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Neuroradiology Case of the Week

Case 289

Ashwani K. Sharma, MD and P-L Westesson, MD, PhD, DDS

Clinical Presentation: Patient is a 55-year-old male who presented with new onset weakness on right side with slurring of speech.

Imaging Findings:
Imaging features to look for acute infarct on CT include:

1. hyperdense middle cerebral artery sign
2. attenuation of lentiform nucleus
3. loss of the insular ribbon
4. hemispheric sulcus effacement

Diagnosis: Insular ribbon sign - acute infarct of insular cortical-subcortical white matter

Discussion: CT is widely used for early evaluation of acute strokes. Most importantly, CT excludes acute hemorrhage or other diseases mimicking ischemia [1]. Therefore, CT is the main imaging examination in patients with brain ischemia and when antithrombotic agents are considered [2,3]. Although CT does not usually show much in the first 24 hours after cerebral ischemia, there are early abnormal findings on CT, such as the hyperdense middle cerebral artery sign (HMCAS) and reduced contrast attenuation of the cerebral parenchyma. HMCAS, first described in 1983, reflects arterial occlusion [4], and its value in predicting secondary large infarcts is subject to controversy [5]. Early parenchymal abnormalities, the attenuation of lentiform nucleus (ALN), loss of the insular ribbon (LIR), or hemispheric sulcus effacement (HSE), occur less frequently [6]. The size, locations, and degree of acute ischemia could influence the time in which these signs appear. Early parenchymal abnormalities might also predict subsequent infarct extension [7] and hemorrhagic transformation [8]. Finally, initial CT findings may help to predict response to therapy [9]. This should have important implications for selecting subgroups of stroke patients in therapeutic trials.
     Truwit, et al. described LIR as a hypodensity involving the insular region [6]. The blood supply to the insular region is mainly provided by the arteries arising from the M2 segment of MCA. In MCA occlusion distal to the lenticulostriate arteries, this territory would be the farthest from the potential collateral flow rising to the anterior or posterior cerebral artery. The insular region would, therefore, become a watershed arterial zone [1].

References:

1. Moulin T, Cattin F, Crépin-Leblond T, Tatu L, Chavot D, Piotin M, Viel JF, Rumbach L, Bonneville JF. Early CT signs in acute middle cerebral artery infarction: predictive value for subsequent infarct locations and outcome. Neurology. 1996 Aug;47(2):366-75. [Medline]
2. Savoiardo M, Grisoli M. Computed tomography scanning. In: Barnett HJM, Mohr JP, Stein BM, Yatsu FM, eds. Stroke. Pathophysiology, diagnosis and management. 2nd ed. New York: Churchill Livingstone, 1992:155-187.
3. Adams HP Jr, Brott TG, Crowell RM, Furlan AJ, Gomez CR, Grotta J, Helgason CM, Marler JR, Woolson RF, Zivin JA, et al. Guidelines for the management of patients with acute ischemic stroke. A statement for healthcare professionals from a special writing group of the Stroke Council, American Heart Association. Stroke. 1994 Sep;25(9):1901-14. [Medline]
4. Pressman BD, Tourje EJ, Thompson JR. An early CT sign of ischemic infarction: increased density in a cerebral artery. AJR Am J Roentgenol. 1987 Sep;149(3):583-6. [Medline]
5. Leys D, Pruvo JP, Godefroy O, Rondepierre P, Leclerc X. Prevalence and significance of hyperdense middle cerebral artery in acute stroke. Stroke. 1992 Mar;23(3):317-24. [Medline]
6. Truwit CL, Barkovich AJ, Gean-Marton A, Hibri N, Norman D. Loss of the insular ribbon: another early CT sign of acute middle cerebral artery infarction. Radiology. 1990 Sep;176(3):801-6. [Medline]
7. Horowitz SH, Zito JL, Donnarumma R, Patel M, Alvir J. Computed tomographic-angiographic findings within the first five hours of cerebral infarction. Stroke. 1991 Oct;22(10):1245-53. [Medline]
8. Bozzao L, Angeloni U, Bastianello S, Fantozzi LM, Pierallini A, Fieschi C. Early angiographic and CT findings in patients with hemorrhagic infarction in the distribution of the middle cerebral artery. AJNR Am J Neuroradiol. 1991 Nov-Dec;12(6):1115-21. [Medline]
9. Okada Y, Sadoshima S, Nakane H, Utsunomiya H, Fujishima M. Early computed tomographic findings for thrombolytic therapy in patients with acute brain embolism. Stroke. 1992 Jan;23(1):20-3. [Medline]