Put your thinking cap on: An illustrative review of the imaging features of central nervous system lipomas

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1 Put your thinking cap on: An illustrative review of the imaging features of central nervous system lipomas Poster No.: C-0248 Congress: ECR 2016 Type: Educational Exhibit Authors: C. Azzopardi, C. Cannataci, R. Grech; Msida/MT Keywords: Neuroradiology brain, Neuroradiology spine, MR, CT, Education, Congenital DOI: /ecr2016/C-0248 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 to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 26

2 Learning objectives 1. To illustrate the multi-modality imaging characteristics of lipomas in the brain and spine 2. To describe the associated congenital anomalies associated with CNS lipomas, most commonly agenesis of the corpus callosum. 3. To highlight the significance of CNS lipomas and their clinical sequelae. Background Intracranial lipomas are considered congenital malformations and in fact are often associated with specific brain malformations. They are often incidental findings and are very rarely associated with symptomatology. Lipomas in the spinal cord, on the otherhand, are more likely to be symptomatic and may present with symptoms such as sensory disturbances, paraplegia and incontinence. Their characteristic imaging findings allows the diagnosis to be made radiologically with no need for a histological diagnosis. Findings and procedure details The earliest reported CNS lipoma dates back to 1818 when a chiasmatic lipoma was described by Meckel [1]. Lipomas of the CNS are a group of congenital malformations of the brain and spinal cord. In the brain, they are more frequently located in the pericallosal cistern and may be associated with other congenital abnormalities [2]. They may present at any age, often when the patient is scanned for an unrelated reason. Pathology of intracranial lipomas: Intracranial lipomas are uncommon lesions which are poorly understood. They are thought to represent malformations resulting from abnormal persistence and Page 2 of 26

3 maldifferentiation of the meninx primitiva during the development of the subarachnoid cisterns. This embryonic concept explains the frequent association of lipomas with other congenital malformations [1]. Clinical presentation of intracranial lipomas: 30% of patients will present with seizures. Intracranial lipomas near the brainstem may present with ataxia, hydrocephalus and nerve palsies. In the paediatric population they may present with non specific problems including psychomotor delay [2]. Most commonly however these lesions are asymptomatic. Imaging characteristics of intracranial lipomas: Intra-cranial lipomas are characteristically hyperintense on both T1 and T2 weighted images. Signal drop out is seen on fat saturated images. In the absence of fat saturation, chemical shift artefact may be used. Vessels and nerves are often seen to course through the fat in cranial lipomas which exert little or no mass effect. Fat density is clearly seen on CT and may be confirmed by assessing the Hounsfield units. These will be negative and range from -100 to -50 (Figure 1). Lack of enhancement is characteristic. Occasionally peripheral calcification may be present [3]. Location of intracranial lipomas: Interhemispheric 45% (Figure 2) Quadrigeminal/ superior cerebellar 25% (Figure 3) Suprasellar/ interpeduncular 14% Cerebello-pontine angle 9% Sylvian cistern 5% The above locations are the most commonly cited and are listed in order of frequency [2]. The most common site for intracranial lipomas are midline structures. Pericallosal lipomas are subdivded into two subgroups: tubulonodular and curvilinear. The tubulonodular type usually measures less than two centimetres and is usually located in the anterior corpus callosum [2]. Curvilinear lipomas are usually thinner and located posteriorly. Hypoplasia of the corpus callosum is observed in the curvilinear type. Associations of intracranial lipomas: Page 3 of 26

4 Intracranial lipomas are rarely associated with congenital neurocutaenous disorders for example, encephalocraniocutaneous lipomatosis or congenital infiltrating lipomatosis [2]. More commonly lipomas are associated with brain malformations such as dysgenesis of the corpus callosum. This is often seen with lipomas sited anteriorly. Figure 4 demonstrates a peri-callosal lipoma with thinning of the splenium. This is most in keeping with a curvilinear type lipoma with the characteristic shape, elongated and curvilinear along the corpus callosum with a posterior location. In this case the corpus callosum is only mildly hypoplastic. Figure 5 and 6 show an anterior lipoma of the tubulonodular type. Peripheral curvilinear calcifications are seen (Figure 6) referred to as the bracket sign on coronal reformats [5]. Spine: The most common lipoma in the spine is a lipoma of the filum terminale. A filar lipoma is a relatively common imaging finding and on its own is not of any clinical concern (Figure 7, 8). A filar lipoma, however may be associated with signs and symptoms of a tethered cord. Radiologically this is seen as a low lying conus and thickened filum. Therefore when a filar lipoma is visualised, the position of the conus should be carefully assessed. Cord tethering is closely linked to spina bifida and patients may present with signs of dysraphism such as a hairy patch, sacral dimple. More serious presentations with incontinence or lower limb weakness may also occur. Tethered cord may be primary as an isolated finding or secondary in association with a lipoma of the filum or a myelomeningococele. These are congenital presentations. Tethering may also occur post spinal surgery secondary to scar tissue formation. Ultrasound is a useful first line test in the paediatric population. The posterior arch of the spine is not ossifed in normal infants and this is an excellent window for ultrasonographic assessment of the spinal cord (Figure 9). If the cause is secondary to a lipoma or a myelomeningiococele this may also be characterised on ultrasound (Figure 10). The normal conus should end at the level of T12-L1. MRI is an excellent tool to assess the level of the conus, thickness of the filum terminale and any associated abnormalities. The infant diagnosed with a filum lipoma and tethered cord went on to have a MRI of the spine. This confirmed the ultrasonographic findings (Figure 11). Page 4 of 26

5 Epi-dural lipomas although not purely CNS lesions are mentioned here because of their clinical importance as they may cause spinal cord compression. They are rare, benign tumours. MRI is useful to characterise the full extent of these lesions, location within the spinal canal and level of cord compression. Patients usually have an excellent prognosis post surgical removal [6] (Figure 12). Differential Diagnosis: The differential will include all fat containing lesions. Intra-cranial masses which may be mistaken for lipomas include: Intra-cranial dermoids Intra-cranial teratomas Epidermoids, in particular white epidermoids (bright on T1) Unlike intra-cranial lipomas, dermoids have more variable imaging features. They are typically high signal on T1 weighted images, fat droplets may be seen in the subarachnoid space if dermoid rupture is present. T2 imaging is more variable. Dermoids do not enhance. Enhancement of the meninges may be seen in a ruptured dermoid secondary to a chemical meningitis [7] (Figure 13,14). Intra-cranial teratomas may be intra or extra-axial. They have a mixture of tissue components and therefore are composed of different densities. A fat component is helpful to narrow the diagnosis. Epidermoids are characteristically located at the cerebello-pontine angle (40-50%) [8]. MR imaging features are usually characteristic, following CSF signal intensity on T1 and T2 weighted sequences. Restricted diffusion is diagnostic. These features should make an epidermoid distinguishable from a lipoma. The diagnostic difficulty arises when the epidermoid is bright on T1 known as a white epidermoid. The diffuse weighted imaging is key to make the diagnosis (Figure 15). The differential diagnosis of spinal lipomas is limited as the presence of fat is diagnostic. A lesion closely related to an epidural lipoma is an angiolipoma. An angiolipoma is composed of vascular elements together with adipocytes. It therefore has features of fat together with a vascular component. Enhancement is therefore a feature which distinguishes it from a simple lipoma. Angiolipomas are usually found in the thoracic region. They may be infiltrating, however malignant transformation has not been reported [9] (Figure 16). Page 5 of 26

6 Images for this section: Fig. 1: The 'region of interest' is observed to be measuring the Hounsfield units. The value of confirms this mass in the quadrigeminal cistern is actually fat. Page 6 of 26

7 Fig. 2: Unenhanced CT of the brain demonstrates an interhemispheric lipoma (red arrow). This is the most common site of intra-cranial lipomas (45%). Page 7 of 26

8 Fig. 3: Non contrast CT brain at the level of the quadrigeminal plate showing a lipoma in the quadrigeminal cistern (red arrow). Page 8 of 26

9 Fig. 4: Sagittal T2-weighted image (left)demonstrates a peri-callosal lipoma posteriorly (red arrow) with thinning of the splenium. FLAIR (Fluid Attenuation Inversion Recovery) axial image (middle) demonstrates a hyperintense peri-callosal lipoma (red arrow). STIR (Short Tau Inversion Recovery) axial image (right) clearly illustrates fat suppression (red arrows). Page 9 of 26

10 Fig. 5: T1-weighted sagittal MR image showing an anteriorly sited lipoma (red arrow) draped over the corpus callosum. The splenium is thinned posteriorly. Page 10 of 26

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12 Fig. 6: Axial unenhanced CT brain illustrates a central lipoma situated anteriorly (red arrow). Curvilinear, peripheral calcifications are seen. Fig. 7: T1 (left) and T2 fat sat (right) sagittal images of the lumbar spine demonstrate a small thin lipoma of the filum terminale. There is no associated cord tethering. Page 12 of 26

13 Fig. 8: T1 sagittal image (left) and T2 sagittal image (middle) demonstrate the typical imaging characteristics of a filar lipoma (red arrows). This is of high signal intensity on both sequences. Axial T1 weighted image (right) demonstrates an intra-dural lipoma of high signal intensity which is intimately related to the conus medullaris. No associated cord tethering. Page 13 of 26

14 Fig. 9: Ultrasound image of the spine demonstrates a low lying conus medullaris with syringohydromyelia (red arrow). Tethering of the cord resulted secondary to a lipoma. Page 14 of 26

15 Fig. 10: Lipoma of the filum on ultrasound (calipers) this was associated with a tethered cord and secondary syringohydromyelia. Page 15 of 26

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17 Fig. 11: Sagittal T2 fat sat image confirms a low lying conus medullaris. It is a associated with a filar lipoma which demonstrates characteristic signal drop out on fat saturation (red arrow). Fig. 12: Sagittal T2 (left), Sagittal T1 (middle), Axial T2 (right) images showing an epidural lipoma which is narrowing the spinal canal but not yet causing spinal cord compression. The epidural lesion is of high signal intensity on both T1 and T2 in keeping with fat. Page 17 of 26

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19 Fig. 13: T2 weighted axial image shows a well circumscribed, predominantly T2 hyperintense lesion in the right frontal lobe (red arrow). Its heterogeneity on T2 weighted imaging makes it more likely to be a dermoid. Fig. 14: Coronal T1 fat sat post contrast image illustrates a dermoid in the right frontal lobe. The lesion is hypointense in keeping with fat suppression with no contrast enhancement. Page 19 of 26

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22 Fig. 15: Axial T2 weighted image showing a lesion of high T2 signal at the left cerebellopontine angle (red arrow). This is a location typical for epidermoids. Correlation with T1 and diffusion weighted images is mandatory. Page 22 of 26

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24 Fig. 16: T1 post contrast sagittal image of the thoracic spine illustrates an epidural angiolipoma with enhancement of the vascular component. Page 24 of 26

25 Conclusion The features of CNS lipomas are often quite distinctive, allowing the radiological diagnosis to be made with accuracy. The characteristic abnormalities and their appearance on multi-modality imaging will enable the reporting radiologist to make a diagnosis with confidence and know which associated abnormalities to look for. Personal information Dr. Christine Azzopardi Higher Specialist trainee Medical Imaging Department, Mater Dei Hospital, Malta azzopardi.christine87@gmail.com Dr. Christine Cannataci Basic Specialist trainee Medical Imaging Department, Mater Dei Hospital, Malta christinecannataci@gmail.com Dr. Reuben Grech Consultant Neurointerventional radiologist Medical Imaging Department, Mater Dei Hospital, Malta reubengrech@yahoo.com Page 25 of 26

26 References Truwit C L and Barkovich A J. Pathogenesis of intracranial lipoma: an MR study in 42 patients. American Journal of Roentgenology. 1990;155: A Ramírez- Zamora, J Asconape. Intracranial Lipomas; Radiographic and Clinical Characteristics. The Internet Journal of Neurology Volume 12 Number 1. Ichikawa T, Kumazaki T, Mizumura S, Kijima T, Motohashi S, Gocho G. Intracranial lipomas: demonstration by computed tomography and magnetic resonance imaging. J Nippon Med Sch Oct;67(5): Ketonen L, Hiwatashi A, Sidhu R. Pediatric brain and spine, an atlas of MRI and spectroscopy. Springer Verlag. (2005) ISBN: Rao AS, Rao VR, Mandalam KR et-al. Corpus callosum lipoma with frontal encephalocele. Neuroradiology. 1990;32 (1): Frank AM, Trappe AE, Goebel WE. Dorsal extradural lipoma as cause of spinal claudication. Case report and review of the literature. Zentralbl Neurochir. 1998;59(1):23-6. Osborn AG, Preece MT. Intracranial cysts: radiologic-pathologic correlation and imaging approach. Radiology. 2006;239 (3): Chen CY, Wong JS, Hsieh SC et-al. Intracranial epidermoid cyst with hemorrhage: MR imaging findings. AJNR Am J Neuroradiol. 2006;27 (2): Leu NH, Chen CY, Shy CG et-al. MR imaging of an infiltrating spinal epidural angiolipoma. AJNR Am J Neuroradiol. 2003;24 (5): Page 26 of 26