With increased awareness of health screening and the widespread use of imaging (ultrasound, CT , MRI, and even PET-CT), “cystic lesions” of the kidney are increasingly being detected. The most common benign renal cystic lesions are often seen, and patients are often asked how to rule out the few malignant renal cysts that are known as cystic kidney cancer.
Does a “cystic lesion” in the kidney necessarily mean “cystic kidney cancer”?
Does a cystic kidney lesion necessarily mean a cystic kidney cancer?
Cystic kidney lesions are classified into 4 types based on imaging:
- Type I is a simple renal cyst;
- Type II is also a benign lesion with 1 to 2 thin-walled compartments;
- Type III is a complex cystic lesion with indeterminate malignancy and may have homogeneous wall thickening and calcified nodules with irregular enhancement of the wall and compartments;
- Type IV is a cystic renal carcinoma, which presents with inhomogeneous thickening of the cyst wall, or with a thicker wall, with marked enhancement and visible nodules, or with soft tissue shadowing after enhancement.
The vast majority of cystic kidney cancers present as type III or type IV of the above staging, and most scholars believe that one criterion for defining cystic kidney cancer is that it has a cystic component of at least 75%, can occur at any age, is more common in middle-aged and older adults, and is more common in men than in women.
Bosniak’s classification of renal cysts
| Bosniak Classifieds | CT Features | Malignant potential | Management |
| Class I |
|
1.7% | No treatment or follow-up needed |
| Class II |
|
0 to 14% | No treatment or follow-up needed |
| II Class F |
|
18.5% | Close follow-up of changes in cyst size and imaging features |
| Three categories |
|
33% | Surgical excision or ablation |
| Four categories |
|
92.5% | Surgical excision or ablation |
What causes cystic kidney cancer?
The etiology and pathogenesis of cystic kidney cancer are not well understood. Related research reports focus on 4 possibilities:
- Tumor cells originate from renal tubular epithelial cells, and some of them grow as single or multiple capsules, gradually forming single or multiple-compartment cystic renal carcinoma of variable size, disconnected, plasma-filled and pseudo-enveloped, and some of the lesions may have calcification, and the tumor often has a pseudo-envelope;
- Nephrocalcinoma may have hemorrhage, necrosis, and cystic lesions resulting in pseudocyst formation due to inadequate blood supply, sometimes with calcification;
- Very few renal cancers originate from the epithelial tissue of the cyst and form tumor nodules or nests of cancer cells at the base of the cyst, with thin and regular walls and little calcification, which are easily confused with renal cysts;
- The tumor causes obstruction of the renal tubules or small arteries, forming a cyst, and when the cyst increases in size, the tumor is embedded in the cyst wall.
Currently, cystic renal carcinoma formed by the first two pathological bases accounts for 90% and cystic renal carcinoma caused by the latter two accounts for 10%, thus dividing cystic renal carcinoma into 4 subtypes based on pathological features:
- Single-compartment cystic kidney cancer
- Multi-compartmental cystic kidney cancer
- Simple cystic carcinoma
- Cystic renal carcinoma
In addition, some studies have suggested that age (≥50 years), obesity, proteinuria, microscopic hematuria, reduced glomerular filtration rate (GFR), and hypertension are independent risk factors for the malignancy of simple renal cysts.
What symptoms does cystic kidney cancer cause?
The symptoms of cystic kidney cancer are not specific and are largely similar to those of kidney cancer. Most patients are asymptomatic and are often discovered incidentally through physical examination or when they visit the doctor for other diseases, sometimes manifesting as low back discomfort, lumbar pain, carnal hematuria, abdominal mass, wasting, and fever. The low incidence of cachexia and paraneoplastic syndrome may be related to its low stage, low grade, and low malignancy.
How is cystic kidney cancer treated?
The prognosis of cystic kidney cancer is related to pathologic staging, histologic grading, histologic subtype of renal cell carcinoma, microvascular infiltration, tumor necrosis, and collecting system invasion. Most cystic renal carcinomas are confined to the kidney, with lower staging and grading and lower malignancy, and therefore have a good prognosis; however, the cystic lesion subtype of renal carcinoma is highly malignant and has a poor prognosis.
The choice of treatment mostly depends on the size of the tumor and the patient’s kidney function, with surgery being the preferred option, either kidney unit-preserving surgery or radical kidney cancer surgery. The surgeon will choose the surgical treatment according to the following:
- If cystic kidney cancer is suspected preoperatively, and the tumor is small (<4 cm in diameter), solitary, and located at the edge of the kidney, renal unit-preserving nephrectomy may be chosen directly according to the indications for kidney-preserving surgery;
- For type III complex cystic lesions, if the nature of the lesion is not clear and the size is large, surgical exploration can be performed and the surgical option can be decided based on intraoperative rapid freezing, with partial nephrectomy with preservation of the renal unit if benign or radical nephrectomy if malignant;
- For patients with a more aggressive treatment intention, radical nephrectomy can be considered for cystic kidney cancer if the diagnosis is clear and the contralateral kidney function is good.
In addition, there are minimally invasive surgical options such as radiofrequency ablation, cryoablation, and high-intensity focused ultrasound, which can be carefully chosen according to the patient’s specific situation.
What should I pay attention to after surgery for cystic kidney cancer?
There are no effective and feasible postoperative adjuvant treatment options recommended for cystic kidney cancer. In order to avoid postoperative recurrence or metastasis, the main emphasis is on the choice of surgical approach and strict adherence to the principles of tumor-free technique and non-incision during surgery. Some relevant postoperative considerations are the same as for renal cancer:
- Regular review: Return to the hospital for review 3 months after surgery and use contrast with caution. The examination includes renal function, chest X-ray, B ultrasound, CT, etc. The main purpose is to assess whether the residual renal function can meet the needs of the body after surgery and determine whether the tumor has metastasized or recurred, and then review regularly according to the doctor’s orders.
- Consciousness of protection: Disease treatment focuses on choosing drugs with low nephrotoxicity, regular testing of kidney function, and control and treatment of underlying diseases such as hypertension and diabetes.
- Adjustment of diet: It is recommended to focus on light, easy-to-digest food, avoid spicy and alcoholic drinks, as well as to maintain a good and positive state of mind, and to exercise appropriately to enhance physical fitness and improve one’s immune system. The Chinese medicine treatment can be done by visiting a Chinese medicine hospital according to your situation.