Imaging diagnosis
Case 175
【Progress】
After receiving lumbar MRI, they went back to each local clinic with a MRI disc and MRI findings we made.
【Discussion】
Lumbar spondylolysis indicates deficit or injury of hemi-lateral or bilateral pars interarticularis (1). It presents approximately 6% of the population and usually occurs asymmetrically (2). It arises from congenital or stress fracture. Congenitally, it is born with spina bifida occult and/or meningocele (3). When acquired, it arises from forceful or repetitive sports such as volleyball in adolescents (4 - 6). Its etiology remains still unknown.
Pars interarticularis is a short part of vertebra and connects pedicle in front and lamina in back. From pars interarticularis, superior articular process and inferior articular process extend to make connection with other vertebrae up and down.
Imaging modality for diagnosis of spondylolysis includes radiograph, CT and MRI. Lumbar vertebra radiograph prefers oblique viewpoint to visualize pars interarticularis rather to anterior-posterior or lateral viewpoints. It is known to supply an image looking like Scottie dog. Namely, Scottie dog’s neck is the pars interarticularis, its eye the pedicle, its ear the superior articular process, its fore legs the inferior articular process, its nose the transverse process and its hindlegs the spinous process (7 – 9). Spondylolysis is diagnosed when the continuity of Scottie neck is lost.
Lumbar vertebra CT prefers coronal and/or sagittal view to axial view simply because they are better to visualize pars interarticularis. Axial image is sometimes confusing deficit of pars interarticularis from nerve root. CT is excellent to show fatigue fracture of pars interarticularis but not in case of prior to fracture: bone marrow edema (7 - 9).
Lumbar vertebra MRI uses various sequences: T1WI, T2WI, fat suppression T2WI, and supplies axial, coronal and sagittal images. The merit of MRI is that MRI can show deficit or fracture of pars interarticularis as well as bone edema prior to fracture. Deficit or aged fracture of pars interarticularis is shown high signal intensity on T1WI and T2WI, indicating that fat is replaced after deficit or fracture. Edema of pars interarticularis is shown low signal intensity on T1WI and high signal intensity on fat suppression T2WI, indicative of bone marrow edema. According to grading system for spondylolysis by Leone A et al.(9), it is reported as follows: grade 1 bone marrow edema with intact cortical margin, grade 2 bone marrow edema with incomplete fracture not extending through pars interarticularis, grade 3 bone marrow edema with complete fracture extending through pars interarticularis, grade 4 chronic established deficit without bone marrow edema but with complete deficit extending through pars interarticularis.
In our cases, MRI in Case 1 showed left pedicle (pars interarticularis) with high signal intensity on fat suppression T2WI and low signal intensity on T1WI. It indicates bone edema, early stage of stress load or fracture, grade 1. If management starts in the early stage, spondylolysis might be blocked and the continuity of pars interarticularis would be preserved. Actually, an orthopedist in a local clinic did not realize spondylolysis on lumbar vertebra radiograph. Meanwhile, in Case 2 showed high signal intensity of pars interarticularis on both T1WI and T2WI, taking place of fat instead of fracture deficit of pars interarticularis. It indicates chronic phase of spondylolysis, grade 4. Hence, MRI can say excellent imaging modality for showing spondylolysis, irrespective of acute or chronic.
【Summary】
We present two cases of a fourteen-year-old girl and a nine-year-old boy suffering from spondylolysis. Lumbar vertebra MRI showed left pars interarticularis with high signal intensity on fat suppression T2WI and low signal intensity on T1WI in Case 1. It indicates bone edema, early stage of stress load or fracture. Meanwhile, in Case 2 MRI showed high signal intensity of pars interarticularis on both T1WI and T2WI. It indicates fat, chronic stage of spondylolysis. It is borne in mind that MRI is superior in diagnostic modality for spondylolysis to radiograph and CT in terms that MRI can show the early phase of spondylolysis on T1WI and fat suppression T2WI as well as chronic phase on T1WI and T2WI.
【References】
1.WebMD (2009). "spondylolysis". Webster's New World Medical Dictionary (3rd ed.). Houghton Mifflin Harcourt. p. 399
2.Altaf F, et al. Back pain in children and adolescents. Bone Joint J. 2014 Jun;96-B(6):717-23
3.Macleod S, et al. "Congenital absence of a lumbar pedicle. A case report and a review of the literature". Pediatr Radiol. 1982; 12: 207–10.
4.Kim HJ, Green DW. Spondylolysis in the adolescent athlete. Curr Opin Pediatr. 2011 Feb;23(1):68-72
5.Iwamoto, J., et al. Returning athletes with severe low back pain and spondylolysis to original sporting activities with conservative treatment. Sports Scandinavian Journal of Medicine and Science in Sports. 2004;14(6):346–351
6.Canzonieri, C, et al The Occurrence and Possible and Aetiology of spondylolysis in a Pre-Contact California Population. International Journal of Osteoarchaeology. 2012, 24:602-613
7.McTimoney, M. & Micheli, L. J. Current Evaluation and Management of Spondylolysis and Spondylolisthesis. Current Sports Medicine Reports. 2003, 2:41–46.
8.McTimoney, M. & Micheli, L. J. Current Evaluation and Management of Spondylolysis and Spondylolisthesis. Current Sports Medicine Reports. 2003, 2:41–46
9.Leone A, Cianfoni A, Cerase A, Magarelli N, Bonomo L. Lumbar spondylolysis: a review. Skeletal Radiol. 2011 Jun;40(6):683-700
2019.12.25