In an environment of increasing concern regarding the long-term effect of ionizing radiation exposure particularly in young patients a reappraisal of imaging algorithms for spinal evaluation is taking place. MRI has long been a mainstay for the assessment of soft tissue spinal pathology involving the discs or ligaments with CT, plain radiography and nuclear studies maintaining a prominent role in osseous evaluation. The application of MRI, which is free of ionizing radiation and its attendant concerns to common categories of osseous spinal pathology, has the potential to improve on diagnostic efficacy and reduce patient risk.
An example is the diagnosis of spondylolysis and the prelytic microtrabecular injuries which may precede frank lysis. Cortical lysis is well demonstrated on CT and nuclear bone scan but subtler types of osseous injury which may proceed to lysis may be better appreciated on MRI. Earlier diagnosis and intervention at a stage when healing is more likely to occur than after cortical disruption has taken place may improve ultimate prognosis.
The MRI based analysis of osseous injuries described by Pomeranz and Fredrickson has a very useful application to this type of spinal injury. In this formulation, STIR, T1 and T2 images are used to categorize the severity of sublytic bone injury based on signal abnormalities on various sequences in the periosteal cancellous and cortical compartments. This approach has been found to correlate with prognosis as well as the findings of nuclear scintigraphy without the radiation exposure of that examination
I. Increased periskeletal signal on STIR
II. Increased cancellous signal on STIR only
III. Abnormal cancellous signal on T1 and STIR
IV. Cortical lysis
MRI can also be utilized to assess the chronicity of these and other spinal osseous lesions which may be useful in patient management as well as in certain medicolegal circumstances. A microtrabecular injury which is the result of acute trauma will exhibit signal characteristics reflective of bone edema manifested as an increase in bone water signal. Increased bone water will be bright on T2 and STIR sequences and a decreased signal intensity on T1.
As healing proceeds, bone edema resolves and the lesion heals through a process of which fatty replacement is a component. Fat has different signal characteristics than water on MRI. An area of fatty replacement may also be bright on T2, but unlike the acute edematous lesion is also bright on T1. A pars pedicle complex lesion bright on T1 and T2 sequences can be considered chronic and inactive.
STIR or proton density SPIR is also useful in this setting. As a sequence which suppresses the signal of fat, the lesion healed through fatty replacement will demonstrate low signal in contrast to the high signal seen at the time of acute injury.
Utilizing similar principles, aggressive lesions of bone such as metastatic deposits may be distinguished from chronic non-aggressive bone masses such as hemangioma based on the signal characteristics of the lesion as well as the surrounding reaction such as edema or perilesional fat.
The information that MRI provides, if properly utilized, has the potential to improve our ability to arrive at accurate diagnoses of osseous lesions while at the same time lowering patient risk. In young patients for whom the concern of cumulative exposure to ionizing radiation is greatest, MRI should be considered as the initial and often only diagnostic study. The improved understanding of MRIs potential to augment diagnostic efficacy in several categories of spinal pathology should encourage its consideration in clinical circumstances previously studied with other modalities.
Learn more about ProScan Imaging.
An example is the diagnosis of spondylolysis and the prelytic microtrabecular injuries which may precede frank lysis. Cortical lysis is well demonstrated on CT and nuclear bone scan but subtler types of osseous injury which may proceed to lysis may be better appreciated on MRI. Earlier diagnosis and intervention at a stage when healing is more likely to occur than after cortical disruption has taken place may improve ultimate prognosis.
The MRI based analysis of osseous injuries described by Pomeranz and Fredrickson has a very useful application to this type of spinal injury. In this formulation, STIR, T1 and T2 images are used to categorize the severity of sublytic bone injury based on signal abnormalities on various sequences in the periosteal cancellous and cortical compartments. This approach has been found to correlate with prognosis as well as the findings of nuclear scintigraphy without the radiation exposure of that examination
I. Increased periskeletal signal on STIR
II. Increased cancellous signal on STIR only
III. Abnormal cancellous signal on T1 and STIR
IV. Cortical lysis
MRI can also be utilized to assess the chronicity of these and other spinal osseous lesions which may be useful in patient management as well as in certain medicolegal circumstances. A microtrabecular injury which is the result of acute trauma will exhibit signal characteristics reflective of bone edema manifested as an increase in bone water signal. Increased bone water will be bright on T2 and STIR sequences and a decreased signal intensity on T1.
As healing proceeds, bone edema resolves and the lesion heals through a process of which fatty replacement is a component. Fat has different signal characteristics than water on MRI. An area of fatty replacement may also be bright on T2, but unlike the acute edematous lesion is also bright on T1. A pars pedicle complex lesion bright on T1 and T2 sequences can be considered chronic and inactive.
STIR or proton density SPIR is also useful in this setting. As a sequence which suppresses the signal of fat, the lesion healed through fatty replacement will demonstrate low signal in contrast to the high signal seen at the time of acute injury.
Utilizing similar principles, aggressive lesions of bone such as metastatic deposits may be distinguished from chronic non-aggressive bone masses such as hemangioma based on the signal characteristics of the lesion as well as the surrounding reaction such as edema or perilesional fat.
The information that MRI provides, if properly utilized, has the potential to improve our ability to arrive at accurate diagnoses of osseous lesions while at the same time lowering patient risk. In young patients for whom the concern of cumulative exposure to ionizing radiation is greatest, MRI should be considered as the initial and often only diagnostic study. The improved understanding of MRIs potential to augment diagnostic efficacy in several categories of spinal pathology should encourage its consideration in clinical circumstances previously studied with other modalities.
Learn more about ProScan Imaging.