Pearls & Oy-sters: Hyperdense or pseudohyperdense MCA sign
A Damocles sword?
Bhawna Jha, MD, MRCPsych and
Milind Kothari, DO
From the Hershey Medical Center, Hershey, PA.
Address correspondence and reprint requests to Dr. Bhawna Jha, Department of Neurology, Hershey Medical Center, 500 University Drive, Hershey, PA 17033 drbhawnajha{at}yahoo.com
The hyperdense middle cerebral artery (MCA) sign is an insensitivebut specific sign suggestive of vascular thrombosis in patientspresenting with ischemic stroke.
The presence of a true hyperdense sign can be confirmed by measuringattenuation value as compared to the normal-appearing contralateralside.
Mimics of a hyperdense sign (i.e., a pseudohyperdensesign)include vascular calcification, raised hematocrit, andintravenouscontrast medium.
Careful attention should alsobe paid to the surrounding brainparenchyma to assess for hypodensityor any differentiatingfeatures suggestive of tumor, infection,or contusion.
Unenhanced CT of the head is usually the first diagnostic studyperformed for the investigation of acute neurologic signs andsymptoms. Specific diagnostic features are helpful for accurateand prompt management of these patients. A hyperdense sign ofthe MCA was first described in 19831 as an indirect sign ofischemic stroke. Subsequently, numerous articles have detailedthe causes of this sign, measured the attenuation differencesbetween normal and thrombosed vessels, and elucidated otherconditions which may give a false impression of a hyperdenseMCA sign.2 We present a case report of a patient who presentedwith seizures and had a pseudohyperdense MCA sign. We discussthe differential diagnosis of hyperdense MCA sign and featuresto differentiate it from pseudohyperdense MCA sign.
A 60-year-old man presented with generalized seizures. Apartfrom confusion, there were no other neurologic abnormalities.A CT was performed which demonstrated an apparent hyperdenseMCA on the left side with hypodensity of the adjacent brainparenchyma (figure, A). However, the absolute attenuation valueof the hyperdense-appearing left MCA was 36 Hounsfield units(HU) and on the normal- appearing right side was 35 HU. MRIand magnetic resonance angiography demonstrated a mildly enhancinginfiltrating left frontal and temporal mass (figure, B) witha patent MCA (figure, C) and no evidence of infarct. Biopsyconfirmed a low-grade astrocytoma.
Figure Head CT (A), brain MRI (B), and brain magnetic resonance angiography (C)
(A) Head CT: unenhanced CT head axial image which demonstrates a relatively hyperdense appearing left middle cerebral artery (MCA) with hypodensity of adjacent brain parenchyma. The absolute attenuation value of the left MCA was 36 HU and of the right MCA was 35 HU. (B) Brain MRI: axial T2-weighted image of the brain demonstrates a hyperintense infiltrating mass of the left posterior frontal and temporal lobe with mass effect. Normal flow void is also noted through the left MCA branches. (C) Brain magnetic resonance angiography: maximum intensity projection image of MRA of the brain which demonstrates a patent MCA on the left side (arrow).
The hyperdense MCA sign on unenhanced CT of the head in patientspresenting with presumed acute ischemic stroke has been reportedto have high specificity and positive predictive value for thromboembolicocclusion of the MCA. It is associated with poor prognosis.In a study3 to establish objective criteria for hyperdense MCAsign, the authors concluded that an absolute attenuation valueof abnormal MCA above 43 HU and a ratio of dense abnormal MCAattenuation to normal-appearing contralateral MCA attenuationof more than 1.2 correctly identified all the hyperdense MCAsassociated with acute ischemic stroke.
It is important, however, to recognize conditions in which thehyperdense MCA sign is misleading. It has been noted that theMCA may appear hyperdense without any intraluminal thrombosis.This pseudohyperdense MCA sign may be seen in the presence ofconditions affecting the density of intraluminal content, walldensity, and extraluminal density.4 Intraluminal hyperdensitymay be due to increased hematocrit, contrast medium from a differentsource, or increased serum density from ingested substancessuch as cocaine. Partial volume averaging artifact from vascularwall hyperdensity, such as in vascular wall calcification, canalso result in pseudohyperdensity. This may be seen with diabetes,hypertension, and elevated cholesterol, or it may be idiopathic.The hyperdense MCA sign is generally transient, but hyperdensitydue to vessel wall calcification will be stable, and so comparisonwith a previous study, if available, will help to confirm thediagnosis. Another important cause of pseudohyperdense MCA signis a normal density MCA appearing hyperdense due to adjacentabnormal parenchymal hypodensity. This may appear in the settingof infection, tumor, or contusion. Comparison of the attenuationvalue of the abnormal-appearing vasculature with other vesselsin the intracranial cavity will reveal no significant differences,as it did in our case. Abnormal enhancement may also help todifferentiate ischemia from infection and tumor. Characteristicareas of involvement may help diagnose infections such as herpesencephalitis. Evidence of calcification may also suggest a neoplasticor dysplastic lesion. Further imaging with MRI can help to distinguishthese situations.
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Nicola Petitti. The hyperdense middle cerebral artery sign. Radiology 1998;208:687–688.[Free Full Text]
Koo CK, Teasdale E, Muir KW. What constitutes a true hyperdense middle cerebral artery sign. Cerebrovasc Dis 2000;10:419–423.[Medline]
Rauch RA, Bazan C 3rd, Larsson EM, Jinkins JR. Hyperdense middle cerebral arteries identified on CT as a false sign of vascular occlusion. AJNR Am J Neuroradiol 1993;14:669–673.[Abstract]
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PEARL: HYPERDENSE MCA SIGN
OY-STERS: PSEUDOHYPERDENSE MCA...
