Renal cyst: diagnostic rules
Renal cysts are always fluid-filled; they lack a true parenchymal cavity. An important rule: renal cysts must not be biopsied. First, aspiration yields only fluid, which precludes adequate histological examination. Second, if the contents are malignant, capsule puncture can lead to the spread of tumor cells throughout the body and the development of carcinomatosis. This restriction applies not only to the kidneys, but also to other organs where a malignant process is suspected, such as the breast.
Tympanites in the hypochondriac region in clinical practice is usually associated not with renal pathology, but with the accumulation of intestinal gas in the colon, which must be considered during physical examination.
Case 1: renal mass and resection
A patient around 50 years of age, somatically stable, without major comorbidities. CT revealed a renal mass measuring approximately 30×26×27 mm without signs of invasion of the renal capsule or Gerota's fascia. For small-sized masses without invasion into adjacent structures, partial nephrectomy (organ-sparing surgery) is indicated.
Postoperative histological report — oncocytoma. This is a benign neoplasm managed and followed by urologists rather than oncologists. Oncocytomas are excised despite their benign nature for two reasons:
- benign and malignant characteristics can only be reliably differentiated after surgical intervention and histological examination;
- oncocytomas tend to grow and can eventually compress surrounding renal structures.
Case 2: suspected renal cell carcinoma
A 47-year-old male presenting with left-sided flank pain for two months. Renal cell carcinoma typically manifests after age 40, although younger patients are encountered (a case in a 32-year-old female has been described in practice).
Laboratory tests revealed an elevated ESR (30 mm/h) and up to 10 fresh erythrocytes per high-power field in the urine. CT scan shows the left kidney is enlarged, with the contour of the middle third bulging due to a 40 mm mass with a central hypodense area and good blood supply.
The combination of hematuria and hypervascularity of the mass raises suspicion of a malignant renal neoplasm. With a size of 40 mm and a location sparing the capsule and vascular pedicle, partial nephrectomy is feasible. A key condition for choosing organ-sparing surgery is that the mass does not invade the capsule and Gerota's fascia and is located in an area accessible for safe removal (e.g., at the renal pole, away from vessels). If the mass is close to the vascular pedicle, the risk of vascular injury is high, and total nephrectomy is more frequently performed in such cases.
Case 3: angiomyolipoma
A female of the same age, asymptomatic, with normal laboratory results. A left renal mass was detected incidentally on ultrasound during routine screening, then evaluated further on CT: a 2 cm mass in the middle third, with a smooth, well-defined contour clearly demarcated from the renal parenchyma, showing contrast enhancement predominantly centrally and minimally at the periphery.
The sharp contour and absence of adhesion to surrounding tissues favor a benign process. The most common benign renal tumor is angiomyolipoma. These lesions are managed by urologists, who are required to monitor them dynamically, as angiomyolipomas can increase in size. Growth of the mass is an indication for elective surgical removal.
Case 4: large renal cyst
A 60-year-old female with nagging pain in the left lower abdomen for six months. Urinalysis shows rare leukocytes, blood counts are normal. CT revealed a 10 cm mass with a density of 5 Hounsfield units, no contrast enhancement on intravenous administration, well-defined borders, and no adhesion to surrounding tissues.
Low density and lack of contrast enhancement indicate fluid contents — a cyst. Despite its large size, the well-defined borders point toward a benign nature of the lesion. However, the 10 cm size and presence of pain are indications for surgical excision of such a cyst.
Preoperative workup before renal surgery
Prior to elective surgery, especially in patients aged 60+, a comprehensive workup is performed to assess general risks and prevent intraoperative complications.
- Evaluation of renal function — determination of GFR (glomerular filtration rate), excretory urography, or nephroscintigraphy;
- ECG and echocardiography assessing ejection fraction, which should be above 60% by the Simpson method; lower values require a cardiology consultation;
- Brachiocephalic artery ultrasound to rule out pathologic tortuosity and arterial stenosis that could lead to cerebrovascular events during surgery;
- Lower extremity venous ultrasound to rule out thrombosis and prevent pulmonary embolism (PE) during prolonged positioning on the operating table;
- Gastroscopy to detect occult gastric mucosal erosions that could complicate with bleeding during surgery.
Key points
- Renal cysts are strictly contraindicated for biopsy due to the risk of carcinomatosis and non-diagnostic samples.
- Oncocytoma is a benign renal tumor monitored and treated by urologists, but always surgically excised.
- Partial nephrectomy is feasible in the absence of capsule and Gerota's fascia invasion and with favorable localization away from the vascular pedicle.
- The combination of hematuria and hypervascularity of a renal mass increases the suspicion of a malignant process.
- Angiomyolipoma is the most common benign renal tumor and requires active surveillance by a urologist.
- Large renal cysts (10 cm or more) with clinical symptoms require surgical removal even if benign features are present.
- Before renal surgery, ECG, echocardiography with ejection fraction assessment, neck vessel and lower extremity venous ultrasound, and gastroscopy are mandatory.
- A low ejection fraction (less than 60% by Simpson) requires a cardiology consultation prior to surgery.