Non traumatic spine fractures are a common diagnostic problem, notably in old age patients, and always causes diagnostic dilemma (6).
In this study we assessed the value of in-phase/ opposed-phase quantitative chemical shift method, in differentiating benign from malignant vertebral fractures using a new scoring system bases on radiological data. This technique is based on unequal precession frequencies of fat and water protons, which are present in vertebral marrow (7,8).
At 1.5 T, fat and water protons are in phase with each other at a TE of 4.6 ms, and are at opposed 180 degrees with TE of 2.4 ms, because of this, the presence of roughly equal amounts of fat and water in the normal marrow, results in a suppression in the signal intensity on opposed phase images (8,9).
In osteoporosis induced fractures, although signal intensity on the conventional spin-echo sequences being abnormal, there is no abnormal marrow replacement. The presence of normal marrow fat causes a suppression in the signal intensity on opposed-phase images, while, in pathologic fractures, underlying marrow infiltration results in the lack of signal suppression on the out-of-phase images (9).
The presence of para-vertebral soft tissue masses as well as infiltration of posterior elements supports the diagnosis of malignant fracture (10).
Some morphological changes seen compression fractures may suggest benign or malignant nature, but in many cases an overlap can occur in both categories (11). Cicala et al revealed that some morphological changes plus other additional findings can suggest metastatic etiology for compression fracture such as vertebral body convex posterior border, involvement of the pedicle or posterior element, the presence of epidural or paraspinal mass and affection of other vertebral bodies by metastatic lesions (11).
Features that were described favoring osteoporotic compression fracture includes retropulsion of a posterior bone fragment, sparing of normal bone marrow signal intensity of the vertebral body,
the presence of low signal intensity band on T1- and T2-weighted images, fluid signal and intra-vertebral vacuum cleft sign, as well as multiple compression fractures (11). This agrees with our study, four cases of malignant fractures were reported to have a convex posterior border as well as enhancing epidural masses, which confirmed that morphological features can assess in separating benign from malignant compression fractures.
Post contrast enhancement of compression fracture is highly suggestive of underlying malignant infiltrative process. However, Zhou et al and Dalia et al reported enhancement in 9 out 17 of benign fractures, which all showed a signal drop on the out of phase image compared to the in phase image, a benign SIR, and were proved benign on follow up of patients, and thus the authors concluded contrast enhancement is not specific for differentiation between benign and malignant lesions (7, 12).
In our study, there were contrast enhancement in all the twelve patients of malignant fractures, which all showed no drop of signal on the out of phase image compared to the in phase image and a malignant SIR, and were proved malignant on follow up. Contrast enhanced sequences used only in patients with suspected underlying neoplastic cause. Patient with acute spine infection were excluded from our study.
So, in our study, we did not rely on contrast enhancement as a way of differentiation, but to assess the presence the epidural and para vertebral components.
The findings were expressed in the form of a ratios, by comparing the signal intensity in the abnormal bone marrow on the out-of-phase and in-phase images. This signal intensity ratio was calculated as the mean signal intensity on out-of-phase images divided by the mean signal intensity on the in-phase images.
By using this formula which was also used in studies by Eito, Ogura, Dalia and Erly, et al, we calculated a mean signal intensity ratio of 1.72 ± 0.14 (range 0.8–2.96) for the neoplastic group and 0.73 ±0.07 (range 0.12–1.2) for the benign group (P <.0001), (9, 10, 12, 13).
In our study SIR cutoff value was 0.91 to differentiate benign from malignant vertebral compression fractures, that was similar to what reported by Dalia et al (12). Our ratios was higher than that reported by Erly & Disler et al. (13,14), namely 0.8, but less than the cutoff value of 1 reported by Eito & Ogura et al, (9,10).
Our SIR cutoff value of 0.91 showed 100% sensitivity, 91.6% specificity with 95% accuracy in the separating benign and malignant vertebral compression fractures. These results agreed with Disler et al. (14) who reported 89% sensitivity and 80% specificity, as well as Erly et al. (13) who reported a 95% sensitivity and 89% specificity and Dalia et al. (12) who reported sensitivity 93%, specificity of 82%.
Geith et al. (15) had different results in which 69.2% of all osteoporotic fractures showed a hyperintense signal on opposed phase images (false-positive). No significant difference in signal intensity were found on the opposed-phase images of benign and malignant vertebral fractures and were able to reach a sensitivity of only 50%, and a specificity of 88.5%. We tried to explain their results by focusing merely on definite osteoporotic and neoplastic collapse. Cases with atypical hemangiomas showed minimal signal drop on out-of-phase images, due to the presence of microscopic quantities of fat, such cases are difficult to distinguish from malignant neoplastic on conventional routine MRI sequences.
In cases with degenerative sub-endplate sclerosis type 3, there were no appreciable signal drop on out of phase with increased SIR ratio to a suspicious level, but this is usually not problematic for diagnosis on conventional MR imaging. The term of edema like signal intensity refers to fluid hyperintense signal on T2- weighted images and is nonspecific to any pathological etiology, meaning it can result from different etiologies (e.g., degenerative, infectious, inflammatory, traumatic, and neoplastic changes). This can explain our false positive case, that was classified as malignant due to the presence of degenerative vertebral osteonecrosis in a known patient with hepatocellular carcinoma, who showed no significant signal drop in out phase images, with SIR >1, was due to sclerosis like degenerative changes, with unequal amount of fat and water. This case was confirmed by additional CT examination, which showed marked degenerative bony changes, with cortical bone defect, intra vertebral vacuum phenomenon & stability on serial follow up
False negative results were reported by Swartz et al. (16) and explained the presence of dense sclerotic or fat containing metastases. They also reported false positive pitfall, due the presence of marrow fibrosis. We didn’t encounter similar cases in our cases.
The main limitations in this study were the small number of patients and unavailability of tissue diagnosis in some cases.