MRI of occult sacral insufficiency fractures following radiotherapy

Abstract

Following radiation therapy, marrow abnormalities noted on magnetic resonance imaging (MRI) are frequent and may mimic metastases. Specific radiotherapy changes are usually easily identifiable; however, traumatic lesions cause more interpretive difficulties. We assessed the incidence and MRI characteristics of insufficiency fractures in this population. During a 5-year span (1987-1991), 546 patients received pelvic radiotherapy for primary malignancies. MRI was performed in 25 of these patients at least 3 months after treatment. The mean dose in this group was 53 Gy. These MRI scans were retrospectively reviewed for the appearance of the sacrum with particular attention to the presence of insufficiency fractures. This was correlated with clinical course and scintigraphic findings. Presumed insufficiency fractures on MRI paralleled the sacral side of the sacroiliac joint, enhanced with Gd-DTPA, were most prominent or initially seen anteriorly, and had ill-defined margins on all imaging sequences. The incidence of occult sacral insufficiency fractures was at least 20%. Insufficiency fractures of the sacrum in the post-radiotherapy patient are a relatively frequent occurrence which can mimic metastases. Consideration of this phenomenon and knowledge of differential features may avoid overdiagnosis of osseous metastases.

Magnetic resonance imaging of bone marrow in oncology, Part 2

“…Multiple fractures may develop within 24 months [29]. The incidence of RT-induced sacral insufficiency fractures seen on MRI is 20-80% [29,30]. The fracture lines usually parallel the sacroiliac joints and show ill-defined margins in all sequences.…”

Insufficiency Fractures of the Sacrum following Stereotactic Body Radiotherapy for Sacral Tumors

“…However, CTs may not detect transversely oriented fractures or fractures with a significant horizontal component. On magnetic resonance imaging, presence of fracture lines on T1-weighted images and high signal intensity parallel to the sacroiliac joints on T2-weighted images are virtually pathognomonic of insufficiency fractures [17,18]. While MRIs can detect early changes of sacral insufficiency with a reported sensitivity at or near 100%, CTs provide the most specific information for the detection of these fractures and for the exclusion of recurrent malignancy and are extremely useful in confirming equivocal findings on MR imaging.…”

“…While MRIs can detect early changes of sacral insufficiency with a reported sensitivity at or near 100%, CTs provide the most specific information for the detection of these fractures and for the exclusion of recurrent malignancy and are extremely useful in confirming equivocal findings on MR imaging. It is now recognized that CT and MRI scans are most useful in identifying insufficiency fractures of the sacrum, that they provide complementary information and that their combined use is ideal [16][17][18]. For the patients in our study all of whom had pre-existing neoplastic disease involving the sacrum, either primary or secondary, both CT and MRI scans were reviewed, where available.…”

Female Pelvis: Genital Organs

“…The incidence of radiation-induced sacral insuffi ciency fractures seen on MRI is 20-80 % (Blomlie et al 1995 ;Mammone and Schweitzer 1995 ), most commonly affecting postmenopausal women.…”