Pictorial Essay
FOCUS ON: Pediatric Imaging
November 23, 2012

Susceptibility-Weighted Imaging of the Pediatric Brain

Abstract

OBJECTIVE. The purpose of this article is to present and discuss the susceptibility-weighted imaging signal characteristics of the normal pediatric brain and those of a variety of pediatric brain pathologic abnormalities.
CONCLUSION. Its high susceptibility for blood products, iron depositions, and calcifications makes susceptibility-weighted imaging an important additional sequence for the diagnostic workup of pediatric brain pathologic abnormalities. Compared with conventional MRI sequences, susceptibility-weighted imaging may show lesions in better detail or with higher sensitivity. Familiarity with the pediatric susceptibility-weighted imaging signal variance is essential to prevent misdiagnosis.
Susceptibility-weighted imaging is a high-spatial-resolution 3D gradient-echo MRI technique accentuating the magnetic properties of blood, blood products, nonheme iron, and calcifications [1]. A mask is created to enhance the phase differences between susceptibility artifacts and surrounding tissues. The contrast-to-noise ratio is optimized by multiplying the mask and magnitude images. A minimal intensity projection is created to facilitate differentiation between veins and focal lesions (Fig. 1). The difference in the magnetic properties of oxygenated and deoxygenated hemoglobin leads to a phase difference between regions with various concentrations of oxygen. This is the basis of blood oxygen level–dependent venography. We show how susceptibility-weighted imaging improves the diagnosis of various pediatric neurological disorders [24].

Pitfalls in Susceptibility-Weighted Imaging Interpretation

The signal intensity of veins depends on blood oxygenation. Veins are hypointense compared with arteries. The magnetic properties of intravascular deoxygenated hemoglobin and the resultant phase differences with adjacent tissues cause signal loss [5]. Thus, veins draining hypoperfused brain regions appear hypointense on susceptibility-weighted imaging (Fig. 2). Veins are, however, typically less hypointense in intubated children because of the high oxygen concentrations (less susceptibility-weighted imaging signal loss) and the high carbon dioxide concentration, which increases the blood flow. The veins consequently appear nearly isointense to the brain. To achieve good susceptibility-weighted imaging venous contrast, the carbon dioxide level should be kept below 30–35 mm Hg [6]. To prevent misregistration of vessels versus focal lesions, the thickness of the minimal intensity projection should be adjusted to the brain size to minimize partial volume effects, particularly in neonates.

Traumatic Brain Injury

Large intracranial hemorrhages are easily detected by CT or conventional MRI. Susceptibility-weighted imaging is, however, three to six times more sensitive than T2*-weighted MRI for the detection of small hemorrhages in diffuse axonal injury [7]. Multiple susceptibility-weighted imaging–hypointense lesions are typically seen along fiber tracts and at the gray matter–white matter junction (Fig. 3). Sensitive detection of diffuse axonal injury is important to predict outcome. Susceptibility-weighted imaging also detects prognostically important microhemorrhages in the brainstem, which may go undetected on conventional MRI (Fig. 4).

Brain Death

Marked prominence of intramedullary and sulcal veins is typically seen in severe diffuse cerebral edema or brain death (Fig. 5) as a result of increased oxygen-extraction fraction, engorgement or stasis of veins, or venous dilation due to adenosine release [8].

Vascular Malformations

Vascular malformations can be slow flow (i.e., cavernomas, developmental venous anomalies, or capillary telangiectasia) or high flow (i.e., arteriovenous malformations). Conventional MRI identifies high-flow lesions with high sensitivity, but susceptibility-weighted imaging is more sensitive for slow-flow malformations [9]. Large and small cavernomas are easily detected by susceptibility-weighted imaging because of the “blooming” effect of blood degradation products within the cavernomas [9] (Fig. 6). Small cavernomas may be missed by conventional MRI. Their identification is, however, important for differentiating familial and sporadic cavernomatosis. Susceptibility-weighted imaging is highly sensitive in detecting microcavernomas (Fig. 6). Susceptibility-weighted imaging is also helpful in identifying developmental venous anomalies, which are anatomic variants of the venous drainage but may be associated with various vascular malformations [9].

Neurocutaneous Disorders

Susceptibility-weighted imaging is helpful to identify and evaluate Sturge-Weber syndrome by revealing the abnormal venous vasculature [10] (Fig. 7). The venous prominence is related to venous stasis or the subsequent lower blood oxygenation due to increased oxygen extraction [3]. Susceptibility-weighted imaging is also highly sensitive in detecting cortical calcifications secondary to chronic venous ischemia.

Hemorrhage, Stroke, and Sinovenous Thrombosis

Compared with CT and T2*-weighted MRI, susceptibility-weighted imaging is more sensitive for the detection of a hemorrhagic conversion of an infarction. Susceptibility-weighted imaging typically shows prominent susceptibility-weighted imaging–hypointense medullary veins in brain regions with diminished or critical perfusion because of an increased deoxygenated hemoglobin concentration in that area (Fig. 8). These areas typically match hypoperfused areas on perfusion-weighted imaging. Susceptibility-weighted imaging may evaluate hypoperfused viable brain regions without using IV contrast agent. The ischemic penumbra can be identified by correlating susceptibility-weighted imaging with diffusion-weighted imaging [11]. Susceptibility-weighted imaging detects acute thromboemboli, which appear hypointense because of high contents of deoxygenated hemoglobin. In sinovenous thrombosis, susceptibility-weighted imaging shows large hypointense sulcal veins because of venous stasis and higher concentrations of deoxygenated hemoglobin and parenchymal hemorrhages secondary to the venous infarction [12] (Fig. 9). Susceptibility-weighted imaging is highly sensitive for the detection of germinal matrix hemorrhages, and residual blood depositions may be noted many months or years later. In neonatal periventricular hemorrhagic infarctions, dilated or thrombosed intramedullary veins may be noted. Susceptibility-weighted imaging may also identify engorged intramedullary veins in hypoxic-ischemic encephalopathy (Fig. 10).

Hemiplegic Migraine

Hemiplegic migraine is a rare form of migraine with motor aura that may be difficult to differentiate from acute stroke. In hemiplegic migraine, there is no restricted diffusion. Susceptibility-weighted imaging may show widened susceptibility-weighted imaging–hypointense sulcal veins matching areas of hypoperfusion on perfusion-weighted imaging contralaterally to the side of hemiplegia [13] (Fig. 11).

Brain Tumors

Susceptibility-weighted imaging is helpful in detecting calcifications, hemorrhages, and abnormal tumor vascularity, yielding information about the tumor grade. Calcifications are typical of low-grade tumors, hemorrhages and increased vascularity are typical of high-grade tumors [14] (Fig. 12).

Infections

Focal calcifications are characteristic for congenital (Fig. 13) and parasitic infections and may be visualized and differentiated with susceptibility-weighted imaging phase imaging. In acute bacterial meningitis, susceptibility-weighted imaging may visualize leptomeningeal microbleeding (Fig. 14). Infarctions can occur as complication of bacterial meningitis and are due to sinovenous thrombosis or arterial vasculitis.

Neurometabolic or Neurodegenerative Disorders

Because of its high sensitivity for iron deposition and calcifications, susceptibility-weighted imaging is helpful in diagnosing various neurodegenerative disorders, such as pantothenate-kinase–associated neurodegeneration, Cockayne syndrome, Aicardi-Goutières syndrome, Kearns-Sayre syndrome, and neurodegeneration in Langerhans cell histiocytosis. In neurodegeneration in Langerhans cell histiocytosis, susceptibility-weighted imaging reveals calcifications in the globi pallidi, substantia nigra, and dentate nuclei [15] (Fig. 15).
Fig. 1 14-year-old girl with unremarkable MRI examination of head.
A–D, Typical set of axial susceptibility-weighted images includes unprocessed magnitude image (A), phase map (B), processed magnitude image (C, combining A and B), and minimal intensity projection (12.0 mm) image (D). Sulcal veins appear hypointense on minimal intensity projection (D), relative to intermediate signal intensity of cerebral gray and white matter. Globus pallidum appears mildly hypointense because of higher degree of intrinsic iron concentration relative to putamen. Skull has no appreciable signal, and CSF is of low signal intensity.
Fig. 2 1-day-old boy with severe perinatal hypoxic-ischemic injury.
A and B, Initial axial minimal-intensity-projection susceptibility-weighted image (A) was obtained at effective arterial blood oxygenation level of 80%, and follow-up axial minimal-intensity-projection susceptibility-weighted image (B) was obtained 3 days later with blood oxygenation level of 100% using identical imaging parameters. Comparison of images confirms high signal variance related to differences in blood oxygenation. Venous blood oxygen level–dependent signal loss is effectively suppressed by high blood oxygen concentrations. On initial susceptibility-weighted minimal-intensity-projection image (A), all veins of superficial and deep venous system, including intramedullary veins, are prominently hypointense. For correct interpretation of susceptibility-weighted images, radiologists should be aware of effective blood oxygenation to avoid misdiagnosis. Children who are examined under general anesthesia are typically hyperoxygenated, resulting in higher signal of veins on susceptibility-weighted imaging.
Fig. 3 16-year-old boy with severe traumatic brain injury after high-velocity motorcycle accident. Initial Glasgow coma scale score was 3.
A and B, Axial T2-weighted image (A) and minimal-intensity-projection susceptibility-weighted image (B) obtained 14 days after injury show T2-hyperintense lesions in right frontal subcortical and left parietooccipital white matter secondary to transient ventricular drainage and intracranial pressure monitoring device, respectively. Few scattered T2-hyperintense foci are seen within right frontal white matter and posterior corpus callosum, suggestive of shear injuries. Susceptibility-weighted image (B) shows multiple hemorrhagic shear injuries in frontal and parietal white matter bilaterally and in corpus callosum. Most lesions were not identified on T1- or T2-weighted sequences. Susceptibility-weighted imaging consequently allows identification of exact degree of shear injury in much better detail compared with conventional T1- and T2-weighted MRI sequences, enhancing prediction of final outcome.
Fig. 4 7-year-old boy with history of severe traumatic brain injury after being struck by speeding car.
A and B, Axial T1-weighted image (A) and minimal-intensity-projection susceptibility-weighted image (B) acquired 2 months after initial injury show multiple susceptibility-weighted-imaging–hypointense hemorrhagic lesions in dorsal brainstem, left middle cerebellar peduncle, and hippocampus bilaterally. Hemorrhagic components were not visible on conventional T1-weighted image (A). High sensitivity of susceptibility-weighted imaging for hemorrhagic components facilitates correct identification of full extent of shear injury, which may otherwise go undetected on conventional MRI.
Fig. 5 1-day-old girl with severe perinatal asphyxia. Neurologic examination and electroencephalography findings were compatible with severe brain injury.
A, Axial CT image shows severe brain edema with global hypodensity of brain, completely obscured corticomedullary differentiation, effaced brain sulci, and slitlike compressed ventricles.
B, Axial minimal-intensity-projection susceptibility-weighted image shows marked hypointensity of all deep, intramedullary, and sulcal dilated veins throughout both hemispheres. Hypointensity and prominence of veins on susceptibility-weighted imaging likely result from combination of low venous oxygen concentration due to increased or maximized oxygen extraction fraction, limited or absent brain perfusion due to increased intracranial pressure, resulting venous stasis, or venous dilatation due to injury-induced adenosine release.
Fig. 6 2.5-year-old girl with focal epileptic seizures related to known cavernoma.
A and B, Axial T2-weighted image (A) and minimal-intensity-projection susceptibility-weighted image (B) show mixed T2-hypointense and T2-hyperintense and susceptibility-weighted-imaging–hypointense cavernoma within left parietal white matter. Cavernoma is surrounded by small rim of vasogenic edema. Importantly, minimal-intensity-projection susceptibility-weighted image (B) shows multiple additional susceptibility-weighted-imaging–hypointense cavernomas that remained undetected on conventional sequences.
Fig. 7 13-year-old boy with Sturge-Weber syndrome.
A–C, Axial contrast-enhanced T1-weighted image (A), phase susceptibility-weighted image (B), and minimal-intensity-projection susceptibility-weighted image (C) show prominent leptomeningeal angiomatosis. On T1-weighted image (A), moderate cortical parietooccipital atrophy is noted. On susceptibility-weighted images (B and C), marked cortical calcifications (arrows) are seen. Intracortical calcifications induce mild phase shift on phase susceptibility-weighted image (B).
Fig. 8 6-year-old boy with known sickle cell disease presenting with acute left-side hemiplegia and decreased responsiveness.
A, Acute apparent diffusion coefficient (ADC) map shows restricted diffusion characterized by low ADC values within right insula and frontal operculum. Additional focal lesions with restricted diffusion are seen in right frontopolar region as well as in left anterior basal ganglia and left central region.
B, Matching minimal-intensity-projection susceptibility-weighted image shows prominent intramedullary veins matching area of diffusion abnormality. In addition, prominent sulcal veins are noted along left hemisphere draining region of brain that exceeds region of diffusion abnormality.
C, Follow-up CT shows progressing demarcation of ischemic lesion in right hemisphere and progression of infarction in left hemisphere where sulcal veins appeared prominently susceptibility-weighted-imaging hypointense and widened. This susceptibility-weighted imaging and diffusion-weighted imaging mismatch apparently reflects ischemic penumbra. Susceptibility-weighted imaging may consequently serve as fast map that renders relevant hemodynamic information about brain tissue with critical perfusion. Modified and reprinted with permission from [11].
Fig. 9 17-year-old girl with left-sided stroke and sinovenous thrombosis probably secondary to heterozygous prothrombin 20210 mutation and simultaneous oral contraceptive use.
A and B, Axial T1-weighted image (A) and minimal-intensity-projection susceptibility-weighted image (B) show T1-hyperintense signal within left sigmoid sinus with dilated susceptibility-weighted-imaging–hypointense veins in left cerebellum that drain into adjacent superficial venous system. Small petechial microhemorrhages (arrow, A) are noted within left temporal lobe. Findings are compatible with left-sided sigmoid and transverse sinus thrombosis.
C, On T2-weighted image of left temporal lobe, extensive left temporal cortical and subcortical vasogenic edema or venous ischemia is seen.
D, On additional minimal-intensity-projection susceptibility-weighted image, engorged dilated hypointense sulcal veins (arrows) are noted along left hemisphere that should drain into thrombosed superficial venous system. Dilated sulcal veins are easily depicted on minimal-intensity-projection susceptibility-weighted images, confirming diagnosis. Small intracortical petechial hemorrhages as complication of venous ischemia are also best seen on minimal-intensity-projection susceptibility-weighted imaging.
Fig. 10 Term newborn boy with moderate-degree hypoxic-ischemic brain injury. Axial minimal-intensity-projection susceptibility-weighted image shows multiple mildly prominent or dilated susceptibility-weighted-imaging–hypointense intramedullary veins (arrow) that drain toward subependymal deep venous system of lateral ventricles. This finding is typically seen in brain edema and may occur in perinatal hypoxic-ischemic injury. This finding may solidify diagnosis of hypoxic-ischemic encephalopathy.
Fig. 11 10-year-old girl with hemiplegic migraine presenting with progressive right-sided tingling and arm weakness.
A–C, Axial diffusion-weighted image (A), cerebral blood flow map (B), and minimal-intensity-projection susceptibility-weighted image (C) show unremarkable distribution and quality of diffusion throughout brain. Perfusion map (B) shows reduced cerebral blood flow in left hemisphere, which is not confined to arterial territory. Minimal-intensity-projection susceptibility-weighted image (C) shows hypointense widened sulcal veins in left parietooccipital region that match area of reduced cerebral blood flow. Susceptibility-weighted imaging might consequently have important noninvasive diagnostic role in assessing vascular complications of hemiplegic migraine.
Fig. 12 4-year-old girl with atypical teratoid rhabdoid tumor presenting with vomiting and vision loss.
A,Conventional MR image shows large well-circumscribed T2-weighted heterogeneous hyper- and hypointense left frontal mass lesion.
B and C, Minimal-intensity-projection susceptibility-weighted image (B) and phase susceptibility-weighted image (C) reveal dense calcifications within center of tumor, which result in phase shift on phase images. Calcifications are best seen on susceptibility-weighted images and would go undetected on conventional MRI. In addition, comparing magnitude and phase images, it is possible to identify engorged draining veins within tumor. In brain tumors, susceptibility-weighted imaging may provide important information (i.e., hemorrhages, vascularity, and calcifications) about inner architecture and texture of tumor, which may be essential in grading lesion.
Fig. 13 8-month-old boy with congenital cytomegalovirus infection presenting with microcephaly, developmental delay, and seizures.
A, CT scan shows moderate hydrocephalus and white matter volume loss as well as subtle subependymal calcifications.
B, Extent of calcium depositions is, however, much better appreciated on susceptibility-weighted image.
C, On phase image, phase shifts are easily appreciated. It is possible, however, that susceptibility-weighted imaging may not detect all calcifications visible on CT (in this patient, calcification in left parietooccipital periventricular regions is visible on CT, but not on susceptibility-weighted image). Overall, in congenital virus infections, other, rubella, cytomegalovirus, and herpes simplex virus infection, susceptibility-weighted imaging may be very helpful to better detect extent of calcifications even compared with CT.
Fig. 14 24-day-old boy with herpes simplex meningitis.
A and B, Axial T2-weighted image (A) and matching apparent diffusion coefficient (ADC) map (B) show multiple areas of inflammation with complicating cytotoxic edema due to ischemic injury (restricted ADC-hypointense diffusion) affecting pons and cerebellar hemispheres.
C, Minimal-intensity-projection susceptibility-weighted image shows extensive hemorrhages (arrows) within inflamed or infarcted regions, in particular within pons. These hemorrhagic complications may be of essential importance to predict outcome.
Fig. 15 18-year-old woman with neurodegeneration in Langerhans cell histiocytosis presenting with progressive cognitive impairment and behavioral disorders.
A, Extensive bilateral T2-hyperintense white matter signal alterations are seen within cerebellar hemispheres. In addition, mild T2-hypointense calcifications or iron depositions are seen within dentate nuclei bilaterally.
B, Minimal-intensity-projection susceptibility-weighted image shows degree and extent of calcifications or iron depositions related to neurodegeneration in Langerhans cell histiocytosis in better detail. Calcifications or iron depositions are noted within dentate nuclei and along periphery of cerebellar T2-hyperintense white matter signal alterations. In neurodegenerative disorders, susceptibility-weighted imaging may detect calcifications or iron depositions with higher sensitivity.

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Information & Authors

Information

Published In

American Journal of Roentgenology
Pages: W440 - W449
PubMed: 22528925

History

Submitted: October 10, 2011
Accepted: November 9, 2011

Keywords

  1. children
  2. MRI
  3. pediatric
  4. susceptibility-weighted imaging

Authors

Affiliations

Sylvia Verschuuren
Division of Pediatric Radiology, Russell H. Morgan Department of Radiology and Radiological Sciences, The Johns Hopkins University School of Medicine, 600 N Wolfe St, Nelson Basement B-173, Baltimore, MD 21287-0842.
Department of Radiology, Sophia Children’s Hospital, Erasmus University Medical Center, Rotterdam, The Netherlands.
Andrea Poretti
Division of Pediatric Radiology, Russell H. Morgan Department of Radiology and Radiological Sciences, The Johns Hopkins University School of Medicine, 600 N Wolfe St, Nelson Basement B-173, Baltimore, MD 21287-0842.
Division of Pediatric Neurology, University Children’s Hospital of Zurich, Zurich, Switzerland.
Sarah Buerki
Division of Pediatric Neurology, University Children’s Hospital of Berne, Berne, Switzerland.
Maarten H. Lequin
Department of Radiology, Sophia Children’s Hospital, Erasmus University Medical Center, Rotterdam, The Netherlands.
Thierry A. G. M. Huisman
Division of Pediatric Radiology, Russell H. Morgan Department of Radiology and Radiological Sciences, The Johns Hopkins University School of Medicine, 600 N Wolfe St, Nelson Basement B-173, Baltimore, MD 21287-0842.

Notes

Address correspondence to T.A.G.M. Huisman ([email protected]).

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