| Abstract|| |
To establish the role of routine MR sequences in diagnosis of dural venous sinus thrombosis.
Materials and Methods - As dural venous sinus thrombosis has a non specific presentation, all the patients coming to our department for MRI head between March 2003 and May 2005 were looked for abnormal signal intensity within the dural sinuses. Twenty seven cases having loss of normal flow void within the major dural venous sinuses on routine sequences (FSE T2, SE T1 & FLAIR) were thought of having dural sinus thrombosis and so were further evaluated by MR venography. This study was carried out using 0.2 Tesla open magnet MR scanner (GE signa profile 4).
Results - On routine MR sequences absence of dural sinus flow void was noted in twenty seven patients and suspicion of cerebral venous thrombosis was raised. The diagnosis of thrombosis was confirmed in twenty three patients by 2-D TOF MR venography and no thrombosis could be demonstrated in remaining four patients. Thirteen patients had multiple sinus involved whereas in ten patients only single sinus was involved. Out of these twenty three patients, apart from thrombosis, six had infarcts, three had mastoiditis and one of them had cerebellar abscess too. Hemorrhage was noted in five patients and the most interesting fact was that nine patients had normal brain parenchyma.
Conclusion - Dural venous sinus thrombosis appears as loss of normal flow void on routine sequences especially on FSE T2W and FLAIR images. This fact may help us suspect DVT, and the finding can be confirmed by MR venography so that further management can be planned promptly.
Keywords: Dural venous sinus thrombosis, MRI, MR venography
|How to cite this article:|
Kumar A, Mukund A, Sharma G L. Dural venous thrombosis - A neglected finding on routine MRI sequences. Indian J Radiol Imaging 2006;16:276
|How to cite this URL:|
Kumar A, Mukund A, Sharma G L. Dural venous thrombosis - A neglected finding on routine MRI sequences. Indian J Radiol Imaging [serial online] 2006 [cited 2019 Nov 17];16:276. Available from: http://www.ijri.org/text.asp?2006/16/2/276/29110
| Introduction|| |
Dural venous sinus thrombosis has long been a neglected entity because of complexities in diagnosis and non specific clinical presentation. Now-a-days due to the development of higher non invasive modalities and raised awareness venous sinus thrombosis is being diagnosed more frequently, but still most of the patients being diagnosed as having venous sinus thrombosis have developed the complications. Rather it is the complications which points toward the underlying cause i.e. venous sinus thrombosis. So most of the time diagnosis is made retrospectively. Therefore this study is an effort to exploit the non-invasive and non-ionizing nature of MR imaging to raise suspicion and diagnose cerebral venous sinus thrombosis at an early stage to prevent progression of the thrombus and development of its complications.
Dural venous sinus thrombosis generally occurs in young and middle aged adults with a number of clinical features caused by either raised intracranial tension or infarction. The patients usually present with headache, vomiting, seizures or focal neurological deficit and may have papilledema.
The various predisposing factors are pregnancy and post partum state, infections, tumor, dehydration, hypercoagulable states but no cause is identified in 20% to 35% of cases .
The most common finding on MR imaging is replacement of the flow void within an affected dural sinus by abnormal signal intensity. On unenhanced T1 weighted images there is iso or hyperintense signal relative to gray matter.
On T2 weighted images there is hyper or isointense signal but sometimes there may be hypointense signal which simulates normal flow void.
Although, many of the time these findings are ignored but if taken into consideration, especially if they are seen on T2 weighted images and FLAIR images may give us a clue and help us raise suspicion regarding patient having dural venous thrombosis, one of the under diagnosed and neglected condition. This can be further evaluated and confirmed by MR venography which will demonstrate absence of signal consistent with thrombosis in the affected dural sinus .
| Materials and Methods|| |
This had been a prospective study designed to suspect and establish findings of dural venous thrombosis on routine MR sequences (FSE T2, SE T1 & FLAIR). All the patients presenting to our department for MRI cranium from March 2003 to May 2005, with severe headache alone or along with other symptoms and focal neurological deficit were taken into account. After having their MRI done, specific criteria, absence of flow void within the dural venous sinuses, was used to decide the inclusion of patients into the study and other patients having normal flow void within the sinuses were excluded. Total twenty seven patients having loss of normal flow void within the major dural sinuses were selected and included in the study. Based on clinical and imaging features they were suspected as having dural sinus thrombosis and for confirmation were subjected to 2-D TOF (time of flight) MR venography. Depending on patients condition and need, appropriate patient were administered anticoagulants (heparin) and where ever possible follow up scan was done during and after the treatment (upto 1 year). The study was done in department of Radio-diagnosis (Vidya MRI center) with a positive support from the department of neuro-surgery. The MR examination was performed on 0.2 Tesla open magnet MR scanner (GE signa profile 4).
| Results|| |
In one thousand three hundred and sixty five patients who underwent MRI head in a period of two years, twenty seven patients had loss of normal flow void in the major dural venous sinuses and so the possibility of dural sinus thrombosis was kept in mind therefore for further evaluation MR venography was done in all the twenty seven patients in same sitting.
Out of these twenty seven patients having bright cerebral venous sinus for which suspicion was raised as having thrombosis, twenty three turned out to be thrombosis on MR venography. In rest of the four patients complete block could not be demonstrated on MR venography. The hyperintense signal within the major dural sinus of these patients were either due to partial block, sluggish flow or imaging artifacts. Those having thrombosis were assessed and as per clinical requirements were put on anticoagulants / thrombolytic agents, antibiotics and symptomatic treatment [Figure - 1]a,b,c,d. Follow up scan was done after fifteen days to one month, in seven patients partial recanalization of sinuses was seen [Figure - 1]e.
The twenty three patients comprised thirteen women and ten men. Ages were between 20 years and 84 years. The mean age of the patients was 41.6 years.
Clinically four patient presented in puerperium along with headache and neurological features, seven had only neurological deficits, three showed symptoms of infection and rest had non specific symptoms. [Table - 1]
Venous sinus thrombosis occurred during post-partum period in four patients. The predisposing factor was nearby infection in three patients [Figure - 2], [Figure - 3]a,b. Oral contraceptive use was present in one patient. Anemia was present in twelve patients. Cholesterol was elevated in five patients. In one patient there was protein C and protein S deficiency. In six of them no predisposing factor could be recognized.
MRI findings demonstrated six of the patients having infarcts [Figure - 4]a,b,c, five had hemorrhage [Figure - 5]a,b,c , three showed some infective foci and rest were normal. [Table - 2]
(Lt. Sig S = Left sigmoid sinus, Rt. Sig S = Right sigmoid sinus, Lt. Tr S = Left transverse sinus, Rt. Tr S = Right transverse sinus, SSS = Superior sagittal sinus, ISS = Inferior sagittal sinus, Str S = Straight sinus)
Although various studies say that superior sagittal sinus is the most common sinus to be affected followed by transverse sinus but in our study we found sigmoid sinus followed by transverse sinus to be the most frequently affected dural venous sinus.
Of particular interest was the fact that nine patients were having severe symptoms but normal brain parenchyma [Figure - 6]a,b,[Figure - 7]a,b. The only remarkable finding noted was bright venous sinuses.
They all presented with headache of long duration and six of them also had papilledema and raised CSF pressure, who previously were diagnosed as having migraine / cluster headache but when they were treated for dural sinus thrombosis there was dramatic improvement in the symptoms. Also the follow up imaging revealed development of collaterals and partial canalization of thrombosed sinus in most of the cases in 4 to 8 months.
No statistical analysis were performed because of the small size of the study population and increased probability of error.
| Discussion|| |
Venous sinus thrombosis generally occurs in young and middle aged adults with a number of clinical features caused by either raised intracranial tension or infarction. The patient presents with headache, vomiting, seizures or focal neurological deficit also he may have papilledema. The major entities with which dural sinus thrombosis can be confused on clinical grounds are migraine headache and pseudotumor cerebri . CT and MR imaging play a fundamental role in distinguishing dural sinus thrombosis from these entities . The superior sagittal sinus and transverse sinus are the dural sinuses most commonly affected . In contrary to the various studies our study has demonstrated that sigmoid sinus is the most common dural sinus to be affected followed by transverse sinus.
Venous sinus thrombosis results due to blockade of venous sinus either due to partial thrombus, adjacent inflammatory process or external compression which leads to complete occlusion due to progression of the thrombus and further retrograde extension of thrombus may lead to infarction .
The numerous conditions that can cause dural sinus thrombosis are pregnancy, postpartum state, surgery, head trauma, infection, paraneoplastic and autoimmune diseases and the use of oral contraceptive pills. Despite the continuing description of new causes, the proportion of cases of unknown etiology is between 20% and 35% . Dural venous sinus thrombosis has been described as a continuing process in which the balance of prothrombotic and thrombolytic processes is disturbed, leading to progression of the venous thrombus with time . This slow growth of the thrombus and the good collateralisation of the venous vessels probably explain the usually gradual onset of symptoms, frequently over weeks and months ,. Sudden onset, however, has been described . However early diagnosis is of prime importance in both the conditions; to prevent the progression of the thrombus and further save the patient from its complications.
Computerized tomography (CT), prior to MR was the most reliable method to diagnose dural sinus thrombosis. CT features of dural sinus thrombosis include a hyperdense dural sinus, cord sign and hemorrhagic venous infarct on unenhanced CT and an unenhanced central portion of the affected sinus after administration of contrast material (the "empty delta" sign) ,. However, the diagnosis of dural sinus thrombosis is often difficult to establish on CT for a number of reasons. The affected sinus may not be perpendicular to the imaging plane; this position would render the empty delta sign useless.
Though CT venography, can demonstrate the intracranial venous system it requires multislice spiral CT and a large volume of iodinated contrast. Besides it involves ionizing radiation and cannot be used as a screening modality in pregnant patients ,.
With the advent of magnetic resonance (MR) imaging; in particular after the introduction of the MR angiographic techniques has made it possible to visualize the intracranial venous system without the use of contrast. Besides, this technique is noninvasive and does not involve ionizing radiation .
On routine MRI, patent dural venous sinuses show signal voids on spin-echo images. Both the intravascular thrombus and its complications (mass effect, edema, infarction, hemorrhage, hydrocephalus) may be identified with MRI.
In venous sinus thrombosis the expected signal void is replaced by an abnormal signal, the specific nature of which depends on the sequence parameters and age of thrombus . On unenhanced T1-weighted images, the thrombosed dural sinus generally appears isointense or hyperintense relative to gray matter; after administration of contrast material, the central portion of the sinus typically fails to enhance . On T2-weighted images, the thrombosed dural sinus is typically hyperintense or isointense with gray matter but may be hypointense and simulate a normal flow void .
However, spin-echo MR imaging may be misleading with a false diagnosis of dural venous thrombosis, resulting from flow related enhancement or even-echo rephasing or false impression of vessel patency resulting from intracellular deoxy/meth hemoglobin mimicking a normal signal void on long TR (T2 weighted images). Subdural clot lying along a dural sinus may also be confused with a intraluminal thrombus. Sometimes even sluggish flow within the sinus may simulate thrombosis.
Though it is a bit difficult to diagnose venous sinus thrombosis on routine sequences of MRI performed for the examination of cranium, but just having attentive look towards the sinuses with a high index of suspicion may help us diagnose venous sinus thrombosis. However MR differential diagnosis of venous sinus thrombosis is primarily imaging artifacts that mimic intravascular clot but absence of normal dural sinus flow void with hyperintense signal on FSE T2 and FLAIR sequences are strong indicators of thrombosis of the segment involved.
The most common finding on MR imaging is replacement of the flow void within an affected dural sinus by abnormal signal intensity. During the first 5 days the thrombus is isointense compared with brain tissue on T1-weighted images and hypointense on T2 weighted images  because of blood products in the state of deoxyhemoglobin. During the period of day 5 through day 15, the thrombus is hyperintense initially on T1 weighted and subsequently on T2 weighted images because of blood products in the state of methemoglobin. Thereafter, the thrombus becomes progressively inhomogeneous and decreased in signal intensity on all image sequences because of recanalization .
As MR venography is said to be robust adjunct to MRI in the evaluation of the normal intracranial venous system and in diagnosis of dural venous thrombosis . So with above findings MR venography may be performed and projection images can be gained to further evaluate and confirm dural sinus thrombosis. Typical MR venography findings consist of the absence of signal consistent with thrombosis in the affected dural sinus .
The two most common MR venography techniques are based on time of flight effects of moving spins (Time of flight - TOF) or on motion induced phase shifts (Phase Contrast - PC). With either of the two, MR venogram may be obtained by MIP (maximum intensity projection) ray tracing algorithm (which emphasizes the brightest voxels within a vessel at the expense of less bright voxels).
It is important to note that the projection images provide only an overall "roadmap" to cerebral venous anatomy / pathology, so source images should be examined to confirm the findings.
Coming to the most important observation that, sometimes patient coming with symptoms of long duration but absolutely normal brain parenchyma and the only remarkable finding being loss of normal flow void within the major dural venous sinuses should not be ignored. As in our study this group of patients were being treated as case of migraine/vascular headache but were not getting relief rather few patients gradually deteriorated and had severe symptoms. When this group of patients were treated with anticoagulants (heparin) there was great improvement with symptomatic relief. So the main emphasis of our study is to raise a doubt of thrombosis whenever we encounter hyperintense signal intensity within the dural venous sinuses in FSE T2 and FLAIR sequences, especially when the brain parenchyma is absolutely normal as the symptoms of the patients may be due to venous sinus thrombosis leading to raised intracranial tension.
| Conclusion|| |
So with the fact that venous sinus thrombosis presents as loss of normal flow void on routine sequences especially on FSE T2W and FLAIR images we may suspect venous sinus thrombosis on routine MRI sequences, and the finding can be confirmed by MR venography so that further management can be planned promptly and patient can be saved from its complications. This is especially important in subacute cases in which the balance of prothrombotic and thrombolytic processes is disturbed, the thrombus is in gradual growing process and there is no brain parenchymal damage.
Hence we strongly insist and reiterate that absence of normal flow void within the dural sinus should be taken into account and further evaluated by MR venography to confirm the finding.
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Source of Support: None, Conflict of Interest: None
[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6], [Figure - 7]
[Table - 1], [Table - 2], [Table - 3]