Renal and urinary tract masses: Pathology review

Definitions & Key takeaways

Renal and urinary tract masses are abnormal growths that can develop in the kidneys, ureters, bladder, and urethra. These masses may be either cysts or tumors. Renal cysts on ultrasounds appear to be tiny sacs filled with black fluid. Cysts can be either simple or complex when they have septations within. Renal tumors can be benign, like renal oncocytoma, or malignant, like renal cell carcinoma. Common urinary tract tumors include: Renal cell carcinoma: the most common type of renal cancer. It develops in the renal tubules and can metastasize to surrounding tissue. Transitional cell carcinoma: develops in the urothelial cells lining the urinary tract. Wilms' tumor: a rare type of kidney cancer typically affecting children.

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Case Study0:00–0:41

In the emergency department. Two people are coming in.
One of them is 68 year old Randy who has left flank pain and gross hematuria. On the physical examination, there's also a palpable mass in the left abdomen.
Randy also has a history of heavy smoking for the past 40 years. The other person is 54 year old UA who came in because of painless hematuria.
A while ago, UA took cyclophosphamide for a condition he had called Hodgkin's disease. Both individuals had an ultrasound done which showed a mass in Randy's left kidney and a mass in Uriah's bladder.
Ok. So Randy has a mass in his left kidney.

Pathology0:41–1:12

Uriah has one in his bladder. Let's first talk about renal masses which can develop in both adults and Children.
These masses may be either cysts or tumors in turn renal cysts can be either simple or complex while tumors can be benign like renal oncocytoma or malignant like renal cell carcinoma regarding masses of the urinary tract.
The main concerns are transitional cell carcinoma and squamous carcinoma of the bladder. Now, let's look at them one by one simple cysts are very common and account for most of renal masses.

Renal Cysts1:12–2:30

They are typically small and occur in adults with otherwise healthy kidneys on an abdominal ultrasound, they are perfectly round and have a thin wall and are filled with fluid.
This liquid is produced by the kidney. The ultra filtrate is the plasma without proteins that results after the filtration process that happens in the glomeruli, specifically in Bowman's capsule.
This makes simple cysts anechoic on ultrasound. Since the fluid does not produce an echo and thus appears black.
Usually they're asymptomatic and are discovered incidentally during an ultrasound or a ct scan done for other reasons. On the other hand, complex cysts are larger than simple cysts.
Additionally, on an ultrasound, they have thick irregular walls and are multilocular meaning they have septations within that separate the cyst cavity into compartments.
Sometimes complex cysts may even have a solid component within. Now, complex cysts are more likely to cause symptoms like flank pain.
For example, they also have a higher chance of becoming malignant. And that's why for your tests.
Remember that complex cysts require additional follow up and even surgical removal. All right, let's now talk about renal oncocytoma, which is a benign tumor that usually appears in adults.

Renal Oncocytoma2:30–3:07

It originates from the intercalated cells of the collecting ducts. Macroscopically, the tumor appears as a circumscribed mass with a central scar microscopically.
Unlike RCA renal oncocytoma has large eosinophilic cells without perinuclear clearing. Individuals can present with painless hematuria, flank pain and an abdominal mass most of these benign tumors are resected in order to rule out malignancies like RC, moving on to renal cell carcinoma or RCC, which is the most common renal malignancy.

Renal Cell Carcinoma3:07–6:29

It usually appears in males between the ages of 50 to 70. Risk factors for RCC include smoking and obesity.
It's associated with mutations that cause gene deletions on chromosome three. These mutations can be sporadic or inherited as a part of Von Hippel Lindau syndrome, which is characterized by the formation of cysts and tumors in different parts of the body like the kidneys and pancreas.
Now RCC originates from the proximal convoluted tubules, epithelial cells for your tests. Remember that the most common type of RCC is a clear cell carcinoma where the cancerous cells are polygonal and filled with lipids and carbohydrates.
They appear clear on microscopy because the standard tissue fixation and staining techniques dissolve the lipids and glycogen leaving clear empty spaces behind.
Now RC can invade the renal vein and if it invades the renal vein on the left side, it can lead to varicocele. This is because the venous drainage from the left testis travels through the left testicular vein and then through the left renal vein and finally in the inferior vena cava.
So if RCC invades the left renal vein, then the venous drainage of the left testis is blocked leading to a varicocele. Remember for your exams that this can never happen on the right side because the venous drainage from the right testis goes directly into the inferior vena cava.
Now that we've got that covered RC can also invade the inferior vena cava via the renal veins and through hematogenous spread, it can cause metastasis to the lungs and bones RC can be asymptomatic, but it can also present with the classic triad of flank pain, hematuria and palpable masses.
That's because if the tumor is big enough, it will compress the surrounding tissues leading to flank pain and the palpable mass.
This compression can also damage the kidney causing hematuria in more advanced stages. Weight loss can also be present.
Now, RCC can also be associated with signs and symptoms of a paraneoplastic syndrome. First, the tumor can secrete erythropoietin and this will affect the bone marrow making it produce more red blood cells.
In which case, there will be polycythemia. In other cases, the tumor can also secrete a pth related protein which acts just like parathyroid hormone and which causes the bones to release more calcium leading to hypercalcemia.
It can also produce act which causes the adrenal glands to overproduce cortisol and there will be signs of Cushing syndrome like moon facies, Buffalo, hump and hypertension.
Finally, it can also produce renin which is normally produced by the kidneys renin, further activates the renin angiotensin aldosterone system leading to hypertension.
Now, treatment of RC mostly depends on whether metastasis has occurred. If the tumor is strictly localized in the kidneys, then surgery or ablation of the tumor can be done if there's metastasis.
However, then immunotherapy with aldesleukin or targeted therapy can be done in selected cases. But unfortunately RC is resistant to chemo and radiation therapy.
Now, let's focus on Wilms tumor also called nephroblastoma. This is the most common malignancy of early childhood and appears between the ages of two and four.

Wilms Tumor6:29–8:01

The tumor contains embryonic glomerular structures and it originates in the metanephric blastoma, which is the embryologic structure from which the nephrons develop.
It's associated with mutations of tumor suppressor genes. Wt one and wt two that are located on chromosome 11.
It presents with a large palpable unilateral flank mass and sometimes even hematuria. Wilms tumor can be a part of several syndromes.
If there's wt one deletion, then we get Wagr syndrome where W stands for Wilms tumor, A for aniridia, meaning the lack of iris, G for genitourinary anomalies like ambiguous genitalia and R which is the outdated term for mental retardation, which is now called intellectual disability.
Wt One mutation is also associated with Denny's Drash Syndrome, which is a triad of Wilms, tumor diffuse mesangial sclerosis with early onset nephrotic syndrome and dysgenesis of gonads or male pseudohermaphroditism.
Wt two mutation is associated with Beck with Weidman syndrome, which is a pediatric overgrowth syndrome where there's Wilms, tumor, organomegaly, macroglossia or enlarged tongue and hemihyperplasia where structures on one side of the body are larger than the other.

Transitional Cell Carcin8:01–9:15

Ok. We're done with renal masses.
Let's move on to urinary tract carcinomas. Let's begin with transitional cell carcinoma.
This is also known as urothelial carcinoma because it originates in the epithelium that lines the organs of the urinary system.
Because of this transitional cell carcinoma can occur in the renal calices, renal pelvis or in the ureters. But it's most commonly found in the bladder.
Risk factors include smoking, the use of cyclophosphamide, the use of aniline dyes, which is a compound that was found in hair coloring products.
And finally, the use of phenacetin, which is an analgesic that's no longer used. One important symptom of transitional cell carcinoma that's commonly tested is painless hematuria.
Also because hematuria in this case comes from the urinary tract and not from the kidney on microscopy. There will be no casts in the urine.
An abdominal and pelvic ct scan can also be used to locate the tumor as well as determining how much the tumor has invaded.
And if there's any metastasis, a cystoscopy can be done where a thin tube containing a camera is inserted through the urethra to allow visualization of the bladder and also to take a biopsy of the tumor.

Squamous Cell Carcinoma 9:15–10:31

Finally, there's squamous cell carcinoma of the bladder, which is also derived from the urothelium. It's associated with chronic irritation of the bladder.
See, the bladder is lined up with multiple layers of epithelial cells that form a so called transitional epithelium which can contract and expand depending on how full the bladder is now irritation in the bladder can damage these cells and eventually lead to metaplasia, which is when the normal cells of a certain tissue convert to another type of normal cells usually found elsewhere in the body.
And in this case, the epithelial cells lining the bladder, which are typically cuboidal or columnar become squamous cells which are normally found in the skin.
Now, metaplasia can further lead to dysplasia or the cells become completely different from any normal cells in the body.
And this eventually leads to the development of squamous cell carcinoma. Risk factors include infection with schistosoma, hematobium, a type of urinary blood fluke common in the Middle East, chronic cystitis, smoking and chronic nephrolithiasis.
All of these factors irritate the bladder and damage the cells lining it for your tests. Remember that squamous cell carcinoma of the bladder also can present with painless hematuria.
A cystoscopy and an abdominal pelvic ct scan can also be done. Ok.

Review10:31–11:47

Let's review. Renal masses include simple cysts that are basically tiny balloons filled with black fluid on an ultrasound and don't give any symptoms or complex cysts which on ultrasound have septations within and need follow up because they can be malignant.
Then there's a benign tumor called renal oncocytoma where on microscopy, the cells are eosinophilic and there's no perinuclear clearing.
Next, there's renal cell carcinoma, which is the most common type of renal cancer and appears in males aged between 5070 other risk factors include smoking and obesity.
Symptoms include palpable masses, flank pain, hematuria, weight loss and even fever on microscopy. The most common type of RC is a clear cell carcinoma.
Finally, there's Wilms tumor which typically appears in early childhood and can be a part of several syndromes like Wagr syndrome, Denise drash syndrome, or Beckwith wean syndrome.
Urinary tract carcinomas include transitional cell carcinoma, which is the most common tumor of the urinary tract and can present with painless hematuria.
Then there's squamous cell carcinoma of the bladder, which appears as a result of the chronic irritation of the bladder.

Summary11:47–12:40

Now, back to our cases, Randy came in with the left flank pain and gross hematuria and there was also a palpable mass in his abdomen.
The ultrasound showed a mass in his left kidney. Now, considering his age and the fact that he is also a smoker, it's likely that Randy has renal cell carcinoma.
But first a ct scan of the abdomen and the chest should be done to detect any tumors and metastasis. If a tumor is found, a biopsy of the mass might need to be done before confirming the diagnosis and starting treatment, then there's ua who presents with painless hematuria and who seems to have a mass in his bladder.
Now, considering that UA at some point was treated with cyclophosphamide, he most likely has transitional cell carcinoma.
But further investigations are needed such as cystoscopy and a CT scan of the pelvis and abdomen.