Percutaneous puncture of cystic or solid lesions of the kidney and the adjacent retroperitoneum is usually performed for diagnostic purposes, in some cases in combination with therapeutic intentions such as drainage of fluid collections or obliteration of renal cysts (Tables 8–2 and 8–3). Because most of these lesions are radiolucent and are not enhanced with intravenously administered contrast dye, they cannot be visualized by fluoroscopy. Thus, ultrasound or CT scans are the imaging techniques of choice to depict these lesions and guide percutaneous puncture. The technique of ultrasonically guided puncture is the same whether the target is the renal collecting system or a cystic or solid renal or extrarenal lesion. For cytologic aspiration, a fine-needle (20–22 gauge) aspiration technique is used that is comparable with fine-needle aspiration biopsy of the prostate. There is no evidence that one type of needle is preferable to the others. For aspiration and evacuation of renal cysts or extrarenal fluid collections (urinoma, lymphocele), the same coaxial needle/catheter system can be used as for percutaneous puncture of the renal collecting system. A small catheter (6–10F) is placed for a few days to ensure complete drainage of fluid. When fluids of high viscosity (abscess, hematoma) are to be drained, large-bore catheters (14–20F) must be inserted, necessitating dilation of the percutaneous tract. Percutaneous renal biopsy for histologic diagnosis and classification of renal disease is performed with 14- to 16-gauge needles (eg, Franklin–Silverman, Tru-Cut) at the lower pole of the kidney.
Renal cysts are found in about 50% of autopsy specimens in persons older than 50 years and are a frequent accidental finding on ultrasound or CT studies. Only a few cases require diagnostic percutaneous puncture. Indications for diagnostic puncture of a cystic lesion are an irregular, thick wall and internal echoes on ultrasound examination; density numbers on CT higher than those of serous fluid; and hematuria. Puncture for therapeutic procedures (evacuation of fluid and instillation of a sclerosing agent) is indicated only if, due to its size or location, the cyst causes compression and urinary obstruction of the neck of a calyx or the ureter, or discomfort and pain.
Various tests may be performed on aspirated fluid. No one test is pathognomonic except cytologic findings of malignant cells. However, neoplasms within a cyst are exceedingly rare, and cystic degeneration of a renal neoplasm can usually be easily identified by ultrasound and CT. Benign cysts contain clear, straw-colored fluid with low fat and protein content and lactic acid dehydrogenase levels of <250 mIU/mL. Cancer is suspected if the fluid is bloody or murky and has a high content of fat, protein, and lactic acid dehydrogenase. After aspiration of 20–30% of the cystic fluid, the same amount of 60% contrast dye is injected, and diagnostic radiographs are obtained in the prone, supine, upright, decubitus, and Trendelenburg positions. If necessary, another 20–30% of the cystic fluid may be replaced by air for obtaining double-contrast radiographs.
For therapeutic obliteration of cysts, sclerosing agents such as Pantopaque or 95% ethanol can be injected after complete evacuation of the cystic fluid. A volume of 10–100 mL of 95% ethanol, approximating 10–20% of the original volume of cystic fluid, is injected into the cyst and should be drained after 30 minutes.
Retroperitoneal Fluid Collections
Low-viscosity retroperitoneal fluid collections (urinoma, lymphocele) are usually a complication of surgical procedures. However, urinoma may also be caused by exogenous trauma or by fornix rupture due to acute ureteral obstruction. Percutaneous techniques of catheter drainage eliminate the need for open surgical revision in most cases.
Insertion of a small (8–10F) catheter (with numerous side holes) is usually sufficient. Adjuvant measures are required to allow for sealing of a fluid leak or obliteration of a cyst. In cases of urinoma, the upper urinary tract must also be drained by a ureteral catheter or percutaneous nephrostomy catheter until drainage from the urinoma stops. Lymphoceles that develop following pelvic or retroperitoneal lymphadenectomy or renal transplantation often undergo spontaneous regression and usually do not require puncture and drainage. However, large lymphoceles developing after retroperitoneal lymphadenectomy may cause pain and even ureteral obstruction (Figure 8–11). Patients should be treated with parenteral nutrition, systemic administration of somatostatin, and abdominal compression by bandaging, but if lymph drainage after percutaneous puncture and catheter placement persists for >1 week, surgical intervention with intraperitoneal marsupialization of the lymphocele and ligation or electrocoagulation of lymphatic vessels is indicated.
Percutaneous drainage of a lymphocele causing ureteral displacement and compression.
High-viscosity fluid collections (hematoma, abscess) usually require a large-bore (14–20F) percutaneous catheter for sufficient drainage. Perirenal hematomas are most frequently caused by surgical or exogenous trauma and rarely develop spontaneously in the presence of a bleeding disorder or due to rupture of a renal tumor. Indications for percutaneous drainage are rare, as most small hematomas resolve spontaneously and should be followed by ultrasound or CT only. A hematoma that increases in size requires surgical intervention rather than percutaneous drainage. Secondary infection of a hematoma may be an indication for percutaneous drainage.
A perirenal abscess is mostly a complication of surgery; hematogenic renal abscess (renal carbuncle) is less frequent. Indications for puncture and drainage should be based on CT finding of a unifocal process that can be effectively and safely drained percutaneously. Multifocal renal abscess formation is not amenable to percutaneous drainage.
Renal and Retroperitoneal Tumors
Percutaneous aspiration biopsy of renal and retroperitoneal tumors is indicated if less invasive radiographic studies are inconclusive and if cytologic findings may have an impact on further medical or surgical therapy (Figure 8–12). If curative treatment by open surgery seems to be feasible, aspiration biopsy is generally not indicated. If the identity of a renal lesion is questionable or if conservative, organ-sparing surgery is technically feasible, surgical excision of the lesion with intraoperative frozen sections is preferable over percutaneous aspiration biopsy. However, aspiration biopsy may be indicated to avoid radical nephrectomy of a possibly benign lesion. In multifocal or possibly metastatic lesions, cytologic evaluation can be crucial for planning surgical or medical therapy, and in these cases, aspiration biopsy is usually indicated. Interpretation of cytologic findings is limited by a 10–25% incidence of false-negative findings and the difficulty in discriminating normal renal tubular cells from low-grade renal cell cancer. As a rare complication, tumor seeding in the puncture tract has been described. The aspirate is immediately spread on glass slides. For standard Papanicolaou stains, alcohol fixation must be used.
Percutaneous fine-needle biopsy. Left: Aspiration biopsy of a renal lesion. Right: Guidance with computed tomography scanning for fine-needle aspiration biopsy of an exophytic renal cell carcinoma.
The widespread use of ultrasound has led to an increased rate of incidental diagnosis of small renal tumors, which account for 48–66% of renal cell carcinoma diagnoses. With the advent of minimally invasive techniques and improved radiodiagnostic possibilities, nonresectional renal tumor ablation has emerged and is gaining increased attention. However, cryotherapy, radiofrequency ablation (RFA), and high-intensity focused ultrasound (HIFU) are still considered experimental procedures in the clinical setting. However, cryotherapy and RFA are proving to be viable strategies for the treatment of small renal masses based on short-term and intermediate-term oncological outcomes. In a meta-analysis by treatment modality, 77.8% of tumors were treated by partial nephrectomy, 7.7% by cryoablation, 9.4% by RFA, and 5.1% by active surveillance. The therapeutic strategies of local energy application aim at selective tumor destruction with minimal injury to the surrounding normal kidney parenchyma and reduced morbidity. Cryotherapy is the most evaluated probe ablative method for the treatment of small renal masses. The biological principle of cryotherapy is tissue destruction by repeated rapid freeze and thaw cycles down to temperatures below −20°C. Liquid argon and liquid nitrogen are the two most commonly used freezing agents. The cell destruction mechanism comprises intra- and extracellular ice crystal formation leading to intracellular dehydration and ultimately cell disruption. This is followed by a delayed cell death, which occurs during the thaw phase owing to vasoconstriction and microcirculatory failure. Repeating the freeze–thaw cycle intensifies tissue damage. However, since the freezing effect decreases with increasing distance from the freezing probe, the “iceball” has to extend approximately 1 cm beyond the tumor margin to ensure complete tumor destruction. RFA involves coagulation of tumors by directly applying temperatures of 50–100°C throughout the tumor via needle electrodes. Since tissue carbonization at the electrode tip increases the impedance for radiofrequency transmission, tissue conductivity can be maintained by simultaneously irrigating saline through the tissue (“wet” RFA), resulting in larger RFA lesions for therapy of larger renal tumors. This can also be accomplished by multiple electrodes, which create overlapping ablation fields. The vicinity of larger caliber vessels results in dissipation of heat (“heat sink effect”) and influences the efficacy of RFA negatively. Thus, peripheral exophytic tumors seem to be controlled better than central tumors in the vicinity of larger vessels.
Indications are similar for both techniques and are presently restricted to patients with comorbidity and/or advanced age who are not suitable to surgical treatment, impaired renal function, multiple bilateral tumors as in von Hippel–Lindau disease, and renal tumors in a solitary kidney. Guidelines for cryotherapy do not recommend treatment of tumors >3 cm in size and for RFA not >5 cm. Further relative contraindications for both procedures include hilar or central tumors and cystic tumors. An absolute contraindication is untreated coagulopathy.
The tumor mass can be approached by open surgery, laparoscopy, or percutaneously using fine probes and high-resolution imaging techniques. However, the minimally invasive character of the procedure itself ideally deserves a less invasive approach than open surgery. Proponents of laparoscopy emphasize the advantage of mobilizing the tumor and providing excellent exposure, thus avoiding damage to adjacent structures. It also allows for precise confirmation of probe positioning and monitoring the progress of the procedure such as development of the iceball in cryotherapy under direct vision. Percutaneous management requires MRI, CT scan with technical capabilities to construct three-dimensional pictures, or real-time ultrasound guidance for monitoring probe placement and progress of therapy. The percutaneous approach may be performed as an outpatient procedure, and it is typically reserved for posterior tumors. Special patients requiring multiple procedures as in von Hippel–Lindau disease thus may benefit from a percutaneous treatment. In contrast to cryoablation, which has the advantage of intraoperative laparoscopic and sonographic monitoring of the ice ball, RFA lacks reliable real-time monitoring of the therapeutic progress. However, the introduction of real-time MRI guidance and monitoring of RFA may overcome this difficulty.
Both methods, cryotherapy and RFA, have shown promising results in carefully selected patients. Cryotherapy is associated with 93% and 81% 5- and 10-year cancer-specific survival, respectively. However, significantly increased local progression rates were calculated for cryoablation (relative risk = 7.45) and RFA (relative risk = 18.23) as compared with partial nephrectomy. And follow-up of partial nephrectomy series is still considerably longer than for ablative techniques. It must be emphasized that a significant selection bias exists in the application of these techniques. Published series of ablative treatment options include statistically significant older patients and smaller tumors as compared with the standard of partial nephrectomy. Also, a significant number of tumors treated with ablative techniques have unknown or indeterminate histology that could influence oncological results as a confounding factor. Furthermore, it is important to consider that different criteria may be used to define disease recurrence for ablative and for resectional techniques, hampering comparison of results. In contrast to cryotherapy, where tumor size decreases with time, tumor size after RFA remains mostly constant. Tumor size after successful cryotherapy can decrease up to 75% over 3 years, and tumors may even completely disappear on MRI in some cases. This fact is important for posttreatment surveillance. A major drawback of ablative techniques is the lack of reliable histologic confirmation of complete tumor ablation. Assessment is commonly done by CT scan. After RFA, a successfully ablated lesion becomes fibrotic and nonperfused and does not show contrast enhancement as compared with a viable tumor.
Complication rates (major and minor) of cryotherapy are 1.4% and 12.2%, and complication rates of RFA are 2.2% and 6%, respectively. The most commonly observed complications of cryotherapy and RFA are pain, paresthesia, and hemorrhage at the probe insertion site, occurring in approximately 5% of all patients. Rare complications include perinephric hematoma, renal rupture, UPJ obstruction, and damage to adjacent organs. Anteriorly or centrally located tumors that abut the UPJ pose an increased risk for complications, especially colonic injuries or lesions of the renal collecting system and ureter. Bleeding complications have decreased with the use of ultrathin probes (1.5 mm diameter). Specifically for RFA, bleeding can be minimized by active coagulation of the puncture tract while removing the probe. Conversion rates for cryoablation (3.5%) are similar to laparoscopic partial nephrectomy rates (3.9%) and higher than RFA rates (1.6%).
Ablative methods are still constantly evolving. Uncertainties exist regarding the exact amount of energy required, duration of treatment, mode of energy delivery, and types of electrodes used and render comparison of published results difficult. The adjunctive use of chemotherapeutic agents such as cyclophosphamide, 5-fluorouracil, and bleomycin or radiotherapy may have a synergistic effect on cryoablation and intensify its ablative capabilities. Further development of imaging techniques and combination with new technologies, such as single-port laparoscopic and natural orifice transluminal endoscopic surgery (NOTES), may potentially expand the indication range for ablative surgery.
Other techniques with limited animal and clinical experience that remain experimental include HIFU, microwave thermotherapy (MT), laser interstitial thermotherapy (LITT), pulsed cavitational ultrasound, chemoablation with or without radiofrequency, and radiosurgery.
Renal biopsy for diagnosis and classification of medical renal disease can be performed percutaneously or by open surgery. Because specimens, rather than aspirates, are needed for diagnostic histologic study, large-bore (14–16 gauge) Franklin–Silverman or Tru-Cut needles are used. Ultrasonic or fluoroscopic guidance is preferable to blind renal puncture. However, even with puncture aimed precisely at the dorsal aspect of the lower pole of the kidney, where accidental injury to large vessels is less likely, bleeding is to be expected because of the vascularity of the parenchyma and is the major complication of this procedure (about 5% of cases, with a mortality rate of 0.1%). Hematoma can usually be followed conservatively by ultrasound or CT scan, but transvascular embolization, open surgical revision, and even nephrectomy have been required following diagnostic renal biopsy. Therefore, open surgical biopsy rather than percutaneous biopsy is indicated in patients with solitary kidneys or uncontrolled hypertension.