Marisa Kastoff Blitstein 1 Glenn A. Tung

Transcription

1 litstein and Tung MRI of Cerebral Microhemorrhages Neuroradiology Pictorial Essay 09_07_2249_litstein.fm 7/27/07 Marisa Kastoff litstein 1 Glenn. Tung litstein MK, Tung G Keywords: cerebral microhemorrhages, MRI DOI: /JR Received November 4, 2006; accepted after revision pril 19, oth authors: Department of Diagnostic Imaging, rown Medical School, Rhode Island Hospital, 593 Eddy St., Providence, RI ddress correspondence to M. K. litstein (marisa_kastoff@alumni.brown.edu). JR 2007; 189: X/07/ merican Roentgen Ray Society OJECTIVE. The purpose of this pictorial essay is to discuss the differential diagnosis of cerebral microhemorrhages on T2*-weighted gradient-echo MRI. CONCLUSION. Cerebral amyloid angiopathy and chronic systemic hypertension are the two most common causes of cerebral microhemorrhages. Less common causes include diffuse axonal injury, cerebral embolism, cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, multiple cavernous malformations, vasculitis, hemorrhagic micrometastasis, radiation vasculopathy, and Parry-Romberg syndrome. erebral microhemorrhages have C been defined as multiple ovoid foci of marked loss of signal intensity on T2*-weighted, gradient-recalled echo MRI. Compared with FLIR and turbo spin-echo T2-weighted sequences, the T2*-weighted gradient-echo sequence has greater sensitivity for the local magnetic field inhomogeneity produced by microscopic deposits of hemosiderin that can remain in macrophages for years after microhemorrhage. Cerebral microhemorrhages, also known as microbleeds or lacunar hemorrhages, must be differentiated from vascular flow voids and cerebral calcifications. Size criteria have been inconsistent. Whereas most studies define microhemorrhages as being smaller than 5 mm in diameter, an upper limit of 10 mm is sometimes used [1]. Once thought to be an incidental finding, cerebral microhemorrhages are now recognized as a marker of microangiopathy and have diagnostic and prognostic implications. We discuss common, uncommon, and rare causes of cerebral microhemorrhages. Common Causes Congophilic myloid ngiopathy Congophilic amyloid angiopathy is progressive deposition of amyloid within small- to medium-sized blood vessels leading to fibrinoid necrosis and vascular fragility. Congophilic amyloid angiopathy is a major cause of primary lobar intracranial hemorrhage in the elderly and is a common cause of cerebral microhemorrhages. In patients older than 60 years, the diagnosis of congophilic amyloid angiopathy should be suspected if there are two or more lobar hemorrhages of any duration, areas of high signal intensity in the white matter, and multiple cerebral microhemorrhages at the corticomedullary junction (Fig. 1). s the number of microhemorrhages increases, so does the risk for intracerebral lobar hemorrhage and associated neurologic impairment [2]. Hypertensive Cerebral ngiopathy Hypertensive cerebral angiopathy is the development of intimal hyperplasia and hyalinosis in deep penetrating brain arterioles as the result of chronic systemic hypertension. These microangiopathic changes can lead to subclinical cerebral microbleeding. Unlike congophilic amyloid angiopathy, cerebral microhemorrhages associated with chronic hypertension are more commonly found in the thalamus, basal ganglia, cerebellum, and pons, sites of hypertensive intracerebral hematoma (Fig. 2). It is postulated that hypertensive cerebral microhemorrhage is a risk factor for subsequent intracerebral hematoma [3]. Uncommon Causes Diffuse xonal Injury Diffuse axonal injury is a type of traumatic brain injury in which torsional forces generated by rapid acceleration or deceleration of the head cause the shearing of axons. reas most vulnerable to shear injury include the cerebral gray white matter junction, splenium of the corpus callosum, and dorsolateral brainstem. Diffuse axonal injury is recog- 720 JR:189, September 2007

2 nized as multiple small foci of hyperintensity on FLIR, T2-weighted, and occasionally diffusion-weighted MR images owing to the presence of white matter edema from the axonal shear injury. Diffuse axonal injury can be accompanied by petechial tissue-tear microhemorrhages that are more apparent on T2*- weighted MR images than on images obtained with other sequences [4] (Fig. 3). Neurovasculitis Vasculitis is inflammation of the blood vessel wall usually associated with ischemia from compromise of the vessel lumen. Neurovasculitis is considered primary when the vasculitis is confined to the CNS and secondary when a systemic disorder or meningitis causes inflammatory vasculopathy. In primary angiitis of the CNS, vasculitis is isolated to the vessels of the CNS, most commonly the arterioles, and is characterized by brain ischemia and microhemorrhages at the corticomedullary junction. CNS vasculitis that complicates bacterial meningitis is an example of secondary neurovasculitis and is the result of either direct angioinvasion by the microbe or collateral vascular injury from the host inflammatory response to meningeal infection. Ischemic infarction, occasionally with hemorrhage, typifies the imaging presentation and may be associated with cerebral microhemorrhages [5, 6] (Fig. 4). Cerebral Cavernous Malformations Cavernous malformations are a type of low-flow cerebral vascular malformation characterized by tightly packed, variably thickened vascular channels that lack both elastic fibers and smooth muscle. Unlike pial arteriovenous malformation, low-flow cavernous malformation is not associated with a nidus or enlarged supplying arteries. Multiple cavernous malformations are found in as many as 33% of sporadic cases and in as many as 75% of cases of familial disease. One unusual presentation of cavernous malformation than can be indistinguishable from cerebral microhemorrhages on T2*-weighted gradient-echo MRI is type 4 cavernous malformation. ccording to the classification scheme of Zabramski et al. [7], type 4 cavernous malformation may represent a minute form of cavernous malformation or a histologically distinct precursor (Fig. 5). Rare Causes Hemorrhagic micrometastasis from melanoma or renal cell carcinoma can manifest as cerebral microhemorrhages, and microhemorrhages have been reported after external beam radiation with or without methotrexate in therapy for lymphoblastic leukemia [8] (Fig. 6). Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CDSIL) is an inherited form of cerebral arteriopathy that leads to precocious demyelination and ischemic white matter infarction. The underlying defect in CDSIL affects smooth-muscle cells in small blood vessels that are affected by a unique type of nonarteriosclerotic amyloid-negative angiopathy characterized by the presence of granular osmiophilic deposits at electron microscopy. The clinical features of CDSIL include recurrent ischemic events, cognitive deficits, migraine with aura, and psychiatric disorders. MRI may show symmetric confluent areas of high signal intensity in the frontal and anterior temporal lobe white matter and within the external capsules. Cerebral microhemorrhages have been reported to occur in 25 70% of cases of CDSIL but have no characteristic distribution [2] (Figs. 7 and 8). Parry-Romberg syndrome, also known as progressive facial hemiatrophy, is rare disorder of possible neurovascular origin characterized by unilateral wasting of the facial skin and subcutaneous tissue with variable involvement of underlying musculoskeletal and neural tissue. This disorder may be a form of linear scleroderma called coup de sabre, which is characterized by linear atrophy of the forehead likened to a saber strike. Fifteen percent of patients with Parry-Romberg syndrome have neurologic manifestations, including epilepsy, migraine, hemiplegia, ptosis, and enophthalmos. Findings on brain MRI are usually ipsilateral to the facial hemiatrophy and include leptomeningeal enhancement, diffuse areas of high signal intensity in the white matter, unilateral focal infarctions in the corpus callosum, and multiple intracranial aneurysms [9]. We encountered one case of Parry-Romberg syndrome in which unilateral cerebral microhemorrhages were found ipsilateral to facial hemiatrophy (Fig. 9). cknowledgments The authors acknowledge Stephen Salloway and Michael Vecchione for their contribution of case material for this article. References 1. Koennecke HC. Cerebral microbleeds on MRI. Neurology 2006; 66: Viswanathan, Chabriat H. Cerebral microhemorrhage. Stroke 2006; 37: Tsushima Y, Tanizaki Y, oki J, Endo K. MR detection of microhemorrhages in neurologically healthy adults. Neuroradiology 2002; 44: Scheid R, Preul C, Gruber O, Wiggins C, von Cramon DY. Diffuse axonal injury associated with chronic traumatic brain injury: evidence from T2*- weighted gradient-echo imaging at 3 T. m J Neuroradiol 2003; 24: y H, Sahin G, Saatci I, et al. Primary angiitis of the central nervous system and silent cortical hemorrhages. m J Neuroradiol 2002; 23: Jan W, Zimmerman R, ilaniuk LT, et al. Diffusion-weighted imaging in acute bacterial meningitis in infancy. Neuroradiology 2003; 45: Zabramski JM, Wascher TM, Spetzler RF, et al. The natural history of familial cavernous malformations: results of an ongoing study. J Neurosurg 1994; 80: Chan MS, Roebuck DJ, Yuen MP, Li CK, Chan YL. MR imaging of the brain in patients cured of acute lymphoblastic leukemia: the value of gradient echo imaging. m J Neuroradiol 2006; 27: Grosso S, Fioravanti, iasi G, et al. Linear scleroderma associated with progressive brain atrophy. rain Dev 2003; 25:57 61 JR:189, September

3 litstein and Tung Fig year-old woman with congophilic amyloid angiopathy. and, Transaxial T2*-weighted gradient-echo MR images show innumerable microhemorrhages predominantly at cerebral gray white matter junction. Microhemorrhages are not present in basal ganglia, pons, or cerebellum. Large focal hemorrhages are present in left superior parietal lobe (arrows, ) and right inferior parietal lobe (arrow, ). Fig year-old man with history of chronic hypertension, dementia, and multiple strokes who presented with new right-sided weakness., Transaxial T2*-weighted gradient-echo MR image shows hemorrhage in left basal ganglia (solid arrow) and multiple microhemorrhages in left putamen (solid arrowhead), right caudate nucleus head (open arrow), and thalamus (open arrowhead)., Transaxial T2*-weighted gradient-echo MR image shows microhemorrhage (arrowhead) in basis pontis and left peridentate cerebellum. 722 JR:189, September 2007

4 C Fig year-old boy with postconcussive syndrome and microhemorrhages from diffuse axonal head injury., Unenhanced CT scan at presentation shows single punctuate hemorrhage in right frontal lobe and extensive scalp hematoma. and C, FLIR () and T2*-weighted gradient-echo (C) MR images obtained 6 months after show bilateral corticomedullary microhemorrhages evident only on gradientecho MR images. Fig year-old man with sickle cell trait and cerebral vasculitis secondary to meningococcal meningitis. Transaxial T2*-weighted gradient-echo MR image shows numerous microhemorrhages and larger hemorrhages at corticomedullary junction. Fig. 5 9-month-old girl with family history of cerebral cavernous malformation who presented with 1-month history of simple focal seizure. and, Transaxial T1-weighted () and T2*-weighted () gradient-echo MR images show subacute hematoma (arrow, ) and vasogenic edema associated with right parietal cavernoma. In this child, multiple microhemorrhages on gradient-echo MRI are consistent with other smaller cavernous malformations (type 4 cerebral cavernous malformation). JR:189, September

5 litstein and Tung Fig year-old man with biopsy-proven cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy. Transaxial T2*-weighted gradient-echo MR image shows extensive confluent areas of high signal intensity in cerebral white matter, right frontal lobar hemorrhage (arrow), and single microhemorrhage (arrowhead) in right superior parietal lobe. C D Fig year-old man with hemorrhagic micrometastasis from renal cell carcinoma. and, Transaxial T2*-weighted gradient-echo MR images show microhemorrhages in right frontal (arrowhead, ), left occipital (arrow, ), and left temporal (arrow, ) lobes. C and D, Contrast-enhanced T1-weighted images show small enhancing foci consistent with hemorrhagic micrometastasis in right frontal (arrowhead, C), left occipital (arrow, C), and left temporal (arrow, D) lobes. Fig year-old man with biopsy-proven cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy. Transaxial FLIR MR image shows extensive and confluent areas of high signal intensity in cerebral white matter and three microhemorrhages. 724 JR:189, September 2007

6 FOR YOUR INFORMTION Fig year-old man with Parry-Romberg syndrome (facial hemiatrophy)., Transaxial FLIR MR image shows skin and softtissue atrophy of left frontal scalp and multifocal areas of high signal intensity in white matter, confluent in left parietooccipital lobe, and ipsilateral to forehead hemiatrophy., Transaxial T2*-weighted gradient-echo MR image shows scattered microhemorrhages in left frontal lobe, thalamus, and parietooccipital white matter. The comprehensive book based on the RRS 2007 annual meeting categorical course on Neuroradiology is now available! For more information or to purchase a copy, see JR:189, September