Adjunct value of qualitative and quantitative analysis of diffusion-weighted imaging in musculoskeletal tumors
Authors: Dewan Sannidhi , Mehta Nirad , Agarwal Manish , Thakkar Jay 
Published: October 2023

Abstract:

BACKGROUND AND AIM:
Diffusion-weighted imaging (DWI) has now become an integral component of the musculoskeletal tumor protocol magnetic resonance imaging (MRI). Although a conventional radiograph is still considered the primary modality, MRI is invariably performed for further characterization of the tumor. Being a fast noncontrast sequence and considering its role in detecting highly cellular lesions, DWI can prove as a helpful tool for those who have inconclusive radiographic or conventional MRI diagnosis. The aim of this study was to determine the role of DWI and apparent diffusion coefficient (ADC) value in the evaluation and differentiation of malignant and benign bones and soft-tissue neoplasms. We also derived a cutoff ADC value to differentiate the above two.

MATERIALS AND METHODS:
This is an IRB-approved retrospective study of 85 patients with histopathologically proven bone (n = 61, 47 malignant and 14 benign) or soft-tissue (n = 24, 21 malignant and 3 benign) neoplasms. Conventional MR features such as size, margins, T1/T2 signal intensity, cortical breach/bone expansion/medullary involvement, and neurovascular bundle involvement were assessed. DWI analysis was done by a blinded radiologist having MRI reporting experience of 3 years by placing three regions of interest on solid (nonnecrotic) components, and mean ADC values were derived for each neoplasm. These were confirmed by another senior radiologist with an experience of more than 15 years with MRI. Histopathological diagnosis was considered a gold standard. Mean ADC values of the benign and malignant groups were compared statistically. Sensitivity, specificity, and diagnostic accuracy were obtained. Receiver operating characteristic (ROC) curves were generated, and a cutoff ADC value was derived to differentiate benign and malignant tumors.

RESULTS:
True visual diffusion restriction was confirmed among 34/47 malignant bone tumors on b-800 DW images, whereas 10/14 benign bone tumors showed facilitated diffusion. Similarly, visual restriction was seen among 20/21 malignant soft tumors, whereas 2 out of 3 benign soft-tissue tumors showed visually facilitated diffusion. Statistically, a significant difference was noted between the mean ADC value of malignant (1.20 ± 0.68 × 10−3 mm2/s) and benign bone tumors (1.57 ± 0.69 × 10−3 mm2/s) (P = 0.04). Relatively high ADC values were noted in the chondrosarcoma group (n = 19), with 11/19 chondrosarcomas showing facilitated diffusion with a mean ADC value of 1.73 × 10−3 mm2/s. Similarly, among benign bone tumors, contrary to expectation, relatively lower ADC values were noted in giant cell tumors (n = 4) with a mean ADC value of 1.18 × 10−3 mm2/s. For soft-tissue tumors, a lower mean ADC value was noted for the malignant (0.85 ± 0.26 × 10−3 mm2/s) versus the benign group (1.33 ± 0.20 × 10−3 mm2/s) (P = 0.006). For bone neoplasms, a cutoff mean ADC value of 1.1 × 10−3 mm2/s was derived from the ROC curve with sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 72.3%, 71.4%, 89.5%, and 43.5%, respectively. For the soft-tissue group, a cutoff mean ADC value of 1.0 × 10−3 mm2/s was achieved with sensitivity, specificity, PPV, and NPV of 100%, 85.7%, 50%, and 100%, respectively.

CONCLUSIONS:
In addition to conventional MR, DWI with ADC analysis is a powerful tool in musculoskeletal tumor evaluation and an ADC cutoff value may help differentiate benign from malignant neoplasms. In chondroid malignancies, relatively high ADC values may be seen and DWI analysis may not be as useful.