الفهرس 
Gross anatomy of the liverOnly 14 pages are availabe for public view
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Abstract
Image-guided cancer therapies are based on the premise that local tumor control may result in enhanced survival. Surgical resection has been shown to improve survival in patients with small or isolated primary and metastatic neoplasms.
Many patients with primary and secondary tumors may not be considered candidates for surgery due to age, co-morbidity, extent of disease or refusal of surgery.
For the past two decades, a variety of imaging guided tumor ablation techniques for the local control of malignant tumors has been introduced and clinically evaluated.
Percutaneous image guided tumor ablation with use of thermal energy sources such as microwaves, high-intensity focused ultrasound, cryotherapy, and laser and percutaneous ethanol injection have recently received much attention as minimally invasive strategies for the local treatment of solid malignancies.
Recent trends toward these minimally invasive surgical options have emphasized decreased cost and time as well as reduced morbidity and mortality rates. Successful minimally invasive, image-guide local treatments will have to meet these expectations without sacrificing efficacy.
Percutaneous radiofrequency thermal ablation is being added to the arsenal of minimally invasive treatments of localized cancer.
RF systems consist of a generator and needlelike electrodes with an insulated metal shaft and a non-insulated exposed distal active tip of variable length that is inserted into the lesion with imaging guidance. The exposed tip forms a direct electric contact with the surrounding tissue. The patient is made into an electrical circuit by placing grounding pads on the thighs or back muscles.
Radiofrequency ablation induces in situ thermal coagulation necrosis through the delivery of high frequency alternating current to the tissue. Imaging helps to detect treatable lesions, guide the placement of the probe, and assess the effect of therapy. CT is used most frequently to determine whether the ablation is complete and to screen for early recurrences that may benefit from reablation.
Potential advantages of RF in situ tumor ablation include decreased cost, minimal morbidity, minimal complications, and the possibility of treatment of patients while under conscious sedation by using medications. The procedure can also be performed with general anesthesia, which can be helpful when lesions are unusually large and or difficult to target and when the patients has low tolerance for pain.
Also the possibility of performing the procedure on an out patient basis, suitability for real-time imaging guidance, the ability to easily treat recurrent tumors, and the possibility of treating patients who would not be considered candidates for surgery.
Radiofrequency thermal ablation of primary and secondary tumors can be performed safely using percutaneous, laparoscopic, or open surgical techniques. Percutaneous approach has several advantages over other approaches. The percutaneous approach is the least invasive, produces minimal morbidity, can be performed on an outpatient basis, requires only conscious sedation, relatively inexpensive and can be repeated as necessary to treat recurrent tumors.
A careful clinical evaluation is also necessary to establish the indication for RF ablation and should include history and full clinical and laboratory assessment. In addition, staging protocol including abdominal US, spiral CT, or MRI, chest X-ray or chest spiral CT and bone scintigraphy must be carried out.
Patients with cirrhosis are usually at increased risk of bleeding because of impaired coagulation, a prothrombin concentration more than 50% and a platelet count more than 50,000/ml are required to keep the risk of bleeding at an acceptably low level.
Exclusion criteria include coagulation disorders (prothrombin activity > 50% - prothrombin time < 22 seconds), a platelet count > 50.000 / ml, a severe liver cirrhosis, an advanced neoplastic disease (tumor size < 9cm, infiltrating tumor ) or a tumor located adjacent to the gall bladder, hepatic hilum, vessels, or other visceral organs. The presence of a clear and easy to detect target for needle placement is crucial for an optimal outcome.
Tumor size should be ideally smaller than 4 cm. in the greatest dimension. Nevertheless, larger lesion can also be treated by using newer RF generators and multiple needle insertions.
Technologic advances in radiofrequency equipment, methods of altering tissue response to radiofrequency treatment, and combined therapies will likely yield an improvement in the complete ablation rate of small tumors and make the treatment of larger tumors a clinically available treatment alternative. This has, in turn, led to wider clinical applications in oncology.
A directly proportionate relationship was noticed between the survival rate and the tumor response. On the contrary, both tumor size and multiplicity are inversely related to the survival rate, so early diagnosis and selection of patients is mandatory to achieve better results.
Promising results have been reported in clinical trials for using RFA IN the treatment of hepatocellular carcinoma, lung, breast, renal, adrenal and bony tumors and painful bone metastases, hepatic, splenic, and cerebral metastasis.
Radiofrequency ablation has been used as palliative treatment of RCCs. Some investigators have described the successful use of radiofrequency ablation to treat intractable gross hematuria resulting from large RCCs. In these cases, hematuria failed to resolve with standard techniques, including renal artery embolization. Radiofrequency ablation was performed without complications and led to resolution of hematuria
For adequate destruction of tumor tissue, the entire volume of a lesion must be subjected to cytotoxic temperatures. Hence, effective heating throughout the target volume (i.e. the tumor and 5 to 10 mm thickness of normal tissue) is required to ensure complete ablation of the entire tumor.
The preliminary studies have shown that radiofrequency ablation is superior to other ablation therapies as ethanol or microwave ablation therapies.
In comparison with PEI, the principal alternative, RF appears easier to perform and capable of achieving complete tumor necrosis in fewer treatment sessions compared with multisession PEI or with fewer complications compared with single-session PEI.
However, Ethanol injection may still have a valuable role for those patients who are not suitable candidates for RF ablation because of an unfavorable tumor location. Appropriate use of each treatment technique can be accomplished only when the therapeutic strategy is decided by a multidisciplinary team and is tailored to the individual patient and to the features of the disease.
Compared to surgery, RF ablation offers the advantages of being less expensive and considerably less invasive. It may thus be reasonable to use RF ablation rather than surgery as a first-choice local therapy, particularly given from the natural history of this disease, which suggests that local therapies (eg, surgery and in situ tumor ablation) will be curative in only a minority of patients.
The use of RF ablation does not prevent the simultaneous or subsequent use of other, potentially complementary, treatments. Hormonal therapy, systemic chemotherapy, and intra-arterial infusion chemotherapy each can be given before or after RF ablation, according to local preferences and practice guidelines in attempts to treat larger tumors and to reduce the incidence of development of new recurrences and, thus, improve the overall survival rate of these patients.
Patients are admitted to the hospital for a 24 hours observation after ablation unless complications necessitated longer hospitalization. Clinical examination and laboratory investigations (as complete blood count, liver function tests, renal function tests and tumor markers) are repeated in patients before discharge.
Imaging after the procedure is crucial to judge the completeness of ablation and later on to detect early recurrences.
Contrast enhanced CT, with the same parameters as at pretreatment scanning, is performed on the day following treatment to check the short term effects then the patients are scheduled for follow-up at 1, 3, 6, 12, 18, and 24 months. At the time of each follow-up imaging included CT or MR imaging of the abdomen before and after intravenous administration of contrast medium are performed for early detection of recurrences or incomplete ablation and complications.
The most important morphologic features of complete ablation are the size and characteristic smooth margins of the defect. The defect should be centered on and, at early follow-up, larger than the treated tumor to ensure tumor-free margins. The interface between the liver and the lesion should be sharp. This interface is best assessed after administration of contrast medium, when an abrupt change between the unenhanced necrotic tissue and adjacent parenchyma can be defined.
The procedure is tolerated by the patients with no major complications. In addition to well-known complications of percutaneous needle procedures such as bleeding, infection, tumor seeding, and pneumothorax, two complications specific to methods of thermal ablation therapy, which are grounding pad burns and thermal damage to adjacent organs. Complications are usually of minor degree and needs no treatment with spontaneous resolution.
Also delayed syndrome after ablation consists of flu-like symptoms (low-grade fever [up to 38.3 Cْ ] accompanied by general malaise that begin 3-5 days after the ablation and persist for approximately 5 days is encountered. Appropriate treatment of the syndrome is primarily supportive.
In conclusion, RFA of primary and secondary tumors has been proved to be an effective, minimally invasive, relatively simple and safe procedure for local control of the tumor growth with minimal morbidity and mortality rates and no treatment-related death was observed.