Presentation
Right leg pain, weakness, and numbness w/ history of pelvic radiation and rectal adenocarcinoma
Patient Data
Fatty marrow within the sacrum is in keeping with radiation therapy. Decreased signal intensity in the sacral vertebrae demonstrating marrow edema, which in this patient with known underlying malignancy, could raise the possibility of metastatic disease. Coronal imaging tells the rest of the story.
Marrow edema related to the bilateral sacral ala and extending horizontally across the body of the sacrum (Honda sign).
Case Discussion
An insufficiency fracture is the result of normal stresses on abnormal bone.
Risk Factors: Osteoporosis, rheumatoid arthritis, Paget disease, osteomalacia, diabetes, long-term bisphosphonate use.
Prior pelvic radiation is present in 21%–34% of patients with sacral insufficiency fractures.
Approximately 45% of patients with SIFs have a history of malignancy.
T2 STIR sequences can identify early marrow edema in sacral insufficiency fractures as early as 18 days before any symptoms are present.
Coronal oblique images in the plane of the sacrum do well to demonstrate the vertically oriented fractures and should be included in the imaging protocol when there is clinical suspicion.