Characterization of T2 hypointense lesions within pediatric diffuse intrinsic pontine glioma using susceptibilityweighted, diffusion-weighted, dynamic susceptibilityweighted contrast-enhanced perfusion and conventional MR imaging Poster No.: C-2622 Congress: ECR 2010 Type: Educational Exhibit Topic: Neuro - Tumor Authors: U. Löbel, J. Sedlacik, M. Kocak, W. E. Reddick, A. Broniscer, C. M. Hillenbrand, Z. Patay; Memphis, TN/US Keywords: Susceptibility-weighted imaging, Dynamic susceptibility-weighted contrast-enhanced perfusion imaging, Diffusion tensor imaging Keywords: Neuroradiology brain, Neuroradiology peripheral nerve, Neuroradiology spine, Oncology, Neoplasia DOI: 10.1594/ecr2010/C-2622 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related Page 1 of 30
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Learning objectives This exhibit will illustrate and discuss the conventional magnetic resonance imaging (MRI) appearance and significance of T2 hypointense foci in diffuse intrinsic pontine gliomas. We will describe how the following advanced MRI techniques can aid in the confident identification and differential diagnosis of these lesion components: Susceptibility-weighted imaging (SWI) Diffusion-weighted imaging (DWI)/ Diffusion tensor imaging (DTI) Dynamic susceptibility-weighted contrast-enhanced (DSC) perfusion MR imaging and Proton MR spectroscopy (MRS) Page 3 of 30
Background In children, tumors arising from the brainstem (midbrain, pons, and medulla oblongata) account for almost 12% of all central nervous system (CNS) tumors (CBTRUS, 2005, Fig. 1 on page 6). Brainstem gliomas are either focal (<20%) or diffuse (>80%) tumors (Kaplan et al., 1996). The conventional MR imaging features of diffuse intrinsic pontine gliomas (DIPG) are usually characteristic enough to allow a confident diagnosis without biopsy prior to treatment (Barkovich et al., 1990; Fischbein et al., 1996). Diagnostic criteria for DIPG by conventional MR imaging are (Barkovich, 2005) (Fig. 2 on page 6): The tumor field is mainly hyperintense on T2-weighted imaging The tumor involves more than 75% of the cross sectional area of the pons Expansion of the tumor toward the 4th ventricle (typically without supratentorial hydrocephalus) Encasement of the basilar artery (without invasion) Although the tumor field is dominantly T2 hyperintense, we found that through careful analysis, T2 hypointense lesion components of varying appearance can frequently be identified, too (Fig. 3 on page 7). The differential diagnostic considerations of T2 hypointense lesions include: True lesions: Hemorrhage and calcification Histologically/biologically different lesion components (e.g. focal anaplasia) Normal Structures: Fiber tracts Normal, not yet infiltrated parenchyma Confident identification and differentiation of these lesion components is important since they may influence management and prognosis, and may impact developing treatment Page 4 of 30
strategies. Since patients with DIPG generally do not receive tumor biopsy, a more accurate biological characterization of the tumor (including the identification of areas of possible focal anaplasia) is clinically important. Advanced MRI techniques have shown the potential to provide valuable information about functional and structural integrity of brain parenchyma, therefore are considered to be adequate tools for investigating the above outlined "unusual" imaging features of DIPGs. Page 5 of 30
Images for this section: Fig. 0: Distribution of all childhood primary brain and CNS tumors (0-19 yr) by site, CBTRUS 1998-2002 (n=5,455). CBTRUS 2005-2006 Primary Brain Tumors in the United States Statistical Report Page 6 of 30
Fig. 0: Conventional T2-weighted image of a DIPG in a 7-year-old child at diagnosis. The mainly T2 hyperintense tumor is characterized by involvement of the pons (>75% of the axial diameter), expansion of the tumor toward the 4th ventricle (black arrow) and encasement of the basilar artery (white arrow). Radiological Sciences, St. Jude Children's Research Hospital - Memphis/US Page 7 of 30
Fig. 0: Appearance of T2 hypointense foci within the mainly T2 hyperintense DIPG. Radiological Sciences, St. Jude Children's Research Hospital - Memphis/US Page 8 of 30
Imaging findings OR Procedure details METHODS The data presented were acquired between 2004 and 2009. During this time, various protocols were used in our institution in the treatment of patients with DIPG. Those protocols differed in the use of chemotherapeutic agents (e.g. carboplatin and etoposide, cisplatin, irinotecan and temozolomide), adjuvant anti-angiogenic agents (vandetanib) and the administration of radiation therapy (conformal, fractionated, hyperfractionated). Imaging protocols were also different with regards to the use of advanced MR techniques, reflecting the continued technological advances, the resultant improvements (singlevoxel spectroscopy vs. 2D-CSI) and the introduction of new technologies (SWI, DTI). Therefore, when addressing our different research objectives, we used subgroups of patients, as deemed appropriate, in order to ensure consistency in their MRI evaluation. 1. Hemorrhage and calcification: SWI SWI is a robust MRI technique, which enhances the visualization of magnetically susceptible substances (e.g. hemorrhage and calcification) (Reichenbach and Haacke, 2001; Tong et al., 2008). In many ways, SWI is similar to T2*-weighted gradient echo imaging (T2*-GRE). The major difference between the two techniques is that T2*-GRE is a 2D method while SWI is a 3D method. Due to the larger slice thickness of T2*-GRE, small hemorrhages could easily be missed. For the same reason, T2*-GRE is also more prone to additional signal loss and phase dispersion caused by field inhomogeneities induced by bone-tissue interfaces, in particular in the posterior fossa. Homodyne filtered phase images (using 25% of the original k-space information which allows for a meaningful interpretation) are available with both techniques, while SWI data sets also included SWI maps and minimum intensity projections (minip) of the SWI maps (Reichenbach and Haacke, 2001). Phase images are essential for the differentiation of hemorrhage and calcification by susceptibility-sensitive techniques (Gronemeyer et al., 1992) (Fig. 1 on page 15). SWI maps further increase the contrast between magnetically susceptible substances and the surrounding tissue. They are obtained by applying a phase mask to the magnitude image, essentially combining magnitude and phase images. The minip Page 9 of 30
images increase the conspicuity of susceptibility effects across several partitions (Fig. 2 on page 15). T2 hypointense foci on T2*-GRE and SWI images were evaluated using the following criteria: Hemorrhage: hyposignal on magnitude images and hypersignal on phase images (Fig. 1, upper left image). Calcification: hyposignal on both magnitude and phase images (Fig. 1, lower left image) Important note: the appearance of hemorrhage and calcification on SWI phase images depends on the signal encoding, is vendor specific and may be inverted (Deistung et al., 2006). However, since hemorrhages show the same contrast as venous vessels on phase images and calcifications show an inverted phase they can always be verified even if no detail about the vendor or the signal encoding is known. Lesions which were determined to be hemorrhagic were recorded and measured along their larger diameter in the axial plane by two blinded reviewers. 2. Foci of anaplasia: DWI, DSC perfusion and MRS Focal anaplasia is common in higher-grade cerebral neoplasms, but may also be found in predominantly low-grade lesions at histopathological evaluation of biopsy or autopsy specimen (Black, 1991). Recently, a case of a histologically confirmed focal anaplasia within a cerebellar juvenile pilocytic astrocytoma was reported (Lach et al., 2003), which at MR imaging showed a peculiar constellation of MRI signal properties: T2 hyposignal Signal enhancement after contrast injection Restricted water diffusion DIPG are generally low-grade (WHO grade I/ II) at the time of clinical presentation (Mantravadi et al., 1982; Yoshimura et al., 2003), but rapidly evolve towards high-grade lesions and the vast majority of these tumors are found to be glioblastoma multiforme at autopsy (personal communication, A. Broniscer). In a subset of patients with DIPG, we identified T2 hypointense lesion areas showing similar imaging characteristics as described above and hypothesized that these foci may also correspond to focal anaplasia. To test our hypothesis, we collected diffusion tensor imaging (DTI) and dynamic susceptibility-weighted contrast-enhanced Page 10 of 30
(DSC) perfusion MR images. The rational for choosing these techniques was that the apparent diffusion coefficient (ADC, calculated by DTI) has been identified as a reliable metric of differentiation between low- and high-grade cerebellar tumors (Rumboldt et al., 2006) and that an increase in relative cerebral blood volume (rcbv) is believed to reflect angioneogenesis and has been shown to be an accurate predictor of outcome in supratentorial hemispheric tumors (Law et al., 2004). ROIs representing the T2 hypointense foci (T2HIF) and the typical T2 hyperintense tumor (TU) were placed on ADC maps and transferred to fractional anisotropy (FA), cerebral blood volume (CBV) and cerebral blood flow (CBF) parametric maps. Relative CBV and CBF values (rcbv, rcbf) were calculated with respect to normal cerebellar gray matter. MR spectroscopy (MRS) was not used in our initial evaluation of suspected focal anaplasia; however, MRS has been shown to aid significantly in the differentiation of lowgrade and high-grade tumors and helps to monitor disease progression. Several cut-off values to differentiate low-grade from high-grade gliomas have been established (Law et al., 2003; McKnight et al., 2002; Stadlbauer et al., 2006; Tzika et al., 2004), but it seems that the Choline/N-acetylaspartate (Cho/NAA) ratio is most frequently used. For that reason, we recently started performing 2D-CIS MRS in patients with suspected focal anaplasia, providing us with some preliminary data. 3. Fiber tracts: DTI On conventional MR images, fiber tracts of a healthy brain stem are generally not well delineated because tracts blend into the surrounding tissue. However, fiber tracts may be visualized on color coded fractional anisotropy (FA) maps using DTI (Fig. 3 on page 16). In patients with DIPG, corticospinal tracts and transverse pontine fibers may be visible on conventional T2-weighted images as relative T2 hypointense structures within the surrounding T2 hyperintense tumor. We show T2-weighted images, ADC maps and FA color maps of three patients with DIPG and explain how DTI aids in the differentiation of fiber tracts. The involvement of whiter matter tracts in patients with DIPG has been previously been investigated in great detail (Helton et al., 2006; Helton et al., 2008). The authors describe 4 categories of tract involvement (Helton et al., 2006): Displaced tracts, characterized by normal FA values (Fig. 4 on page 17 and Fig. 5 on page 18) Page 11 of 30
Edematous tracts, which appeared T2 hyperintense, but were characterized by normal FA values Infiltrated tracts, which had low FA values, but remained visible on the FA color maps Disrupted tracts, which had low FA values and were not anymore visible on the FA color maps. We applied the approach as described above in our patient cohort and we illustrate different patterns of fiber tract involvement in three representative cases of DIPG. RESULTS 1. Hemorrhage and calcification: SWI Seventeen children (9F/8M, age: 3-17yrs) with DIPG were evaluated for the presence of intratumoral hemorrhagic lesions at baseline and during combined treatment with the angiogenesis inhibitor vandetanib and conformal radiation therapy. Hemorrhages were defined as hematoma if the lesion was equal to or larger than 5 mm and as petechial hemorrhages if it measured less than 5 mm in diameter (Kidwell and Wintermark, 2008). We found that: 47% of patients presented with at least one hemorrhage at baseline. By 6 months of treatment, 88.2% of patients presented with at least one hemorrhagic lesion Lesion diameters ranged between 0.10 and 2.56 cm. 5.22% of lesions were hematomas. No significant neurological event was recorded in our patients regardless of the number and size of intratumoral hemorrhages. The number of hemorrhages identified by SWI in our study was higher as compared to previous reports (Broniscer et al., 2006; Hargrave et al., 2008; Kaplan et al., 1996; Packer et al., 1993; Smith et al., 1990), and we believe that those constitute an important differential diagnostic category of T2 hypointensities. Our higher incidence numbers are most likely due to the superior sensitivity of SWI compared to T1-weighted, T2-weighted and T2*-GRE used in earlier studies. 2. Foci of anaplasia: DWI, DSC perfusion and MRS MR images of 86 patients with DIPG who were treated at our institution between 2004 and 2009 were retrospectively reviewed. Intratumoral T2 hypointense lesion Page 12 of 30
components fulfilling all aforementioned MRI criteria were identified in 10 patients at initial diagnostic MRI work-up (11%, 6M/4F, mean age 5.8 yrs). T2 hypointense foci which showed contrast enhancement and restricted water diffusion could be divided into 3 subgroups (Fig. 6 on page 19): Small, well-defined (focal) T2 hypointense lesion Larger, less well-defined (diffuse) T2 hypointense lesion T2 hypointense lesion with central necrosis (often, but not always, larger and less well-defined) ADC values were significantly lower (p<0.01) in T2HIF (1.2±0.4 DWI 2 2 µm /ms) compared to TU (1.8±0.2 µm /ms), suggesting increased hypercellularity of T2HIF compared to the rest of the tumor. DSC perfusion rcbv was significantly higher (p=0.014) in T2HIF (1.45±0.72) compared to TU (0.85±0.44). Fig. 7 on page shows the CBV map of a patient with suspected focal anaplasia demonstrating increased perfusion within the right pons. rcbf did not differ significantly (p=0.25) when T2HIF (0.88±0.43) were compared to TU (0.72±0.37). MR spectroscopy The tumor of this patient with DIPG (Fig. 8 on page 20, the same patient as described in Fig. 7) showed an exophytic component with faint T2 hyposignal which was characterized by contrast enhancement and restricted water diffusion on the ADC map (white arrows). Multi-voxel MRS demonstrated a prominent increase of Cho/NAA ratio in this area. This is in keeping with the DSC perfusion MRI findings with the same area showing significantly increased relative cerebral blood volume compared to the rest of the tumor. In addition, the images obtained in this patient nicely demonstrate the differential diagnosis of fiber tracts (black arrow) which show no contrast enhancement and diffusion restriction. On the FA map, fibers of the exophytic component seem somewhat disturbed (white arrow), while the corticospinal tracts can be confidently identified (black arrow). 3. Fiber tracts: DTI Page 13 of 30
Patient 1 (Fig. 9 on page 21) On T2-weighted imaging, hypointensities can be delineated within the anterior pons (black arrow). Based on their location, these are likely corticospinal tracts, visualized because of the surrounding T2 hyperintense tumor. This is in consistence with the FA map which suggests that the corticospinal tracts are fairly intact on the left (dark blue). There seems to be an incomplete loss of anisotropy on the right (light blue). The transverse pontine fibers are visualized on the T2-weighted image, but their normal appearance on the FA color map is lost. Patient 2 (Fig. 10 on page 22): T2 hypointensities can be identified within both hemispheres of the pons (black and white arrows). On FA maps, these appear to be intact fiber tracts, displace by tumor tissue. Patient 3 (Fig. 11 on page 23) The two T2 hypointensities in this patient are distinct from each other. Corticospinal tracts of both hemispheres are displaced to the left (black arrows). The lesion on the right (white arrow) is characterized by contrast enhancement (not shown), central necrosis and low ADC. Therefore, the lesion fits into the category of focal anaplasia. On the FA color map, this lesion shows a disturbed pattern suggesting disruption of fiber tracts. Page 14 of 30
Images for this section: Fig. 0: Hemorrhage (white arrow) and calcification (black arrow) show identical signal properties on magnitude images (left, top). However, the SWI phase image (left, bottom) shows hypersignal for the hemorrhagic lesion and hyposignal for the calcification (confirmed by CT, right) allowing differentiation of the two entities. Important note: the appearance of hemorrhage and calcification on SWI phase images depends on the signal encoding, is vendor specific and may be inverted (Deistung et al., 2006). Radiological Sciences, St. Jude Children's Research Hospital - Memphis/US Page 15 of 30
Fig. 0: SWI datasets included magnitude (upper left) and phase (upper right) images as well as SWI maps (lower left) and minimum intensity projection (lower right) images. Radiological Sciences, St. Jude Children's Research Hospital - Memphis/US Page 16 of 30
Fig. 0: Appearance of a normal pons on FA color maps. The corticospinal tracts (black arrows), medial lemnisci (white arrows) and transverse pontine fibers (white dotted arrow) are visualized. Fibers in superior-inferior direction are coded with blue color, in left-right direction in red and in anterior-posterior direction they are displayed in green color. Radiological Sciences, St. Jude Children's Research Hospital - Memphis/US Page 17 of 30
Fig. 0: T2 weighted image of DIPG displacing the corticospinal tracts (arrows). Radiological Sciences, St. Jude Children's Research Hospital - Memphis/US Page 18 of 30
Fig. 0: FA color map of DIPG displacing transverse pontine fibers (white arrow) and medial lemnisci (dotted white arrow). Radiological Sciences, St. Jude Children's Research Hospital - Memphis/US Page 19 of 30
Fig. 0: Varying appearance of T2 hypointense lesions in DIPG presenting with contrast enhancement and restricted water diffusion: small, focal (top row) and larger, diffuse (middle row) T2 hypointense lesion and T2 hypointense lesion with central necrosis (bottom row). Radiological Sciences, St. Jude Children's Research Hospital - Memphis/US Page 20 of 30
Fig. 0: Value of MR spectroscopy. The tumor of this patient with DIPG showed an exophytic component with faint T2 hyposignal (white arrows) which was characterized by contrast enhancement and restricted water diffusion (Trace and ADC map). Multi-voxel MRS demonstrated a prominent increase of Cho/NAA ratio in this area as high as 10.3. In addition, these images nicely demonstrate the differential diagnosis of fiber tracts (black arrow) which show no contrast enhancement and diffusion restriction. On the FA map, fibers of the exophytic component seem somewhat disturbed (white arrow), while the corticospinal tracts can be identified confidently (black arrow). Radiological Sciences, St. Jude Children's Research Hospital - Memphis/US Page 21 of 30
Fig. 0: Fiber tracts, patient 1: Corticospinal tracts can be identified on the T2-weighted image. The FA map suggests they are fairly intact on the left (dark blue), but seem to be an incomplete loss of anisotropy on the right (light blue). The transverse pontine fibers are visualized on the T2-weighted image, but their normal appearance on the FA color map is lost. Radiological Sciences, St. Jude Children's Research Hospital - Memphis/US Fig. 0: Fiber tracts, patient 2: T2 hypointensities can be identified within both hemispheres of the pons (black and white arrows). On FA maps, these appear to be intact fiber tracts, displace by tumor tissue to different degree. Page 22 of 30
Radiological Sciences, St. Jude Children's Research Hospital - Memphis/US Fig. 0: Fiber tracts, patient 3: Two distinct T2 hypointensities are present in this patient. Corticospinal tracts of both hemispheres are displaced to the left (black arrows). The lesion on the right (white arrow) likely corresponds to focal anaplasia which shows a disturbed pattern on the FA maps suggestive of disrupted fiber tracts. Radiological Sciences, St. Jude Children's Research Hospital - Memphis/US Page 23 of 30
Conclusion 1. Hemorrhage and calcification: SWI SWI allows the most confident identification of hemorrhage and their differentiation from calcification using phase images. Petechial hemorrhages in patients with DIPG are more frequently identified using SWI than conventional MR sequences, including T2*-GRE. Hematomas (>0.5cm) are rare (likely also explaining the lack of significant adverse neurological correlates in our study). Intratumoral hemorrhages increase in number during treatment. The significance of these finding needs to be determined in future studies. 2. Foci of anaplasia: DWI, DSC perfusion and MRS Intratumoral T2 hypointense foci are relatively rare, but not exceptional in DIPG at diagnosis. Their recognition based on conventional MRI is fairly straightforward, but their significance is yet poorly understood. Lower ADC values indicate higher cellularity. Higher rcbv values are likely related to angioneogenesis and resultant expansion of the intralesional blood compartment compared to T2 hyperintense tumor. Our data support the hypothesis that T2 hypointense foci within DIPG may indeed correspond to areas of focal anaplasia, if they meet the above criteria. 3. Fiber tracts: DTI FA color maps aid in the identification of fiber tracts and help determine the tumor involvement of fiber tracts (which may be related to neurological disability). We propose a diagnostic algorithm for the differentiation of T2 hypointense lesion components in DIPG, shown in Fig. 1 on page 25. Page 24 of 30
Images for this section: Fig. 0: Diagnostic algorithm for the differentiation of T2 hypointense lesions in DIPG. Radiological Sciences, St. Jude Children's Research Hospital - Memphis/US Page 25 of 30
Personal Information Dear Reader, Thank you for your interest in our research. If you have any comments or questions, please do not hesitate to contact us. It would be a pleasure to discuss our work with you in more detail. We are very much looking forward to hear from you! Ulrike Löbel, MD Postdoctoral Research Associate ulrike.loebel@stjude.org Zoltán Patay, MD, PhD Chief, Section of Neuroradiology zoltan.patay@stjude.org 262 Danny Thomas Place Mail Stop 220 Memphis, TN 38105-3678 USA Page 26 of 30
Images for this section: Fig. 0: St. Jude Children's Research Hospital, Memphis, TN USA Radiological Sciences, St. Jude Children's Research Hospital - Memphis/US Page 27 of 30
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