Adverse events during radiofrequency treatment of 582 hepatic tumors

Hepatectomy plus intraoperative radiofrequency ablation and chemotherapy to treat technically unresectable multiple colorectal liver metastases

BACKGROUND

Results and indications of intra-operative radiofrequency (RF) ablation of liver metastases (LM) are not well defined in the literature.

AIM

To appreciate the survival rate of patients with strictly unresectable LM (defined on technical but not oncological criteria) when undergoing liver resection plus RF, along with optimal systemic chemotherapy.

PATIENTS AND METHODS

Sixty three patients with technically unresectable LM (either >5, or bilateral with no sparing of at least one sector of the liver, or with tumor proximity to central major vascular structures) were treated. Extrahepatic metastases were also resected in 27% of patients. All patients received perioperative chemotherapy. The median follow-up was 27.6 months (range: 15-74).

RESULTS

There was no postoperative mortality and the morbidity rate was 27%. The 2-year overall survival rate of the 63 patients was 67% with a median survival of 36 months. The local recurrence rates were similar for the three types of local treatments: 7.1% for the 154 RF ablations, 7.2% for the 55 wedge resections, and 9% for the 44 segmental anatomic resections (P = 0.216). Hepatic recurrences occurred in 71% of patients.

CONCLUSION

The combination of anatomic segmental and wedge resections, RF ablation, and optimal chemotherapy in patients with technically unresectable LM results in a median survival of 36 months.

Needle Tract Seeding after Radiofrequency Ablation of Hepatic Tumors

PURPOSE

To determine the incidence and risk factors associated with needle tract seeding after radiofrequency ablation (RFA) of liver tumors.

MATERIALS AND METHODS

A prospective data base of patients with hepatic tumors treated by RFA from December 1999 until August 2003 was reviewed to identify patients with needle tract seeding. During this period, 200 patients (148 men, 52 women) with 299 lesions underwent 298 treatment sessions. Patients with both primary (153 hepatocellular carcinoma, two cholangiocarcinoma) and a variety of secondary tumors (35 colorectal, 10 other) were treated. RFA was performed percutaneously with computed tomography (CT) and/or ultrasound (US) guidance, or with US guidance at laparoscopy or laparotomy. All procedures were performed with a LeVeen needle electrode. The needle tract was not routinely coagulated or embolized.

RESULTS

Eight patients out of 200 (4%) were identified with needle tract seeding, based on imaging findings or surgical reintervention. This corresponds to a rate of eight of 298 (2.7%) per treatment session and eight of 299 (2.7%) per lesion. Statistically significant risk factors for neoplastic seeding included treatment of a subcapsular lesion (OR = 11.57, P = .007), multiple treatment sessions (OR = 2.0, P = .037), and multiple electrode placements (OR = 1.4, P = .006).

CONCLUSIONS

Neoplastic seeding may occur after RFA of liver tumors. The results show that the frequency of this complication is not insignificant, and are at the upper end of rates reported in the literature of 0.5% to 2.8%. Specific risk factors identified in this study include treatment of subcapsular lesions, patients treated in multiple sessions, and lesions requiring more than one electrode placement.

Changes in bile ducts after radiofrequency ablation of hepatocellular carcinoma: frequency and clinical significance

OBJECTIVE

The purpose of our study was to determine the frequency of bile duct changes after radiofrequency ablation for hepatocellular carcinoma and to evaluate their clinical significance.

MATERIALS AND METHODS

Between April 1999 and August 2003, 389 patients with 521 hepatocellular carcinomas underwent a total of 571 sessions of radiofrequency ablation. The maximum dimension of the tumors measured on sonography was 2.4 +/- 0.9 cm (mean +/- SD) (range, 0.5-5.0 cm). The frequency and type of bile duct changes resulting from radiofrequency ablation, the time interval between radiofrequency ablation and the first appearance of bile duct changes, and the serial changes at follow-up CT were analyzed. Complications related to bile duct changes were also evaluated by reviewing medical records and CT scans.

RESULTS

Bile duct changes occurred in 69 (12%) of 571 sessions and 66 (17%) of 389 patients. Bile duct changes seen on CT included mild dilatation of upstream bile ducts surrounding the ablation zone in 57 patients (82.6%), biloma in the ablation zone in four patients (5.8%), and both in eight patients (11.6%). The mean time interval between radiofrequency ablation and the initial appearance of bile duct change was 1.6 months (range, immediate-9 months). Most (87%) of the 69 patients with bile duct changes showed no progression on follow-up CT, and only nine (13%) had slight progression. All patients but one, in whom cholangitis developed, had no major complications requiring specific treatment during the follow-up period.

CONCLUSION

Although bile duct changes were frequent after the radiofrequency ablation of hepatocellular carcinoma, most were of no clinical significance, and major complications requiring additional treatment were rare.

Radiofrequency ablation of colorectal liver metastases

BACKGROUND

Untreated patients with colorectal liver metastases rarely survive 3 years, and the 3-year survival rate for patients treated with chemotherapy is 3%. The best survival rates are for the small subgroup that has operable disease, i.e., 39% at 5 years. Radiofrequency ablation (RFA) offers a new opportunity to destroy liver metastases in patients who are not surgical candidates because of disease distribution or comorbidity.

METHODS

Acceptance criteria were a maximum of four or five liver lesions with a maximum diameter of 4 or 5 cm and no evidence of active extrahepatic disease. Nearly all treatments were performed percutaneously using ultrasound, computed tomography, or magnetic resonance imaging (or some combination) for guidance and monitoring. RFA is a minimally invasive procedure that can be readily repeated. General anesthesia facilitates the procedure but is not essential. Multiple overlapping ablations are required to ensure optimal treatment in all but the smallest tumors.

RESULTS

In our cohort of 167 patients with colorectal liver metastases, 73 fulfilled the optimal acceptance criteria (5 or fewer tumors that were </=5 cm). The median survival periods were 38 months, with a 5-year survival rate of 30%, after the diagnosis of liver metastases and 31 months, with a 5-year survival rate of 25%, after the first ablation.

CONCLUSION

RFA increases the therapeutic options for patients with colorectal metastases. Until controlled trials can better define the role of RFA, there are several groups of patients who are not surgical candidates and can be considered for RFA.

Factors for early tumor recurrence of single small hepatocellular carcinoma after percutaneous radiofrequency ablation therapy

AIM: To evaluate the factors affecting the early tumor recurrence within one year in cirrhotic patients having a single small hepatocellular carcinoma (HCC) after complete tumor necrosis by radiofrequency ablation (RFA) therapy.

METHODS: Thirty patients with a single small HCC received RFA therapy by a RFA 2000 generator with LeVeen needle. Tri-phase computerized tomogram was followed every 2 to 3 mo after RFA. The clinical effects and tumor recurrence were recorded.

RESULTS: The initial complete tumor necrosis rate was 86.7%. Twenty-two patients were followed for more than one year. The local and overall recurrence rates were 13.6% and 36.4%, 33.3% and 56.2%, 46.6% and 56.2% at 12, 24 and 30 mo, respectively. No major complication or procedure-related mortality was found. The risk factors for early local tumor recurrence within one year were larger tumor size, poor pathologic differentiation of tumor cells and advanced tumor staging. The age of patients with new tumor formation within one year was relatively younger (55.1±8.3 vs 66.7±10.8, P = 0.029).

CONCLUSION: Large tumor size, poor pathologic differentiation of tumor cells and advanced tumor staging are the risk factors for early local tumor recurrence within one year, and young age is the positive predictor for new tumor formation within one year.

Radiofrequency thermal ablation of liver tumors

Radiofrequency ablation (RFA) of liver tumors was first proposed in 1990. New technologies enable us to produce liver thermal lesions of approximately 3-3.5 cm in diameter; RFA has consequently become an emerging percutaneous therapeutic option both for small hepatocellular carcinoma (HCC) and for non-resectable liver metastases, mainly from colorectal cancer. New devices (for example, triplet of cooled needles, wet needles) and combined therapies (tumor ischemia and RFA) have made it possible to treat large tumors. RFA can be carried out by a percutaneous, laparoscopic or laparotomic approach. Percutaneous RFA can be performed with local anaesthesia and mild sedation; deep sedation or general anaesthesia are also used. The guidance system is generally represented by ultrasound. CT or MR examinations are the more sensitive tests for assessing therapeutic results. The series of patients treated with RFA allow the technique to be considered as effective and safe, achieving a relatively high rate of cure in properly selected cases; it should be classified as curative/effective treatment for HCC, replacing percutaneous ethanol injection. The complication rate of RFA is low but not negligible; key elements in a strategy to minimize them are identified.

Successful Treatment of Hepatocellular Adenoma with Percutaneous Radiofrequency Ablation

OBJECTIVE

The purpose of our study was to report the safe and successful treatment of hepatocellular adenoma with percutaneous radiofrequency ablation.

CONCLUSION

Our limited experience indicates that percutaneous radiofrequency ablation is both safe and effective in the treatment of the small hepatocellular adenoma in carefully selected patients.

Reduced tumor growth with combined radiofrequency ablation and radiation therapy in a rat breast tumor model

PURPOSE

To determine whether use of combined radiofrequency (RF) ablation and external-beam radiation therapy increases end-point survival beyond that with either RF ablation or radiation therapy alone in an animal tumor model.

MATERIALS AND METHODS

With a protocol approved by the institutional animal care and use committee, R3230 mammary adenocarcinoma (12.5 mm +/- 0.6 [standard deviation]) was implanted subcutaneously into 107 female Fischer 344 rats. Initially, 42 tumors were randomized into four treatment groups: (a) RF ablation (70 degrees C for 5 minutes) alone, (b) RF ablation followed by radiation therapy with a total dose of 20 Gy, (c) 20-Gy radiation alone, and (d) no treatment. Another 19 tumors were randomized to receive (e) RF ablation (70 degrees C for 5 minutes) followed by 5-Gy radiation, (f) 5-Gy radiation alone, or (g) no treatment. Animals were followed up until survival end point (either until tumor growth to 30 mm in diameter, or for 120 days if no tumor was seen in mammary fat pad or chest wall). Results were analyzed with the Kaplan-Meier method. Histopathologic analysis was performed in 15 additional tumors at survival end point and 18 other representative tumors at other specified end points.

RESULTS

Combined RF ablation and 20-Gy radiation resulted in complete local control in nine (82%) of 11 tumors, compared with one (9%) of 11 tumors treated with RF ablation alone and one (17%) of six treated with RF ablation and 5-Gy radiation (P < .001). No local control was achieved in rats with radiation therapy alone or in controls. Median end-point survival was 12 days for controls, 20 days with RF ablation or 5-Gy radiation alone, 30 days with RF ablation plus 5-Gy radiation, 40 days with 20-Gy radiation alone, and 120 days with RF ablation plus 20-Gy radiation. Mean end-point survival was 13 days +/- 5 (standard deviation) for the control group, 34 days +/- 31 with RF ablation alone, and 43 days +/- 16 with 20-Gy radiation alone. Mean survival was significantly greater with 20-Gy radiation and RF ablation combined: 94 days +/- 34 (P < .001 compared with all other groups). Mean survival for rats that received 5-Gy radiation with RF ablation versus without was 46 days +/- 37 versus 24 days +/- 11, respectively.

CONCLUSION

Combined RF ablation and external-beam radiation therapy increased animal survival compared with that with either of the treatments alone or with no treatment.

Percutaneous radiofrequency ablation of hepatic colorectal metastases: technique, indications, results, and new promises

Surgical resection is the standard of care for colorectal metastases isolated to the liver. However, only 10-25% of the patients are eligible for resection because of extent and location of the disease in the liver or concurrent medical conditions. Image-guided radiofrequency (RF) ablation is a minimally invasive technique that is emerging as a viable alternate treatment of nonsurgical patients with limited hepatic metastatic disease. Several series have shown that RF ablation can result in complete tumor eradication in properly selected candidates and have provided indirect evidence that the treatment improves survival. In a recent multicenter trial including 423 patients, overall survival of RF-ablation treated patients reached 47% at 3 years and 24% at 5 years. RF ablation technology is undergoing continuous improvement, and its clinical application has been successfully expanded to the treatment of colorectal metastases to the lung. Randomized trials comparing RF ablation with either surgical resection or chemotherapy protocols, however, are still missing. In this article, we review technique, indications, clinical results, and future prospects of RF ablation in the therapeutic management of metastatic colorectal cancer patients.

Hybrid radiofrequency and cryoablation device: preliminary results in an animal model

PURPOSE

To determine whether the simultaneous application of combined bipolar radiofrequency (RF) ablation and cryoablation in a hybrid system produces larger ablation zones than RF or cryoablation alone.

MATERIALS AND METHODS

Multiple 15-minute ablations were performed in ex vivo bovine liver (n = 167) with a hybrid applicator system with RF ablation alone (0.3-0.7 A), cryoablation alone (3,500 psi, two freeze/thaw cycles), and combined RF/cryoablation (0.4-0.7 A, 1,000-3,500 psi) with use of a novel applicator consisting of two 2.5-cm active bipolar RF poles located on the same 18-gauge needle separated by two embedded cryoablation nozzles. Resultant coagulation diameters were compared with use of analysis of variance for more than three groups or Student t tests for two groups. Confirmation of the optimal parameters of combination RF/cryoablation was performed by reassessing a range of argon pressure (1,000-3,500 psi) and RF current (0.4-0.7 A) in in vivo porcine liver (n = 36). Arrays of two to four RF/cryoablation applicators were also assessed in ex vivo (n = 54) and in vivo (n = 12) liver.

RESULTS

In ex vivo liver, simultaneous RF/cryoablation (0.6 A, 3,000 psi) produced 3.6 cm +/- 0.4 of short-axis coagulation. This was significantly larger than that achieved with optimal RF alone or cryoablation alone (1.5 cm +/- 0.3 and 1.6 cm +/- 0.3, respectively; F = 95; P < .01). The coagulation diameter with simultaneous combination RF/cryoablation was related in parabolic fashion to argon pressure and current with a multivariate r(2) of 0.68. For in vivo liver, optimal combination RF/cryoablation achieved 3.3 cm +/- 0.2 of coagulation, which was significantly larger than that achieved with RF alone (1.1 cm +/- 0.1; P < .01) or cryoablation alone (1.1 cm +/- 0.1 and 1.3 cm +/- 0.1; F = 203; P < .01). The greatest contiguous coagulation was achieved with multiple-applicator arrays. For ex vivo liver, short-axis coagulation measured 5.3 cm +/- 0.1, 6.4 cm +/- 0.1, and 7.6 cm +/- 0.1 for two-, three-, and four-applicator arrays, respectively. For in vivo liver, two-, three-, and four-applicator arrays produced 5.1 cm +/- 0.2, 5.8 cm +/- 0.5, and 7.0 cm +/- 0.5 of confluent coagulation, respectively.

CONCLUSION

Simultaneous combination RF and cryoablation with use of a novel applicator design yielded significantly larger zones of coagulation than either modality alone. The large ablation diameters achieved warrant further investigation of the device.

Radiofrequency ablation in metastatic disease

The liver is the most common site of metastas from colorectal cancer. Hepatic metastases are the major cause of morbidity and mortality in those patients. Surgical resection provides the greatest potential for cure in patients with secondary liver tumors but can be offered to only a small number of patients (5%-20%). In selected patients image-guided radiofrequency ablation (RFA) takes over the role as curative treatment option, especially in patients who are technically not eligible for surgery. Technical aspects, criteria for patient selection, aspects concerning follow-up imaging and results of percutaneous radiofrequency ablation in liver metastases from colorectal cancer are discussed.

Percutaneous radiofrequency ablation for hepatocellular carcinoma

BACKGROUND

Radiofrequency ablation (RFA) was introduced recently as a therapeutic modality for hepatocellular carcinoma (HCC), an alternative to percutaneous ethanol injection therapy (PEIT), which is coming into use worldwide. Previously reported treatment efficacy and complication rates have varied considerably.

METHODS

Between February 1999 and February 2003, the authors performed 1000 treatments of RFA to 2140 HCC nodules in 664 patients with a cooled-tip electrode at the University of Tokyo Hospital (Tokyo, Japan). Short-term and long-term complications were analyzed by treatment and session basis. Cumulative survival was also assessed in 319 patients who received RFA as primary treatment (naive patients) and 345 patients who received RFA for recurrent tumor after previous treatment including resection, PEIT, microwave coagulation therapy, and transarterial embolization (nonnaive patients).

RESULTS

A total of 40 major complications (4.0% per treatment, 1.9% per session) and 17 minor complications (1.7% per treatment, 0.82% per session) were observed during the observation period until March 31, 2004. There were no treatment-related deaths. Surgical intervention was required in one case each of bile peritonitis and duodenal perforation. The cumulative survival rates at 1, 2, 3, 4, and 5 years were 94.7%, 86.1%, 77.7%, 67.4%, and 54.3% for naive patients, whereas the cumulative survival rates were 91.8%, 75.6%, 62.4%, 53.7%, and 38.2% for nonnaive patients, respectively.

CONCLUSIONS

The authors confirmed the safety and efficacy of RFA for HCC in a large-scale series and long-term prognosis was satisfactory.

Complications After Percutaneous Saline-Enhanced Radiofrequency Ablation of Liver Tumors: 3-Year Experience with 336 Patients at a Single Center

OBJECTIVE

Our objective was to report the complications that occurred in a large series of patients with primary or metastatic liver tumors treated with percutaneous saline-enhanced radiofrequency ablation under sonographic guidance at a single center during 3 years of experience.

SUBJECTS AND METHODS

Between September 2000 and October 2003, 336 consecutive patients (221 men and 115 women; age range, 44-78 years; mean, 67 years) with 407 malignant liver tumors were treated at our institution using radiofrequency ablation. Of these patients, 287 had hepatocellular carcinoma from cirrhosis, 47 had liver metastases (38 from colon, six from breast, two from lung, and one from cutaneous melanoma), and two had primary cholangiocarcinoma. Adverse events related to radiofrequency ablation were prospectively recorded.

RESULTS

The number of sessions performed was 375 (39 patients had two sessions). The number of patients with major complications, including death, was three (0.9%). The overall mortality rate was 0.3% (1/336). One patient died because of worsening liver decompensation. Two other major complications occurred. In one patient (0.3%), liver abscess and sepsis developed and were successfully treated with percutaneous sonography-guided needle (18-gauge) aspiration and IV antibiotics. Mild posttreatment ascites occurred in one patient (0.3%). One patient showed self-limiting subcutaneous cellulitis along the electrode-needle path that healed in 2 weeks. Fever lasting 1-3 days and pain lasting 12-24 hr were observed in 141 patients (42%) and 211 patients (63%), respectively. So far, no cutaneous or abdominal wall seeding has been observed clinically or sonographically.

CONCLUSION

Radiofrequency ablation of liver tumors can be considered safe. Life-threatening acute liver failure can be considered a rare possible complication.

Hepatocellular carcinoma treated with interventional procedures: CT and MRI follow-up

In the past decade, a variety of interventional procedures have been employed for local control of hepatocellular carcinoma (HCC). These include transcather arterial chemoembolization (TACE) and several tumour ablation techniques, such as percutaneous ethanol injection (PEI), radio-frequency ablation (RFA), or percutaneous microwave coagulation therapy (PMC), laser-induced interstitial thermotherapy (LITT), etc. For a definite assessment of the therapeutic efficacy of interventional procedures, histological examination using percutaneous needle biopsy may be the most definite assessment of the therapeutic efficacy of interventional therapy, however, it is invasive and the specimen retrieved does not always represent the entire lesion owing to sampling errors. Therefore, computed tomography (CT) and magnetic resonance imaging (MRI) play a crucial role in follow-up of HCC treated by interventional procedures, by which the local treatment efficacy, recurrent disease and some of therapy-induced complications are evaluated. Contrast enhanced axial imaging (CT or MR imaging) may be the most sensitive test for assessing the therapeutic efficacy. The goal of the review was to describe the value of CT and MRI in the evaluation of interventional treatments.

A tamponade leading to death after radiofrequency ablation of hepatocellular carcinoma

A case of hemorrhagic cardiac tamponade after radiofrequency ablation (RFA) of hepatocellular carcinoma (HCC) leading to death is presented. The complication occurred during a procedure performed under general anesthesia with an expandable needle system for a 2-cm HCC sited in the second segment of the liver close to the diaphragm. Thermal damage to the organs surrounding the liver are major complications of liver tumor RFA. For lesions that are adjacent to the cardiac cavities, a discussion of better therapeutic options remains necessary and has to take into account the effectiveness and complication rate of each technique.

Review of radiofrequency ablation for renal cell carcinoma

This review will discuss how minimally invasive, image-guided radiofrequency (RF) tumor ablation [i.e., coagulating tumor using short-duration heating (<15 minutes) by directly applying temperatures >50 degrees C via needle electrodes] is being incorporated as a clinical tool for the treatment of renal cell carcinoma. RF ablation has been used to treat focal liver tumors. Potential benefits of this thermal therapy include reduced morbidity and mortality compared with standard surgical resection and the ability to treat nonsurgical patients. More recently, this technique has been introduced to treat focal renal tumors, particularly incidental lesions smaller than 3 cm in elderly patients and those with comorbid conditions. Other uses have included treatment in patients with von Hippel-Lindau syndrome and other diseases that predispose patients to multiple renal carcinomas, where renal parenchymal preservation is desired. Techniques, complications, and results will be discussed. Additionally, strategies that we are currently studying to improve RF outcomes and enable the potential treatment of larger tumors will be addressed. Most notably, recent data on increased coagulation achieved by combining RF ablation with antivascular/antiangiogenic therapies, such as arsenic trioxide, that reduce blood flow and promote heat retention are provided.

Radio-frequency ablation of colorectal liver metastases in 167 patients

The objective of this paper is to report our results from a prospective study of 167 patients with colorectal liver metastases treated with radio-frequency ablation (RFA). Three hundred fifty-four treatments were performed in 167 patients, 99 males, mean age 57 years (34-87). The mean number of metastases was 4.1 (1-27). The mean maximum diameter was 3.9 cm (1-12). Fifty-one (31%) had stable/treated extra-hepatic disease. Treatments were performed under general anaesthesia using US and CT guidance and single or cluster water-cooled electrodes (Valleylab, Boulder, CO). All patients had been rejected for or had refused surgical resection. Eighty percent received chemotherapy. Survival data were stratified by tumour burden at the time of first RFA. The mean number of RFA treatments was 2.1 (1-7). During a mean follow-up of 17 months (0-89), 72 developed new liver metastases and 71 developed progressive extra-hepatic disease. There were 14/354 (4%) major local complications and 22/354 (6%) minor local complications. For patients with < or =5 metastases, maximum diameter < or =5 cm and no extra-hepatic disease, the 5-year survival from the time of diagnosis was 30% and from the time of first thermal ablation was 26%. Given that the 5-year survival for operable patients is a median of 32%, our 5-year survival of 30% is promising.

Thermal Protection during Percutaneous Thermal Ablation of Renal Cell Carcinoma

Thermal injury to collateral structures is a known complication of thermal ablation of tumors. The authors present the use of CO(2) dissection and inserted balloons to protect the bowel during percutaneous radiofrequency (RF) ablation and cryotherapy of primary and locally recurrent renal cell carcinoma. These techniques offer the potential to increase the number of tumors that can be treated with RF ablation or cryotherapy from a percutaneous approach.

Rapid progression of hepatocellular carcinoma after Radiofrequency Ablation

AIM: To report the results of radiofrequency ablation (RFA) of hepatocellular carcinoma (HCC) in cirrhotic patients and to describe the treatment related complications (mainly the rapid intrahepatic neoplastic progression).

METHODS: Eighty-seven consecutive cirrhotic patients with 104 HCC (mean diameter 3.9 cm, 1.3 SD) were submitted to RFA between January 1998 and June 2003. In all cases RFA was performed with percutaneous approach under ultrasound guidance using expandable electrode needles. Treatment efficacy (necrosis and recurrence) was estimated with dual phase computed tomography (CT) and alpha-fetoprotein (AFP) level.

RESULTS: Complete necrosis rate after single or multiple treatment was 100%, 87.7% and 57.1% in HCC smaller than 3 cm, between 3 and 5 cm and larger than 5 cm respectively (P = 0.02). Seventeen lesions of 88(19.3%) developed local recurrence after complete necrosis during a mean follow up of 19.2 mo. There were no treatment-related deaths in 130 procedures and major complications occurred in 8 patients (6.1 %). In 4 patients, although complete local necrosis was achieved, we observed rapid intrahepatic neoplastic progression after treatment. Risk factors for rapid neoplastic progression were high preoperative AFP values and location of the tumor near segmental portal branches.

CONCLUSION: RFA is an effective treatment for hepatocellular carcinoma smaller than 5 cm with complete necrosis in more than 80% of lesions. Patients with elevated AFP levels and tumors located near the main portal branch are at risk for rapid neoplastic progression after RFA. Further studies are necessary to evaluate the incidence and pathogenesis of this underestimated complication.