1. IntroductionClassic signs on CTMagnetic resonance venographyDiagnostic Pitfalls Dural sinus thrombosis (DST) is an uncommon but potentially devastating cause of stroke. It is often misdiagnosed, often precluding appropriate intervention that may minimize morbidity and mortality. Imaging plays a key role in the diagnosis. A knowledge of the clinical features and radiologic manifestations is important to ensure prompt diagnosis and aggressive management. Clinical features of DST Etiologies: Generalized causes: Hypercoagulability: malignancy, pregnancy, oral contraceptive Systemic inflammatory processes Local/regional causes: Temporal bone fracture Sinusitis, mastoiditis, odontogenic infections Presenting symptoms are nonspecific: Most common: headache. Also: impaired consciousness, seizures, paresis/aphasia. Frequently misdiagnosed as: subarachnoid hemorrhage, meningitis, pseudotumor cerebri, or arterial hemorrhage. ED presentation is usually 7 to 10 days after the onset of symptoms. Treatment: varies with clinical stage. Most cases are treated with systemic anticoagulation. More severe cases need combination of anticoagulation, selective venous thrombolysis and/or thrombectomy. Anatomy of dural sinuses Delta signEmpty delta sign Non-enhanced CT (A): “Delta” or “Dense Triangle” Sign: dense thrombus in posterior aspect of superior sagittal sinus has a triangular shape (arrow). “Cord” Sign – thrombosed dense cortical veins or transverse sinus (not shown). Contrast-enhanced CT (B): “Empty delta” sign: enhancement of dural collaterals in the walls of thrombosed sinus (arrow). MR of acute DST Same patient as above. A (T1WI): Thrombus in the superior sagittal sinus is isodense to brain tissue (arrowheads). B (T2WI): Hypointense right transverse sinus thrombus (arrow). C, D (T1WI post gadolinium): Isointense thrombus in transverse and superior sagittal sinuses and torcular herophili surrounded by enhancing sinus wall (arrows). “Empty delta” sign equivalent is present in D (arrow). MR of subacute DST Three methods of MRV: Time-of-flight (TOF) Phase-contrast (PC) with/without IV contrast 3-D contrast-enhanced short TE gradient echo TOF: Blood flowing into saturated (dark) stationary tissue becomes bright. Flowing blood is most enhanced when it is perpendicular to the image plane. Subacute thrombus can be mistaken as normal flow as it is hyperintense. PC: Moving protons create signal while stationary protons do not. Thus PC does not depend on the stage of the thrombus. It is time consuming. Contrast-enhanced Gradient Echo: Allows direct visualization of thrombus. Secondary brain findings Causes of false negatives on CT and MRI: Hyperdense thrombus (delta sign) on CT is of low sensitivity. In the transverse sinuses it can be missed due to volume averaging or be misdiagnosed as subtentorial hematoma. On T2, acute thrombus may be mistaken as a normal flow void as both are hypointense. An organized thrombus may enhance with contrast on both CT & MR, result in a false negative delta sign. Occasional contrast enhancement of the dura along the tentorium & falx may be mistaken for other leptomeningeal pathologies. Causes of false negatives on MR venogram: Subacute thrombus may simulate normal flow on TOF MRV as it is hyperintense. In-plane flow artifact Hypoplastic sinus A (T1WI): Hyperintense thrombus in superior sagittal and straight sinuses (arrowheads). B (T2WI) and C (FLAIR): Hyperintense thrombus bilateral transverse sinuses (arrows). Brain edema Unilobar hemorrhage Multifocal hemorrahges Parasagittal infarcts Radiologic-pathologic patterns of parenchymal changes: Normal Brain swelling, no edema Brain swelling with edema Brain swelling/edema with hemorrhages A (CT): Bilateral transverse sinus thrombi with cerebral edema (arrows). Note lack of gray- white matter differentiation and bilateral uncal herniations (*). B (CT): Venous hemorrhage frequently has finger-like projections (arrowheads). C (CT): Venous infarcts are frequently multifocal, in this case they also became hemorrhagic. Edema is outlined by arrowheads. D (DWI): Theoretically with venous congestion, blood supply to water-shed areas are reduced, producing parasagittal infarcts in this case. Note hyperintense clots in sinuses (arrowheads). A: Aaxial MIP shows lack of flow in the right transverse sinus (tracing). B: Coronal MIP is best in preventing this type of artifact. A: Coronal MIP shows lack of flow in half of the right transverse sinus (arrowhead), which improves on sagittal MIP (B). C: Coronal source image confirms normal flow. References Back G, et al. Neuroradiology 1997;39:566-70. Bousser MG. Stroke 1985;16:199-213. Chiras J. Neuroradiology 1985;27:593-600. De Bruijn SFTM, et al. J Neurol Neurosurg Psychiatry 2001;70:105-8. Causes of false positives: A false positive delta sign may result from a small subdural hematoma adjacent to a dural sinus. Arachnoid granulation and luminal septa/fenestrations may produce filling defects. On MRI, slow flow within a sinus can simulate a thrombus (flow-related enhancement). On TOF MRV, signal loss can occur with intravoxel spin phase dispersion or in-plane saturation effects (see below). Absence/hypoplasia of a dural sinus is common, requiring careful evaluation of source images on MR venogram (see below). Keiper MD. J Comp Assist Tomogr 1995;19:527-31. Provenzale JM. AJR 1998;170:777-83. Pui MH. J Clinical Imaging 2004;28:85-9. Soleau SW, et al. Neurosurgery 2003;52:534-44. Yuh WTC, et al. AJNR 1994;15:309-16. Super sagittal sinus Inferior sagittal sinus Straight sinus Transverse sinus Torcular herophili Sigmoid sinus Internal Jugular vein A, B (MIP) show lack of flow in the left transverse and sigmoid sinuses extending to internal jugular vein as indicated by tracings. C (axial source) confirms the findings. A B C D A BC AB C D B A B C T h e O h i o S t a t e U n i v e r s i t y M e d i c a l C e n t e r * * B A C A AB