Hyperintense vertebral lesions

Introduction

Disk disease and especially disk herniation is commonly the best recognized form of degenerative disease of the spine. However, it has always to be remembered that spine degeneration is a multilevel and multistructural disorder of both soft tissue and bony elements of the spine. At the particular level it affects several anatomical structures of diskovertebral unit: intervertebral disk, vertebral bodies, facet joints, ligamenta flava, longitudinal ligaments [1–3].

Involvement of the vertebrae is a typical feature of the degenerative disease of the spine and is present already in the earliest stages of the pathological process. Spine degeneration begins simultaneously in the intervertebral disk and the adjacent vertebral endplate cartilage which results in the inflammatory reaction in the parts of the vertebral bodies located in the direct vicinity of the endplates and thus increased water content in these areas. This early stage is defined as the so called aseptic spondylodiscitis or discovertebritis and is equivalent to Modic type 1 vertebral body degeneration lesions. It has to be differentiated from infectious spondylodiscitis (see below). In the later stages vertebral changes also follow degenerative lesions of the other spine structures and present as the other types of vertebral degeneration, like fatty degeneration (Modic type 2 lesions), sclerotic degeneration (Modic type 3 lesions), erosive osteochondrosis of the vertebral endplates and facet joint degeneration [1–6].

Degenerative hyperintense lesions of the vertebrae

MR is an imaging method of choice in diagnostics of the spine degeneration, including vertebral degeneration. The most common types of the vertebral degeneration, i.e. Modic type 1 and type 2 lesions, could be visualized only with MR. Modic type 1 lesions are hyperintense on T2-weighted and fat saturation images, while Modic type 2 lesions are typically hyperintense on T1-weighted and to the lesser extent on T2-weighted images. These hyperintense areas are located always adjacent to the vertebral endplates, however they can involve variable part of the vertebral bodies, from the narrow band to the entire vertebral body [7–10].

Hyperintensities could be also seen in the other types of vertebral degeneration. Osteophytes of the vertebral bodies are often hyperintense on T1 and/or T2-weighed images. Degeneration of the facet joints may exhibit hyperintensive areas in the articular processes. Erosive osteochondrosis, apart from the irregularities of the vertebral endplates is usually accompanied by degenerative hyperintense lesions in the adjacent parts of the vertebral bodies. Degenerative spondylolisthesis is typically associated with hyperintense changes of the vertebral bodies and articular processes of the facet joints at the affected level. Spinal stenosis always involves vertebral structure and thus results again in hyperintense Modic type 1 and/or type 2 lesions of the vertebral bodies and articular processes [3, 5].

Full evaluation of the hyperintense vertebral lesions requires their assessment with multiple MR sequences and sometimes with the other modalities. MR protocol must always include T1-weighted, T2-weighted and T2- fat saturation (FatSat) images; sometimes it should be supplemented by post-contrast T1-weighted images. Modic type 1 lesions are hyperintense on T2-weighted and FatSat images, while hypointense on T1-weighted images (Fig. 1). Modic type 2 lesions have increased signal on T1-weighted images, intermediate signal on T2-weighted images and decreased signal on FatSat images (Fig. 2).

Fig. 1

MR sagittal T1-weighted (a), T2-weighted (b) and FatSat (c) images. Modic type 1 changes in L5 and S1 vertebral bodies

Fig. 2

MR sagittal T1-weighted (a), T2-weighted (b) and FatSat (c) images. Modic type 2 changes in L2, L4 and L5 vertebral bodies

It is important to remember that Modic type 1 lesions may enhance on post-contrast T1-weighted images. This is understandable, because – as it has been already mentioned above – it is a kind of inflammatory reaction. This enhancement is better appreciated if we use T1-weighted FatSat images (Fig. 3). As the routine MR protocol in degenerative disease of the spine does not include post-contrast sequences, it may cause some diagnostic problems for less experienced readers [7–10].

Fig. 3

MR sagittal T1-weighted (a), Fat-Sat T2-weighted (b) and T1-weighted post-contrast (c) images. Modic type 1 changes in L5 and S1 vertebral bodies a,b,c. Modic type 1 changes with contrast enhancement (c) on on post-contrast T1w image

Neither type 1 nor type 2 Modic changes are visible on plain radiographs and CT scans, however type 2 lesions may be accompanied by areas of sclerotisation which can be visualised by the modalities mentioned above. On the other hand Modic type 1 changes may have increased uptake in bone scintigraphy, which again can be explained by inflammatory background of this pathology.

From the clinical point of view assessment of the possible relations between Modic changes and low back pain is of high importance. In the literature, many authors have reported a strong association between Modic changes and nonspecific low back pain. It has been shown that Modic changes type 1, especially at L5-S1, are more likely to be related to low back pain than other types of Modic changes and other levels [7, 10]. The reason is probably that Modic lesions type 1 represent the earlier stage of inflammatory process in which more proinflammatory chemical mediators have been produced [7].

Differential diagnosis of the degenerative hyperintense vertebral lesions

Degenerative hyperintense vertebral lesions are extremely common in the course of the degenerative disease of the spine and in a large majority of the cases are diagnosed very easily based on their typical signal characteristics, location adjacent to the vertebral endplates and coexistence of other signs of spine degeneration, e.g. degenerative disk disease. However, in some cases it may be difficult to differentiate vertebral degeneration from other pathological processes, especially infectious and neoplasmatic ones.

The most common problem is differentiation of the Modic type 1 lesions from infectious spondylodiscitis. The appearance of vertebral changes in both entities may be quite similar: hyperintense areas on T2-weighted and FatSat images adjacent to the vertebral endplates, which are hypointense on T1-weighted images and can enhance after contrast injection. Moreover, if Modic type 1 changes are accompanied by erosive osteochondrosis (Fig. 4) they may also have similar appearance of the vertebral endplates, which are irregular, like in infectious spondylodiscitis [11, 12].

Fig. 4

MR sagittal T1-weighted (a), T2-weighted (b) and FatSat (c) images. Modic type 1 changes in L4 and L5 vertebral bodies accompanied by erosive osteochondrosis

There are however significant differences which enable differentiation in the vast majority of cases. First of all one has to remember that degenerative hyperintense vertebral lesions are extremely common, while infectious spondylodiscitis is relatively rare. Secondly, in patients with degenerative process, the intervertebral disks adjacent to hyperintense vertebral lesions are almost always hypointense on T2-weighted image due to degenerative dehydration, while in spondylodiscitis they are hyperintense due to inflammatory process, which increases the amount of the water (Fig. 5). Besides, in infectious spondylodiscitis there is usually strong enhancement of both involved parts of vertebrae and intervertebral disk, while in degenerative disease there could be only weak enhancement of the vertebrae and sometimes part of the disk in the direct vicinity of the endplates. There is also a difference in the appearance of the endplates in erosive osteochondrosis and spondylodiscitis, because in the former the black line of the endplates’ cortical bone is irregular but intact, while in the latter it is almost invariably destroyed. Finally, the presence of any soft tissue mass, either in perivertebral area or in the spinal canal epidural space is a definite evidence of infectious spondylodiscitis [11, 12].

Fig. 5

MR sagittal FatSat T2-weighted (a), T1-weighted (b) and FatSat T1-weighted post-contrast (c) images. Spondylodiscitis at L2-L3 level

The differentiation which is discussed above is much more difficult in patients after spine surgery (especially in the early postoperative period), in whom the postoperative changes may mimic spondylodiscitis, including intervertebral disk enhancement and enhancing soft tissue mass in the spinal canal epidural space (which is compatible with granulation or scar tissue). Therefore in postoperative cases careful analysis of both the imaging pattern and clinical data is needed. Contrast administration is mandatory, however it is of limited value in the first 3 or even 6 month after surgery, because of the normal postoperative enhancement in this period [13].

The second important entity which must be differentiated from degenerative hyperintense vertebral lesions is neoplastic disease (Fig. 6). Many neoplasms such as multiple myeloma, lymphoma, chordoma, tend to have high T2 signal. Bone metastases present with hypointense to isointense signal on T1-weighted images, but it may have various signal intensity on T2-weighted images depending on the tumor’s osteoclastic and osteoblastic activity and the presence or absence of associated hemorrhage and pathologic fracture [14–17]. On the other hand, the vast majority of T1 hyperintense vertebral lesions are benign, although metastatic melanoma has been demonstrated to produce T1 hyperintense vertebral lesions, which have been attributed to hemorrhage or melanin [18].

Fig. 6

MR sagittal T1-weighted (a), and FatSat T1-weighted post-contrast (b) images. Vertebral metastases in T12, L1, L3 and L5 vertebral bodies

The differentiation between degenerative and neoplastic hyperintense vertebral lesions is easier than in the case of spondylodiscitis, because neoplastic foci (e.g. metastatic) are typically located away from the vertebral endplates and are not usually accompanied by other degenerative changes in the adjacent structures. However in case of any doubt, the imaging should be supplemented by CT (to exclude osteolytic neoplastic foci), bone scintigraphy and/or PET/CT (to exclude neoplastic foci with increased uptake or metabolism, respectively).

The other possible method of differentiation is application of diffusion weighted imaging (DWI). In the literature, there have been some studies which have attempted to assess the value of the apparent diffusion coefficient (ADC) in differentiation between benign (e.g. vertebral fractures due to osteopenia) and malignant (usually metastatic) bone marrow lesions [19–24]. The results of these studies have shown that vertebral lesions with high cellularity, such as malignant neoplasms, demonstrate reduced water diffusion and present low ADC values, while benign lesions, such as posttraumatic bony oedema reveal increased diffusion with high ADC values. However infectious disease of the vertebrae have shown ADC values similar to malignancy. Therefore ADC values seem to be a useful complementary tool in the differential diagnosis between acute benign fractures from malignant and infectious lesions, but do not help in differentiation malignant from infectious changes. Moreover, even in benign fractures, the ADC values may decrease in the subacute phase, until they reach the values of a normal bone marrow in a chronic stage [19–24]. Therefore, the assessment of the ADC score in the subacute phase of benign vertebral fracture may result in misdiagnosis of malignancy.

The typical Modic type 2 lesions’ mimic is vertebral haemangioma, which usually has similar signal characteristics. An association between the signal characteristics of the haemangioma and the proportion of adipocytes, vessels and interstitial oedema has been demonstrated. A typical vertebral haemangioma shows high signal intensity on both T1- and T2-weighted images. Lesions with a higher proportion of intervening adipocytes have higher signal on T1-weighted images and become hypointense on FatSat images (Fig. 7), while haemangiomas with a greater vascular component present with more intermediate signal on T1-weighted images and higher signal on T2-weighted images.

Fig. 7

MR sagittal T2-weighted (a), T1-weighted (b) and FatSat (c) images; axial T2 (d) image. Vertebral haemangiomas of T11 and T12 vertebral bodies

The differentiation between haemangiomas and degenerative hyperintense vertebral changes is usually easy, because the former are well defined round or oval lesions and are located in the different parts of the vertebral bodies, commonly away from the endplate. However, in some patients haemangiomas have to be differentiated from malignant lesions. In doubtful cases CT and/or bone scintigraphy should be performed. On CT an intraosseous polka-dot pattern representing prominent trabeculae is helpful in making the correct diagnosis of vertebral hemangioma [14, 15, 25, 26]. In bone scintigraphy no significant uptake is expected in a hemangioma, in contrast to malignant lesion.

Summary

Hyperintense vertebral lesions are common findings in the degenerative disease of the spine. They are usually accompanied by other spine degeneration’s signs, like intervertebral disk degeneration, bulging or herniation; vertebral bodies’ osteophytes, erosive osteochondrosis, facet joints’ and ligament flava degeneration, degenerative spondylolisthesis or spinal stenosis. They are consistent with Modic type 1 and 2 changes. To diagnose hyperintense vertebral lesions, T2-weighted, T1-weighted and FatSat images must be evaluated. The differential diagnosis, which includes infectious spondylodiscitis, neoplastic lesions and vertebral heamangiomas, requires in most patients applications of post-contrast T1 FatSat sequence and sometimes additional techniques like CT, bone scintigraphy or PET/CT; in some cases DWI may be also of value.