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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 31  |  Issue : 3  |  Page : 1036-1043

A comparative study of ultrasonography and computed tomography in diagnosing renal masses


Department of Radiodiagnosis, Menoufia University Hospitals, Shebeen El-Kom, Egypt

Date of Submission13-Feb-2017
Date of Acceptance23-Apr-2017
Date of Web Publication31-Dec-2018

Correspondence Address:
Mohammad A. H. El-Batt
21 Mohi-Eldin Abo El-Eiz Street, Sherbin 35661, Dakahleya
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/mmj.mmj_113_17

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  Abstract 


Objective
The aim of this study was to compare the role of ultrasonography (US) with computed tomography (CT) in diagnosing renal masses.
Background
New technological US and CT techniques are being designed to diagnose patients with renal masses. These new techniques will help doctors define and easily diagnose neoplastic and non-neoplastic renal masses.
Patients and methods
A total of 50 patients were included in the present study (27 males and 23 females; age range 3–67 years; mean age 32.7 ± 21.96 years). Detailed medical history of all patients was obtained, and all of them underwent general examination, routine laboratory investigations, especially those related to the renal system, real-time pelvic-abdominal US with color Doppler, and preintravenous and postintravenous contrast-enhanced CT of the abdomen and pelvis.
Results
Using US, we found 26 cases with malignant renal masses and 24 cases with benign renal masses. Using CT, we found 24 cases with malignant renal masses and 26 cases with benign renal masses. After correlation with histopathology results, we found that US detected four false-positive cases and one false-negative case, whereas by using CT we found only one false-positive case (P = 0.002).
Conclusion
US is the first-choice imaging procedure to detect characteristic features of renal masses. It can be performed safely as it is noninvasive and painless as well as relatively inexpensive. CT is considered to be the gold standard for accurate characterization of renal masses, differentiation of malignant from benign masses according to some criteria, and staging of these malignant masses showing distant metastasis and lymph node enlargement.

Keywords: computed tomography, renal cell carcinoma, renal masses, ultrasonography, Wilm's tumor


How to cite this article:
El-Mekkawy ESE, Abdella TF, El-Batt MA. A comparative study of ultrasonography and computed tomography in diagnosing renal masses. Menoufia Med J 2018;31:1036-43

How to cite this URL:
El-Mekkawy ESE, Abdella TF, El-Batt MA. A comparative study of ultrasonography and computed tomography in diagnosing renal masses. Menoufia Med J [serial online] 2018 [cited 2019 Jun 19];31:1036-43. Available from: http://www.mmj.eg.net/text.asp?2018/31/3/1036/248714




  Introduction Top


The incidence of renal tumors has gradually increased over the years, which can be partly explained by increased detection. As imaging modalities such as ultrasonography (US) and computed tomography (CT) have become widely available, they are used in numerous fields and often detect renal cell carcinoma (RCC) incidentally[1].

Renal masses can be divided into cystic and solid lesions. The most common have been cysts in up to 27% of patients over 50 years. Eighty-five percent of expansive solid masses are malignant. Therefore, a solid, enhancing mass must be considered malignant unless proven otherwise. RCC is the most common malignant tumor with a rising incidence of about 3% per year since 1975. Benign tumors account for ∼20% of all solid renal cortical tumors. Non-neoplastic renal masses include inflammatory pseudotumours with and without abscess formation, hematoma, and replacement lipomatosis with coexistent xanthogranulomatous pyelonephritis (XGPN)[2].

US is an appropriate initial test for nearly all patients who present with symptoms suggestive of renal disease. It is quick, effective, noninvasive, widely available, and involves no radiation. The main limitation of US is the limited ability to detect small renal lesions, particularly if they do not distort the renal parenchyma. US only provides a sensitivity of 67% for tumors that are up to 3 cm in diameter[3].

US studies of the size, attenuation features, and vascular distribution of a renal mass may reportedly suggest the pathological nature of the lesion and may add useful diagnostic information to that of other imaging techniques[4].

Furthermore, Doppler US allows for noninvasive assessment of vascular flow signals from tumor neovascularity. Thus, vascular flow detected by color Doppler US was reported to be strongly suggestive of conventional clear-cell histology[5].

CT represents the gold standard of cross-sectional imaging for the diagnosis, staging, and surveillance of RCC, especially after the latest developments in CT scanner technology, since the introduction of the helical scanners in the early 1990s. Recently, multidetector row CT scanners have been developed that use multiple rows of detectors with a widened beam shape able to obtain a true volume scan and ultra-thin sections (<0.5 mm) with minimal time for motion artifacts[6].

Multidetector CT allows the possibility to scan in multiple phases of enhancement and to obtain high-resolution multiplanar and three-dimensional images of the affected kidney with excellent anatomical details[7].

The aim of this study was to compare the role of US and the role of CT in the diagnosis of patients with renal masses.


  Patients and Methods Top


This study was conducted on 50 (27 males and 23 females; age range 3–67 years; mean age 32.7 ± 21.96 years) patients from May 2014 to March 2016 at the Medical Imaging Department of Damietta Cancer Institute, Damietta, Egypt.

All patients had undergone a safety and caution measure agreement. The confidentiality of patients was highly considered. Our targeted patients were males and females with renal masses. We, however, excluded pregnant women, patients with impaired renal functions, those with known allergy to contrast media, treated patients, and finally those with history of primary extrarenal malignancy.

Imaging protocol: we started with an overview of patients' detailed medical history with stress on history of similar illnesses or any associated renal symptoms. We then carried out a general examination on blood pressure, pulse, and temperature to avoid any side-effects. We also carried out routine laboratory investigations, especially those related to the renal system – for example, routine urine analysis, serum urea, creatinine, and electrolytes. Next, the patients underwent abdominal US to determine the nature, shape, and the location of any mass in the kidneys using Real-time US devices with color Doppler capacity (Xario XG, Toshiba, Japan). Finally, patients underwent four-detector row CT that included precontrast and postcontrast examination using light speed, GE Medical System (Milwaukee, Wisconsin, USA).

We made sure that the radiologists were present at the time of examination. We also made sure that only professionally trained CT technicians performed the examinations.

US technique: patients were initially examined in the supine position, starting at the midline below the xiphoid using the highest-frequency transducers of 7.5 MHz for infants and 5 MHz for adults. The examination included longitudinal and transverse views of both kidneys. Right or left lateral position of the patient was needed to detect the renal mass. When a mass is detected, examination of the affected kidney must be carried out for assessing the size of the mass, whether it is cystic or solid in nature, if there are any calcified foci, whether the lesion is confined to the capsule of the kidney or extends beyond, assessment of vascular flow signals by color Doppler US, whether there are enlarged lymph nodes (LNs) or not, and whether there are distant metastases such as liver deposits or not.

Computed tomography technique

The position of the patient on the CT examination table is supine. The table moves through the scanner to determine the correct starting position for the scans from the diaphragmatic copula to the symphysis pubis, and then the table moves slowly through the machine as the actual CT scanning is being performed with 5-ml slice thickness and precontrast images are obtained. Injection of nonionic iodinated contrast medium (1–2 mg/kg body weight; Ultravist, Shanghai, China) was carried out, and the postcontrast images were obtained, which consisted of an arterial or corticomedullary phase through the liver and kidneys (between 25 and 70 s after the start of contrast injection) and a portal venous or nephrographic phase of the entire abdomen (between 80 and 180 s). The excretory phase (>180 s) is occasionally helpful.

An initial series of unenhanced scans provides a baseline from which to measure the enhancement within the lesion, and multiplanar reconstructed images can be obtained.

The study was approved by the local ethics committee of our institute, and informed consent was obtained from all participants before study initiation.

Statistics analysis

The diagnostic standard reference in all cases was the histopathology results. We determined the sensitivity (how accurate the test is in positive cases), specificity (how accurate the test is in negative cases), overall accuracy of the test, positive predictive value, and negative predictive value (how accurate the test is when it gives a negative result).

All statistical analyses were performed using statistical package for the social sciences (SPSS), v. 22.0 (IBM Corp., Armonk, New York, USA).


  Results Top


Our study included 50 (27 males and 23 females) cases with different types of renal masses. Their ages ranged from 3 to 67 years.

The studied cases presented clinically with different symptoms included hematuria, abdominal swelling, loin pain, and weight loss.

We first analyzed the radiological diagnosis obtained by US and CT in all patients, and the results were compared with histopathological studies [Table 1].
Table 1: The different diagnoses obtained by ultrasonography and computed tomography correlated to the histopathological results of patients of the present study

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Using the US modality, we found 26 patients as having malignant renal masses [Figure 1] and [Figure 2]. There were 22 true-positive cases and four cases were false positive. Among those with benign renal masses [Figure 3], there were 23 true-negative cases and one case was false negative.
Figure 1: (a and b) US images showing two, well-defined, rounded, isoechoic masses, one in each kidney. The right renal mass is seen at the upper pole, whereas the left renal mass is seen at the lower pole. (c) Contrast-enhanced CT coronal reformatted image showing the two masses that appeared well defined, rounded lesions, bulging beyond the renal capsule, and displaying heterogeneous enhancement. The findings of US and CT correlated with the histopathological results, which revealed bilateral renal cell carcinoma. CT, computed tomography; US, ultrasonography.

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Figure 2: (a) US image showing a well-defined, rounded, hypoechoic, soft-tissue mass seen arising from the mid zone of the left kidney, with lower hydrocalycosis. (b) Contrast-enhanced axial CT image showing a well-defined soft-tissue mass, occupying the left mid renal zone, infiltrating the renal pelvis. It displays heterogenous postcontrast enhancement with areas of cystic degeneration inside and no foci of calcification. The findings of US and CT were correlated with histopathological results, which revealed left renal Wilm's tumor. CT, computed tomography; US, ultrasonography.

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Figure 3: (a) US image showing well-defined, rounded, soft-tissue mass, markedly hyperechoic relative to the renal parenchyma and accompanied by acoustic shadowing. (b) Unenhanced CT image showing left renal mass of mixed attenuation interspersed with areas of fat attenuation (−20 HU). (c) Postcontrast axial CT image showing mild heterogenous enhancement. The findings of US and CT were correlated with histopathological results, which revealed left renal angiomyolipoma. CT, computed tomography; US, ultrasonography.

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Using CT, we found 24 patients as having malignant renal masses [Figure 1] and [Figure 2] – 23 were true-positive cases and one case was false positive [Figure 4]. Among the 26 patients with benign renal masses, all of them were true negative.
Figure 4: (a) US image showing a well-defined, rounded, isoechoic mass, seen in the lower pole of the left kidney. (b and c) Contrast-enhanced axial CT images showing isodense mass with intense peripheral enhancement and central hypodense area (stellate scar). The radiological provisional diagnosis was left renal cell carcinoma, but the lesion was proved by histopathology to be left renal oncocytoma. CT, computed tomography; US, ultrasonography.

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These results were compared with histopathological studies to detect sensitivity, specificity, and accuracy of US and CT modalities in diagnosing benign and malignant renal masses [Table 2].
Table 2: Sensitivity, specificity, and accuracy of ultrasonography compared with computed tomography in diagnosing renal masses of the studied group

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The number of different pathological types of benign and malignant renal masses of the studied groups and their percentages are shown [Table 3] and [Table 4].
Table 3: Different pathological types of benign renal masses

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Table 4: Number of different pathological types of malignant renal masses of the patients of the study and their percentage

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The renal masses are classified according to their consistency into cystic and solid. Cystic masses [Figure 5] were found in 21 cases representing 42%, whereas solid masses were present in 29 cases representing 58%.
Figure 5: (a and b) US images showing enlargement of both kidneys, with multiple hypoechoic cysts of variable size and shape, not communicating with each other or with the renal collecting system. (c) Unenhanced CT image showing enlargement of both kidneys with multiple, hypodense, rounded lesions. (d) Contrast-enhanced axial CT image showing enlargement of both kidneys with multiple, well-defined, nonenhanced rounded cysts within the enhanced residual renal parenchyma. The findings of US and CT correlated with histopathological results, which revealed autosomal-dominant polycystic kidney disease. CT, computed tomography; US, ultrasonography.

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  Discussion Top


In the present study, we tried to evaluate the role of US and CT in the diagnosis of patients with renal masses. Our study included 50 (27 males and 23 females) cases with different types of renal masses, which were classified into the following: benign masses (27 cases) representing 54% and malignant masses (23 cases) representing 46%.

US was the first imaging investigation performed in patients with a renal mass. US can be performed safely as it is noninvasive, painless, and is relatively inexpensive. US is usually able to provide good differentiation of solid from cystic masses[8].

Furthermore, Doppler US allows for noninvasive assessment of vascular flow signals from tumor neovascularity. Color Doppler US has a diagnostic accuracy similar to dynamic CT in most patients with renal solid tumors[9].

Although US continues to be the major imaging modality utilized in uroradiology, CT has developed a well-recognized role in the diagnosis of various cases and remains the gold standard for the diagnosis of renal masses because of better image quality[10].

In our study, we used US and CT in evaluating malignant tumors, to identify the role of US and CT in detecting, staging, and surgical planning of these renal masses according to the findings, and also to evaluate the nature of these masses and see whether it is possible to differentiate between benign and malignant lesions.

In our study, the sensitivity, specificity, and accuracy of CT in diagnosing renal masses of the studied groups were 100, 96.25, and 98%, respectively. This is in agreement with Catalano et al.[11], who stated that in evaluating Robson stage I of renal cell carcinoma, they were able to diagnose fat infiltration on 1 mm scans with 96% sensitivity, 93% specificity, and 95% accuracy; the positive and negative predictive values were, respectively, 100 and 93%. Nazim et al.[12] also stated that the specificity of CT for capsular invasion, nodal disease, and adrenal involvement was 85, 82, and 98% respectively. The specificity was over 97% for tumor thrombus in renal vein and inferior vena cava (IVC).

In our study, the sensitivity, specificity, and accuracy of US in diagnosing renal masses of studied group were 95.6, 85.1, and 95.8%, respectively. Leveridge et al.[13] stated that US has been compared directly to CT in pathologically confirmed renal tumors. At a size of 1 cm, US was only able to identify 20% of masses, compared with 76% identified by CT. This rate improved to 70% for US at a size of 2 cm, but was still inferior to that of CT (95%). US and CT were only equivalent for the detection of renal masses at a size of 3.5 cm or greater. Once a mass was detected, US was as effective as CT in characterizing it as cystic or solid. US can also be used in the staging of RCC, with CT and US being almost equivalent in predicting T stage (76 and 85% accurate, respectively), and in the identification of tumor thrombus in the renal vein and IVC.

In our study, US showed RCC as a well-defined mass distorting the renal parenchyma, and the echogenicity was variable. One case showed bilateral RCC, two cases were complicated with IVC thrombus, and four cases were complicated with enlarged LNs.

CT showed the tumor as a solid mass of mixed density. Postcontrast CT showed heterogeneous enhancement: one case showed bilateral RCC, one case was associated with metastases in both lungs, two cases were complicated with IVC thrombus, and four cases were complicated with enlarged LNs.

In our study, US and CT had the same sensitivity for diagnosing RCC. This is in contrast to the study by Herts[14], who stated that US and CT have variable sensitivities in the diagnosis of RCC. US is less sensitive in detecting small renal lesions, especially those that do not deform the contour of the kidney; however, US has been shown to be highly sensitive in distinguishing cystic from solid lesions. CT has nearly 100% accuracy in the diagnosis of RCC, whereas US is less accurate than CT in staging RCC.

In our study, we found that Wilm's tumor accounts for the majority of malignant pediatric renal tumors (six cases). As stated by Miniati et al.[15], the peak incidence of Wilm's tumor occurs between 2 and 4 years of age, with 95% of children being diagnosed before the age of 10 years. In our study, six cases with Wilm's tumor were included, and the average age of incidence was 4 years.

In our study, in all patients with Wilm's tumors scanned by US, the mass appeared to be well-defined and heterogenous, distorting the renal parenchyma with areas of cystic degeneration.

CT showed the tumor to be a hypodense renal mass, and postcontrast CT revealed mild heterogeneous enhancement of the mass with areas of cystic degeneration as well as foci of calcification in one case: one case showed bilateral Wilm's tumors, and two cases had para-aortic LN enlargement.

In our study, two patients were diagnosed with lymphomatous infiltration of the kidneys, who presented with anemia, weight loss, and abdominal pain.

CT is more helpful than US in evaluating lymphomatous involvement of the LNs as well as other solid organs in the abdomen[16].

In our study, US revealed enlarged kidneys with multiple hypoechoic nodular lesions infiltrating the renal parenchyma. This is in agreement with Reznek et al.[17], who stated that imaging findings of lymphoma were variable and included multiple renal masses or nodular diffuse infiltration.

In our study, CT revealed multiple hypodense lesions infiltrating the kidney. After intravenous contrast injection, the lesions remained homogenous (showing no enhancement), and this is in agreement with Lowe et al.[18], who stated that lymphomatous masses had nonspecific CT appearance and that they are usually homogeneous and hypodense on precontrat and postcontrast CT; this may mimic multiple renal cysts.

Transitional cell carcinoma (TCC) accounts for 90% of all tumors arising from the renal pelvis urothelium and is divided into papillary (more common) and nonpapillary types. TCC is frequently multifocal and may involve any part of the collecting system. Only 2–4% of patients with bladder cancer develop upper tract TCC, but 40% of patients with upper tract TCC develop bladder cancer[19].

In our study, one patient was diagnosed with TCC. US revealed TCC as an ill-defined, rounded, hyperechoic, solid mass in the renal pelvis with hydronephrosis. This is in agreement with Kirkali[20] who stated that duringt US renal pelvic TCC typically appears as a central soft-tissue mass in the echogenic renal sinus, with or without hydronephrosis. TCC is usually slightly hyperechoic relative to the surrounding renal parenchyma; occasionally, high-grade TCC may show areas of mixed echogenicity.

On CT scan, it appeared as a hypodense filling defect in the renal pelvis with hydronephrosis, less enhanced compared with the renal parenchyma, and maintains a normal renal shape unlike RCC that tend to distort the renal outline. This is in agreement with Ronan et al.[21], who stated that renal TCC is typically seen as a sessile filling defect in the excretory phase, which expands centrifugally with compression of the renal sinus fat. Other appearances include pelvicalyceal irregularity, focal or diffuse mural thickening, oncocalix, and focally obstructed calices. Early tumors confined to the muscularis are separated from the renal parenchyma by renal sinus fat or excreted contrast material and have normal-appearing peripelvic fat. Advanced TCC extends into the renal parenchyma in an infiltrating pattern that distorts normal architecture. However, reniform shape is typically preserved, unlike in RCC.

In our study, four patients were diagnosed with renal angiomyolipomas (AMLs): three cases presented with a single unilateral lesion and one case had multiple, bilateral lesions associated with tuberous sclerosis. This is in agreement with Rimon et al.[22] who stated that there are two types of AML – a sporadic type that occurs predominantly in older patients and presents with a single unilateral lesion and a type associated with tuberous sclerosis in which lesions are multiple and bilateral. The sporadic type constitutes 80% of all cases.

US revealed AML as a well-defined solid mass that is markedly hyperechoic relative to renal parenchyma. CT revealed solid renal mass interspersed with areas of fat attenuation (−20 HU), displaying heterogenous postcontrast enhancement.

Fat within a renal mass is diagnostic of AML, and this is in agreement with Lane et al.[23], who stated that most AML contain substantial amounts of adipose tissue.

Oncocytoma is the second most common benign renal cell neoplasm constituting ∼3–7% of renal epithelial tumors. The incidence of oncocytoma peaks in the seventh decade, with a higher prevalence in men[24].

In our study, one case was pathologically proved to be renal oncocytoma. On radiological imaging, it could not be diffrentiated from RCC; this is in agreement with Tickoo et al.[25], who stated that distinguishing oncocytoma and RCC is the one of the most challenging issues. These two renal tumors are both known to originate from the intercalated cells of the collecting duct. Therefore, these tumors have common characteristics in morphological, histochemical, and ultrastructural aspects.

On US, oncocytoma as a well-defined, rounded, isoechoic renal mass with strip-like blood flow signals within the mass. On CT, oncocytoma appears as a solitary, well-demarcated, intense, peripheraly enhancing renal cortical tumor with central hypodense areas (stellate scar).

In our study, one case was diagnosed with bilateral XGPN, who presented clinically with bilateral flank pain, fever, dysuria, and weight loss. This is in agreement with Stunell et al.[26], who stated that the classic symptoms of pyelonephritis include an abrupt onset of chills, fever, and unilateral or bilateral flank pain with costovertebral tenderness. These ‘upper tract signs’ are often accompanied by dysuria and urinary frequency and urgency.

US revealed bilateral XGPN as enlargement of both kidneys with bilateral renal pelvic stones and multiple hypoechoic round areas corresponding to the pus-filled dilated calices replacing the normal corticomedullary differentiation. This is in agreement with Dwivedi et al.[27], who stated that the radiographic finding of a large staghorn calculus is present in most, but not all, cases. However, this finding in itself is nonspecific and is not typically associated with the extensive inflammatory process that characterizes XGPN.

On CT scan, both kidneys were enlarged and had multiple hypodense edge-shaped areas with hyperenhancing walls and central obstructing calculi (staghorn stones). The renal fascia was thickened and hyperenhancing. Pronounced stranding and inflammation of the perirenal fat were observed.

In our study, 12 patients were diagnosed with simple cysts. US revealed simple renal cysts as sharply defined anechoic masses with paper-thin wall, no septations, calcification, or mural nodules. This is in agreement with Bosniak[28] who stated that the sonographic criteria used to diagnose a simple cyst include the following characteristics: internally anechoic, posterior acoustic enhancement, and a sharply defined, imperceptible, smooth far wall. Simple cysts are usually round or ovoid in shape. For CT scan, criteria for a simple renal cyst were similar to that of US (see above). The most important criterion was no contrast media enhancement of the cyst or the cyst wall. Six patients presented with multiple simple renal cysts, with three of them showing bilateral simple renal cysts.

In our study, four cases were diagnosed with complicated renal cysts. US and CT revealed criteria similar to those for simple renal cysts with few hair-line septations in three cases and fluid level in one case. This is in agreement with Israel and Bosniak[29] who stated that benign cysts that may contain a few hairline-thin septae, fine calcification, or a short segment of slightly thickened calcification may be present in the wall or septae and are included in category 2.

In our study, we found three cases with autosomal-dominant polycystic kidney disease (ADPKD). US revealed enlargement of both kidneys with increased parenchymal echogenicity and poor corticomedullary differentiation. This is in agreement with Traubici and Daneman[30] who stated that the typical US appearance of ADPKD is large echogenic kidneys with poor corticomedullary differentiation. Macrocysts, a feature of ADPKD, are not generally present at birth, but they are not uncommon as the disease progresses.

CT showed that both kidneys were massively enlarged and were hypoattenuating with multiple, well defined, nonenhanced, cystic lesions within the enhanced residual renal parenchyma. This is in agreement with Verghese et al.[31], who stated that in ADPKD noncontrast CT scanning reveals smooth, enlarged kidneys. With intravenous contrast, kidneys have a striated appearance due to accumulation of contrast in dilated tubules.

This study included two patients with multicystic dysplastic kidney. US showed enlarged kidneys with multiple cystic structures seen all over the kidney not communicating with each other, associated with atrophy of the renal parenchyma, and normal contralateral kidney. CT revealed multiple, variable-sized, nonenhanced simple cysts replacing most of the renal parenchyma, and the contralateral kidney was normal. This is in agreement with William et al.[32], who reported that the kidney appears to be an enlarged mass of cysts. There are multiple cystic structures of variable sizes with no recognizable renal pelvis and loss of renal parenchyma; therefore, surgery for multicystic dysplastic kidney is usually considered unnecessary unless the kidneys are massively enlarged.


  Conclusion Top


US is the first imaging procedure to detect the characteristic features of renal masses. It can be performed safely as it is noninvasive and painless as well as relatively inexpensive. US was usually able to provide good differentiation of solid from cystic masses. Furthermore, Doppler US allowed for noninvasive assessment of vascular flow signals from tumor neovascularity.

CT is considered the golden standard for accurate characterization of renal masses, differentiation of malignant from benign masses according to some criteria, and staging of these malignant masses showing distant metastasis and LN enlargement. CT detects small renal masses, with narrow slice thickness (<0.5 mm) and decreased partial volume effects, allowing the detection of smaller lesions.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

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