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RCC的image character: 

==>CT是最好的診斷及staging的工具,除非CT結果無法判斷時才用US或MRI輔助.
  1)病灶   2)當CT上看不到LAP時不一定就沒有LN involvement,可能只是沒有變大,所以可用MRI去輔助.

==>RCC在CT的特徵:
  1) 大多數with contrast呈現solid lesion with enhancement of 15-20Hu;有時合併central necrosis or calcification
  2) 有些為cystic lesion with thick septum and wall nodularity
  3) 有些完全solid with high enhancement

==>MRI上的特色:
  T1WI w/o C呈現hypointensity, T2WI呈現hyperintensity,不過都是heterogenous.

==>US上的特色:
  hyper, hypo或是iso都有可能.所以sono的角色是看這個病灶內部的性質.用來輔助為主.所以並非通常是高回音性的.

Preferred Examination: Although a variety of examinations (ultrasound [US], magnetic resonance imaging [MRI], angiography) can be used in the workup of patients with suspected RCC, the preferred method of imaging these patients is dedicated renal computed tomography (CT). In most cases, this single examination can be used to detect and stage RCC and to provide information for surgical planning without additional imaging.

In the few patients in whom the CT findings are equivocal, MRI or US can be useful. Recent literature suggests a use for contrast-enhanced Doppler US for lesions that show equivocal enhancement at CT. Angiography is rarely used in the workup of suggested RCC, but it can provide information about the origin of the tumor in troublesome cases. At present, no accepted protocol has been developed for RCC screening among asymptomatic individuals in the general population. Patients with a hereditary predisposition for RCC should be periodically examined by using dedicated renal CT.

Limitations of Techniques: The primary limitation of CT is the characterization of hypoattenuation in masses smaller than 8-10 mm, in which pseudoenhancement may be a problem. In these cases, US may be of some use in characterizing the lesions as cysts. In addition, spread to regional lymph nodes in the absence of lymph node enlargement can be missed. If contrast material cannot be intravenously administered, CT is a poor choice for evaluating RCCS. MRI should be performed instead.

The primary limitations of US include problems related to incomplete staging (bones, lungs, regional nodes) and to the detection of small non–contour-deforming masses. In addition, large patients are not good candidates for US because of technical difficulties in obtaining adequate images.

MRI is limited by patient cooperation because MRI is more sensitive to motion artifact than CT. In addition, MRI is more expensive and less readily available than CT. Furthermore, patients with pacemakers, those with certain types of medical implants, and those with severe claustrophobia are excluded from undergoing MRI. 


CT character:

On initial nonenhanced CT scans, RCCs may appear as isoattenuating, hypoattenuating, or hyperattenuating relative to the remainder of the kidney. Calcifications may be present and are usually amorphous and internal, although rimlike calcifications can also be present.

On contrast-enhanced CT scans, RCC is usually solid, and decreased attenuation suggestive of necrosis is often present. Sometimes RCC is a predominantly cystic mass, with thick septa and wall nodularity.

RCC may also appear as a completely solid and highly enhancing mass.

MRI character:

On nonenhanced T1-weighted images, RCCs usually appear isointense or hypointense relative to the remainder of the kidney. With chemical shift imaging, some clear cell carcinomas show focal or diffuse loss of signal intensity. On T2-weighted images, RCCs are usually hyperintense. Most often, they are heterogeneous. 

US character:

On sonograms, RCC can be isoechoic, hypoechoic, or hyperechoic relative to the remainder of the renal parenchyma. Smaller lesions with less necrosis are more likely to be hyperechoic and may be confused with AMLs. Isoechoic tumors are detected only by distortion of the renal contour, focal enlargement of a portion of the kidney, or distortion of the central sinus fat.
 

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