Needle biopsy technique: image guidance and type of biopsy
The two principle variables of renal mass biopsy are image-guidance modality and needle type and size. In addition, there are many factors that affect efficacy and safety, including patient-related variables such as body habitus and cooperativeness, tumor-related variables such as size, location, and vascularity, and operator-related variables such as technical expertise with renal biopsy, the availability of technology, and relationships with other sub-specialties.
Ultrasound (US) and CT are the most commonly used image-guidance techniques. MRI is rarely used. Although the different imaging modalities have not been compared head-to-head, the risk of complications and reported failed biopsy rates are similar. Unfortunately, the literature is often imprecise with respect to definition of failed biopsy, making it difficult to evaluate studies comparatively.
Failed biopsy—an absence of tumor cells—is usually due to erroneous sampling of normal kidney, fibrosis, fat, inflammation, necrosis, or blood. This must be differentiated from indeterminate biopsy, in which tumor tissue is present but it is impossible to differentiate benign from malignant cells due to insufficient cells, morphological overlap, or cellular heterogeneity.
Each imaging technique has its own benefits and limitations. US is the least expensive modality and can be used at the bedside by the urologist. Additionally, US provides multi-planar imaging without ionizing radiation. Limitations of US include its inability to visualize bowel and pleural space and the needle tip. US is also of limited value in obese patients and those with renal masses that are isoechoic to surrounding renal parenchyma. CT, with the use of intravenous contrast as necessary, can visualize almost all renal masses, as well as bowel, pleural space, and needle tip.
CT may also demonstrate intra-tumoral changes such as hemorrhagic zones, allowing the operator to avoid these and thus increase biopsy yield. The greatest drawback to CT is the risk of ionizing radiation. MRI is valuable for biopsy of masses that are not well-visualized on US or CT, or when MRI-guided treatment is planned. The use of MRI is limited by availability and expense, as it requires use of costly MRI technology and specialized non- ferromagnetic needles.11
Biopsy needles vary in size, and authors typically divide these into two classes: fine (19-gauge or thinner) or large (20-gauge or larger). Fine needles are typically used for fine-needle aspiration (FNA) in which the sample is examined cytologically rather than histopathologically. These samples may also be examined using immunohistochemistry (IHC), flow cytometry, fluorescent in situ hybridization (FISH), apoptosis assays, and picrosirius red F3BA staining.11 Large needles are typically used for core biopsies, which are examined histologically and using IHC. In general, core biopsy offers greater sensitivity. Larger caliber needles, as one might guess, will likely increase accuracy and decrease failure rate.12
Silverman and colleagues13 recommend beginning with a fine needle and asking an on-site cytologist to examine specimens intra-procedurally. If the specimen is adequate, the procedure can be completed with fine needle alone. If not, then a large needle should be used. Others have suggested performing both types of biopsy during the same procedure.14 In this case, FNA should be performed first to reduce the amount of blood in the cytological specimen.11
The authors prefer core needle biopsy alone as we firmly believe that there is indeed a superior ability to gain an accurate diagnosis with this practice. With respect to the number of biopsies performed, the literature advises at least two core biopsies.11,12 For FNA, as many passes as necessary should be performed to ensure a diagnostic smear.
Techniques for image-guided renal mass biopsy have been described in detail.15 In short, once the patient is positioned properly and the mass visualized, a guiding cannula is advanced on to the tumor surface and the needle is passed through the cannula into the tumor. Use of the cannula avoids direct contact between the tumor tissue and the retroperitoneal tissue through which the needle passes during percutaneous biopsy, theoretically decreasing the risk of tract seeding.
Office-based renal biopsy technique
The authors have recently been performing office-based renal biopsy under local anesthetic. Office-based renal biopsy has allowed for improved coordination and ease of scheduling, leading to more expeditious and precise management of small renal cortical neoplasms. Once biopsy is deemed indicated, and the patient agrees after a discussion of the risks and benefits, a limited retroperitoneal US examination is performed to determine if a biopsy is feasible.
The skin is then marked over the area where the biopsy will be performed. If the patient needs to return on another day for the biopsy, he or she is asked to keep the area marked with a pen after each bathing. On the day of the biopsy, the patient places EMLA cream on the marked area and takes a low dose of diazepam two hours prior to the procedure. Positioning is typically flank or prone. The Hitachi Aloka Preirus US system is used to target the lesion. The system projects a dotted target line through the exact needle path and an 18G needle is deployed through the hole in the transducer (Figure 2). This is familiar to the urologist as it mimics needle biopsy of the prostate. Performing the biopsy under local anesthesia only has tremendous advantages as the patient can participate in the procedure as an “assistant.”
The conscious and alert patient can respond to surgeon requests for deep or shallow inspiration, and can there-fore help to move the kidney (and therefore the tumor) down (via inspiration) to a location where it can be ac- cessed below or between ribs. The patient can also be asked to hold breathing to facilitate a precise needle deployment in an immobile kidney. Immobilizing the kidney at the precise time of biopsy may help minimize the risk of bleeding. In our experience to date, patients typically experience little to no pain. After the procedure, the patient is observed for one to two hours and repeat US is performed in the office to confirm that there is no peri-renal hematoma.