Clinical diagnosis
Case 313
【Progress】
She received a management of a prester cast.
【Discussion】
Stress often damages to bone. Either situation of excessive stress to normal bone or normal stress to fragile bone can create bone contusion or bone fracture. Fatigue fracture is defined to be caused by excessive repeated stress to normal bone (1-4). Insufficient fracture is defined to be caused by normal pressure to fragile bone such as osteoporosis (1-4). One excessive stress to either normal bone or fragile bone such as traffic accident commonly causes bone fracture.
Occult fracture indicates no sign of bone displacement on imaging modalities of radiograph or CT (5, 6). However, MRI usually demonstrate occult bone fracture. Further, MRI demonstrate bone marrow edema caused by bone bruise (same as bone contusion). Occult fracture can occur in any bone. Radial bone (radius) and scaphoid bone are favorable sites of occult fracture (5, 6). In our case, occult fracture by landing on hand was found at distal end of radius whose fracture was not demonstrated on radiograph but on MRI.
Several sequences of MRI are supplied to elevate detectability for lesions in variable organs. To detect lesions of bone, sequences of T1WI, T2WI, fat suppression T2WI and fat suppression T2*WI are used. It is sometimes difficult to differentiate images of extremity bones on between T1WI and T2WI probably because fat component of bone marrow demonstrates high signal intensity. The differential point is signal intensity of muscle: The lower signal intensity is demonstrated on T2WI rather than T1WI. Fat suppression T2WI is useful to detect small volume of fluids than T2WI alone.
T2*WI is obtained by gradient echo acquisition, not by spin echo acquisition like T2WI (7). Compared to T2WI, scanning time of T2*WI is short and inhomogeneous magnetic field is visualized such as small metal like calcium and iron. In clinical reality, T2*WI demonstrate a lesion containing deoxyhemoglobin, methemoglobin and hemosiderin as low signal intensity.
Generally, T2*WI demonstrate bone marrow as low signal intensity because bone marrow includes lots of iron component, indicative of being available to demonstrate a lesion with small fluid component. Further, fat suppression T2WI is also useful to demonstrate a lesion with small fluids because bone marrow contains lots of lipid component. Therefore, combination of fat suppression with T2*WI is also useful to demonstrate a lesion with small fluids. Reversibly, signal intensity of muscle is becoming lowest (darker) on fat suppression T2*WI, followed by fat suppression T2 and last, T1WI.
In our case, occult fracture after trauma on either sequence on T1WI, fat suppression T2WI or fat suppression T2*WI. Meanwhile, signal intensity of muscle was lowest on fat suppression T2WI, followed by T2WI and last, T1WI.
【Summary】
We presented a sixty-seven-year-old female for pain of right wrist pain after landing on her right hand. Radiograph demonstrated no evidence of bone fracture. However, MRI showed marked traverse and longitudinal fracture line of her radius. It is borne in mind that occult fracture can occur in any bone but radius is one of the most susceptible of occult fractures. MRI with T1WI, fat suppression T2WI and fat suppression T2*WI are sensitive to occult fracture. T2*WI image is obtained by gradient echo acquisition and useful to detect deoxyhemoglobin, methemoglobin, and hemosiderin. Fat suppression T2*WI is excellent to detect small fluids in bone marrow, associated with fat suppression T2WI.
【References】
1.National Clinical Guideline Centre (UK). The Management of Hip Fracture in Adults [Internet]. London: Royal College of Physicians (UK); 2011. (NICE Clinical Guidelines, No. 124.) 5, Imaging options in occult hip fracture. Available from: http://www.ncbi.nlm.nih.gov/books/NBK83026/
2.Chen C, et-al. Insufficiency fracture of the sternum caused by osteopenia: plain film findings in seven patients. AJR Am J Roentgenol. 1990;154 (5): 1025-7. AJR Am J Roentgenol (abstract) - Pubmed citation
3.Porrino JA, et-al. Diagnosis of proximal femoral insufficiency fractures in patients receiving bisphosphonate therapy. AJR Am J Roentgenol. 2010;194 (4): 1061-4. doi:10.2214/AJR.09.3383
4.Greaney R, et al. Distribution and Natural History of Stress Fractures in U.S. Marine Recruits. Radiology. 1983;146(2):339-46.
5.Marshall R, et al. Imaging Features and Management of Stress, Atypical, and Pathologic Fractures. Radiographics. 2018;38(7):2173-92. doi:10.1148/rg.2018180073 - Pubmed
6.Mandell J, et al. Stress Fractures of the Foot and Ankle, Part 2: Site-Specific Etiology, Imaging, and Treatment, and Differential Diagnosis. Skeletal Radiol. 2017;46(9):1165-86.
7.Chavhan, GB et al. "Principles, Techniques, and Applications of T2*-based MR Imaging and its SpecialApplications". Radiographics. 2009;29 (5):433–1449. doi:10.1148/rg.295095034. PMC 2799958. PMID 19755604
2023.10.12