European Journal of Cardiovascular Medicine

Soft tissue skin tumours comprise a broad and heterogeneous group of lesions that range from common benign masses to uncommon but potentially aggressive malignant neoplasms. Because clinical examination alone may not reliably distinguish benign from malignant lesions, imaging has an important role in early characterization, risk stratification, and planning of further management. Accurate preoperative differentiation is especially relevant because suspicious lesions may require biopsy, wider surgical excision, or referral to specialized centers, whereas many benign superficial masses can be managed more conservatively [3,4].

Ultrasound is often the first imaging modality used for superficial soft tissue lesions because it is inexpensive, readily available, free of ionizing radiation, and capable of dynamic real-time assessment. It can define lesion size, depth, internal echotexture, vascularity, and relation to adjacent structures, and may help identify features suggestive of malignancy. Recent work has also

highlighted the value of shear wave elastography as an adjunct to conventional ultrasound in improving tissue characterization and benign–malignant differentiation [1]. Thus, ultrasound serves as a practical initial tool in the evaluation of superficial soft tissue tumours [1,3].

MRI, however, remains the most comprehensive imaging modality for assessment of soft tissue tumours because of its excellent soft tissue contrast resolution and multiplanar capability. It provides detailed information regarding lesion margins, internal composition, fascial or muscular extension, neurovascular involvement, and other features that may suggest malignant behaviour. Several studies have examined MRI characteristics useful in distinguishing benign from malignant superficial soft tissue lesions, although overlap in imaging appearances remains an important limitation [2,5,6]. MRI is therefore particularly valuable when lesions are large, deep, atypical, or suspicious on initial evaluation [2,4,6].

Despite advances in imaging, differentiation between benign and malignant soft tissue tumours remains challenging. Certain features such as increasing lesion size, deep location, heterogeneity, irregular margins, and invasive appearance are more frequently associated with malignancy, especially in soft tissue sarcomas, but no single imaging feature is completely definitive [2,4–6]. In addition, even lesions with apparently characteristic imaging appearances may occasionally show histopathologic discordance, as demonstrated in studies comparing MRI findings with pathological diagnosis in lipomatous and other soft tissue tumours [7].

Histopathology therefore remains the gold standard for definitive diagnosis. Nevertheless, both ultrasound and MRI are clinically valuable because they help narrow the differential diagnosis, identify suspicious lesions, and guide decisions regarding biopsy and treatment. Since ultrasound is commonly used as the initial investigation and MRI is often employed for further characterization, comparing their diagnostic performance against histopathology is of practical relevance in routine clinical settings [1,2,6].

Hence, the present study was undertaken to compare the diagnostic performance of ultrasound and MRI in differentiating benign from malignant soft tissue skin tumours, using histopathology as the reference standard.

Objectives

1. To evaluate the diagnostic performance of ultrasound in differentiating benign from malignant soft tissue skin tumours, using histopathology as the reference standard.
2. To evaluate the diagnostic performance of MRI in differentiating benign from malignant soft tissue skin tumours, using histopathology as the reference standard.
3. To compare ultrasound and MRI in terms of sensitivity, specificity, positive predictive value, negative predictive value, and overall diagnostic accuracy in differentiating benign from malignant soft tissue skin tumours.

This comparative diagnostic study was conducted in the Department of Radiodiagnosis in collaboration with the relevant surgical and pathology departments at Government Medical College, Aurangabad, Maharashtra, from January 2017 to July 2017. The study included 100 patients with clinically suspected soft tissue skin tumours who underwent both ultrasound and magnetic resonance imaging (MRI), followed by histopathological examination, which was taken as the reference standard.

Inclusion criteria

1.      Patients presenting with clinically suspected soft tissue skin tumors.

2.      Patients who underwent both ultrasound and MRI evaluation of the lesion.

3.      Patients whose lesions were subsequently confirmed by histopathological examination.

4.      Patients willing to participate in the study.

Exclusion criteria

1.      Patients with recurrent lesions following prior definitive treatment.

2.      Patients with incomplete imaging or clinical records.

3.      Patients in whom histopathological confirmation was not available.

4.      Patients unwilling to participate in the study.

After obtaining informed consent, all patients underwent detailed clinical evaluation. Demographic details, lesion site, lesion size, and provisional clinical diagnosis were recorded. Lesions were categorized according to anatomical site, and lesion depth was assessed on imaging as superficial or deep.

Ultrasound examination was performed initially using a high-frequency linear transducer. The lesions were evaluated for size, depth, margins, internal echotexture, and vascularity. Based on these sonographic findings, each lesion was categorized as likely benign or likely malignant.

MRI was performed in all patients for further lesion characterization. Standard imaging sequences were obtained in appropriate planes according to lesion location. MRI assessment included lesion size, depth, margins, internal signal characteristics, and extent of involvement of adjacent structures. Based on MRI findings, lesions were classified as benign or malignant.

Definitive diagnosis was established by histopathological examination of biopsy or excision specimens, which served as the gold standard. The diagnostic performance of ultrasound and MRI in differentiating benign from malignant lesions was compared against histopathology.

Continuous variables were expressed as mean ± standard deviation, and categorical variables as frequency and percentage. Between-group comparisons were performed using the independent sample t test for continuous variables and the chi-square test for categorical variables. Sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy with 95% confidence intervals were calculated for ultrasound and MRI using histopathology as the reference standard. Paired comparison between the two imaging modalities was performed using McNemar exact test. A p value of less than 0.05 was considered statistically significant.

A total of 100 patients with soft tissue skin tumors were evaluated by ultrasound and MRI, with histopathology used as the reference standard. Of these lesions, 70 were benign and 30 were malignant on final histopathology.

Participant and lesion characteristics

Malignant lesions were significantly larger than benign lesions (5.65 ± 1.71 cm vs 3.20 ± 1.17 cm, p < 0.001) and were more frequently deep seated (70.0% vs 24.3%, p < 0.001). Age, sex distribution, and anatomical site did not differ significantly between the two histopathological groups (Table 1).

Table 1. Participant and lesion characteristics stratified by histopathology

Values are presented as mean ± standard deviation or n (%). p values were calculated for between-group comparisons.

Diagnostic accuracy of ultrasound

Ultrasound correctly classified 84 of 100 lesions (accuracy 84.0%). Against histopathology, ultrasound demonstrated sensitivity of 80.0%, specificity of 85.7%, positive predictive value of 70.6%, and negative predictive value of 90.9% (Table 2).

Table 2. Ultrasound versus histopathology for differentiating benign from malignant soft tissue skin tumors

                 Histopathology was used as the reference standard.

 Diagnostic accuracy of MRI

MRI correctly classified 90 of 100 lesions (accuracy 90.0%). It demonstrated sensitivity of 90.0% and specificity of 90.0%, with positive and negative predictive values of 79.4% and 95.5%, respectively (Table 3).

Table 3. MRI versus histopathology for differentiating benign from malignant soft tissue skin tumors

             Histopathology was used as the reference standard.

Comparative performance of ultrasound and MRI

MRI showed numerically higher sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy than ultrasound (Table 4). However, paired comparison using McNemar exact test did not show a statistically significant difference between the two modalities in overall accuracy (p = 0.263) or in subgroup comparisons for malignant and benign lesions (Table 5).

Table 4. Diagnostic performance of ultrasound and MRI in differentiating benign from malignant soft tissue skin tumors, using histopathology as the reference standard

Values are presented as percentage with 95% confidence interval in parentheses.

Table 5. Paired comparison of diagnostic performance between ultrasound and MRI

Paired comparison between ultrasound and MRI was performed using McNemar exact test. US = ultrasound; MRI = magnetic resonance imaging.

In the present study, both ultrasound and MRI showed good diagnostic performance in differentiating benign from malignant soft tissue skin tumours, with MRI demonstrating higher sensitivity, specificity, predictive values, and overall accuracy than ultrasound. However, this apparent advantage was not statistically significant on paired comparison, suggesting that although MRI performs somewhat better, ultrasound remains a reliable first-line imaging modality.

Malignant lesions in our series were significantly larger and more frequently deep seated than benign lesions. This is consistent with previous studies identifying lesion size as one of the strongest predictors of malignancy. Winn et al. and Morii et al. both reported that larger lesion size is strongly associated with malignant pathology, while Chiou et al. found that a size greater than 5 cm is an important warning feature for malignancy [8,10,15]. Our finding regarding lesion depth also supports the general view that deeper lesions are more suspicious, although not all studies have found depth to be independently significant [8].

The diagnostic accuracy of ultrasound in our study supports its value in routine evaluation of superficial soft tissue masses. Ultrasound is inexpensive, accessible, and allows real-time assessment of lesion morphology and vascularity. Gómez et al. described ultrasound as an ideal triaging tool for superficial soft tissue tumours [11], and Hung et al. reported very high sensitivity and specificity for malignancy detection when ultrasound was performed by experienced radiologists [12]. Although the ultrasound performance in our study was lower than that reported by Hung et al., it remained sufficiently good to justify its continued role as the initial imaging investigation. [11,12]

MRI showed better overall diagnostic indices than ultrasound, reflecting its superior soft tissue contrast and better assessment of lesion extent and surrounding anatomical relationships. Even so, MRI was not perfectly accurate, which agrees with Sen et al., who highlighted that MRI has important limitations in reliably distinguishing benign from malignant soft tissue neoplasms [14]. Thus, while MRI improves diagnostic confidence, it does not replace histopathological confirmation.

Our findings support the practical view that ultrasound and MRI are complementary rather than competing modalities. Griffith emphasized that ultrasound can characterize many soft tissue masses effectively, while MRI adds value mainly in suspicious or indeterminate cases by better defining lesion extent and anatomical relationships [13]. Similarly, Gómez et al. recommended MRI and biopsy for lesions that are large, deep, or atypical on ultrasound [11]. This approach is consistent with our results, where ultrasound provided good baseline discrimination and MRI offered modest additional benefit.

The present study suggests that ultrasound is a useful first-line tool for differentiating benign from malignant soft tissue skin tumours, while MRI provides added value in selected cases. Larger lesion size and deep location were significantly associated with malignancy, in keeping with previous reports [8,10,15]. However, as both modalities showed imperfect accuracy, histopathology remains the gold standard for definitive diagnosis [8,11,14].

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