Utility of Hounsfield Unit: Haematocrit Ratio in Diagnosing Acute Cerebral Venous Sinus Thrombosis on Unenhanced Computed Tomography

Abstract

Introduction: The non-invasive imaging technique of choice in diagnosing Cerebral Venous Sinus Thrombosis (CVST) is Magnetic Resonance Imaging (MRI), but it has its own set of limitations like not being available universally in the acute setting. Computed Tomography (CT) Venography (CTV) can be used as an alternative diagnostic modality with an advantage of being more readily available which can be comparable to MRI in diagnostic accuracy. Aim: To determine the value of Hounsfield unit: haematocrit (H:H) ratio on unenhanced brain CT scans in diagnosing acute CVST and to determine an optimal cut-off value for sensitivity and specificity based on the Receiver Operating Characteristic Curve (ROC) curve. Materials and Methods: This was a retrospective case-control study on 60 adults, divided into two groups A and B consisting of 30 each. Group A consisted of 30 healthy controls who came for unrelated complaints, in whom the imaging findings for CVST were negative, which was confirmed on contrast CTV. Group B consisted of 30 Test subjects with imaging findings of CVST confirmed on CTV. For control images, attenuation was measured in 3 random, but different, venous sinuses in plain CT images. For study group, thrombosed venous sinus was measured on three different locations in the respective sinus by using the cursor. The location and densities of the thrombus was also documented. The nonenhanced CT brain images of both the groups were assessed for the attenuation of the dural sinus. CTV was utilised only to confirm the presence or absence of dural thrombosis. The statistical software namely SPSS 22.0, and R environment ver.3.2.2 were used for the analysis of the data. Results: The average sinus attenuation in the study group of acute CVST (M=84.5 HU, SD=6.1 HU) compared to the control group (M=65.2 HU, SD=4.3HU) demonstrated significant difference of p<0.0001. The average H: H ratio in the study group of acute CVST (M=2.3, SD=0.4) compared to the control group without CVST (M=1.6, SD=0.1); demonstrated significant difference of p<0.0001. On the basis of ROC curves, with 72 HU as cut-off value, the study determined a sensitivity of 100% and a specificity of 96.6%. The study determined a cut-off H: H ratio of 1.8 for 100% sensitivity and a specificity of 96.6%. Conclusion: Both density measurement in the venous sinus and calculation of the H:H ratio will increase the confidence of the radiologist in a setting where CT is the only available modality. Determining the H:H ratio on a per case basis helps in clinical scenarios of such blood disorders like anemia, polycythemia, while considerably reduced the risk of a false negative or a positive diagnosis. The present study is just an attempt to equip the radiologist with another tool at his disposal in cases where he is not able to access MRV/CTV either due to logistical or patient contraindications. Although in this study H:H ratio was accurate and sensitive enough, further large multicenter studies might be needed before utilising H: H ratio parameter for acute CVST.

Keywords

• anaemia
• polycythemia
• primary health center
• superior sagittal sinus
• transverse sinus