Detection of occult vertebral fractures by quantitative assessment of bone marrow attenuation values at MDCT
Introduction
Multidetector computed tomography (MDCT) is regarded as the first imaging technique of choice for the evaluation of vertebral fractures after trauma [1], [2]. MDCT exhibits diagnostic superiority over plain radiographs in inconclusive findings and enables multiplanar reconstructions of vertebral fractures, which is necessary for further therapeutic management [3], [4], [5]. However, as known from other anatomical regions, MDCT may fail in fracture detection if the overlying cortical bone is intact or the degree of trabecular disruption is too small to be directly visualised [6], [7], [8]. Those “occult fractures” are detectable by MRI and/or SPECT/CT, two diagnostic modalities that have been proven to be superior in the visualisation of acute bone trauma [6], [9], [10], [11]. Several comparative studies between MDCT and MRI have demonstrated high numbers of occult vertebral fractures in MDCT, reaching up to 30% [12], [13]. MRI, particularly using a short tau inversion recovery (STIR) sequence, is sensitive in depicting bone marrow oedema as well as subtle fracture lines, which are occult on MDCT.
Detection of occult vertebral fractures is of high clinical relevance as it influences further therapeutic management. Several studies demonstrated the risk of a delayed vertebral collapse in occult fractures, and therefore kyphoplasty or vertebroplasty are recommended as appropriate therapeutic interventions as alternatives to therapy by drugs [14]. Besides strengthening the vertebral body, kyphoplasty and vertebroplasty also result in significant pain relief and functional improvement [15], [16].
Occult fractures are associated with bone marrow oedema, which cannot be depicted visually on MDCT due to the overlying trabecular bone [17]. However, we hypothesised that the bone marrow oedema associated with occult fractures leads to increased Hounsfield attenuation units (HU) at MDCT. Therefore, the aim of our study was to evaluate the bone marrow with objective comparative ROI-based HU measurements to determine a HU cut-off value for valid and reliable detection of bone marrow oedema related to occult vertebral fractures.
Section snippets
Study population
In this retrospective study, we included 36 consecutive patients after spinal trauma (17 female, 19 male; median age, 73.5 years; range 45–90 years) who underwent MRI after MDCT imaging between December 2008 and July 2012 to rule out occult vertebral fractures of the thoracolumbar spine. Delay between MDCT and MRI was between 0 and 7 days (mean, 3 days). Patients were excluded if they suffered from secondary disease such as osseous metastasis or inflammatory osseous diseases. The local
Results
Overall 202 vertebral bodies were imaged in 36 patients. 6 vertebral bodies were excluded from quantitative analysis, one because of vertebral hemangioma, 4 because of vertebral sclerosis due to advanced osteochondrosis and 1 because of total vertebral compression. The remaining 196 vertebrae (97.0%) were further analysed (T9 = 3, T10 = 7; T11 = 17; T12 = 30; L1 = 32; L2 = 32; L3 = 30; L4 = 24 and L5 = 21). The mean area of all 784 ROIs by both readers was 2.8 cm2 ± 0.7 cm2 SD. Investigated levels in patients varied
Discussion
Our study demonstrates that differences in bone marrow density can be used as a valid tool for the detection of post-traumatic bone marrow oedema associated with vertebral fractures.
In correlation with increased amounts of interstitial fluid in the medullary cavity as confirmed by MRI, we observed significantly higher HU values within affected vertebral bodies compared with non-affected levels. However, we observed a large overlap in absolute HU values between affected and unaffected vertebrae,
Conflict of interest
We declare that we have no conflict of interest.
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