Classification and epidemiology
Benign renal neoplasms are most often incidental findings during autopsy and extremely rarely have true clinical significance. The main threat to patients is posed by malignant tumors:
- Renal cell carcinoma (classified as an adenocarcinoma, historical synonyms include hypernephroma, hypernephroid carcinoma). This is the most significant pathology in adults, accounting for 1% to 3% of all visceral cancers.
- Wilms tumor. Characteristic exclusively of childhood.
- Urothelial tumors. Affect the epithelium of the renal calyces and pelvis.
Renal cell carcinoma develops from the epithelium of the renal tubules. Most often, the disease is diagnosed in elderly patients (in their sixth or seventh decade), with men being affected three times more often than women. Cigarette, pipe, and cigar smoking is recognized as the most frequent risk factor. The role of genetics is also proven: in Von Hippel-Lindau syndrome (defect localized on the third chromosome), carcinomas are often multiple and bilateral. In such patients, the pathology may be combined with hemangioblastomas, as well as retinal and central nervous system involvement.
Macroscopic appearance and growth pattern
The tumor process can be localized in any part of the organ, but the poles, especially the upper one, remain the favored site. Visually, the neoplasm is a solitary unilateral spherical node ranging from 3 to 15 centimeters in diameter.
On cross-section, the tumor tissue appears light yellow-gray-white, which sharply distinguishes it from normal parenchyma. A specific "variegated appearance" is characteristic, formed by the alternation of viable tissue with extensive areas of ischemic gray-white necrosis, softening foci, and hemorrhage foci. The boundaries of the node may appear clear due to the formation of a pseudocapsule, but the presence of small accessory nodules in the surrounding tissue indicates an aggressive growth pattern.
The neoplasm is capable of invading the calyces, pelvis, and the wall of the urinary tract, including the ureter. A specific characteristic of carcinoma is venous invasion. Tumor cells form solid cords that penetrate the renal vein. Further spread occurs via major vessels: from the renal vein, masses enter the inferior vena cava and can reach the right side of the heart. Metastasis occurs via both hematogenous and lymphatic routes.
Histological variants
Upon microscopic examination, the parenchyma of the neoplasm may be represented by tubular, solid (trabecular), or papillary structures. Different variants of differentiation are often combined within a single node. The stroma is usually scanty, but features good vascularization. In most cases, the cells are well-differentiated, although forms with marked atypia, containing giant and bizarre cells, are encountered.
Three main histological types are distinguished:
- Clear cell carcinoma (most common — about 70%). Consists of large polygonal or rounded cells. Their abundant cytoplasm appears clear due to the accumulation of lipids and glycogen.
- Papillary carcinoma (about 15%). Formed by granular or clear cells.
- Granular cell carcinoma. The cells have moderately eosinophilic cytoplasm. If the tumor acquires a sarcomatoid growth pattern, this indicates a poor prognosis.
TNM staging system
Assessment of the extent of the process is based on standard criteria:
- T stage (Tumor): describes the primary focus. Stages T2–T3 are characterized by invasion through the muscle layers or extension beyond the bladder wall. At stage T4, the tumor arises from fixed tissue and spreads to adjacent organs and tissues.
- N stage (Nodules): reflects involvement of regional lymph nodes. N1 — one node is affected. N2 — bilateral involvement of lymph nodes on both sides of the bladder, while they remain mobile (displaceable). N3 — metastases become fixed (non-displaceable). N4 — involvement of distant lymph nodes.
- M stage (Metastasis): stage M1 is established in the presence of distant hematogenous metastases.
Briefly: answers to topical questions
How is the T stage (primary tumor) assessed in renal cell carcinoma according to the TNM system?
The T stage in renal cell carcinoma is assessed by the degree of local spread of the primary tumor and vascular invasion.
- Stage T3a — invasion into the renal vein, perirenal tissues, or renal sinus fat, but without extension beyond Gerota's fascia.
- Stage T3b — macroscopic extension of the tumor into the inferior vena cava below the diaphragm.
- Stage T3c — macroscopic extension into the inferior vena cava above the diaphragm or invasion of its wall.
- Stage T4 — extension beyond Gerota's fascia, including direct invasion into the ipsilateral adrenal gland.
To which organs does hematogenous metastasis of renal cell carcinoma most frequently occur?
Hematogenous metastasis of renal cell carcinoma most frequently occurs to the lungs; the lungs are the most common site of recurrence and metastases, detected in 50–60% of disease progression cases. Kidney cancer is also among the tumors that frequently metastasize to bone tissue. Venous invasion is characteristic of renal cell carcinoma: invasion into the renal veins with further spread through the inferior vena cava to the right side of the heart.
What genetic mutations, in addition to Von Hippel-Lindau syndrome, are characteristic of various histological types of kidney cancer?
Papillary renal cell carcinoma is characterized by mutations in the MET proto-oncogene. Activating germline mutations in this gene, located at locus 7q31, lead to constitutive activation of the tyrosine kinase receptor it encodes. This genetic abnormality is the main etiological factor causing the development of multiple type 1 papillary renal cell carcinomas. Other specific mutations for various histological types of kidney cancer, apart from Von Hippel-Lindau syndrome and MET gene mutations, are not described in the presented materials.
What benign kidney tumors exist?
Benign renal neoplasms include angiomyolipomas and adenomas.
- Angiomyolipoma — a benign lesion consisting of adipose tissue, smooth muscle, and abnormal blood vessels.
- Adenoma — a benign neoplasm derived from glandular epithelium; papillary adenoma is among the described variants.
Oncocytoma was previously considered benign, but it is now recognized that it can metastasize.
To memorize the pathway of venous invasion, use the chain "R-I-R": Renal vein → Inferior vena cava → Right side of the heart.
Class and exam questions
Why was renal cell carcinoma historically called hypernephroma?
The term arose due to visual similarity: the tumor has a characteristic yellow color on cross-section, and its clear cells under the microscope resemble cells of the adrenal cortex.
Which histological type of renal cell carcinoma is the most common?
Clear cell carcinoma is the most common, accounting for 70% of all cases. Its cells contain a large amount of lipids and glycogen.
What causes the "variegated appearance" of the tumor on a gross specimen?
This appearance occurs due to the alternation of tumor tissue with large areas of gray-white ischemic necrosis, softening zones, and hemorrhage foci.
What else to study on this topic
- Pathogenesis of Von Hippel-Lindau syndrome and its impact on the development of multiple carcinomas
- Features of the macroscopic and microscopic structure of Wilms tumor in children
- Morphological differences between urothelial tumors of the renal pelvis and renal cell carcinoma
- Sarcomatoid growth pattern in granular cell carcinoma as a factor of unfavorable prognosis
Master the entire topic in the "Pathological Anatomy" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Kidney tumors" and 4,414 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 153 video lessons on the subject
Other topics in the section "Diseases of the Kidneys and Urinary Tract"
Free video lessons: pathological anatomyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.