The Uniform Cortex Sign: A Diagnostic Sign of Diffuse Cortical Injury at MR Imaging of the Brain Authors: Apurva Patel, Basem Bahakeem, Andrew Leung Presentation #: EP-79

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Background Identification of the central sulcus on MR imaging is important for accurate anatomic localization of motor and sensory cortices, especially in patients undergoing surgical treatment Several topographic features can be utilized on CT and MR imaging to localize the central sulcus One such feature is thin cortex sign (TCS), described as the greatest difference in cortical thickness between gyri banking a single sulcus which is found along the central sulcus

Purpose The TCS has been described in earlier studies using T1 and T2 weighted sequences in normal patients and in patients with neoplasms who can have marked distortion of normal anatomy We propose that the TCS is lost in cases of diffuse cortical injury which results in the novel uniform cortex sign (UCS) We also investigate the utility of axial T2, DWI and FLAIR; sagittal FLAIR; and coronal FLAIR sequences in qualitatively identifying the TCS

Materials and Methods From July 2014 to November 2014: The UCS group was formed from patients with diffuse cortical abnormality on MRI The TCS control group was formed from asymptomatic patients undergoing MR examination for aneurysm screening 9 patients with TCS and 8 patients with UCS were obtained

Materials and Methods Radiologist training Using selected MR images from two control (TCS) and one UCS subject, three fellowship trained Neuroradiologists were given a tutorial on the TCS and UCS Two Ax T2, two Ax DWI, two Ax FLAIR, one Sag FLAIR and seven contiguous Cor FLAIR images were shown for all three tutorial patients The remaining seven control and seven UCS subjects were used to determine the utility of the UCS in identifying patients with diffuse cortical injury Each reader was given selected deidentified images (same as above) from the database of 14 patients in random order Each reader was asked to identify and mark the TCS on each image if present If readers felt that the TCS was absent, they were asked to say that a UCS was present

TCS Tutorial Case Can you identify the TCS? Axial FLAIR Axial DWI Axial T2 Cor FLAIR Can you identify the TCS?

TCS Tutorial Case Axial T2 Axial FLAIR Axial DWI Cortical thickness along anterior and posterior banks of the central sulcus is less than that of adjacent sulci Furthermore, the cortical thickness of the posterior bank is less than that of the anterior bank Generalized cortical thinning is qualitatively observed on coronal FLAIR imaging as the pre- and postcentral cortices travel obliquely through the coronal plane Cor FLAIR

UCS Tutorial Case Sag FLAIR Axial FLAIR Axial DWI Cor FLAIR

UCS Tutorial Case Sag FLAIR Axial FLAIR Axial DWI There is loss of the normal thin cortex banking the central sulcus All cortices appear uniform in thickness, giving rise to the UCS (Each red oval marks the region of the central sulcus which was identified using other anatomic landmarks in the absence of TCS) Cor FLAIR

Results   TCS correctly identified Patient Age Gender Indication for exam Reader 1 Reader 2 Reader 3 TCS 1 29 F FHxA. Rule out aneurysm Y TCS 2 46 TCS 3 55 TCS 4 56 M TCS 5 26 TCS 6 52 TCS 7 13 TCS correctly identified in all 7 control cases by all three readers UCS correctly identified in 5/7 cases by all readers UCS2 – All readers thought a TCS was present UCS4 – Reader 2 thought a TCS was present   UCS correctly identified Patient Age Gender Indication for exam Reader 1 Reader 2 Reader 3 UCS 1 12 F HIE due to hanging Y UCS 2 16 M Viral encephalitis N UCS 3 55 HIE due to cardiac arrest UCS 4 75 UCS 5 14 UCS 6 49 UCS 7 18 TCA overdose HIE, hypoxiemic ischemic injury; FHxA, family history of intracranial aneurysms; TCA, tricyclic antidepressants

Results – TCS Patients – Axial T2

Results – UCS Patients – Axial T2

Results – UCS and Severity of Cortical Injury Axial T2 images of patients with mild, moderate and severe cortical injury demonstrate that the UCS is more conspicuous in cases of severe injury Mild Moderate Severe UCS2 UCS4 UCS7

Results – Follow-up exam of Patient UCS 2 All three readers failed to correctly identify the UCS in Patient UCS 2 who presented with mild diffuse cortical injury in the setting of viral encephalitis Comparison of the initial MR to the post-treatment MR confirms that the UCS was indeed present on the initial exam which is no longer evident on the post-treatment exam Initial Exam Post-treatment Exam

Results The TCS was correctly identified by all 3 readers on all the axial T2, sagittal FLAIR and coronal FLAIR images Axial DWI TCS correctly identified 81/84 times (96%) Axial FLAIR TCS correctly identified 70/72 times (97%) Sequence Reader 1 Reader 2 Reader 3 Average Axial DWI 89% (25/28) 100% (28/28) 96% Axial T2 100% Axial FLAIR 100% (24/24) 92% (22/24) 97% Sagittal FLAIR 100% (7/7) Coronal FLAIR

Conclusion We confirm that the TCS can be used as a tool to identify the central sulcus in normal patients The UCS is a reliable indicator of diffuse cortical injury The extent of cortical swelling is variable depending on the severity of cortical injury The sensitivity of UCS may be lower in the setting of mild diffuse cortical injury

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