Renal mass refers to the presence of growths in the kidney which could be cystic [mostly benign] or solid [often malignant].
Thus a renal mass can be benign or malignant swelling.
The smaller renal masses are often benign but larger ones are malignant.
Most of these are diagnosed when they are still localized. A localized mass is one that has not spread out from where it first started.
Depending upon the consistency, the renal mass can be cystic or solid. Cystic masses are often benign.
A renal mass can have many causes. [see below]
The most common renal mass is a cyst, or fluid-filled sac arising from the kidney, a common diagnosis and without any significant health risks. Renal cysts can be simple cysts, which don’t need intervention and may not even need further follow-up or observation. However, some cysts can be complex.
Solid masses could be cancerous.
Cancer of the kidney is the leading cause of death.
Ball and Bean Shaped Masses
Depending on the growth factor, the renal masses can be called the ball-type lesion or bean type.
A ball-type causes the renal contour to alter and leads to a hump or contour bulge. Bean type lesions, on the other hand, use renal tissue as scaffolding for their growth and cause enlargement of the kidney but maintain its shape.
Ball-type growth displaces collecting system whereas bean-type destroys them.
The bean-type lesions use the renal tissue as scaffolding for their growth, thus causing enlargement of the kidney while maintaining its reniform (bean) shape. Collecting system elements are displaced.
- Renal cell carcinoma
- Transitional cell carcinoma, infiltrative renal cell carcinoma
- Medullary carcinoma
- Collecting duct carcinoma
Different Types of Lesion That Could Present as Mass
- Fluid-filled sac
- Mostly simple and do not demand any further workup
- Called complex when thick-walled and contain solid material
- Do not require treatment generally
- Cystic fluctuant swelling of kidney due to build-up of urine
- Can mimic neoplasm when localized
- Pain in the loin when large
- All the features of hydronephrosis
- Septicemia: Fever with rigors and sweating, dry furred tongue, leucocytosis, and positive blood culture
- Urine examination: Pus cells and white cell casts present
- Cystoscopy: Red and swollen ureteric orifice on the affected side
- Evidence of septicemia
- Tenderness and rigidity in the renal angles.
- Scoliosis of the lumbar spine with concavity towards the affected side.
Wilm’s Tumour or Nephroblastoma
- Commonly seen in boys below 5 years of age.
- Painless, huge enlargement of kidneys without hematuria (hematuria occurs later when the tumor bursts into the renal pelvis)
Renal Cell Carcinoma (RCC) or Hypernephroma
- Common in adult males
- Painless hematuria/varicocele
- Evidence of metastasis: Spontaneous fracture, hemoptysis
- Most common tumor
- 80–90% of primary malignant renal neoplasms in adults.
- Clear cell RCC- 80%
- Papillary RCC – 15% of renal cell carcinoma
- Chromophobe RCC- 5% of renal cell carcinoma
- Carcinoma of the collecting ducts (CDC) of Bellini- 1%
- Renal medullary carcinoma
- Renal carcinoma associated with Xp11.2 translocations/TFE3 gene fusions
- Multilocular cystic renal cell carcinoma
- Benign renal epithelial tumor
- Forms from intercalated cell
- Most common, benign, solid, nonfat-containing renal mass
- 3–7% of all renal cortical neoplasms
- Homogeneous hypervascular mass on imaging
- Variable and nonspecific appearance on MRI.
- Primary renal lymphoma -very rare
- The lesion originates in the kidney
- Secondary renal lymphoma (more common)
- Involvement of kidney by lymphoma
- Non-Hodgkin lymphoma, B-cell type is most common
- Can be solitary or multiple
- Primary renal lymphoma rarely invades the renal vein and inferior vena cava and this differentiates it from renal cell carcinoma
- Most common benign solid renal tumor
- It could occur sporadic or along with syndromes such as tuberous sclerosis and lymphangioleiomyomatosis.
- Rare site for metastasis
- Asymptomatic in most of the case, hence missed
- May mimic renal tumors.
- Often bilateral
Transitional Cell Carcinoma
- Radiologically closely mimics centrally located renal cell carcinoma.
- Requires more aggressive surgery and hence needs to be differentiation
- Angiomyolipoma, leiomyoma, hemangioma, lymphangioma, juxtaglomerular cell tumor, medullary fibroma, lipoma, solitary fibrous tumor, and schwannoma.
- Leiomyosarcoma, rhabdomyosarcoma, angiosarcoma, osteosarcoma, synovial sarcoma, fibrosarcoma and malignant fibrous histiocytoma.
Other tumors in this category are cystic nephroma, mixed epithelial, and stromal tumors
- Lesions which mimic renal cancers
- Composed of normal tissue
- Prominent columns of Bertin
- Persistent fetal lobulation
- Dromedary hump
- Splenorenal fusion
- Scarred kidney
- Extramedullary hematopoiesis
- Arteriovenous malformation
Clinical Presentation of Renal Lesions
The majority of these lesions are found incidentally and are asymptomatic. Most of the renal masses are asymptomatic in the early stage. Symptoms, if present could be one or more of the following-
Further Work up and Imaging In Renal Masses
As mentioned earlier, most of these masses are found incidentally on imaging done for some other reason.
After these have been found, the patients need to be evaluated clinically and by further imaging .
Work up is done to evaluate the mass completely.
No further work is required when there are cystic lesions.
In the case of other tumors, the workup is as
- Biochemistry profile
- Complete blood count
- Kidney function tests
- Ultrasounds to look for details of the mass and any spread if present
- Chest x-rays help to find out the stage of the cancer. A mass in the chest usually suggests that the tumor has spread to the lungs.
- Bone scans to find bony involvement.
Ultrasound can differentiate cystic lesions from solid. It can also differentiate simple cysts from the complex.
Ultrasound is useful in staging, detection of metastases and follow-up monitoring.
Both unenhanced and contrast CT is done. Unenhanced images can detect calcification or fat.
Depending on enhancement strength various deductions about the nature of tumors can be made.
Dual-energy CT (DECT) is being increasingly used for the characterization of renal masses.
MRI is better than CT in the accurate diagnosis of a cystic lesion. Renal lesions have distinct features on MRI and it is a useful tool for their detection.
Role of Renal Mass Biopsy
Renal biopsy can be done to identify the cause of the swelling and differentiate between benign and malignant lesions.
Percutaneous pretreatment biopsy in small solid renal masses (<4cm) can be reliably done.
Biopsy saves overtreatment in benign masses detected incidentally.
Some people like to follow up benign-looking lesions on imaging [size< 2cm, cystic] with serial imaging and do biopsy only when there are visible changes on serial imaging.
A biopsy is an essential investigation before tumor removal. A biopsy would be able to tell us the grading and stage of renal tumor and accordingly helps to plan the extent of surgical resection.
Treatment of Renal Masses
In the case of benign lesions, no treatment is needed and further behavior of the lesion would determine tumor treatment.
The goals of monitoring are to note any change and then proceed accordingly. The duration of followups would vary depending on the lesion and its characteristics.
This procedure removes the kidney. It could be partial when only the diseased part or tumor is removed or radical where the complete kidney is removed. In addition, involved surrounding tissues like lymph node or adrenal gland is removed.
More and more surgeons now do laparoscopic or robotic removal instead of open surgery.
Ablation destroys the tumor with extreme heat or cold. It is done only in small renal masses. It can be done percutaneously when the tumor is in a suitable location.
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