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Renal cysts and cancer: Clinical practice




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Renal cysts and cancer: Clinical practice


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USMLE® Step 2 style questions USMLE

5 questions

A 65-year-old man comes to the office to establish routine healthcare. He recently moved to California to live with his daughter after the death of his spouse. The patient has no active complaints. Past medical history is significant for hemorrhoids. Family history is significant for diabetes mellitus in his father and prostate cancer in his paternal grandfather. He has smoked a pack of cigarettes daily for 20 years; he does not drink alcohol. Vitals are within normal limits. Digital rectal examination shows irregular nodularity on the posterior prostate. The rest of the examination is normal. Serum prostate specific antigen is 7 ng/mL. Medical recods show that it was 4.5 ng/mL a year ago. Which of the following is the most appropriate diagnostic study to obtain at this time?  


Content Reviewers:

Rishi Desai, MD, MPH

Renal masses can develop in both adults and children, and sometimes, they’re due to genetic mutations.

These masses may be either cysts or tumors, and they can be discovered incidentally during an abdominal ultrasound or a CT-scan or when an individual has symptoms like abdominal or flank pain.

Renal cysts can be simple or complex, and they can also be solitary - meaning there’s just one cyst, or there can be multiple cysts - sometimes affecting both kidneys.

Simple cysts are the most common type of renal mass, and they typically occur in adults with otherwise healthy kidneys.

On an abdominal ultrasound, they’re usually smaller than 1 centimeter, but can be up to 4 centimeters. They’re round and have a thin regular wall and are filled with liquid which makes them anechoic - so it basically looks like a small balloon filled with black fluid.

Additionally, there can also be some fine septa and calcifications within the simple cyst.

Usually they’re asymptomatic, and don’t need treatment.

On the other hand, complex cysts are larger than 1 centimeter. On an ultrasound, they have thick, irregular walls and are multilocular- meaning they have septations within, that separate the cyst cavity into compartiments.

Complex cysts can cause symptoms like flank pain, and they can cause complications like infections, hemorrhage, and hypertension.

An infected cyst can cause symptoms like fever and fatigue.

Sometimes, the infection can spread to the renal parenchyma, causing an acute pyelonephritis with symptoms like fever, acute flank pain or diffuse abdominal tenderness.

A CBC shows leukocytosis and neutrophilia, and the ESR and CRP are elevated.

If the infection is limited to the cyst, then the urinalysis may be normal, whereas if the cyst causes acute pyelonephritis then pyuria, bacteriuria and proteinuria are present.

Blood cultures may be positive with both a simple cyst infection and acute pyelonephritis, whereas urine cultures are typically positive only with acute pyelonephritis.

An ultrasound can show a thick cystic wall.

The ultrasound can show a clear separation between urine, which is a low density fluid, and pus, which is a high-density fluid.

The initial treatment of an infected cyst is empirical. If the symptoms are mild, then an oral fluoroquinolone like ciprofloxacin or trimethoprim-sulfamethoxazole is given for 4 to 6 weeks.

If the symptoms are severe, then IV ciprofloxacin is given until the symptoms resolve and then oral ciprofloxacin is given to finish the treatment course.

If the blood or urine cultures identify a pathogen, then the antibiotic is adjusted accordingly.

Now, if the individual doesn’t respond to antibiotic therapy within 72 hours or has persistent fevers for more than a week, then a CT-scan is done.

If the cyst is larger than 3 centimeters, then percutaneous drainage may be needed.

Another complication is cystic hemorrhage which can cause hematuria.

Cystic hemorrhage is treated with bed rest, pain medication like acetaminophen, and aggressive fluid hydration - usually more than 2 liters per day to prevent blood clot formation.

If there’s severe bleeding that causes hemodynamic instability, a blood transfusion may be required, and with persistent bleeding, segmental arterial embolization, or surgery may be needed.

Finally, hypertension occurs when one or more cysts compress the renal parenchyma. In part, that’s because the epithelial cells that form the wall of the cysts release renin, which stimulates angiotensin and aldosterone, causing vasoconstriction of the renal artery and sodium retention, leading to hypertension.

Treatment relies on ACE inhibitors - like captopril, or angiotensin receptor blockers - like candesartan, with a goal of keeping the blood pressure below 125/75 mmHg.

Now, every complex cyst, regardless of whether there are complications, should be further worked up to see if there’s an underlying malignancy. That starts with a urinalysis, which might show hematuria.

Also an abdominal CT-scan with contrast should be done to classify the cyst according to the Bosniak system - which has 5 grades - I, II, IIF, III, and IV.

The higher the grade, the more malignant it appears on the CT scan.

Sometimes, the diagnosis is still uncertain after CT and MRI scans, and in those situations a percutaneous needle biopsy may be done to determine whether the cyst is benign or malignant.

Now, in terms of the grades - grade I and II are simple cysts.

With grade I, there’s a single cyst or multiple cysts without septa or calcifications.

With grade II, there are only fine septa and calcifications may be seen within the cyst.

Grade I and grade II cysts have no malignancy risk, so no further evaluation is needed.

Next, there’s a grade IIF cyst - which is between grade II and grade III; there are multiple fine septa within the cysts, the wall is thickened, and there are calcifications in the wall or septa. There’s a low risk of malignancy, so an abdominal CT-scan or an MRI is done within 6 months to see if the cyst has gotten bigger - in which case surgical resection may be needed.

With grade III and grade IV cysts, there are many septations within and the wall is thick and irregular.

About half of grade III cysts, and nearly all grade IV cysts are malignant, so surgical resection of the cyst or radiofrequency ablation are frequently needed.

Radiofrequency ablation involves using a radiofrequency generator, to generate high-frequency current to heat a needle. That hot needle is inserted into the tumor, which destroys the tissue.

Now, let’s switch gears and talk about renal cell carcinoma or RCC for short.

RCC originates in the renal cortex, and it’s the most common type of renal cancer in the elderly.

A malignant complex cyst is typically RCC, but not all RCCs arise from a complex cyst.

Some individuals are asymptomatic and diagnosed incidentally when a renal mass is found on an abdominal CT-scan. Others have symptoms, and the classic triad is flank pain, hematuria, and palpable abdominal mass.

Lab studies include a CBC- which may show anemia or in rare cases, erythrocytosis- when the tumor secretes erythropoietin.

Liver function tests may show elevated alkaline phosphatase if there’s hepatic dysfunction or bone metastasis.

If there’s a high alkaline phosphatase, bone scintigraphy is done to check for bone metastasis.

Finally, if there’s a paraneoplastic syndrome, the serum calcium may be elevated because RCC can increase the release of calcium from bone.

An ultrasound typically shows a complex cyst, an abdominal CT-scan can show local and regional involvement, and a chest CT-scan can show pulmonary or mediastinal lymph node metastasis.


Renal cysts refer to fluid-filled sacs that can develop in the kidneys. They can be simple, or complex. Simple renal cysts are typically asymptomatic and appear as enveloped round small masses filled with anechoic fluid on ultrasound. Simple cysts often need no treatment. Complex cysts on ultrasound appear as larger masses with irregular walls and septations. Complex cysts can cause symptoms like flank pain, and complications like infections, hemorrhage, and hypertension. So, all these complications might need to be managed accordingly.

On the other hand, there is renal cancer, specifically renal cell carcinoma (RCC). RCC originates in the renal cortex and can cause a triad of symptoms: flank pain, hematuria, and abdominal mass. An ultrasound and a CT scan can be done to diagnose and classify the tumors, and people with no metastasis are often treated with surgical tumor resection alone. People with metastases will need biopsies of the metastatic sites and may need chemotherapy in addition to surgery.