Renal masses represent a broad spectrum of pathologies, ranging from simple cysts and benign neoplasms to aggressive malignant tumors such as renal cell carcinoma (RCC). The early and accurate detection of these masses is crucial for timely intervention and optimal patient outcomes [1]. With the increasing use of imaging for various clinical indications, the incidental detection of renal masses has become more frequent, necessitating reliable imaging techniques to distinguish between benign and malignant lesions [2].

Ultrasound (USG) is widely used as the initial imaging modality for renal mass evaluation due to its non-invasiveness, cost-effectiveness, and accessibility. It plays a critical role in identifying lesion morphology, assessing internal characteristics such as solid versus cystic nature, and evaluating vascularity using Doppler imaging [3]. Ultrasound is particularly useful in diagnosing simple renal cysts, which typically appear as anechoic structures with well-defined margins and posterior acoustic enhancement. However, its accuracy in differentiating complex cystic lesions and solid tumors is often limited, especially in cases where internal septations, calcifications, or heterogeneous echotexture are present [4]. Additionally, ultrasound has inherent limitations related to operator dependency and the inability to provide detailed information on lesion enhancement characteristics.

Computed tomography (CT), particularly contrast-enhanced CT (CECT), has emerged as the preferred imaging modality for detailed renal mass characterization. It provides superior anatomical resolution and allows for assessment of lesion enhancement patterns, tumor vascularity, extracapsular extension, and lymph node involvement. The ability of CT to delineate hypervascularity and washout characteristics is particularly valuable in diagnosing renal cell carcinoma, distinguishing it from benign lesions such as angiomyolipomas or hemorrhagic cysts. Moreover, CT is instrumental in staging renal malignancies by evaluating renal vein or inferior vena cava invasion, a feature that significantly impacts surgical planning and prognosis [5].

Several studies have demonstrated that the combination of ultrasound and CT enhances diagnostic accuracy in renal mass evaluation. While ultrasound remains the first-line modality for detecting renal abnormalities, its limitations in characterizing complex or indeterminate lesions necessitate further assessment with CT [6]. The role of a stepwise imaging approach, where ultrasound serves as an initial screening tool and CT provides confirmatory characterization, has been widely advocated to optimize diagnostic precision. However, in resource-limited settings, where CT may not be readily available, the reliance on ultrasound for primary diagnosis and follow-up remains significant [7].

This study aims to compare the diagnostic accuracy of ultrasound and CT in differentiating benign and malignant renal masses in a tertiary care setting. By analyzing lesion characteristics, including size, echotexture, vascularity, and enhancement patterns, the study seeks to determine the strengths and limitations of each modality. The findings will provide insights into the role of ultrasound as a first-line investigative tool and establish its reliability in guiding further imaging and management decisions.

This hospital-based prospective study was conducted over a period of one year, from January to December 2021, at department of Radio diagnosis, SVS Medical College & Hospital, Mahabubnagar, Telangana, India. The study aimed to evaluate the diagnostic accuracy of ultrasound in detecting and characterizing renal masses and to compare its findings with computed tomography (CT), which served as the reference standard.

Study Design and Population

A total of 150 patients with clinically suspected or incidentally detected renal masses were included in the study. Patients were recruited from outpatient and inpatient departments based on abnormal clinical findings, hematuria, flank pain, or incidental renal abnormalities detected on prior imaging.

Inclusion Criteria

• Patients aged 18 years and above with renal masses detected on ultrasound.
• Patients with clinically suspected renal tumors undergoing further imaging evaluation.
• Patients who underwent both ultrasound and contrast-enhanced CT (CECT) for lesion characterization.

Exclusion Criteria

• Patients with diffuse renal parenchymal disease without focal masses.
• Patients with known renal malignancies undergoing follow-up imaging rather than new evaluation.
• Pregnant women and individuals with contraindications to contrast-enhanced imaging (e.g., renal impairment, contrast allergy).
• Patients in whom complete imaging evaluation with both ultrasound and CT was not feasible.

        Imaging Protocol

Ultrasound Evaluation

All patients underwent ultrasound examination using a high-resolution B-mode ultrasound scanner with color Doppler capability. Evaluations were performed by an experienced radiologist. The following lesion characteristics were assessed:

• Size and location of the renal mass.
• Echotexture (hyperechoic, hypoechoic, isoechoic, or mixed).
• Lesion margins (well-defined or ill-defined).
• Cystic versus solid nature of the mass.
• Presence of internal septations, calcifications, or necrotic areas.
• Vascularity assessment using color Doppler imaging to detect hypervascularity.

Computed Tomography (CT) Evaluation

All patients underwent contrast-enhanced CT (CECT) with a multiphasic imaging protocol, including non-contrast, arterial, venous, and delayed phases. CT scans were performed using a multi-detector CT scanner for optimal resolution. The following lesion characteristics were analyzed:

• Enhancement patterns (homogeneous, heterogeneous, peripheral, or no enhancement).
• Washout characteristics, particularly in suspected renal cell carcinoma.
• Presence of necrosis, hemorrhage, or calcifications.
• Capsular invasion and perinephric spread.
• Renal vein or inferior vena cava (IVC) involvement in suspected malignancy.

Data Collection and Analysis

All imaging findings were recorded and analyzed. The diagnostic accuracy of ultrasound was determined by comparing findings with CT, which served as the reference standard. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of ultrasound in differentiating benign from malignant renal masses were calculated.

The correlation between ultrasound and CT findings was assessed using appropriate statistical methods, including the Chi-square test and Pearson correlation coefficient. A p-value of <0.05 was considered statistically significant.

Ethical Considerations

The study was conducted in accordance with ethical guidelines, and approval was obtained from the Institutional Ethics Committee. Written informed consent was obtained from all participants before inclusion in the study.

A total of 150 patients with renal masses were included in the study. The mean age of the participants was 55.8 ± 10.2 years, with a male-to-female ratio of 1.9:1. The majority of cases were detected incidentally during imaging for unrelated conditions, while some patients presented with clinical symptoms such as hematuria, flank pain, weight loss, or palpable renal mass.

Table 1 presents the distribution of benign and malignant renal masses in the study population. Malignant lesions constituted 64% of cases, while 36% were benign.

Table 1: Overall Distribution of Renal Masses

Table 2 outlines the distribution of benign renal masses. Simple renal cysts were the most common, accounting for 52% of benign lesions, followed by angiomyolipomas (31%) and oncocytomas (12%).

Table 2: Distribution of Benign Renal Masses

Table 3 presents the distribution of malignant renal masses. Renal cell carcinoma (RCC) was the most common, seen in 78% of malignant cases, followed by urothelial carcinoma (13%) and Wilms tumor (9%).

Table 3: Distribution of Malignant Renal Masses

Table 4 presents the diagnostic accuracy of ultrasound in differentiating benign from malignant renal masses. Ultrasound showed an overall sensitivity of 85.4% and specificity of 89.1%. The positive predictive value (PPV) and negative predictive value (NPV) were 87.3% and 86.5%, respectively.

Table 4: Diagnostic Accuracy of Ultrasound

Table 5 presents the size distribution of renal masses. Malignant masses were significantly larger, with 60% measuring >5 cm, whereas benign lesions were more frequently in the 2–5 cm range (65%).

Table 5: Size Distribution of Renal Masses

Table 6 presents the echotexture distribution of renal masses on ultrasound. Most benign lesions were anechoic (58%), while malignant lesions were predominantly hypoechoic (62%).

Table 6: Echotexture Distribution of Renal Masses on Ultrasound

Table 7 presents the vascularity assessment of renal masses using color Doppler ultrasound. Malignant lesions demonstrated significantly higher internal vascularity.

Table 7: Vascularity Patterns on Color Doppler Ultrasound

Table 8 outlines the enhancement patterns observed on CT scans. The majority of malignant masses exhibited heterogeneous enhancement (70%), while simple cysts and some benign lesions demonstrated no enhancement (48%).

Table 8: Enhancement Pattern on CT

Table 9 presents the role of CT in lesion characterization, showing that CT provided a definitive diagnosis in 92% of cases, compared to 84% by ultrasound alone.

Table 9: Diagnostic Certainty of Ultrasound vs CT

Table 10 presents the correlation between ultrasound and CT findings, showing a statistically significant agreement (p < 0.001) in lesion classification.

  Table 10: Statistical Correlation between Ultrasound and CT

Renal masses encompass a wide range of pathologies, including benign cysts, angiomyolipomas, oncocytomas, and malignant tumors such as renal cell carcinoma (RCC) and urothelial carcinoma. The increasing use of imaging techniques has led to more frequent incidental detection of renal masses, necessitating accurate differentiation between benign and malignant lesions. The findings of this study emphasize the complementary roles of ultrasound and computed tomography (CT) in renal mass evaluation, with ultrasound serving as an essential first-line diagnostic tool and CT providing definitive lesion characterization [8].

The distribution of renal masses in this study revealed that 64% of cases were malignant, while 36% were benign, which is consistent with previous studies indicating a higher prevalence of malignancies among detected renal masses [9]. Among malignant cases, RCC was the most common histological subtype (78%), followed by urothelial carcinoma (13%) and Wilms tumor (9%). The predominance of RCC is well established in the literature, particularly among older adults and individuals with risk factors such as smoking, obesity, and hypertension. Among benign masses, simple renal cysts accounted for 52%, while angiomyolipomas represented 31%, highlighting the common occurrence of these lesions in routine clinical practice [10].

Ultrasound demonstrated an overall sensitivity of 85.4% and specificity of 89.1% in differentiating benign from malignant renal masses. The positive predictive value (PPV) and negative predictive value (NPV) were 87.3% and 86.5%, respectively. These findings indicate that while ultrasound is highly effective in detecting renal masses and distinguishing cystic from solid lesions, it has limitations in the detailed characterization of complex cystic and solid tumors. The high specificity observed in this study suggests that ultrasound can reliably exclude malignancy in well-defined benign lesions, but in cases where sonographic features are ambiguous, additional imaging with CT remains necessary [11].

The size distribution of renal masses revealed that malignant lesions were significantly larger, with 60% measuring more than 5 cm, whereas benign lesions were predominantly in the 2–5 cm range (65%). This aligns with established data suggesting that larger renal masses have a higher likelihood of malignancy. Small renal tumors (<2 cm) pose a diagnostic challenge on ultrasound, as their echogenicity and vascularity patterns may overlap with benign entities. The findings support the role of size-based criteria in guiding further imaging and clinical decision-making [12].

Echotexture assessment demonstrated that most benign lesions were anechoic (58%), while malignant tumors were predominantly hypoechoic (62%). Hypoechogenicity has been widely recognized as a characteristic feature of RCC, whereas anechoic lesions typically correspond to simple cysts. However, some malignancies exhibited mixed echogenicity, emphasizing the importance of incorporating additional sonographic features such as vascularity, calcifications, and septations when differentiating between benign and malignant masses [13].

Color Doppler evaluation revealed that 67% of malignant renal masses exhibited internal vascularity, compared to only 5% of benign lesions. This reinforces the significance of vascular patterns in renal mass assessment, as malignancies tend to demonstrate increased blood flow due to tumor angiogenesis. Peripheral vascularity was noted in 30% of benign lesions and 18% of malignant lesions, suggesting that while vascularity can be an important differentiating factor, it is not entirely specific, and further imaging with CT or MRI may be required in equivocal cases [14].

CT evaluation provided definitive lesion characterization in 92% of cases, compared to 84% by ultrasound alone. The ability of CT to assess contrast enhancement patterns was particularly useful in distinguishing RCC from benign solid lesions such as oncocytomas and angiomyolipomas. In this study, 70% of malignant renal masses exhibited heterogeneous enhancement, while 48% of benign lesions showed no enhancement. These findings are consistent with prior research highlighting that tumor enhancement characteristics on CT are crucial in differentiating benign and malignant renal masses, particularly when ultrasound findings are inconclusive [15].

The statistical correlation between ultrasound and CT findings demonstrated a highly significant agreement (p < 0.001) in lesion classification. However, discrepancies were noted in complex cystic lesions and small renal tumors, where ultrasound misclassification rates were higher. These findings reinforce the need for a multimodal imaging approach, integrating ultrasound as an initial screening tool with contrast-enhanced CT for definitive lesion characterization. In select cases, magnetic resonance imaging (MRI) may further aid in differentiating ambiguous lesions, particularly those with equivocal enhancement patterns.

This study underscores the importance of a stepwise imaging approach, where ultrasound serves as an accessible and cost-effective screening modality, while CT remains the gold standard for further characterization and staging. The results highlight that ultrasound alone may be sufficient for diagnosing simple cysts and small angiomyolipomas, but in cases of solid, complex, or vascular renal masses, CT should be performed for definitive diagnosis. Additionally, in resource-limited settings where CT availability is constrained, contrast-enhanced ultrasound (CEUS) may serve as an alternative, though further research is needed to validate its diagnostic accuracy.

Despite the strengths of this study, certain limitations must be acknowledged. The relatively small sample size may limit the generalizability of the findings, particularly for rare renal tumors. Additionally, histopathological confirmation was not available for all cases, as some diagnoses were based on imaging criteria alone. Future studies with larger cohorts and biopsy correlation would provide a more comprehensive assessment of the accuracy of imaging modalities in renal mass evaluation.

This study demonstrates that ultrasound is a valuable first-line imaging modality for detecting renal masses, offering high sensitivity and specificity in differentiating cystic from solid lesions. However, computed tomography (CT) remains the gold standard for definitive characterization, particularly in distinguishing benign from malignant tumors. The findings highlight that renal cell carcinoma (RCC) was the most common malignancy (78%), while simple renal cysts (52%) and angiomyolipomas (31%) were the most frequent benign lesions.

Ultrasound exhibited an overall sensitivity of 85.4% and specificity of 89.1%, making it a reliable screening tool, especially for simple cysts and small solid tumors. However, complex renal masses, vascular involvement, and enhancement characteristics were better delineated on CT, leading to a significantly higher diagnostic certainty (92%) compared to ultrasound alone (84%). The statistical correlation between ultrasound and CT findings (p < 0.001) reinforces the importance of a stepwise imaging approach in renal mass evaluation.

While ultrasound provides an accessible and cost-effective method for initial renal mass detection, its limitations necessitate further imaging with contrast-enhanced CT in cases of solid, complex, or equivocal lesions. In settings where CT is unavailable, contrast-enhanced ultrasound (CEUS) or MRI may serve as alternative imaging modalities, though further research is needed to validate their diagnostic accuracy.

The study underscores the need for a structured diagnostic algorithm, integrating ultrasound, CT, and where required, histopathological evaluation, to ensure optimal renal mass diagnosis and appropriate clinical management. Future research with long-term follow-up and biopsy correlation would provide further insights into refining diagnostic strategies for renal tumors.

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