Abstract
Diffusion-weighted magnetic resonance imaging (DWI) analyzes water diffusion in tissues, indirectly reflecting cellular density and aiding tumor characterization. Our objective was to explore the utility of DWI in three topics: (i) differentiation of bone and soft tissue sarcomas with respect to tumor type/grade; (ii) correlation with chemotherapy response in Ewing's sarcoma and osteosarcoma; and (iii) differentiation of benign from malignant soft tissue and bone tumors. The aim of the review article was to assess the existing literature detailing the insight that can be provided by DWI when addressing bone and soft tissue tumors. A search was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines using Pubmed, Scopus, Embase, and CENTRAL databases from 1 January 2013 to 30 November 2023. Eligible studies were assessed for quality using the Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) scoring system. In total, 22 studies met the inclusion criteria. DWI proved effective in select scenarios when distinguishing among bone and soft tissue sarcomas (sensitivity = 48%–89%, specificity = 75%–100%), correlating chemotherapy response with histopathology results (sensitivity = 25%–85%, specificity = 50%–100%), and differentiating between benign and malignant bone tumors (sensitivity = 54%–92%, specificity = 39%–92%) and soft tissue tumors (sensitivity = 68%–91%, specificity = 60%–81%). DWI is a valuable tool for the diagnosis and prognosis of bone and soft tissue sarcomas, treatment effect of primary bone tumors, and distinguishing benign from malignant bone/soft tissue tumors. Though promising, the technology has shown mixed results, warranting further research.
Keywords
Introduction
The evolution of magnetic resonance imaging (MRI) techniques has allowed for detailed insights into the landscape of bone and soft tissue tumors. Although primary malignant bone tumors account for <1% of malignancies and soft tissue sarcomas represent approximately 0.5%–1.0% of malignancies, they are a top five cause of cancer deaths for those aged under 20 years (1–3). With a wide range of histopathology, they require comprehensive characterization, as management can vary tremendously, depending on the diagnosis. The gold standard to establish a tumor's diagnosis is an open or core needle biopsy (4). Although core needle biopsy has a substantially lower complication rate than incisional biopsy (<1% vs. 16%), these procedures all carry inherent anatomic and anesthetic risks (5,6). Furthermore, traditional MRI sequences, although useful in detecting tumor necrosis and hemorrhage, are limited in their ability to quantify the oncologic response to radiation and systemic therapies (7–14). Diffusion-weighted imaging (DWI) adds another dimension to the ability of MRI characterization of bone and soft tissue tumors (15).
Since its inception in 1985, DWI has undergone continuous development and assumes a pivotal role in characterizing tissue functionalities within many organs such as the liver and brain. DWI provides imaging contrast by analyzing the diffusion property of water in tissues, illustrating the cellular density (16). When pathological processes occur in the human body, disturbances in water distribution between cells and extracellular compartments alter these diffusion properties. DWI provides insights into these changes, particularly in cases like high-grade malignancies where intracellular proportion increases, leading to more restricted diffusion (17). Images obtained through DWI can be utilized to calculate apparent diffusion coefficient (ADC) values, typically derived through non-linear regression applied to a series of images obtained with varying levels of diffusion weighting (diffusion moments or b-values) (18).
The aim of this systematic review was to assess the existing literature detailing the insight that can be provided by DWI when addressing bone and soft tissue tumors. To this end, this systematic review aimed to evaluate the collective body of evidence in three topics (Table 1) The three topics present in this table will be referenced as topic 1, topic 2, and topic 3 herein. This review aims to characterize the role that DWI plays in bone and soft tissue lesion diagnostics, ultimately improving clinical understanding of when and how to use this tool, and thereby improving clinical decision-making.
Topic summary with title, aim, and QUADAS-2 criteria.
DWI, diffusion-weighted imaging; MRI, magnetic resonance imaging.
Material and Methods
Review protocol
This retrospective review followed the Preferred Reporting Items for Systematic Reviews and Meta Analysis (PRISMA) (19).
Search strategy
The authors searched Pubmed, Scopus, Embase, and The Cochrane Central Register of Controlled Trials (CENTRAL) for relevant studies. The exact search criteria are shown in Table 2. The date range of the query was set to 1 January 2013 to 30 November 2023.
Query criteria for database search.
Study eligibility and selection and quality of included studies
Our search strategy resulted in a total of 2143 articles requiring further analysis for inclusion. The exact breakdown of the number of articles from each database is shown in Table 2. Then, a title and abstract review were independently conducted by each of the authors. Articles that met criteria for further analysis included prospective cohort studies, retrospective cohort studies, and case-control studies that discussed DWI in the context of musculoskeletal oncology. We purposefully stayed broad at this step, trying to encompass all relevant studies analyzing DWI with respect to bone and soft tissue oncologic pathologies due to the paucity of literature available. This approach aimed to summarize the landscape of use cases for DWI in musculoskeletal oncology comprehensively. Case reports, animal studies, cadaveric studies, non-English studies, other systematic reviews, and author replies were excluded. Disagreements were resolved by the corresponding author. A total of 121 studies resulted after this due diligence. The full text of all eligible studies was then independently reviewed by the authors using the Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) for quality assessment , resulting in 22 qualifying studies (Figure 1).

Flow chart of literature review. After primarily excluding studies through title and abstract review and secondarily excluding additional studies with full-text review and applying QUADAS-2 criteria, 22 studies qualified for inclusion.
QUADAS-2 is widely used in systematic reviews as a guide to evaluate the methodological quality of diagnostic accuracy studies and can be helpful in identifying potential sources of bias and variations in quality across different studies. It consists of four domains: (i) patient selection, (ii) index test, (iii) reference standard, and (iv) flow and timing. Within each domain, specific items are assessed to determine the risk of bias and concerns regarding applicability (domain 4 [Flow and Timing] is only used to assess concerns regarding applicability). It is important to note that for the purposes of this systematic review, QUADAS-2 was used independently in the context of topics 1, 2, and 3 – each topic was assigned a separate review question, which was formulated using a patient selection, index test, reference standard, and target condition for the three aforementioned topics to properly address risk of bias and concerns regarding applicability (Table 1). This modification was made to ensure QUADAS-2 was applied appropriately for each topic discussed in this systematic review (20).
Fig. 2 provides a visualization of the assessment of all relevant articles with respect to risk of bias and concern of applicability. The articles that were determined to have low risk of bias and low concern of applicability were ultimately included. The evaluation of the included studies using QUADAS-2 alongside each study's location, population, and imaging technique can be found in Table for topics 1, 2 and 3, respectively.

Graphs of overall risk of bias and concern of applicability for all relevant studies by QUADAS-2 domain.
Location, population, and imaging details of studies included for topics 1, 2, and 3.
*Values are given as mean ± SD or median (range).
DWI, diffusion-weighted imaging; MRI, magnetic resonance imaging.
Summary of results of topics 1, 2, and 3.
Note: Teo et al was excluded due to different study design/parameters.
a) ADC Mean values were not correlated or compared statistically between lesion types
b) Represents the difference in ADC values before and mid-course/after treatment
c) Represents p-value related to the difference between the mean ADC values in malignant and benign bone lesion groups
* indicates statistical significance
The specific ADC metric (e.g., mean) is not specified, as group-specific ADC values were reported using different summary measures across studies. The metric of interest is noted in parentheses in the “Variable Being Evaluated” column.
Results
Quality of the included studies
Among the studies assessed utilizing QUADAS-2, 22 were found to have low risk of bias with low concern of applicability, five were found to have low risk of bias with high concern of applicability, 10 were found have to high risk of bias with low concern of applicability, and three were found to have high risk of bias with high concern of applicability. The findings of the QUADAS-2 assessment are depicted in Fig. 2, while the results of all studies are displayed in Table 4.
Topic 1:
Evaluating the accuracy of DWI-MRI in differentiating among bone and soft tissue sarcomas
ElDaly et al. identified an ADCmean cutoff of ≤1.4 ×10−3 mm2/s, achieving a sensitivity of 85%, specificity of 100%, and P <0.0001 in detecting recurrent postoperative soft tissue sarcoma tumors (23). Surov et al. found that muscle lymphoma had significantly lower ADCmean values than muscle metastases (P = 0.01) and muscle sarcoma (P = 0.001) (21). An excellent example of DWI characterizing lymphoma is shown in Fig. 3. Zeitoun et al. observed that osteoblastic osteosarcoma exhibited the lowest ADCmean values among osteosarcoma subtypes (22). Chhabra et al. reported that ADC cutoffs between 0.74 to 0.98 ×10−3 mm2/s provided a sensitivity of 48%–66% and specificity of 75%–88% in differentiating tumor grades (39). Gowda et al. found significant ADCmean differences in liposarcomas versus non-liposarcomas and synovial tumors versus non-synovial tumors, highlighting variability within soft tissue sarcomas (36).
Topic 2:
Accuracy of DWI-MRI when correlating chemotherapy response in the treatment of Ewing's sarcoma and osteosarcoma to histopathology results

(a, b) A 45-year-old woman with a history of lymphoma with multiple enhancing lesions throughout the osseous structures: axial T1 post-contrast. (c) DWI B800 and (d) ADC sequences demonstrating the typical avid diffusion restriction associated with highly cellular tumors such as lymphoma. Reference the lesion in the left ilium (arrow), which has an ADC measurement of 0.66 ×10−3 mm2/s. ADC, apparent diffusion coefficient; DWI, diffusion-weighted imaging.
Studies by Lee et al. and Habre et al. demonstrated that DWI could predict chemotherapy response in osteosarcoma, with post-treatment ADCmean and ADCskewness being strong indicators of poor treatment response (24,25). Saleh et al. showed that post-chemotherapy ADCmean values significantly increased for osteosarcoma (0.90 to 1.62 ×10−3 mm2/s) and Ewing's sarcoma (0.71 to 1.6 ×10−3 mm2/s; P <0.001) (27). An example of ADC value in osteosarcoma correlating with partial chemotherapy response can be seen in Fig. 4. Asmar et al. confirmed these findings in pediatric populations, reporting significant increases in ADCmean (1.191 to 1.534 ×10−3 mm2/s; P = 0.03) and ADCmin (0.134 to 0.388 ×10−3 mm2/s; P = 0.02) (26). However, Teo et al. noted that integrating DWI with conventional MRI did not improve tumor necrosis estimation accuracy (28).
Topic 3:
Accuracy of DWI-MRI when differentiating benign from malignant soft tissue and bone tumors

A 27-year-old woman with a large, heterogenous left distal femur osteosarcoma with significant soft tissue mass: (a) sagittal STIR; (b) coronal T1 post-contrast). (c) Pre-treatment (axial) and (d) post-neoadjuvant chemotherapy (sagittal) DWI/ADC images obtained show significant decrease in diffusion restriction (ADC increase from 1.05 ×10−3 mm2/s to 1.62 ×10−3 mm2/s) after four cycles of neoadjuvant chemotherapy, suggesting partial response to therapy. Final pathology after surgical excision revealed 50% necrosis of the tumor. ADC, apparent diffusion coefficient; DWI, diffusion-weighted imaging.
Malignant versus benign bone tumors
Douis et al. found ADCmean effective in differentiating benign from malignant bone tumors, with restricted diffusion (P = 0.026) (29). Pozzi et al. reported that ADCmean cutoffs of approximately 0.904 ×10−3 mm2/s had a sensitivity of 90% for differentiating primary from metastatic malignancies (30). Padhani et al. identified a cutoff of 0.774 ×10−3 mm2/s as consistent with malignancy (P <0.001) (31). Wang et al. showed that an ADCmean ≥1.10 ×10−3 mm2/s provided a sensitivity and specificity of 90% and 85%, respectively, for distinguishing benign from malignant tumors (32). Setiawati et al. demonstrated that an ADC cutoff ≥1.15 ×10−3 mm2/s effectively differentiated benign from malignant cartilaginous tumors (P <0.001) (33). In Fig. 5, we show a pelvic dedifferentiated chondrosarcoma with ADC value measuring 1.01 ×10−3mm2/s. Ahlawat et al. found an ADCmin cutoff of 0.9 ×10−3 mm2/s with 92% sensitivity and 78% specificity for differentiating benign from malignant bone tumors (34). Nouh et al. found that an ADCmean cutoff value ≥1.10 ×10−3 mm2/s effectively characterized a tumor as benign, resulting in a sensitivity and specificity of 86% and 63%, respectively (35). Guirguis et al. highlighted the utility of whole tumor and darkest area ADC measurements but noted that conventional MRI alone was sufficient for bone tumor characterization (37,38).

A 61-year-old woman with a large dedifferentiated chondrosarcoma involving the right pelvis. (a, b) T1 post-contrast axial (a) and coronal (b) images demonstrate a heterogeneously enhancing destructive mass with large soft tissue component. (c) DWI B800 and (d) ADC sequences depicting areas of diffusion restriction, with ADC measuring as low as 1.01 ×10−3 mm2/s. ADC, apparent diffusion coefficient; DWI, diffusion-weighted imaging.
Malignant versus benign soft tissue tumors
Pekcevik et al. reported that benign cystic tumors had higher ADCmean values than benign or malignant solid/mixed tumors (P <0.001 and P = 0.003, respectively). The authors also found that malignant solid or mixed tumors had lower ADC values than that of benign solid or mixed tumors (P = 0.02) (36). This concept is illustrated well by Fig. 6 (rhabdomyosarcoma with ADC value of 1.11 ×10−3 mm2/s and benign myxoma with an ADC value of 2.62 ×10−3 mm2/s). Song et al. identified ADCmean and ADCmin cutoffs of ≥1.35 × 10−3 mm2/s and ≥0.81 × 10−3 mm2/s, respectively, as effective for differentiating malignant from benign soft tissue tumors (P <0.001 and P = 0.001) (37). Robba et al. confirmed these findings, with an ADCmean cutoff ≥1.45 ×10−3 mm2/s showing a sensitivity and specificity of 91% and 60% in differentiating benign from malignant soft tissue tumors (38).

(a–c) A 60-year-old man with a large right thigh soft tissue rhabdomyosarcoma exhibiting predominantly peripheral irregular nodular enhancement with areas of central necrosis (panel a = axial T1 post-contrast image). (b, c) The enhancing nodular components of the mass demonstrate diffusion restriction, with ADC measuring 1.11 × 10−3 mm2/s. (d–f) In contrast, a 57-year-old woman with a right deltoid benign intramuscular myxoma. (d) Axial T1 post-contrast image shows mild thin peripheral and internal enhancement of the mass. (e) DWI B800 and (f) ADC sequences depicting “T2 shine through,” and thus the lack of diffusion restriction. The ADCmean for this lesion measures 2.62 ×10−3 mm2/s. ADC, apparent diffusion coefficient; DWI, diffusion-weighted imaging.
Discussion
DWI was originally developed for applications in neuroimaging, particularly for detecting acute ischemic stroke (40). DWI functions by analyzing stochastic Brownian motion of water molecules at a microscopic level. Given intracellular water molecules have less freedom to move than extracellular water molecules (due to intracellular organelles and membranes), DWI sequences provide highly detailed information regarding cellularity for an analyzed tissue. This sensitivity was thought to make it useful for detecting changes associated with pathological musculoskeletal conditions where tumor, inflammation, and degenerative processes impact the cellular composition of an analyzed tissue (41). However, the consensus surrounding DWI's utility in musculoskeletal oncology is mixed and nuanced. Promising outcomes have been observed in certain pathologies, such as distinguishing between benign and malignant vertebral fractures, but its use in other musculoskeletal conditions remains more controversial (42).
The application of DWI in distinguishing various bone and soft tissue sarcomas based on ADC values yields consistent trends. Notably, proposed ADC cutoff values demonstrate high sensitivity and specificity in detecting recurrent soft tissue sarcomas in routine surveillance imaging (23). Studies exploring DWI's effectiveness in distinguishing between muscle lymphoma, sarcoma, and metastases reveal statistically significant differences in ADCmean values, supporting its role in differential diagnoses (21). The examination of different pathological subtypes of osteosarcoma further contributes to the consensus, highlighting distinctive ADCmean values for specific subtypes (22). In addition, proposed ADC cutoff values demonstrate notable sensitivity and specificity when distinguishing between various malignant tumor grades (39). Lastly, ADC values from both whole tumor and darkest tumor areas were effective in differentiating various soft tissue sarcoma subtypes (36). These data collectively support that DWI holds promise as a valuable and non-invasive tool for characterizing and differentiating bone and soft tissue sarcomas.
In evaluating the predictive potential of DWI for chemotherapy responses in osteosarcoma and Ewing's sarcoma, multiple investigations highlight significant differences in ADC values during neoadjuvant chemotherapy for osteosarcoma, but they vary in the specific ADC parameters identified as predictors of treatment response. The observed discrepancies extend to distinctions in pre- and post-treatment ADC values for osteosarcoma and Ewing's sarcoma. Although DWI holds promise in predicting treatment responses through consistent trends in ADC value changes, Teo et al. caution about the limitations, particularly in its added value when compared to conventional MRI alone (24–28). Nonetheless, DWI seems to prove itself as a clinically used technology for assessing chemotherapy response.
In the assessment of DWI's diagnostic potential in differentiating benign from malignant osseous tumors, quantitative analysis of mean and ADCmin values emerged as a generally effective method for differentiation. However, Douis et al., in contrast to other authors, reported that quantitative analysis was not useful in distinguishing between benign and malignant skeletal tumors (29). Despite this discrepancy, most authors identified specific ADC cutoff values that exhibit high sensitivity and specificity across various scenarios, including primary and metastatic malignancies, bone marrow, and chondrogenic tumors (30–35,37,38). A similar consensus is reached regarding the role of DWI in differentiating malignant versus benign soft tissue tumors: lower ADC values are associated with more aggressive cellular disease, suggesting that DWI sequences may be useful to establish tumor grade in soft tissue tumors (36–38).
The present study has some limitations. First, the retrospective nature of the included studies introduces biases and limits the establishment of causal relationships. The heterogeneity observed in how treatments are administered across different studies poses a challenge in drawing generalizable conclusions about DWI's effectiveness. In addition, variations in field strength and acquisition protocols may influence the comparability of results. Furthermore, the continued reliance on histologic diagnosis as the gold standard underscores the limitation that DWI, despite its promising results, is not a surrogate for obtaining a biopsy of suspicious bone and soft tissue tumors. Further, our analysis on the response to chemotherapy (topic 2) was limited to Ewing's sarcoma and osteosarcoma due to the current limitations in the literature. Osteosarcoma and Ewing’s sarcoma are the two most common primary bone tumors; as a result, they are the focus of the majority of studies examining DWI protocols in malignant bone tumors, whereas studies on other malignant bone tumors are lacking. Similarly, another significant limitation of our study is the broad focus of the topics, which may not fully reflect the overall biological behavior of bone and soft tissue tumors. This constraint is primarily due to the paucity of high-quality studies assessing DWI technology in musculoskeletal oncology. Our broad inclusion criteria aimed to encompass all relevant studies analyzing DWI with respect to bone and soft tissue pathologies. However, the limited availability of comprehensive studies hindered our ability to perform a more detailed assessment. These limitations emphasize the need for future prospective studies with standardized methodologies to validate the utility of DWI in musculoskeletal oncology.
In conclusion, DWI is a transformative technological innovation that offers significant utility within orthopedic oncology. By enabling a non-invasive and highly sensitive visualization of tissue cellularity, DWI has allowed further diagnostic accuracy in characterizing bone and soft tissue tumors. For instance, ADCmean values of ≤1.1 ×10−3 mm2/s for bone tumors and ≤1.4 ×10−3 mm2/s for soft tissue sarcomas are suggested cutoffs indicating malignancy based on our literature review. However, continued research is needed to fully optimize its role within clinical practice.
Footnotes
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
