high and require regular review and follow-up. The follow-up schedule is as follows:
- A renal malformation tumor smaller than 4 cm can be followed up with observation, and a B-ultrasound or CT review is recommended every 6 months;
- A renal malformation tumor larger than 4 cm can be followed up with observation.
- A renal malformation tumor larger than 4 cm has a significantly increased risk of rupture and bleeding, especially in women who are pregnant, because the changes in hormone levels during pregnancy may cause the tumor to increase rapidly and lead to rupture and bleeding, which may be life-threatening.
Surgical treatment
The primary goals of surgical treatment of renal malignancies are to eliminate symptoms, protect kidney function, and prevent spontaneous rupture and bleeding. The treatment method needs to be decided according to the size and location of the tumor, clinical symptoms, and the family’s wishes. Currently, the common surgical treatment methods include arterial embolization, renal unit preservation surgery, and nephrectomy.
What conditions require surgery?
It is generally accepted that surgery should be performed in patients with tumors <4 cm in diameter with clinical symptoms and a predisposition to malignancy, or in patients with tumors ≥4 cm in diameter, with or without symptoms. An aggressive treatment plan is recommended, with surgery to preserve the renal unit being the preferred option. The reasons are as follows:
- Tumors are small but still have a greater incidence of rupture and bleeding;
- Progressively enlarged tumors may compress renal tissue leading to renal atrophy or compression of adjacent tissues causing damage to other organs;
- There are reports of misdiagnosis of renal cancer as renal malformation tumor that delayed the disease (previous experience);
- Some tumors continue to grow during follow-up and eventually require surgical treatment, while some tumors are short-lived and grow faster, and those with long follow-up periods often miss the best time for treatment;
- When the tumor is small, surgery is safer and facilitates the preservation of kidney tissue for surgical completion, whereas when the tumor is large, the probability of forced removal of the kidney increases.
Preferred: kidney unit-preserving surgery
The most widely used procedure to preserve the renal unit is laparoscopic partial nephrectomy, which is minimally invasive and greatly improves the rate of kidney preservation, maximizes renal function, and improves the quality of patient survival by reducing the time of renal tract block, operative time, bleeding, and postoperative hospital stay.
Robotic partial nephrectomy is also an emerging safe, effective, and reliable treatment, but it is expensive and also demanding on the surgeon. It is currently performed in some local mega tertiary hospitals in China, but for renal malformations >7 cm in diameter, multiple, and complex sites, robotic-assisted laparoscopic surgery is clearly advantageous.
If preservation of the renal unit is not possible because of the undesirable location of the tumor, renal subtotal surgery or embolization can be considered. Sometimes the peritumor is extremely vascular and intraoperative bleeding is not easily controlled and the entire kidney needs to be removed.
Arterial embolization
Renal artery embolization with ethylene-vinyl alcohol copolymer is a feasible, safe, and effective method to perform selective renal artery embolization in renal malformation tumors that have ruptured and bled, which can provide immediate hemostasis, stabilize the disease, avoid nephrectomy, and maximize the protection of normal renal function. The disadvantage is that after embolization, some patients also have re-ruptured bleeding, requiring secondary embolization and surgical treatment.
For large-diameter renal malformation tumors in preparation for surgery, preoperative embolization reduces intraoperative bleeding, shortens operative time, and results in faster postoperative recovery, but increases patient spending and likewise carries the risk of unsuccessful arterial embolization procedures, thus requiring secondary embolization.
When is arterial embolization not indicated? — Interventional embolization is not preferred if the CT-enhanced scan suggests a tumor with a lack of blood supply, that is, if the tumor is not rich in local blood flow.
Percutaneous ablation
Percutaneous ablation is not yet widely used and is usually limited to asymptomatic patients with small tumors. Patients who undergo radiofrequency ablation consist of two parts:
- One group is those with initially suspected renal cell carcinoma, followed by lumpectomy with biopsy suggestive of renal malformation tumor;
- The other group is those who underwent radiofrequency ablation directly after a definitive imaging diagnosis.
The low rate of receiving secondary ablation, tumor recurrence, and complications after radiofrequency ablation also suggests that ablation therapy still has some promise for use.
Drug therapy
For patients with renal malignancies that cannot undergo surgery, embolization, or ablation, oral mammalian target of rapamycin (mTOR) drugs, such as sirolimus and everolimus, are available to stop further tumor growth and even shrink the tumor.