Renal cell carcinoma and its variants
Renal cell carcinoma (Renal Cell Carcinoma, RCC) is a malignant neoplasm that appears on CT as a mass originating from the renal cortex.
A key sign is a sharp increase in X-ray attenuation after the administration of a contrast agent (for example, from 28 to 129 HU). Such reliable and pronounced contrast enhancement indicates tumor vascularization. Heterogeneous, predominantly peripheral enhancement with a central decrease in density (necrosis zone) is characteristic.
In the case of mixed cystic-solid masses, it is important to perform differential densitometry. If the fluid component practically does not change density, while the solid (tissue) component actively enhances, this indicates a malignant process—a tumor with cystic degeneration or a cystic variant of RCC.
Benign tumors: angiomyolipoma and oncocytoma
Some masses have specific features that help determine their nature:
- Angiomyolipoma (Angiomyolipoma). Can occur bilaterally in the setting of tuberous sclerosis. On unenhanced CT, areas of markedly reduced density—fat tissue—are identified within it. The presence of macroscopic fat is a pathognomonic sign. On MRI, the tumor is diagnosed by signal loss in a fat-suppression sequence.
- Oncocytoma (Oncocytoma). Occurs in older adults. On CT, it may appear as a heterogeneous mass with central low attenuation. Important: it is impossible to distinguish oncocytoma from renal cell carcinoma based solely on imaging data.
Collecting system tumors
Transitional cell carcinoma (Transitional cell cancers, TCCs) affects the urinary tract.
On CT and intravenous urography, these tumors manifest as filling defects or focal wall thickening. The "phantom calyx" sign is characteristic in infundibular obstruction.
On ultrasound, TCC is visualized as a mass replacing the hyperechoic fat of the renal sinus. When the ureter is affected, hydronephrosis and the "goblet" sign (irregular narrowing with overhanging edges) may occur. Metastases, blood clots, calculi, and infections can present with a similar picture, so additional diagnostics are always required for verification.
Screening and causes of hematuria
Hematuria often accompanies renal tumors, but also has benign causes. It can be associated with genetic syndromes (Von Hippel-Lindau, tuberous sclerosis), polycystic kidney disease, or sponge kidney.
MRI is preferred for screening renal tumors because it has better contrast resolution compared to unenhanced CT and reduces cumulative radiation exposure, which is especially important for patients with renal failure.
In suspected trauma accompanied by hematuria, unenhanced CT is mandatory to rule out lacerations and parenchymal damage.
Briefly: answers to topical questions
What genetic syndromes predispose to the development of renal masses?
A number of hereditary diseases predispose to the development of renal masses.
- Von Hippel-Lindau disease (Von Hippel–Lindau disease, VHL) is associated with multiple cysts and multifocal clear cell carcinoma.
- BAP1 tumor predisposition syndrome (BAP1 tumour predisposition syndrome) is accompanied by an aggressive form of clear cell carcinoma.
- Tuberous sclerosis (tuberous sclerosis) predisposes to multiple angiomyolipomas and oncocytomas.
- Birt-Hogg-Dubé syndrome (Birt-Hogg-Dubé syndrome) is associated with multiple oncocytomas.
- Lynch syndrome causes a high risk of upper urinary tract tumors.
Angiomyolipomas are also rarely found in neurofibromatosis and autosomal dominant polycystic kidney disease.
What histological subtypes of renal cell carcinoma exist?
There are several main histological subtypes of renal cell carcinoma.
- Clear cell carcinoma (Clear cell carcinoma) is the most frequent type, characterized by intense heterogeneous contrast enhancement.
- Papillary renal cell carcinoma (Papillary cell carcinoma) includes types 1 and 2, and is distinguished by homogeneous and less intense contrast enhancement.
- Chromophobe renal cell carcinoma originates from the collecting duct epithelium and has homogeneous peripheral enhancement.
- Collecting duct carcinoma belongs to a separate group of collecting duct tumors.
The classification also includes multilocular cystic renal cell neoplasm of low malignant potential.
Class and exam questions
How to distinguish a simple cyst from cystic renal cell carcinoma on CT?
A simple cyst does not enhance with contrast agent (density changes slightly). In cystic carcinoma, the solid tissue component of the mass demonstrates a clear increase in density after contrast administration.
Can an accurate diagnosis of "oncocytoma" be made based on CT?
No, the imaging appearance of oncocytoma (including central hypoattenuation) can completely mimic renal cell carcinoma.
Which imaging sign unambiguously indicates an angiomyolipoma?
The detection of macroscopic fat areas (decreased density on CT or signal loss on fat-suppressed MRI) is an absolute sign of angiomyolipoma.
What else to study on this topic
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