الفهرس 
GROSS ANATOMY OF THE KIDNEYOnly 14 pages are availabe for public view
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Abstract
Renal lesions are among the most common incidental findings on ultrasound or abdominal CT. Multislice computed tomography (MSCT) plays a central role in the evaluation of a patient with a suspected renal mass, not only in the detection but also in the characterization of the mass.
Once a renal mass is detected, it is critical to characterize it accurately and to differentiate clinically insignificant renal cysts from solid and potentially malignant renal tumors.
MSCT renal imaging with rapid data acquisition and greatly reduced scanning time, gives the advantage of scanning the same anatomical area repeatedly within a short period of time, so different phases of contrast uptake can be differentiated (arterial, cortico-medullary, nephrographic, and excretory phases) after administration of a single bolus of intravenous contrast material. This is helpful for better discrimination of benign or malignant lesions especially in the highly vascularized kidney. So, it is fundamental to select carefully the appropriate imaging sequence and to choose the phase or the combination of phases that is most appropriate as significant abnormalities could be obscured or become less conspicuous if the timing is not optimal and also to minimize radiation exposure to the patient as possible.
An initial series of unenhanced (pre contrast) scans through the kidneys should be a part of every protocol for evaluation of a suspected renal mass.
Unlike the renal parenchyma, renal mass lesions do not contain functioning renal nephrons, so they exhibit varying degrees of enhancement depending on their vascularity, with the vascular tumors displaying maximum enhancement in the arterial phase (AP). However, many studies have demonstrated that the delayed phases are more sensitive than the arterial phase (AP) for the detection of small (<3 cm) renal lesions, as almost all renal masses have lower attenuation than the homogeneously enhancing surrounding normal renal tissue [Sheth and Fishman, 2006].
Renal cysts are fluid filled lesions, and because they are avascular lesions, they demonstrate no enhancement after intravenous contrast administration. In contrast, renal cell carcinoma (RCC) has a rich vascular supply and enhances significantly after intravenous contrast.
It is very difficult to differentiate oncocytoma from renal cell carcinoma (RCC), however the MSCT appearance of a homogeneously enhancing large mass with a pseudo-capsule and a central scar may suggest the oncocytoma, since a large RCC tends to enhance heterogeneously. Thus, the differentiation by imaging is very important so that partial or radical nephrectomy is decided. Unfortunately, small oncocytomas cannot be reliably distinguished from RCC with imaging.
MSCT remains the most widely available and single most effective modality for staging patients with RCC, with reported accuracy of 80–95% [Hallscheidt et al., 2004]. MSCT has been shown to be highly accurate for diagnosing spread of RCC into the renal vein and inferior vena cava, with reported accuracy reaching up to 100% which is very valuable in patient management. By using the conventional CT the accuracy is only 50-80% [Catalano et al., 2003].
It is often impossible to differentiate between Robson stage I disease (tumour confined by the renal capsule) and stage II disease (tumor spread to the perinephric fat) with MSCT [Ljungberg, 2004]. This distinction has not historically been critical, as the perinephric fat would be routinely excised as part of a radical nephrectomy. On the other hand, by Pretorius (2006), magnetic resonance imaging (MRI) appears to be superior for evaluation of tumor involvement of the perinephric fat.
With the accuracy of MSCT in detection and characterization of small solid renal masses, over one-third of renal cell carcinomas (RCC) are discovered serendipitously, and the majority of these incidental tumors are stage T1 lesions [Leslie et al., 2003].. Paralleling this clinical-stage migration, there is a growing trend for more limited surgical resection, such as adrenal-sparing radical nephrectomy, laparoscopic nephrectomy, or partial, nephron-sparing, nephrectomy.
MSCT is very effective in detecting retroperitoneal lymphadenopathy, however it can not differentiate malignant lymphadenopathy from lymph node enlargement due to reactive hyperplasia.
Three-dimensional MSCT displays the tumor and its relationships to the adjacent organs in multiple planes and orientations which is very valuable to increase diagnostic confidence and help plan surgical resection.
MSCT is the most reliable examination to detect fat components within the small renal masses and thus making the diagnosis of angiomyolipomas, while on the other hand the conventional CT may fail to reveal the fat especially in small tumors or in tumors with small amount of fat. Unfortunately, there is approximately 4.5% of angiomyolipomas contain only a minimal amount of fat that is below the detection threshold of MSCT [Kim et al., 2004].
MSCT can also detect intra or perirenal blood as well as perinephric extension of angiomyolipoma.
Although the CT data acquisition remains limited to the axial plane, reconstructed data from MSCT scanners can provide excellent resolution in the reconstructed planes with better spatial resolution than that of MRI [Pretorius, 2006]. Also there is limitation that calcifications are difficult to detect on MR imaging [Israel and Bosniak., 2004].