Neuroradiology (2006) 48 (Suppl): 18–33 DOI 10.1007/s00234-006-1465-1
ADVANCED CONTRAST MANAGEMENT IN neuroMRI
Cesare Colosimo Alessandro Cianfoni Giuseppe Maria Di Lella Simona Gaudino
Contrast-enhanced MR imaging of the spine: when, why and how? How to optimize contrast protocols in MR imaging of the spine
C. Colosimo () · A. Cianfoni · G.M. Di Lella · S. Gaudino Department of Bioimaging and Radiological Sciences Catholic University of Sacred Heart Policlinico “A. Gemelli” L.go F. Vito 1 00168 Rome Italy E-mail:
[email protected] Tel.: +39-0630154977 Fax: +39-0635501928
Abstract The optimal protocols and the role of contrast agents in spinal MR imaging are controversial. Although the diagnosis of many common spinal diseases can be reliably achieved by means of unenhanced images, contrast use is often necessary to improve lesion detection and differential diagnosis. The heterogeneity of the different spinal compartments and the wide variety of spinal pathology require tailored imaging strategies. Thus, the rules to achieve optimization of contrast protocols for MR imaging of the spine are frequently very different to those for brain imaging, and depend on the location and site of origin of the lesions in a specific spinal
Introduction The intravenous administration of gadolinium contrast agents in MRI of the brain is a routine procedure which is mandatory for the detection and characterization of many common diseases. The mechanism of contrast enhancement of brain lesions and its diagnostic relevance are related to the presence and integrity of the blood–brain barrier in normal tissue and its breakdown in lesions. Efforts to improve the demonstration of tiny and/or faintly enhancing brain lesions have involved increasing the dose (up to triple dose), increasing the delay between contrast agent administration and image acquisition, and adopting sequences that reduce the background signal (e.g. magnetization transfer) [1, 2]. A more advantageous approach comes from the availability of contrast agents
compartment, on the findings of unenhanced imaging, and on the concomitant use of fat-suppression techniques. Furthermore, in most cases, the small size of the examined structures requires a meticulous technique, and the administration of a contrast agent with high relaxivity, such as MultiHance, is advisable to enable the detection of tiny areas of contrast enhancement. The applications and clinical utility of post-contrast MR imaging are discussed with regard to different spinal diseases. Keywords Spine · Magnetic resonance imaging · Gadolinium · Contrast
such as gadobenate dimeglumine (MultiHance, Gd-BOPTA; Bracco Imaging, Milan, Italy), which increases relaxation in blood more than other available gadolinium chelates. The higher relaxivity of this agent results in greater T1 shortening, leading to a higher signal intensity to concentration ratio on T1-weighted MRI sequences. Numerous studies [3–6], as well as ever-increasing daily clinical experience, have demonstrated the superiority of MultiHance over other gadolinium contrast agents for the detection and characterization of enhancing brain lesions. On the other hand, the administration of gadolinium agents for the MR evaluation of spinal pathology requires a different approach, firstly because the diagnosis of many common diseases (such as disk herniations and vertebral metastases) can be reliably achieved without the use of contrast agents, and secondly because the heterogeneity of the different spinal components (spinal cord, nerve roots and spinal nerves, intervertebral disks,
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vertebral bones with their articulations, epidural tissue and vascular structures) makes mechanisms of normal and abnormal contrast enhancement different and more complex [7–10]. The spine anatomy can be divided schematically into a bony compartment, an epidural compartment, an intradural extramedullary compartment and an intradural intramedullary compartment. Each of these compartments has specific anatomy and pathophysiology, is subject to different diseases and pathological processes, and requires individual tailored imaging strategies. Thus, the rules to achieve optimization of contrast protocols for MR imaging of the spine are frequently very different to those for brain imaging and depend on the location and site of origin of the lesions and on the findings of unenhanced imaging. Since the vast majority of lesions in the spine have low signal on T1-weighted sequences there is often a natural high lesion-to-background contrast on unenhanced T1-weighted imaging because of the intrinsic high T1 signal of adipose tissue which is usually extensively present in the vertebral bone marrow, paraspinal soft tissues, and epidural space. On the other hand, the presence of adipose tissue means that rigorous fat-suppression techniques usually have to be applied when T2weighted and contrast-enhanced T1-weighted imaging is performed, in order to make abnormalities stand out against the adipose background [11, 12]. Generally the small size of the examined structures (spinal cord, nerve roots, intervertebral disks, articular pillars, etc.) makes adoption of a meticulous technique a critical prerequisite for the detection of tiny areas of contrast enhancement. In this clinical setting the administration of MultiHance is advisable because better signal-to-noise and lesion-to-background contrast-to-noise ratios (SNR and CNR, respectively) can be achieved [3]. The inherently high T1 relaxivity of this agent in blood enables the contrast enhancement and conspicuity of lesions to be maximized. The indications, diagnostic usefulness and mode of use of intravenous contrast agents in MRI of the spine differ considerably depending on the type of pathological process and the spinal compartment to be studied.
Intradural intramedullary compartment Spinal cord diseases The spinal cord, as part of the central nervous system, possesses a blood–spinal cord barrier which, under normal conditions, prevents contrast enhancement of the spinal cord and associated leptomeninges. As in the brain, the normal background, against which to maximize visualization of lesions, is neural tissue and surrounding cerebrospinal fluid (CSF). The anatomical en-
vironment and the variety of diseases potentially involving the spinal cord are similar to those of the brain. Because of these similarities, contrast-enhanced images are typically acquired with techniques that are similar to those used to image the brain. Thus, high-resolution T1weighted spin echo (SE) sequences with no fat suppression obtained on a high-field magnet (at least 1.0 T) are widely employed [11]. For certain spinal cord diseases, the same MR methodology used for the brain can be adopted to increase the conspicuity and/or detection of abnormal contrast enhancement. Thus, double and triple doses of contrast agent and/or delayed image acquisition can frequently be employed to increase the detection of contrast enhancing areas in instances of spinal cord tumours or spinal cord inflammatory/demyelinating/infectious diseases. Obviously both approaches have drawbacks in terms of increased cost, for the additional amount of contrast material used, and increased machine occupancy time. In addition to the benefits of increased SNR and CNR, the use of a “high relaxivity” gadolinium agent such as MultiHance can help to overcome these drawbacks. Although most randomized studies comparing MultiHance with other gadolinium agents in adults and children have included only a few cases of intramedullary tumours and enhancing cord lesions, the results have consistently demonstrated the superiority of MultiHance [3]. In addition, the benefits of MultiHance have also been demonstrated in patients with multiple sclerosis and other demyelinating diseases [13]. In these patients demonstration of an abnormal blood–spinal cord barrier can be further improved by increasing the interval between contrast administration and image acquisition, with the brain usually being examined before the spine. The proper use of contrast material is of paramount importance in depicting and characterizing blood–spinal cord barrier abnormalities in a wide variety of diseases. In demyelinating diseases, evidence of contrast enhancement within a lesion is thought to be indicative of an acute inflammatory process and can prompt a change of treatment (Fig. 1) [14]. In cases of neoplastic spinal cord lesions, the enhancing portion of the lesion defines the extent of the neoplasm and the ideal surgical resection margins, usually within a larger area of T2 signal abnormality comprising oedema and/or syrinx (Fig. 2) [15]. Enhancement along the wall of a cystic lesion in the spinal cord differentiates a cystic neoplasm from the non-enhancing syrinx cavity [16, 17]. Contrast enhancement is also of diagnostic importance in vascular diseases involving the spinal cord: the pattern of spinal cord enhancement is critical for recognition of ischaemic infarction in the subacute phase, and of venous congestive disease (for example in patients affected by dural arteriovenous fistulas resulting in Foix-Alajouanine syndrome). In such cases, as well as in cases of spinal vascular malformations, contrast-enhanced MR angiography (MRA)
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Fig. 1a, b Blood-spinal cord barrier disruption in inflammatory diseases. Sagittal T2weighted FSE image (a) and contrast-enhanced T1-weighted SE image (b) of the cervical spine in a patient with diagnosed multiple sclerosis. The T2-weighted image reveals an elongated area of abnormal high T2 signal in the spinal cord, with ill-defined borders, encompassing the vertebral body levels C2 and C3. On the T1-weighted image after injection of paramagnetic contrast agent a well-defined area of intense contrast enhancement is clearly visible at the C2 level. The abnormal enhancement in the spinal cord is indicative of blood–spinal cord barrier disruption, suggestive of acute demyelination. This finding, in some cases, leads to a change in clinical management strategy
Fig. 2a, b Spinal cord ependymoma. Sagittal T2weighted FSE image (a) and contrast-enhanced T1-weighted SE image (b) of the cervical and thoracic spine of a young patient with spinal cord ependymoma. The post-contrast T1weighted image better defines the extent of the tumour (arrows), located from C7 to D2, and clearly differentiates it from the associated syrinx (arrowheads), and the cord oedema (asterisk). This represents a presyrinx state. After surgical removal of the enhancing tumour, the syrinx and edema are likely to regress
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is indicated to obtain good quality confirmation of the abnormal intradural vascularity prior to the necessary digital subtraction angiography. MRA can identify the metameric level of the fistula or the anatomy of the malformation on both the arterial and venous sides [18, 19]. Therefore in these patients, after the acquisition of unenhanced T1- and T2-weighted images, multiphase timeresolved contrast-enhanced MRA should be performed, followed by acquisition of contrast-enhanced multiplanar T1-weighted images (Fig. 3).
Intradural extramedullary compartment The intradural extramedullary compartment, corresponding to the subarachnoid space, is contained within the dura. The most important anatomical structures in this compartment are the nerve roots, the leptomeninges (pia mater and arachnoid), the pachymeninges (dura mater) and the arterial and venous intradural spinal vessels. Under normal conditions, leptomeninges and nerve roots do not show significant contrast enhancement. On post-contrast T1-weighted images the arterial spinal vessels are not easily visualized because of their small size (1 mm or less) and because of flow void phenomena. On the other hand, normal venous vessels in the spinal canal may show contrast enhancement due to their larger size and slower flow. Care must be taken not to confuse normally enhancing veins, particularly on the posterior surface of the conus medullaris, with vascular malforma-
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Fig. 3 Venous congestive disease of the spinal cord in a spinal dural A-V fistula. Sagittal T2-weighted FSE image (a), contrast-enhanced MRA reformatted 3D-MIP sagittal image (b) and coronal image (c), and contrast-enhanced T1weighted fat-suppressed SE image (d) of the thoracolumbar spine. Extensive myelopathy with abnormal high T2 signal in the spinal cord parenchyma, associated with multiple serpiginous dilated venous vascular structures are visible on the T2-weighted image as flow voids (a arrowheads) and on the contrast-enhanced MRA and T1weighted images as enhancing linear structures (c, d arrowheads), along the dorsal surface of the cord. The coronal reformatted MIP of the MRA depicts the level of the arteriovenous fistula of the radicular artery (c arrow). Heterogeneous enhancement of the distal spinal cord and conus medullaris is seen on the post-contrast T1-weighted SE image (d), which is indicative of congestive myelopathy
tions or leptomeningeal disease. Pathological processes involving the intradural extramedullary compartment, possibly revealed by post-contrast signal enhancement, include leptomeningeal infectious, inflammatory and neoplastic diseases, and benign and malignant extramedullary tumours such as meningioma, schwannoma, lymphoma and metastasis. The basic assessment of intradural extramedullary lesions comprises unenhanced non-fat-suppressed T1weighted imaging, T2-weighted imaging (fat- or non-fatsuppressed) and SPIR (fat-suppressed) post-contrast T1weighted imaging. In cases of intradural extramedullary tumours, multiplanar SPIR (fat-suppressed) T1-weighted images optimally display both the pattern of contrast enhancement and the relationships with spinal cord, dural surface, nerve roots, and the content of the neural foramina. The most common tumours encountered in this compartment are neural sheet tumours and meningiomas. Neural sheet tumours can arise in different locations along the course of the nerves, from their origin and proximal portion in the subarachnoid space (Fig. 4a) to the distal preforaminal (Fig. 4b) or extraforaminal portion (Fig. 4c). The presence of an expansive enhancing mass extending across the intervertebral foramen is strongly suggestive of a neural sheet tumour, such as a schwannoma, although meningiomas are also known to display this behaviour [20]. The presence of leptomeningeal enhancement along the surface of the spinal cord or along the nerve roots in the subarachnoid space is a nonspecific diagnostic finding that should prompt analysis and cytology of the CSF. The enhancement pattern is usually thin, lin-
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Fig. 4a-c Spinal nerve schwannoma. Post-contrast axial fat-suppressed T1-weighted SE images of the lumbar spine in three different patients (a, b, c) with spinal nerve schwannoma. Each image reveals an intensely enhancing, well-marginated mass in different locations along the course of the spinal nerves: in the intradural extramedullary space (a arrow), in the preforaminal portion (b arrow), and in the typical location across the intervertebral foramen (c arrow). These cases are examples of spinal nerve schwannomas. Contrast-enhanced fat-suppressed T1-weighted SE imaging allows precise anatomical delineation of this benign neoplasm a
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Fig. 5a-c Infectious viral polyradiculoneuropathy. Sagittal (a), coronal (b) and axial (c) post-contrast fat-suppressed T1-weighted SE images of the lumbar spine. The post-contrast T1-weighted images show the diffuse abnormal enhancement of the nerve roots of the cauda equina and of the extraforaminal common lumbar trunks. The thin and uniform pattern of enhancement is suggestive of an inflammatory or infectious aetiology. The final diagnosis was inflammatory postviral (enterovirus) polyradiculopathy
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ear and uniform in infectious and inflammatory processes [21, 22] (Fig. 5), whereas it tends to be thicker and nodular in cases of tumour spread [23, 24] (e.g. in cases of posterior fossa medulloblastomas, ependymomas, germinomas, pinealoblastomas, lymphomas, or in cases of metastatic leptomeningeal carcinomatosis). The appearance of advanced leptomeningeal carcinomatosis, characterized by thick perimedullary and perineural enhancement, is commonly referred to as “sugar coating” (Fig. 6). Postirradiation polyradiculopathy can mimic leptomeningeal tumour, with irregular thickening of the nerve root and leptomeningeal enhancement [25]. The demonstration of leptomeningeal and subarachnoid lesions is easily obtained on conventional post-contrast T1-weighted images, but the use of the above-mentioned post-contrast SPIR images increases the evidence of leptomeningeal linear and nodular enhancement areas along the spinal cord surface and nerve roots, resulting in better differentiation from dural thickening/enhancement. Intravenous contrast administration is indicated for MRI of the intradural extramedullary compartment, particularly for follow-up of intracranial tumours known to produce CSF seeding and drop-metastasis [26, 27], in the presence of CSF examination abnormalities, and in any clinical setting characterized by polyradiculopathy, when findings on noncontrast studies do not fully explain the clinical picture.
Fig. 6a-c Leukaemic spinal leptomeningeal carcinomatosis. Sagittal T2-weighted FSE image (a), and sagittal (b) and axial (c) post-contrast fat-suppressed T1-weighted SE images of the lumbar spine. Abnormal circumferential and irregular thickening of the leptomeninges of the distal thoracic spinal cord, conus and cauda equine is noted. The abnormal tissue has low T2 signal and shows intense enhancement on post-contrast images (arrowheads). The circumferential thick and irregular pattern of enhancement, or socalled “sugar-coating”, is typical of neoplastic leptomeningeal carcinomatosis, in this patient affected by leukaemic CNS involvement
Epidural compartment The epidural compartment is contained between the inner aspect of the bony central canal and the dura mater. The epidural space contains areolar adipose tissue and a rich vascular network, forming the epidural venous plexus, which is more largely represented in the ventral epidural space. Adipose epidural tissue also surrounds the exiting nerve roots and the dorsal root ganglia in the intervertebral foramina. The epidural space is larger in the lumbosacral spine and is nearly a virtual space in the cervical and thoracic spine, and in patients with central canal stenosis. As regards contrast-enhanced MR imaging of epidural spinal diseases, by far the most important technical refinement has been the introduction of fatsuppression techniques, and in particular SPIR sequences. Because of the abundance of fatty material in the epidural space, in the vertebral bone marrow and in preparavertebral areas the use of fat saturation is mandatory to reduce the background signal and to obtain the best possible CNR after intravenous injection of gadolinium-based contrast material. Ideally, post-contrast T1-weighted SPIR sequences should be combined with turbo-SE sequences to minimize the acquisition times and/or to optimize the anatomical coverage. After intravenous administration of contrast material,
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enhancement is seen in the dorsal root ganglia under normal conditions [28] and in the venous channels of the epidural plexus. More prominent enhancement is obtained with the use of fat-suppression techniques. The epidural plexus, in the ventral aspect of the epidural space, and adjacent to the posterior wall of the vertebral body, sometimes appears dilated and congested. Although ectasia of the epidural plexus has been reported to be more frequent at levels affected by some form of pathology [8, 29], it is actually a common and nonspecific finding even in normal patients. Common epidural space lesions include abscesses, haematomas, and tumours. Epidural masses, especially abscesses and haematomas, represent a true neurosurgical emergency because of their potential to rapidly compress the central canal with severe neurological sequelae. Epidural haematomas have variable signal intensity, from isointense to hyperintense on T1-weighted sequences and from hypointense to hyperintense on T2-weighted sequences, depending on the status of the haemoglobin breakdown products. For haematomas that appear hyperintense on T1- and T2-weighted sequences fat suppression allows better delineation of the size of the haematoma against the dark background of the suppressed fat signal, and better appreciation of the relationship with surrounding structures [30]. Haematomas generally do not show significant enhancement, especial-
Fig. 7a-d Postoperative epidural and paravertebral abscess. Sagittal T2-weighted SE image (a), fat-suppressed contrast-enhanced T1-weighted SE image (b), and corresponding axial T2-weighted image (c) and fatsuppressed contrast-enhanced T1-weighted image (d) at level L3-L4. In this patient with FLBSS in the early postoperative phase, a multiloculated fluid collection is seen in the posterior epidural space, compressing the dural sac, and in the left paravertebral soft tissues. Fat-suppressed post-contrast images show the irregular peripheral enhancement and thick septations of the fluid cavity which is suggestive of an infectious abscess. This was later confirmed by microbiology analysis of a fine needle aspiration sample
ly in the early stages. This can be an important diagnostic finding in differentiating these lesions from abscess or tumour. Multiplanar SPIR T1-weighted sequences, following intravenous administration of contrast material, are mandatory in the study of an epidural abscess to define the typical peripheral enhancement and central fluid component, the infectious site of origin which is often the disk space, the vertebral bone marrow or paravertebral space, and its extent (Fig. 7). The contrast-enhanced area often extends beyond the site of infection and is indicative of an inflammatory response and oedema [31]. In certain cases, the protein content in the liquid portion of the abscess, gives the fluid an intrinsic high T1 signal; therefore, in order not to confuse this spontaneous hyperintensity on T1-weighted imaging with enhancement of solid tissue, it is useful to acquire unenhanced SPIR T1-weighted images for comparison with the enhanced images. Tumours in the epidural space are frequently the result of epidural involvement of contiguous neoplasms, arising from the bony vertebral compartment or the paravertebral spaces. In such complex anatomy, good quality unenhanced fat suppressed T2-weighted and post-contrast SPIR T1-weighted images define precisely the extent of the tumour across the different compartments, and its relationship with adjacent structures (Fig. 8). Post-contrast T1-weighted imaging plays a crucial role in
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those patients with metastatic bone disease of the spine associated with neoplastic meningeal infiltration. In such symptomatic patients, unenhanced imaging often does not reveal the meningeal involvement. In these cases a correct diagnosis can only be achieved with the use of contrast agent (Fig. 9). Disk disease and associated postsurgical changes represent by far the most common abnormalities in the epidural space; this subject is discussed in a separate paragraph.
Bone/vertebral diseases Post-contrast SPIR T1-weighted images are extremely useful for MRI of extradural and bony vertebral tumours. For these lesions the best approach to characterization and to precisely defining their extent and rela-
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Fig. 8a-e Vertebral metastasis from colon cancer with epidural soft tissue component. Sagittal fat-suppressed T2-weighted FSE image (a), unenhanced T1-weighted SE image (b), and fat-suppressed contrast-enhanced T1weighted SE image (c) of the lumbar spine, and corresponding axial unenhanced T1-weighted SE image (d) and fat-suppressed contrast-enhanced T1-weighted SE image (e) at level L5. Heterogeneously enhancing bony metastasis replaces the bone marrow of the vertebral body L5 and the sacrum in this patient with known advanced colon cancer. The posterior wall of the vertebral body of L5 appears violated and an enhancing soft-tissue tumour component extends into the epidural space, abutting the ventral surface of the dural sac (e arrows)
tionships is to combine unenhanced non-fat-suppressed T1-weighted imaging with fat-suppressed T2-weighted or STIR imaging, and post-contrast SPIR T1-weighted imaging. In particular it is usually possible to differentiate between purely expansile and infiltrating patterns, thereby narrowing the possible differential diagnoses and addressing the subsequent options for patient management. When the lesions originate in the vertebral bodies or in the posterior elements, primary benign and malignant neoplasms or metastatic disease should be considered. The bone marrow, abundantly represented in the vertebrae, is characterized by a variable signal reflecting the presence of both adipose (“yellow”) marrow and active (“red”) marrow. Bone marrow activity alters with age and in response to stimuli such as recent chemotherapy or radiation treatment. It is important to take into account the signal pattern of the bone marrow in the MR
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Fig. 9a-e Vertebral metastasis with neoplastic meningeal infiltration. Sagittal T2-weighted FSE image (a), unenhanced T1-weighted SE image (b), and fat-suppressed contrast-enhanced T1-weighted SE image (c) of the cervicothoracic spine, and corresponding axial fat-suppressed contrast-enhanced T1-weighted SE images (d, e) at the level of the T2 vertebral body. In this patient with diffusely metastatic breast cancer, the unenhanced T1-weighted MR image depicts focal lesions in the bone marrow of the spine, but, as with the T2-weighted image, does not confirm the clinical evidence of myelopathic syndrome. The post-contrast images not only show the enhancement of the bony lesions, but clearly show the extensive meningeal metastatic spread (c arrowheads) and the circumferential spinal cord compression. A leptomeningeal enhancing plaque is also evident in the upper thoracic spinal cord (c arrow)
examination. Despite its variability, the normal signal of bone marrow on unenhanced T1-weighted images is typically much higher than that of most osseous neoplastic lesions and oedema, and as such it presents an ideal background for the depiction of signal abnormalities. MRI is commonly utilized as an imaging tool to further investigate patients with neoplastic disease with abnormal pooling foci on the bone scan that raises the suspicion of neoplastic metastatic disease. Unenhanced T1-weighted sequences are considered to be the most sensitive sequences for the depiction of focal or diffuse bone marrow abnormalities [32–34]. In the presence of a signal abnormality on unenhanced T1-weighted images, the use of a post-contrast SPIR T1-weighted sequence can provide a “negative” mirror image, thereby increasing the diagnostic specificity (Fig. 9). On the other hand, post-contrast images are not usually recommended when no abnormalities are apparent on unenhanced images [35, 36]. The appropriate use of contrast material is necessary to evaluate the vascularity of bone tumours and to identify vascular tumours such as “aggressive” haemangiomas. Since the imaging features of aggressive haemangiomas are sometimes confusing, accurate preoperative diagnosis is needed to determine the correct therapeutic approach, especially in cases with associated spinal cord compression and considerable intraspinal
and pre-/paravertebral growth; in these patients a dynamic contrast-enhanced study is able to confirm the diagnosis (suspected on unenhanced imaging and supported by vascular patterns of contrast enhancement) and to depict relationships with adjacent vertebral arteries in the cervical spine (Fig. 10). In some primary benign vertebral tumours (e.g. osteoid osteomas and osteoblastomas) it is extremely important to differentiate the tumour itself from adjacent congestive/inflammatory/reactive changes that may occur and which may involve bone marrow, epidural spaces, and nerve roots (Fig. 11). This differentiation is possible only on the basis of signal modification by comparing unenhanced T1- and T2-weighted images with post-contrast fat-suppressed T1-weighted images. When faced with vertebral compression fractures, it is crucial to differentiate between a benign porotic fracture and a malignant underlying lesion. The signal changes visible in the bone marrow of the fractured vertebral body reflect oedema and granulation tissue, and in the acute phase, offer little specificity and negligible help to the differential diagnosis [37]. Helpful diagnostic findings in such a situation include specific morphological features such as a vacuum cleft in the vertebral body [38], a convex aspect of the posterior vertebral wall [39] or an extraosseous soft-tissue component. These features are
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Fig. 10a-e Aggressive haemangioma. Sagittal T2-weighted fat-suppressed FSE image (a), dynamic contrast-enhanced MRA in early (b) and late (c) phase on reformatted MIP images, and sagittal (d) and axial (e) contrast-enhanced fat-suppressed T1-weighted SE images of the cervical spine. a The sagittal T2-weighted image shows C6 vertebral body collapse with replacement of normal bone marrow by pathologic hyperintense tissue. b, c The dynamic contrast-enhanced study shows the progressive contrast filling of the haemangioma and the major vascular structures. The post-contrast fat-suppressed T1-weighted image precisely defines the extraosseous extent of this aggressive benign tumour and its relationship with adjacent structures
usually well evident on post-contrast SPIR T1-weighted images. In recent years, some investigators have introduced MR imaging techniques based on physiological non-morphological parameters to the study of vertebral compression fractures in order to increase the specificity of the causative diagnosis. Some investigators [40, 41] have advocated a role of specific dynamic enhancement patterns of the bone marrow, to attempt a differentiation between benign and malignant vertebral fractures. Elsewhere, the use of diffusion-weighted spin-echo sequences has proven helpful in differentiating benign fractures from fractures caused by tumour infiltration, based on the restriction of water mobility in tumour cells [37]. For the evaluation of inflammatory diseases of the spine, such as ankylosing spondylitis, the use of fat-suppressed T2-weighted or STIR imaging is considered a sensitive screening technique for focal areas of oedema in the bone marrow, spinal joints and spinal ligaments, while post-contrast SPIR T1-weighted imaging has a role in cases that require focused further assessment [42].
Diseases of the spinal nerve roots and plexuses The use of contrast agents is fundamental for evaluation of diseases of the spinal nerves and nerve plexuses. The growing application of high-resolution studies (with fatsuppressed unenhanced T2- and post-contrast T1-weighted imaging) has resulted in reconsideration of the diagnostic approach to neuropathies and plexopathies. In this relatively new and expanding application, the high T1 relaxivity of MultiHance has a critical role because the small size of the nerves necessitates optimal lesion-to-background CNR. Abnormal contrast enhancement implies an abnormal blood–neural barrier which may be indicative of a non-specific consequence of inflammatory, demyelinating, infectious, neoplastic or traumatic injury. The most recent and emerging application concerns brachial and lumbosacral plexopathies of various aetiologies. Neoplastic (breast and lung cancer), traumatic and “idiopathic” diseases in the brachial plexus are demonstrable on highresolution fat-suppressed T2-weighted images and post-
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Fig. 11a-d Osteoid osteoma. CT scan (a), fat-suppressed T2-weighted FSE image (b), unenhanced T1-weighted SE image (c), and contrast-enhanced fat-suppressed T1-weighted SE image (d) of the cervical spine. The bone CT shows a well-demarcated lesion (nidus) surrounded by sclerosis in the left lamina of C6 in this young patient with a painful neck. The reactive oedema in the bone marrow, epidural space, and paraspinous soft tissues is visible on the fat-suppressed T2-weighted image. The impressive enhancement after contrast administration (d), clearly reveals the extent of the reactive inflammatory reaction to this osteoid osteoma
contrast fat-suppressed T1-weighted images [43, 44]. A technical challenge is posed by the anatomical complexity and inhomogeneous magnetic field of the region. The inhomogeneous magnetic field is a cause of confusing uneven fat-suppression. The use of an optimized technique and a high relaxivity contrast agent permits post-traumatic avulsion of brachial plexus trunks and divisions to be visualized as abnormally thickened and enhancing structures in the subacute phase. To increase the sensitivity of the demonstration of avulsion of cervicothoracic roots from the spinal cord, 3D T1-weighted gradient echo images should be obtained, enabling the enhancing radicular stumps to be visualized with submillimetre contiguous slices [45]. Similarly, idiopathic, compressive and demyelinating lumbosacral plexopathies can be demonstrated in the presacral and pelvic course using the above-mentioned combination of fat-suppressed T2- and post-contrast T1-weighted images (Fig. 12).
Degenerative spine, disk disease, and postoperative spine The most common indication for MRI of the spine is back pain, and by far the most frequent imaging scenario faced by the radiologist concerns the wide array of degenerative changes of the spine, which are often consid-
ered age-related changes. For anatomical and biomechanical reasons, the lumbar spine and lumbosacral junction are the most frequently involved segments. Under normal conditions, the disk, annulus fibrosus, synovial facet joint, and fibrous spine ligaments do not show significant enhancement after intravenous administration of contrast agent. Degenerative arthritis is characterized by disk dehydration, cartilage erosion, subchondral sclerosis, and hypertrophic changes. Granulation tissue and reactive inflammation incite also hypervascularization, possibly resulting in abnormal post-contrast enhancement of the disk, annulus fibrosus, subchondral bone and synovia [46]. In cases of sequestered disk herniation, the disk fragment causes an inflammatory reaction, resulting in granulation tissue which is revealed as peripheral enhancement. Abnormal enhancement can also be seen along the impinged nerve root, and most likely arises due to compressive damage [47]. Nevertheless, contrast enhancement rarely provides additional useful diagnostic information to the MR examination and therefore contrast administration is usually not needed for correct diagnosis. When degenerative changes are responsible for the clinical syndrome, contrast enhancement rarely leads to significant changes in patient management [11, 48]. On the other hand, the use of intravenous contrast agent can be of diagnostic utility in some atypical cases, to
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Fig. 12a-c MR neurography of the lumbosacral plexopathy. Axial fat-suppressed T2-weighted FSE image (a) and corresponding axial (b) and coronal (c) contrast-enhanced fat-suppressed T1-weighted SE images of the sacral region. In the absence of degenerative changes of the spine to explain the clinical picture, fat-suppressed T2-weighted and enhanced T1-weighted images of the lumbosacral plexus of this patient with a left sciatic pain reveals thickening, abnormal T2 signal and enhancement of the left common lumbosacral trunk (L5-S1), from which originates the sciatic nerve. High resolution images, meticulous fat suppression, high relaxivity contrast agent, and comparison with contralateral side (arrows and arrowheads) are mandatory in this setting
distinguish between a solid neoplasm in the epidural space, and a synovial cyst or a particularly large, or unusually located, disk fragment (Fig. 13). A contrast-enhanced study is also necessary in rare cases of primary spondylodiskitis. Spondylodiskitis is characterized on MRI by oedema and contrast enhancement in the disk, in the disk end-plates and in the subchondral bone of the adjacent vertebral bodies. Unfortunately, these findings are not specific; similar enhancement occurs in the inflammatory phase of degenerative disk disease (Modic type 1 changes) [49]. In such cases, accurate differential diagnosis is not achievable solely on the basis of MRI. On the other hand, when abnormal enhancement and/or abscesses are seen in the surrounding paravertebral soft tissues on post-contrast fat-suppressed T1-weighted imaging, the radiological diagnosis of an infectious process can be suggested with greater confidence [50]. Awareness needs to be raised towards the dissociation between imaging and clinical findings often observed in the follow-up of patients affected by infectious diskitis. Resolution of softtissue changes at MRI seems to reflect the clinical evolution with good approximation, whereas enhancement of the disk and of the disk end-plates can be persistent, despite clinical improvement and resolution [51]. Lumbar disk herniation is one of the most common manifestations of degenerative spine disease and a frequent cause of low-back pain and radiculopathy. Laminectomy and diskectomy are common procedures in the management of symptomatic lumbar disk herniation. Complications of such surgery include recurrent/residual disk herniation, epidural scar formation, diskitis, abscess, arachnoiditis and pseudomeningocele. Together, these complications occur as possible causes of the failed lowback surgery syndrome (FLBSS).
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Fig. 13a-c Large disk herniation. Sagittal T2-weighted FSE image (a), and axial unenhanced T1-weighted SE image (b) and contrastenhanced fat-suppressed T1-weighted SE image (c) of the lumbar spine. In this case of an unusually large disk herniation, the T2weighted image shows a large epidural mass with high T2 signal at the level of the L4-L5 disk. The contrast-enhanced fat-suppressed T1-weighted image reveals peripheral enhancement around the disk free fragment (arrowhead), which differentiates it from the focal disk herniation which is still in contiguity with the parent disk (arrow)
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Fig. 14a-c Epidural scar vs. recurrent disk herniation in the postoperative spine. Axial T2-weighted FSE image (a) and corresponding contrast-enhanced fat-suppressed T1-weighted SE image (b) of the lumbar spine of one patient, and axial contrast-enhanced fat-suppressed T1-weighted SE image (c) of a second patient. In these two patients who underwent diskectomy, the post-contrast fat-suppressed T1weighted images reveal the different enhancement patterns of epidural scar (b) and recurrent disk herniation (c). The epidural scar enhances homogeneously and is generally distributed along the surgical access, continuous with the scar in the paravertebral and subcutaneous soft tissues (as seen in b). However, the recurrent disk herniation demonstrates peripheral enhancement, indicative of reactive granulation tissue at its margins (arrows in c)
Fat-suppressed T2-weighted and post-contrast T1weighted sequences are typically needed to detect abnormalities in the disk, the subchondral bone marrow, the epidural space and the paravertebral soft tissues. However, surgical metallic implants and metallic microfragments originating from surgical instruments can sometimes degrade MR image quality because of magnetic susceptibility, and impair fat suppression because of magnetic field inhomogeneity. To minimize these effects, FSE techniques comprising short TE, large FOV, and high bandwidth are recommended [52]. Fat-suppressed contrast-enhanced T1-weighted imaging combined with high-resolution fat-suppressed T2-weighted imaging is the approach of choice for investigating recurrent symptoms following diskectomy [53]. Contrast-enhanced MR imaging of the spine after surgery for lumbar disk herniation almost always shows pathological changes, especially in the early phase. However, the imaging findings do not always correlate with a patient’s clinical symptoms [54]. In the early postoperative period, accurate interpretation of MR images is extremely difficult because of the complicating presence of fat graft, haematoma, gas, granulation tissue, scar and inflammation. Moreover, abnormal enhancement in the disk, the subchondral disk end-plates and the nerve roots can be seen during the first 6 months postoperatively, even in asymptomatic patients [55]. Although epidural scar is a known cause of dural sac distortion, nerve root entrapment and radiculopathy, scar is almost invariably
present after diskectomy [53]. More important is to differentiate epidural scar from recurrent disk herniation. The correct differentiation of these two entities can be a determining factor in the successful management of a patient with FLBSS: management should be conservative in the case of epidural scar while the option of repeat surgery should be considered in the case of symptomatic recurrent disk herniation. Although a good quality T2weighted scan is often able to differentiate the disk fragment, which is characterized by sharp borders and a polypoid appearance, from epidural scar, which has more ill-defined borders, greater confidence for differentiation is often achieved from the enhancement pattern on T1-weighted images after contrast administration. Typically, the fibrotic scar shows homogeneous enhancement, whereas recurrent disk herniation, which lacks a true blood supply, presents with early peripheral enhancement indicating a surrounding inflammatory reaction, followed by late contrast filling due to passive diffusion (Fig. 14) [56]. In the right clinical setting, enhancement in the disk, along with oedema and inflammatory changes in the adjacent vertebral bodies, raise the suspicion of an infectious complication (Fig. 15). However, as mentioned above with regard to primary spondylodiskitis, accurate differentiation is not always possible, and clinical, laboratory and pathology findings are often necessary for the correct diagnosis and treatment. Patients with FLBSS, and clinical symptoms consis-
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a
b
c
d
Fig. 15a-d Postoperative spondylodiskitis. Sagittal T1-weighted SE image (a), fat-suppressed T2-weighted FSE image (b) and contrast-enhanced fat-suppressed T1-weighted SE image (c) of the lumbar spine, and corresponding axial enhanced fat-suppressed T1-weighted SE at the L4-L5 disk level. In this patient with FLBSS, the unenhanced images show oedematous changes of the L4-L5 disk and of the adjacent disk end-plate and bone marrow of the contiguous vertebral bodies. The sagittal enhanced fat-suppressed image demonstrates diffuse enhancement of the disk and of the adjacent bone marrow; the axial enhanced fat-suppressed image better depicts the involvement of the paraspinal soft tissue. Disk biopsy revealed growth of E. coli
tent with polyradiculopathy, are suspected to be suffering from arachnoiditis. The inflammatory process involving the leptomeninges of the roots of the cauda equina causes adhesions, clumping, distortion and traction of the nerve roots in the dural sac. Axial T2-weighted images reveal clumping of the nerve roots and a characteristic “empty sac” appearance in the most severe cases while contrast enhancement along the nerve roots can sometimes be seen on post-contrast T1-weighted images. However, it is generally accepted that radiological findings do not always correlate with the full clinical picture [57, 58]. A fluid collection in the epidural space or in the paravertebral soft tissues in the postsurgical spine possibly indicates an abscess, a haematoma, a seroma or a pseudomeningocele. Contrast enhancement is often useful in this clinical setting particularly in the case of abscess and haematoma. After contrast agent administration only the abscess would be expected to exhibit peripheral enhancement (Fig. 7). The haematomas that are usually encountered in the early postoperative phase typically show progressive signal changes reflecting haemoglobin breakdown, and may also form fluid–blood levels. In the case of seromas and pseudomeningoceles, when a clear communication with the dural sac is not visible, accurate differentiation is possible because of progressive resorption in the case of seroma. This is seen
during follow-up and in such instances contrast agent administration is not of significant help. In conclusion, postoperative lumbar spine studies often present a technical and diagnostic challenge. The imaging technique has to be rigorous and the careful interpretation of these studies requires knowledge of the time elapsed since surgery, of the normal spectrum of postsurgical changes, and importantly, of the clinical picture.
Conclusion In conclusion, contrast enhancement of spinal diseases is based on multiple factors and not simply on blood– brain–cord barrier modification. Optimization of contrast protocols in MRI of the spine should be performed using a rational approach in which the appropriate technique is selected according to the site of origin and the type of disease. The need for detection of tiny and/or faintly enhancing lesions in an anatomical environment characterized by abundant fat tissue makes the adoption of fat-suppression techniques mandatory and the administration of a high relaxivity contrast agent, such as MultiHance, advisable.
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