on MR imaging, which shows a homogeneous well-circumscribed lesion displaying the characteristic short-t1 and T2 signal of fat [1] (Fig. 1).

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1 Downloaded from by on 02/07/18 from IP address opyright RRS. For personal use only; all rights reserved T he corpus callosum is made up of dense myelinated fibers that usually interconnect homologous territories of the two cerebral hemispheres. The dense compact nature of the white matter tracts, relative to the adjacent hemispheric white matter, makes it a barrier to the flow of interstitial edema and tumor spread. Thus only aggressive tumors, such as glioblastoma multiforme and lymphoma, typically cross or involve the corpus callosum. This densely compact nature of the white matter tracts also makes it more susceptible to shear injury in the event of trauma. ecause it is composed predominantly of myelinated axons, demyelinating processes can affect the corpus callosum. Our pictorial essay shows 11 classic and uncommon lesions of the corpus callosum. Tumors Lipoma Lesions of the orpus allosum: MR Imaging and Differential onsiderations in dults and hildren Eric. ourekas 1, Kaliope Varakis, Douglas runs, Gregory. hristoforidis, Melissa aujan, H. Wayne Slone, Dimitris Kehagias Intracranial lipomas are rare developmental lesions of the central nervous system, which are usually asymptomatic and discovered incidentally. They mainly occur in the region of the corpus callosum and the pericallosal cistern, accounting for up to 65% of all intracranial lipomas and frequently associated with callosal dysgenesis. The diagnosis of intracranial lipoma can easily be made on MR imaging, which shows a homogeneous well-circumscribed lesion displaying the characteristic short-t1 and T2 signal of fat [1] (Fig. 1). Glioblastoma Multiforme Glioblastoma multiforme is an extremely aggressive diffuse astrocytic tumor commonly found in the supratentorial white matter of the cerebral hemispheres. It is the most common primary brain tumor in adults, accounting for 25% of all cases. Glioblastomas most commonly spread via direct extension along white matter tracts, including the corpus callosum, although hematogenous, subependymal, and cerebrospinal fluid spread can also be seen. When the corpus callosum is affected, glioblastoma multiformes commonly display a characteristic bihemispheric involvement, resulting in a classic butterfly pattern. On MR imaging, these tumors typically enhance solidly and intensely in the corpus callosum, although occasionally no enhancement is seen. ecause the corpus callosum is relatively resistant to infiltration, glioblastoma multiforme should be considered for any lesion crossing the corpus callosum [2] (Fig. 2). Lymphoma Primary central nervous system lymphomas are rare aggressive neoplasms of the Pictorial Essay brain, accounting for less than 2% of malignant primary brain tumors. They are almost always of the -cell non-hodgkin s type. ommon locations include the corpus callosum, deep gray matter structures, and the periventricular region. Lymphomas differ from glioblastoma multiformes because they usually have less peritumoral edema, are more commonly multiple, are less commonly necrotic, are highly radiosensitive, and fre- Fig year-old boy with lipoma of corpus callosum. oronal T1-weighted MR image shows large well-defined homogeneous midline mass lesion in region of corpus callosum with characteristic bright signal of lipoma. Note associated dysgenesis of corpus callosum. Received March 14, 2001; accepted after revision January 11, ll authors: Department of Radiology, Section of Neuroradiology, The Ohio State University, 160 Means Hall, 1654 Upham Dr., olumbus, OH ddress correspondence to E.. ourekas. JR 2002;179: X/02/ merican Roentgen Ray Society JR:179, July

2 ourekas et al. Downloaded from by on 02/07/18 from IP address opyright RRS. For personal use only; all rights reserved quently temporarily respond dramatically to steroid administration producing vanishing lesions. These lesions are usually iso- or hypointense on T1-weighted images and hyperintense on T2-weighted images, with 91% showing contrast enhancement [3] (Fig. 3). Juvenile Pilocytic strocytoma Juvenile pilocytic astrocytomas are a distinct low-grade variant of astrocytoma. They are usually well-circumscribed unencapsulated masses, with frequent cyst formation, either microscopic or macroscopic. Most lesions commonly involve the cerebellar vermis, cerebellar hemispheres, optic chiasm, hypothalamus, or floor of the third ventricle. The corpus callosum is an uncommon location. On MR imaging, pilocytic astrocytomas are hypo- or isointense on T1-weighted images and hyper- Fig year-old woman with glioblastoma multiforme., xial T1-weighted MR image shows hypointensity (arrow) of left parietal white matter extending across corpus callosum., xial T2-weighted MR image shows hyperintensity (arrow) in left parietal white matter extending across corpus callosum with mass effect on lateral ventricle., Enhanced axial T1-weighted MR image shows glioblastoma (arrow) of left parietal white matter that extends across corpus callosum, classic for glioblastoma multiforme or lymphoma. Lack of enhancement, however, is unusual for glioblastoma. Fig year-old nonimmunocompromised woman with primary central nervous system lymphoma who presented with disorientation., xial T1-weighted MR image shows hypointense lesion (arrow) in deep left parieto occipital white matter extending into splenium of corpus callosum., xial T2-weighted MR image shows hyperintense lesion involving corpus callosum surrounded by high-signal-intensity edema., Enhanced axial T1-weighted MR image shows markedly enhancing lesion (arrow) of left parieto occipital white matter, crossing corpus callosum in classic butterfly pattern. 252 JR:179, July 2002

3 MR Imaging of the orpus allosum Downloaded from by on 02/07/18 from IP address opyright RRS. For personal use only; all rights reserved intense on T2-weighted images relative to gray matter. The solid portion of the tumor usually enhances, in contrast to most low-grade infiltrative astrocytomas, which tend not to enhance [4] (Fig. 4). Multiple sclerosis is a demyelinating disease of unknown cause that more commonly affects young women. Lesions characteristically involve the periventricular white matter, internal capsule, corpus callosum, and pons, although plaques can be found anywhere in the white matter and less commonly even in gray matter. Demyelinating Diseases Multiple Sclerosis Fig year-old girl with pilocytic astrocytoma., Sagittal T1-weighted MR image shows well-circumscribed hypointense lesion in body of corpus callosum., xial T2-weighted MR image shows that lesion is hyperintense., Enhanced coronal T1-weighted MR image shows marked contrast enhancement of lesion. This figure and Figure 2 show that intense contrast enhancement is not necessarily indicative of high-grade glioma, just as lack of contrast enhancement is not necessarily indicative of low-grade lesion. Fig year-old woman with multiple sclerosis who presented with visual complaints., xial T2-weighted MR image shows multiple hyperintense somewhat ovoid lesions of corpus callosum and periventricular white matter, classic for multiple sclerosis., Sagittal T2-weighted MR image shows multiple hyperintense lesions (arrows) in corpus callosum., Sagittal fluid-attenuated inversion recovery paramedian image obtained through corpus callosum shows multiple ovoid hyperintense lesions (arrow). JR:179, July

4 Downloaded from by on 02/07/18 from IP address opyright RRS. For personal use only; all rights reserved The lesions of the corpus callosum can be focal or confluent nodular lesions and tend to affect the callosal septal interface, which is the central inferior aspect of the corpus callosum. On MR imaging, the prevalence of lesions in the corpus callosum has been reported to be up to 93% in the radiology literature. trophy of the corpus callosum can coexist in long-standing multiple sclerosis, making the diagnosis of corpus callosum lesions difficult. The lesions are hyperintense on long-tr sequences and can best be seen with proton-density and fluid-attenuated inversion recovery (FLIR) sequences. Enhancement is common in the acute stage. Differentiation should be made from ischemia, trauma, and other demyelinating processes on the basis of morphology, location, and the presence of concurrent multiple sclerosis plaques in the periventricular region [5] (Fig. 5). ourekas et al. Progressive Multifocal Leukoencephalopathy Progressive multifocal leukoencephalopathy is an uncommon progressive fatal demyelinating disease that affects immunocompromised patients. The cause is a papovavirus the reutzfeldt-jakob virus. The lesions are usually multifocal and asymmetric, most commonly affecting the subcortical white matter and corpus callosum. In the corpus callosum, focal lesions can occur that enlarge and become confluent as the disease progresses. The lesions are hyperintense on long-tr sequences and hypointense on short-tr/te sequences. The lesions usually do not enhance, although they may enhance faintly at the periphery. Progressive multifocal leukoencephalopathy should be considered in the differential diagnosis of space-occupying lesions in HIV patients. The lack of enhancement and mass effect can act as features differentiat- ing this entity from others such as lymphoma or glioblastoma [6] (Fig. 6). Marchiafava-ignami Disease Marchiafava-ignami disease is a rare demyelinating neurologic disorder, primarily affecting the corpus callosum. It was first described in Italian wine drinkers and is thought to be due to chronic and massive alcohol use. The central layers of the corpus callosum are affected, with sparing of the dorsal and ventral layers (sandwich sign). The disease can follow one of three clinical courses, a fulminate acute form or subacute and chronic forms. The acute form affects the genu and splenium, whereas the chronic form most commonly affects the body. In the acute form, the central corpus callosum enlarges, presumably because of edema. The corpus callosum is of low signal on T1-weighted Fig year-old man with HIV presented with behavioral changes and facial droop caused by progressive multifocal leukoencephalopathy., T2-weighted axial MR image shows asymmetric white matter lesion of frontal lobes with involvement of corpus callosum., Enhanced axial T1-weighted MR image shows no enhancement of lesion. iopsy of lesion (not shown) confirmed progressive multifocal leukoencephalopathy. Fig year-old man with Marchiafava-ignami disease and 30-year history of heavy alcohol use. (Reprinted with permission from [7]), xial T2-weighted MR image shows signal abnormality of corpus callosum and periventricular white matter., Sagittal T1-weighted MR image shows corpus callosum atrophy (short arrow), which is characteristic of chronic form. Involvement of central layers of corpus callosum, indicated by hypointensity, with sparing of dorsal and ventral layers results in the sandwich sign (long arrow). 254 JR:179, July 2002

5 Downloaded from by on 02/07/18 from IP address opyright RRS. For personal use only; all rights reserved MR Imaging of the orpus allosum Infarcts involving the corpus callosum are rare, in part because the corpus callosum is a dense white matter tract and therefore is less sensitive to ischemic injury than gray matter. The anterior and posterior cerebral arteries provide the major blood supply of the corpus callosum via the pericallosal artery and small penetrating vessels that run perpendicular to the parent artery. On MR imaging, infarcts have the same characteristics as strokes elsewhere, with similar enhancement patterns. Differentiation of lacunar infarcts from other entities such as trauma and demyelinating processes can be made by the presence of concurrent infarcts in characteristic sites (centrum semiovale, basal ganglia). With large-vessel ischemic events, the corpus callosum is usually involved as part of a large vascular distribution [8] (Fig. 8). images and high signal on T2-weighted images and often enhances. In the subacute and chronic forms, the lesions involve the central part of the body most commonly and are hypointense on T1-weighted images and hyper- or hypointense (hemosiderin deposits) on T2-weighted images [7] (Fig. 7). Vascular Processes Infarction rteriovenous Malformations rteriovenous malformations of the corpus callosum comprise 9 11% of all cerebral arteriovenous malformations. linically, 84% of patients with these malformations present with intracranial hemorrhage, most with intraventricular hemorrhage. Most are supplied by both the anterior and posterior cerebral arteries, and many have a bilateral blood supply. Drainage is mainly into the internal cerebral vein or interhemispheric superficial veins. The MR imaging characteristics are those of arteriovenous malformations elsewhere, with serpentine flow voids noted through the corpus callosum and the ventricle Fig year-old man with infarct who presented with confusion., xial T2-weighted MR image shows well-defined lesion of corpus callosum genu., xial T2-weighted image obtained 2 weeks after shows that lesion (arrow) is smaller and has decreased in signal., Enhanced axial T1-weighted MR image obtained 2 weeks after shows enhancement of lesion (arrow). D, xial T2-weighted MR image 6 weeks after initial presentation shows that lesion (arrow) is smaller. E, Enhanced axial T1-weighted MR image 6 weeks after initial presentation shows enhancement has essentially resolved, typical of evolution of infarct. D JR:179, July 2002 E 255

6 ourekas et al. and frequently with evidence of intraventricular hemorrhage [9] (Fig. 9). Downloaded from by on 02/07/18 from IP address opyright RRS. For personal use only; all rights reserved Trauma Injury to the corpus callosum occurs commonly with head trauma, being detected on MR imaging in 47% of patients with nonfatal head injuries. The classic triad of diffuse axonal injury is that of diffuse damage to axons located at the gray white matter interface of the cerebral hemispheres, the dorsolateral aspect of the rostral brainstem, and the corpus callosum. The callosal lesions most commonly involve the splenium, are usually eccentric in location, and can involve a focal part or the full thickness of the corpus callosum. On MR imaging, spinecho T2-weighted images and FLIR sequences during the sagittal plane are most sensitive in detecting small nonhemorrhagic lesions. Hemorrhagic lesions are best seen on T2weighted images during the first 4 days after injury and, after 4 days, are better seen on T1weighted images. Furthermore, gradient-echo Fig year-old man with arteriovenous malformation who presented with intraventricular hemorrhage., Sagittal T1-weighted MR image shows hemorrhage (arrows) and multiple flow voids in corpus callosum., xial T2-weighted MR image shows hyperintense lesion (arrow) with flow voids. Fig year-old man with diffuse axonal injury 1 week after motor vehicle crash., Sagittal T1-weighted MR image shows nonhemorrhagic hypointense lesion (arrow) of corpus callosum., xial proton density weighted MR image shows hyperintense lesion of corpus callosum., Sagittal T1-weighted MR image on follow-up examination 10 days after shows hemorrhagic lesion of corpus callosum. D, Enhanced coronal T1-weighted MR image on follow-up examination 10 days after shows hemorrhagic lesion of corpus callosum, with classic shearing-type lesion also seen at gray white junction, both indicative of diffuse axonal injury. D 256 JR:179, July 2002

7 MR Imaging of the orpus allosum Downloaded from by on 02/07/18 from IP address opyright RRS. For personal use only; all rights reserved Fig year-old man with cystic lesions associated with long-standing hydrocephalus, with multiple prior shunt revisions. Patient is asymptomatic other than for headaches, which are probably due to mild hydrocephalus., Sagittal T1-weighted MR image shows well-defined cystic lesions (arrows) of corpus callosum., xial T2-weighted MR image shows abnormal signal (arrow) throughout corpus callosum, which has persisted for many years. T2-weighted sequences are superior in detecting chronic hemoglobin degradation products because of the susceptibility effects of hemosiderin. Differentiation from other lesions such as ischemia should be made on the basis of history and the location of the lesions in the corpus callosum [10] (Fig. 10). Miscellaneous Lesions Lesions in the corpus callosum, both diffuse and focal, have been described in patients with long-standing hydrocephalus after shunting. allosal lesions and tectal neoplasms producing hydrocephalus have been seen in patients with aqueductal stenosis. Patients with these lesions were thought to have long-standing hydrocephalus before ventricular decompression. The exact mechanism responsible for the production of these callosal lesions is unknown, although they may be the result of ischemia with subsequent demyelination caused by prolonged severe stretching of the corpus callosum from ventriculomegaly and subsequent rapid decompression of the ventricles. These lesions appear hypointense on T1-weighted images and hyperintense on T2-weighted images, with sparing of the splenium. lthough the changes may persist on imaging, they appear clinically silent [11] (Fig. 11). References 1. Maiuri F, irillo S, Simonetti L, De Simone MR, Gangemi M. Intracranial lipomas: diagnostic and therapeutic considerations. J Neurosurg Sci 1988; 32: Rees J, Smirniotopoulos J, Jones R, Wong K. Glioblastoma multiforme: radiologic-pathologic correlation. RadioGraphics 1996;16: Johnson, Fram EK, Johnson P, Jacobowitz R. The variable MR appearance of primary lymphoma of the central nervous system: comparison with histologic features. JNR 1997;18: Lee Y, Van Tassel P, runer JM, Moser RP, Share J. Juvenile pilocytic astrocytomas: T and MR characteristics. JNR 1989;10: Gean-Marton D, Vezina LG, Marton KI, et al. bnormal corpus callosum: a sensitive and specific indicator of multiple sclerosis. Radiology 1991;180: Whiteman ML, Post MJ, erger JR, Tate LG, ell MD, Limonte LP. Progressive multifocal leukoencephalopathy in 47 HIV seropositive patients: neuroimaging with clinical and pathologic correlation. Radiology 1993;187: Ishii K, Ikejiri Y, Sasaki M, Kitagaki H, Mori E. Regional cerebral glucose metabolism and blood flow in a patient with Marchiafava-ignami disease. JNR 1999;20: hrysikopoulos H, ndreou J, Roussakis, Pappas J. Infarction of the corpus callosum: computed tomography and magnetic resonance imaging. Eur J Radiol 1997;25: Picard L, Miyachi S, raun M, racard S, Per, Marchal J. rteriovenous malformations of the corpus callosum: radioanatomic study and effectiveness of intranidus embolization. Neurol Med hir 1996;36: Gentry LR, Thompson, Godersky J. Trauma to the corpus callosum: MR features. JNR 1988;9: Suh DY, Gaskill-Shipley M, Nemann MW, Tureen RG, Warnick RE. orpus callosal changes associated with hydrocephalus: a report of two cases. Neurosurgery 1997;41: JR:179, July