Overview of Renal Biopsy
A renal biopsy is a medical procedure where a small piece of kidney is removed to look for any disease or damage. There are two main types: targeted biopsies (TB) and non-targeted biopsies (NTB). A doctor may use a targeted biopsy when a particular area of concern needs to be inspected closely, usually to find out what’s going on with a mass or lump. A non-targeted biopsy, on the other hand, is used to randomly sample healthy parts of the kidney. This is usually done to see how kidneys are reacting to treatments or to diagnose a systemic disease that affects the entire body.
There are various ways to perform a renal biopsy. These can include the percutaneous method (where a needle is inserted through the skin), a transvenous method (inserting a needle into a vein), a laparoscopic method (using a long, thin tube with a camera on the end), and an open surgical approach, which involves making an incision to access the kidney.
The focus here will be on percutaneous image-guided biopsies, whether they’re targeted or non-targeted, meaning using medical imaging (like ultrasounds or CT scans) to help guide the needle to the correct spot on the kidney.
Anatomy and Physiology of Renal Biopsy
The kidneys usually have a single artery that branches into an anterior and a posterior part. These arteries do not have any significant secondary arteries supplying the same area. They end at a point where the anterior and posterior areas meet, referred to as Hyrtl’s or Brodel’s line. This line, positioned on the back side of the kidney, is considered the safest place for obtaining kidney tissue samples for non-invasive biopsies because it is less supplied with blood vessels. This region, however, cannot be seen on typical medical imaging exams.
Your kidney is located in a space behind your abdomen known as the retroperitoneal space. When biopsies are needed, they should be carried out in a manner where the needle only goes into this space, this helps in minimizing complications. The needle should avoid the center of the kidney, a region called the hilum, where the larger blood vessels and ducts are found. For standard biopsies, a small sample of the outer layer of the kidney (known as the renal cortex) is usually taken rather than the inner part (known as the renal medulla), as the outer part contains most of the small filters (glomeruli) used for evaluation.
Before the biopsy procedure, imaging techniques like ultrasound, CT scan, or MRI are used to help guide the needle. If you have an unusual kidney variant like an ectopic or horseshoe-shaped kidney, the procedure might be a bit different compared with someone with a standard kidney structure.
Why do People Need Renal Biopsy
Before deciding to do a kidney biopsy, which can be uncomfortable and costly to patients, doctors will first do less invasive tests like lab work or imaging tests.
Several medical societies have guidelines for when to get a kidney biopsy:
1. “Targeted Biopsies” which are for renal (kidney) tumors:
– The 2018 National Comprehensive Cancer Network (NCCN) guidelines recommended less invasive abdominal imaging tests first, since they are largely accurate for diagnosis. If uncertainty still exists, doctors might consider having a needle biopsy done.
– The 2018 Society of Interventional Radiology (SIR) guidelines discussed how to do a kidney biopsy but not when it might be necessary.
– The 2016 American Urological Association (AUA) guidelines suggest a biopsy might be useful in situations where the doctors need to find out if a mass is due to blood diseases, spread of cancer, inflammation, or infection.
– The 2014 European Association of Urology (EAU) guidelines suggested only performing a biopsy on patients with severely suspicious, contrast-enhancing renal masses seen on CT or MRI scans.
2. “Non-Targeted Biopsies”, which are to understand the causes of kidney diseases:
– Doctors use this approach to identify the causes of sudden or chronic kidney disease if they think the person’s kidney function could be regained. The approach can help the doctors come up with a better treatment plan.
– According to the 2013 American College of Radiology (ACR) guidelines, for acute kidney injury (AKI), a biopsy is typically considered after ultrasound imaging has been done. For chronic kidney disease (CKD), the ultrasound should be done first, but then a biopsy is usually considered more useful than other imaging tests.
– That said, both the American Society of Nephrology and the National Kidney Foundation don’t provide any guidelines of this sort.
In certain cases, a kidney biopsy might be needed:
1. When there’s a tumor likely to be a certain type called an oncocytoma or a type of kidney cancer (RCC) in patients with high surgical risks. Here, understanding the type of tumor through a biopsy can help tailor the best course of treatment.
2. When a renal tumor can’t be removed via surgery – here, doctors often want evidence of the tumor type in the medical record before starting treatment. However, the NCCN nor any other professional society insists on this.
3. If multiple tumors are found in the kidney, or in other parts of the body, a biopsy may be used to determine whether they are primary or metastatic tumors (tumors that started somewhere else in the body and spread to the kidney).
When a Person Should Avoid Renal Biopsy
The 2016 Guidelines from the American Urological Association (AUA) suggest that usually, a biopsy (a procedure where a small piece of tissue is removed for testing) isn’t needed for a solid tumor in two cases:
1) When it involves younger or healthier patients unwilling to accept the uncertainties that come with the biopsy.
2) Older or frailer patients who will get the same treatment regardless of the biopsy results.
There are some signs in the imaging results that suggest a patient should likely not have a biopsy. These signs include:
1) An area that appears to have blood and protein within a complicated cyst in the kidney. This can sometimes look like solid tissue during imaging tests, but other imaging techniques can clarify this.
2) An activity called pseudoenhancement, which makes a spot on the imaging result look more significant than it actually is. It can occur in smaller areas that are less dense than the rest of the kidney.
3) An area in the kidney that glows as brightly as the blood vessels radiate. This can initially look like a solid area but may actually be a blood vessel anomaly (deranged or irregular blood vessels).
Specific types of anomalies often result in non-helpful samples when a biopsy is done. This leads to unnecessary risks, whereas others can result in complications like bleeding.
CT-scan or MRI can also give signs that the tumor is likely not cancerous:
1) The tumor having visible fat on the imaging, which usually indicates a benign (non-cancerous) tumor called angiomyolipoma (AML).
2) A tumor containing tiny amounts of fat, which is a sign of a different type of AML.
3) A rapidly growing poorly-defined mass in a patient with signs of a urinary tract infection. If it remains after the infection has been treated, a biopsy can help determine whether it’s a result of infection or it’s a tumor.
Biopsy comes with risks, such as bleeding, which may be too much for a patient to handle physically or mentally. The patient’s ability to clot properly might also be affected, which include cases of high blood pressure, which also increase the risk of bleeding.
Before the procedure, it’s essential to ask the patient if they might be allergic to any of the drugs planned to use for the procedure. Your doctor will adjust plans accordingly to minimize the risk of allergic reactions.
Equipment used for Renal Biopsy
A transvenous renal biopsy is a test where a catheter (a thin, flexible tube) is used to take a small piece of kidney tissue. This catheter is usually inserted through the jugular vein (a vein in the neck) and directed to the kidney’s vein. A “sheath” or protector is placed into the kidney’s vein. Through this, a spring-loaded needle mounted on a long support device is inserted. This needle collects a small piece from the kidney for testing. This is usually adopted when there are difficulties in aiming the biopsy to a specific area in the kidney.
There are other methods to perform kidney biopsies – either targeting a specific area or not targeting it. These methods are performed with the help of imaging techniques such as ultrasound (US), US with needle guide technology, intermittent computed tomography (CT), fluoroscopic CT, or (in some specialized centers) magnetic resonance imaging (MRI). A retrospective case review is a study that looks back in time at available data. Such a review suggested that using ultrasound guidance leads to fewer bleeding problems than performing a biopsy without any imaging guidance.
Agarwal has reviewed the different needles used for this kind of puncture and the tools used to analyze the tissue samples. Both targeted and non-targeted biopsies in most studies have been done with an 18 or 20 gauge (a measure of needle thickness) spring-loaded needle (often called a “gun”) inserted through a larger gauge needle, respectively, in a coaxial fashion (one inside the other). There have been studies comparing different types of these needle “guns”. Some doctors prefer using thicker needles, but larger studies have not shown that this makes the biopsy quicker or easier. Some needles have removable hubs (known as Van Sonnenberg needles). These can help when targeting a difficult area, as they minimize the risk of multiple mistaken punctures when using a larger gauge needle.
Who is needed to perform Renal Biopsy?
When a biopsy (a procedure to remove a small piece of tissue to check for disease) is performed, there are several healthcare professionals involved, not just the doctor doing the biopsy. Here’s who they are and what they do:
1. A nurse specialising in conscious sedation: This healthcare professional is responsible for giving you medication that will keep you relaxed and pain-free during the procedure. It might be a nurse, a nurse anesthetist (a specially trained nurse who can provide anesthesia), or an anesthesiologist (a doctor who specializes in giving anesthesia). They will also keep a close eye on your vital signs like your heart rate and blood pressure to ensure you’re stable and safe throughout the procedure.
2. A technologist: This person helps handle the medical equipment used during the biopsy. They ensure everything is ready and working correctly for the procedure.
3. A cytotechnologist or pathologist: These are scientific experts who look at the tissue sample taken during the biopsy. They’re there to quickly assess if the sample taken is good enough for testing (this is called a rapid on-site evaluation or ROSE). They also make sure the tissue sample is put into the right preservatives for the lab tests. This helps make sure that the tests done on the sample will give the best information possible for your specific situation.
Preparing for Renal Biopsy
The American Urological Association suggests that it’s important for patients to fully understand why they’re having a biopsy (a medical procedure where a small amount of tissue is taken from the body for examination), what the results might mean, the possible risks involved, and the chances of the results not being conclusive. This information should be discussed with the patient by the doctor who has referred them for the biopsy, such as a urologist (a doctor who specializes in diseases of the urinary tract) or a nephrologist (a doctor who specializes in kidney care), before they schedule the procedure.
The patient should also be aware of how they will be asked to position themselves for the procedure (usually lying face down or on their side), and what kind of sedatives or pain relief will be used. They should be prepared for any arrangements that need to be made after the procedure, like having a family member or friend ready to take them home and assist them if they experience any concerning symptoms.
Before the day of the biopsy, a plan should be in place for how to reach the tissue that needs to be sampled. This is specially needed if the intended location is difficult to reach or the patient is obese, in which case special long needles might have to be ordered. Sometimes, a combination of ultrasound (a test that uses sound waves to create pictures of the inside of your body) and CT scan (an imaging test that uses x-rays and a computer to create detailed pictures of the body) might be used to provide the best possible view of the area. For harder-to-reach areas, particularly those near the upper pole (near the top of the kidney) and protected by the ribs, the CT scan can be angled to estimate the best point and angle for needle insertion.
How is Renal Biopsy performed
The 2014 guidelines by the European Association of Urology (EAU), and the 2016 guidelines by the American Urology Association (AUA), recommend a specific technique for percutaneous biopsy. This technique is known as the coaxial technique, which is when the doctor uses a hollow needle to take the sample. The benefit of this approach is that it has no association with spreading the tumor according to information from many patients. An alternative way is removing and reinserting a needle repeatedly, but both techniques are seen to have similar complications or outcomes according to a small study. However, they have not been compared in a rigorous research study called a randomized controlled trial.
When it comes to taking the sample, having a larger piece of tissue (called a core biopsy) improves the ability to detect and identify potential disease compared to a fine-needle aspiration (FNA), which collects a very small amount of tissue. This is the case for both targeted (TB) and nontargeted biopsies (NTB). Therefore, both the EAU and AUA guidelines recommend taking multiple core biopsies over using the FNA technique for TB. The amount of tissue needed for a TB can vary depending on the pathologist, who is the doctor that investigates the tissues to diagnose any diseases. They may require more tissue if they need to perform tests for genetic markers, flow cytometry (a technique used to measure different characteristics of cells), culture (growing cells or tissue in controlled conditions), and sensitivity (testing how responsive the cells or tissue are to certain treatments or conditions).
For NTBs, a certain minimum number of tiny filters in the kidney called glomeruli is required to make a diagnosis. These numbers can be achieved by taking two to three specimens, which are needed for examination under different types of microscopes. Laboratories do not accept FNA samples for this process.
After the biopsy, some physicians might fill the area through which the needle passed with substances like thrombin, fresh frozen plasma (FFP), or a gelatin sponge to help minimize bleeding. However, there are no rigorous research studies comparing these products or with no intervention or placebo while performing percutaneous renal biopsies in people so far.
Possible Complications of Renal Biopsy
According to guidelines from the Society of Interventional Radiology (SIR), the chances of needing a blood transfusion due to bleeding after using a needle smaller than 18 gage are expected to be less than 3%. If the rate increases to 5%, then the practice needs to be reviewed. The guidelines also suggest that using a larger needle may slightly increase the risk of complications.
Dr. Patel notes the following percentages for particular risks:
– Significant kidney bruising (4.9%)
– Significant pain (1.2%)
– Collapsed lung (0.6%)
– Bleeding that requires a transfusion (0.4%).
From personal experiences in the field, it’s reported that vascular injuries (damages to the body’s network of blood vessels) that don’t need treatment are more common than what’s documented in these studies. This might be because not all patients are thoroughly checked with ultrasound after their biopsy (a medical procedure where a small amount of tissue is removed for examination). But even when arteriovenous fistula (an abnormal connection between an artery and a vein) isn’t mentioned by the SIR guidelines or with Dr. Patel, it’s been noted that around 1% of biopsies could require attention due to this complication. The chances of spotting arteriovenous fistula potentially increase if a doctor specifically looks for them in the post-biopsy ultrasound.
Almost every patient will experience some level of kidney bruising around the kidney, which can be more easily detected using CT or MRI scans than ultrasound. Rarely, complications from kidney biopsies can lead to loss of the kidney or, in a few cases, death.
What Else Should I Know About Renal Biopsy?
Core targeted biopsies, or TBs (samples taken from the body to check for disease), have shown to be quite effective in most studies. These biopsies have proved to be highly sensitive and specific in identifying diseases, with a very good success rate – more than 95%. But there is a catch. Even though they are successful most of the time, there’s still a likelihood, although less than 50%, that they could be wrong.
To understand this better, let’s look at a study which was done on almost 3000 patients and over 3000 biopsies. The results showed that these biopsies had:
– a success rate (sensitivity) of more than 95%,
– could correctly identify the absence of diseases (specificity) more than 95% of the time, and
– if the biopsy result was positive, there was more than 99% chance that the person really had the disease (positive-predictive value).
Histologic subtyping, or categorizing the type of kidney cancer (like clear cell, papillary, or chromophobic types), can be done with about 95% accuracy based on these biopsies. But as of now, this doesn’t change the treatment recommended by the American Urological Association or the National Comprehensive Cancer Network.
One study concluded that in a quarter of cases where there was doubt if the tumor was kidney cancer or a benign tumor called oncocytoma, surgery could have been avoided, as the biopsied tumor turned out to be benign. However, this also means that around 75% of patients who got a biopsy could have directly gone for surgery. Therefore, it’s key that TBs are only done when there’s a good chance that the results will influence the treatment plan.
There are some drawbacks to these biopsies too. The results from the first biopsy may not always be conclusive, leading to a need for a second one, in about 10% of the cases. Also, in a few cases (around 5% or less), a benign oncocytoma might be present with kidney cancer, which can be missed with TB. Besides, these biopsies are not great at predicting if the tumor is not cancerous (low negative predictive value).
It’s also important to note that determining the grade of the tumor, which is a measure of the aggressiveness of the cancer, is only 50-75% accurate based on these biopsies. This variability leads the American Urological Association to state that the accuracy of grading tumors this way isn’t perfect.
Non-targeted biopsies, or NTBs, which involve taking samples from multiple areas, were able to change the initial diagnosis in 44% of cases and the treatment in 31% of cases. This means that NTBs were not needed in about 70% of cases.
In summary, while TBs and NTBs play a role in confirming or changing treatment plans, they may not always benefit all patients. Let’s remember that every person is unique, and what works well for one, may not work as well for another. It’s essential to have an open and informed discussion with your doctor about the benefits and limitations of these procedures.
