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BMJ. 2007 April 14; 334(7597): 794–795.
PMCID: PMC1852020
Rational Imaging

Investigating suspected cerebral venous thrombosis

R Smith, specialist registrar and M D Hourihan, consultant neuroradiologist

This series provides an update on the best use of different imaging methods for common or important clinical presentations. The series editors are Fergus Gleeson, consultant radiologist, Churchill Hospital, Oxford, and Kamini Patel, consultant radiologist, Homerton University Hospital, London

The patient

A previously well 22 year old woman presented acutely to the accident and emergency department with collapse after several days of insidious onset headache. No focal neurological signs were seen, but she was sleepy, with generalised apathy. The remainder of the clinical examination was normal. As the patient's father had factor V Leiden deficiency, she was referred for imaging to detect cerebral venous thrombosis.

Learning points

  • Imaging plays a key role in diagnosing cerebral venous thrombosis, a condition that can be mimicked by several other neurological entities
  • Prompt diagnosis and anticoagulation affects patients' outcome
  • Diagnostic imaging of cerebral venous thrombosis depends on which modality is readily available, and local experience in image interpretation
  • CT venography is a sensitive, quick investigation that can be performed immediately after unenhanced CT, reducing time to diagnosis and treatment

What tests should I order?

Cerebral venous thrombosis is an uncommon but important diagnosis, as it is potentially reversible when promptly recognised and treated. Diagnosing this condition, which accounts for <1% of strokes, is challenging, as the clinical manifestations and aetiological factors are many and varied.1 Imaging is mandatory to confirm the diagnosis.

Imaging findings of cerebral venous thrombosis can be direct, with visualisation of the thrombus, or indirect, with oedema, infarction, and haemorrhage as a consequence of ischaemia from obstructed venous flow.

Unenhanced scanning

Standard computed tomography (CT) of the brain should be done first to exclude common causes of neurological symptoms, such as subarachnoid haemorrhage and tumours. Parenchymal infarction or haemorrhage inconsistent with an arterial vascular territory should raise the suspicion of venous thrombosis.

In the first two weeks of its development, thrombus may be seen as linear high density in the vein or sinus on the non-contrast scan (fig 1)1).. Polycythaemia or normal non-myelinated brain in infants may mimic this. After two weeks, thrombus is isodense to brain parenchyma and is usually seen only on contrast enhanced scans.

figure smir446765.f1
Fig 1 Axial unenhanced computed tomography shows linear hyperdense thrombus within the internal cerebral veins (arrow) and straight sinus (arrowhead), and subtle low density due to ischaemia within the right thalamus

Contrast enhanced scanning

Contrast enhanced scanning will show the thrombus as a filling defect within the vessel, whereas the dura surrounding the clot are enhanced. This radiological “empty delta” sign is found in 25-75% cases, and is more readily detected if the clot is located in the superior sagittal sinus or torcula. Over time, organised thrombus can also enhance, and the empty delta sign is no longer apparent.

CT venography

CT venography may be done if the diagnosis is in doubt or if the initial unenhanced scan suggests venous thrombosis. This technique uses fast, thin slice, helical acquisition following a bolus of iodinated intravenous contrast; the timing of the scan coincides with optimal opacification of the cerebral venous circulation.2 3 4 5 The source images are reviewed, and appropriate software allows subtraction of adjacent bony structures, and excellent multiplanar and three dimensional visualisation of the enhanced veins.

Compared with conventional digital subtraction angiography, CT venography is a sensitive (95%), specific (91%), and reliable technique.6 It provides better venous anatomy than time of flight MR (magnetic resonance) venography, and detects thrombosis with equal accuracy.4 7 A recent study quotes sensitivity of 75-100%, specificity of 81-100%, positive predictive value of 75-100%, and negative predictive value of 89-100% for CT venography, using MR venography as the reference standard.7 The difference in range of values depends on the sinus or vein involved; overall accuracy is 90-100%.

The main advantage of CT venography is that it can be done immediately after the unenhanced CT scan, thereby enabling a prompt diagnosis.

MR venography

Normal blood flow results in a “black” signal void within vessels on standard magnetic resonance imaging (fig 2)2).. Phase contrast, time of flight (fig 33),), and contrast enhanced MR venography are commonly used for detecting cerebral venous thrombosis. Parenchymal changes, including microhaemorrhages, can be detected earlier with magnetic resonance imaging than with computed tomography (table(table).8 9

figure smir446765.f2
Fig 2 Sagittal T1 weighted (left) and axial FLAIR (right) magnetic resonance imaging: straight sinus shows abnormal high signal (absence of normal black flow void), in keeping with venous thrombosis (arrowheads). Note bilateral ischaemia of the thalami ...
figure smir446765.f3
Fig 3 Sagittal time of flight MR venogram: normal flow in the superior sagittal sinus shows high signal (arrowheads), but the straight sinus is absent (arrow) due to thrombosis
Computed tomography (CT) and magnetic resonance (MR) venography in diagnosing cerebral venous thrombosis

Differences in intensity of the signal within cerebral vessels depend on the evolution of the thrombus, physiology of normal flow, and artefacts of imaging. Knowing the potential pitfalls in diagnosis is essential when interpreting the images.

Patient outcome

The patient was initially imaged with unenhanced computed tomography, cerebral venous thrombosis was diagnosed promptly, and intravenous heparin, the mainstay treatment, was started.1 She subsequently had MR venography to define the extent of the thrombus and any associated parenchymal changes and was also found to have factor V Leiden deficiency. We give anticoagulants even if a haemorrhagic venous infarct is seen on imaging, and thrombolysis is advocated only if the patient clinically deteriorates despite adequate intravenous heparin.1

Useful reading

  • Leach JL, Fortuna RB, Jones BV, Gaskill-Shipley MF. Imaging of cerebral venous thrombosis: current techniques, spectrum of findings and diagnostic pitfalls. Radiographics 2006;26(suppl 1):S19-43.
  • Rodallec MH, Krainik A, Feydy A, Helias A, Colombani JM, Julles MC, et al. Cerebral venous thrombosis and multidetector CT angiography: tips and tricks. Radiographics 2006;26(suppl 1):S5-18.

Notes

Contributors: Both authors equally contributed to the research, design, content, and editing of the manuscript.

Funding: None.

Competing interests: None declared.

Provenance and peer review: Commissioned and peer reviewed.

References

1. Einhaupl K, Bousser MG, de Bruijn SF, Ferro JM, Martinelli I, Masuhr F, et al. EFNS Guideline on the treatment of cerebral venous and sinus thrombosis. Eur J Neurol 2006;13:553-9. [PubMed]
2. Alberico RA, Barnes P, Robertson RL, Burrows PE. Helical CT angiography: dynamic cerebrovascular imaging in children. AJNR Am J Neuroradiol 1999;20:328-34. [PubMed]
3. Casey SO, Alberico RA, Patel M, Jimenez JM, Ozsvath RR, Maguire WM, et al. Cerebral CT venography. Radiology 1996;198:163-70. [PubMed]
4. Ozsvath RR, Casey SO, Lustrin ES, Alberico RA, Hassankhani A, Patel M. Cerebral venography: comparison of CT and MR projection venography. AJR Am J Roentgenol 1997;169:1699-707. [PubMed]
5. Hagen T, Bartylla K, Waziri A, Scmitz B, Piepgras U. The place of CT angiography in the diagnosis of cerebral sinus thrombosis. Radiology 1996;36:859-66. [PubMed]
6. Wetzel SG, Kirsch E, Stock KW, Kolbe M, Kaim A, Radue EW. Cerebral veins: comparative study of CT venography with intraarterial digital subtraction angiography. AJNR Am J Neuroradiol 1999;20:249-55. [PubMed]
7. Khandelwal N, Agarwal A, Kochhar R, Bapuraj JR, Singh P, Prabhakav S, et al. Comparison of CT venography with MR venography in sinovenous thrombosis. AJR Am J Roentgen 2006;187:1637-43. [PubMed]
8. Yuh WT, Simonson TM, Wang AM, Koci TM, Tali ET, Fisher DJ, et al. Venous sinus occlusive disease: MR findings. AJNR Am J Neuroradiol 1994;15:309-16. [PubMed]
9. Isensee C, Reul J, Thron D. Magnetic resonance imaging of thrombosed dural sinuses. Stroke 1994;25:29-34. [PubMed]

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