USG and MRI play an important role in the characterization of wrist pathologies. MRI helps in the assessment of various ligaments, tendons, and nerves. It can also aid in the visualization of bones and soft tissue lesions including marrow, cartilage, and blood vessels [7], while USG provides a reliable diagnosis regarding cystic or solid nature of lesions and can help in diagnosis based on their imaging patterns [8].
In our study, USG and MRI agreed in 95% of cases with tendinopathy. Both equally detected synovial thickening, fluid collection, and discontinuity of tendons. USG was better than MRI in the detection of calcification. Significant advantages of USG over MRI are the ability to home in on the area of symptoms and the ability of dynamic examination of the tendons and comparison of the finding in one side with the contra-lateral side.
Our study is in agreement with Robinson, in that USG is an efficient and accurate imaging method for the evaluation of common tendon abnormalities. And its accuracy is equivalent to that of MRI for imaging tendon abnormalities [9]. Also, Hoving et al. found USG (using a high-frequency probe, 10 MHz) equivalent to MRI in the detection of tendon sheath disease at the hand and wrist [10].
Also, Stevic and Dodic [11] concluded that USG is well suited for evaluating tendons. In most cases, its accuracy is at least equivalent to that of MRI for imaging tendon abnormalities. But the advantages of USG such as accessibility, low cost, dynamic capability, and needle guidance make it as a first-line imaging technique in tendon evaluation [11].
As regards to TFCC abnormalities, MRI in our study adequately detects its pathologies (75% sensitivity); it showed promising results with regard to the detection of TFCC tears as compared to USG where no cases were detected by it. Kaddah et al. [12] compared MRI and magnetic resonance arthrography in the evaluation of pathologies of the TFCC and other intrinsic ligaments of the wrist with regard to site and type of tear. Arthroscopy was used as the gold standard for final diagnosis. Their study showed high sensitivity and specificity of MR arthrography in ligamentous pathologies, proving its added advantage over MRI [12].
The poor sensitivity of MRI in the diagnosis of TFCC tears was attributed to the presence of the striated fascicles at the periphery of the TFCC, which were believed to be difficult to be evaluated by MR imaging [13].
In our study, USG missed all cases of TFCC that is diagnosed by MR arthrography. This point was in agreement with Singh et al.’s [14] study, where USG showed less sensitivity compared to MRI with regard to the detection of ligamentous pathologies [14]. So USG is not performed routinely in the practice due to the complex anatomy of wrist ligaments. Against our study, dynamic evaluation of wrist ligaments using USG was performed by Gitto et al. [15]; they described normal USG appearance of wrist ligaments using bony landmarks and dynamic maneuvers [15].
As regards to the evaluation of mass lesions, USG in our study detected 6 of 8 cases (75%) with simple ganglion and 3 of 3 (100%) cases with solid mass lesions. USG missed 2 cases of simple ganglion because they were too small in size with no posterior acoustic enhancement. USG is a good modality in the characterization of mass lesion as solid or cystic and assessment of lesion size, internal structure vascularity, and its relation to surrounding structures. MRI detected 8 of 8 (100 %) cases with simple ganglion and 3 of 3 (100 %) cases with solid mass lesions.
Our study’s result is little different from Teefey et al.’s [16] results in which USG diagnosed 87% of ganglion cases and 73% of solid lesions. It may be due to larger patient sample in their study and USG is an operator-dependent technique [16].
MR imaging helps analyze the tumor matrix by identifying fatty and cystic tissue in a given lesion. MR imaging shows features of aggressiveness and signs of malignancy: poorly defined margins, invasion intovascular-nervous or osseous structures, peritumoral edema, heterogeneous signal in case of necrosis, and intense enhancement. MR imaging helps discriminate between benign and malignant lesions with a sensitivity of 93% and a specificity of 82% [17].
However, USG represents a reasonable technique to assess a mass of the wrist and hand as it helps identify the anatomical structure from which lesions originate. USG is essential to analyze the tumor matrix, by identifying if the lesion is cystic or solid. A cyst appears as a well-circumscribed walled lesion, anechoic with posterior acoustic enhancement. Finally, USG is also part of the treatment plan by guiding infiltration or biopsy procedures [18].
As regards to foreign body assessments, our study found that USG is better than MRI in the detection of foreign bodies and its depth, relations to surrounding structures and surrounding inflammatory reactions if present. USG detected 2 of 2 (100%) cases with foreign body while MRI detected 1 of the 2 (50%) cases. These results were in agreement with Turkcuer et al.’s study in that the overall sensitivity of USG in detecting radiolucent foreign body was 90% [19]. Tahmasebi et al. reported a higher accuracy and sensitivity (90.2% and 97.9% respectively) for USG in detecting radiolucent foreign bodies [17]. If high-resolution USG is available, we recommend it as the first imaging modality for evaluating the patients with clinically suspicious radiolucent foreign body because of its availability, high sensitivity, and absence of radiation. In patients with history of soft tissue foreign body and negative radiography, we recommend USG as the most important diagnostic tool before discharging patients. USG gives important information about the size, depth, and relationship of foreign bodies to other structures such as vessels and tendons and makes exploration easier for the surgeon. Furthermore, an important advantage of USG is the possibility of real-time guided removal of foreign body under sterile condition, and due to its safety and less complication rate, it may replace surgical exploration.
As regards to CTS, USG in our study detected 8 of 9 (88.9 %) cases with CTS using inlet to outlet ratio (IOR), while MRI detected 7 of 9 (77.8%) of the cases. So, we believed that USG is better than MRI in the diagnosis of CTS. These findings were in agreement with Ulaşli et al.’s study in that the largest CSA of median nerve was more sensitive in USG diagnosis of CTS when the cutoff point was set at 10 mm (99% sensitivity) [20]. Also, Tengfei Fu et al., in their study, demonstrated that the IOR improves the diagnostic accuracy of ultrasound for the diagnosis of CTS. Optimal diagnostic cutoff value was 1.3, resulting in a specificity of 93% and a sensitivity of 91% [21].
In our study, we had found that the sensitivity, specificity, and accuracy of MRI assessment of wrist pain were 98.8%, 98.0%, and 94.0 % respectively versus the sensitivity, specificity, and accuracy of USG assessment of wrist pain 79.2%, 96.1%, and 88.0% respectively. In agreement with our results, Kaddah et al. [12] found the overall sensitivity, specificity, and accuracy of MRI in diagnosis of wrist pain were 84.21%, 100%, and 88.15% respectively [12]. Also, Singh et al.’s study showed high sensitivity of USG as well as MRI in wrist pathologies with the added advantage of MRI over USG in wrist abnormalities and ligamentous pathologies [14].
USG is near equal to MRI in the assessment of tendon abnormalities and better than MRI in the diagnosis of CTS and foreign body, but MRI is better than USG in the assessment of swelling (cystic and solid) and characterization of masses.
