Cerebral Venous Sinus Thrombosis, a Nonenhanced CT Diagnosis?


Research Article
Cerebral Venous Sinus Thrombosis,
a Nonenhanced CT Diagnosis?

Ali Alsafi, Amish Lakhani, Lalani Carlton Jones, and Kyriakos Lobotesis

Department of Neuroradiology, Charing Cross Hospital, Imperial College Healthcare NHS, London W6 8RF, UK

Correspondence should be addressed to Ali Alsafi; ali.alsafi03@alumni.imperial.ac.uk

Received 26 December 2014; Revised 2 April 2015; Accepted 4 April 2015

Academic Editor: Andreas H. Mahnken

Copyright © 2015 Ali Alsafi et al. This is an open access article distributed under the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Purpose. Retrospectively evaluate the density of cerebral venous sinuses in nonenhanced head CTs (NCTs) and correlate these
with the presence or absence of a cerebral venous sinus thrombus (CVST). Materials and Methods. Institutional review board
approval was obtained and informed consent waived prior to commencing this retrospective study. Over a two-year period, all CT
venograms (CTVs) performed at our institution were retrieved and the preceding/subsequent NCTs evaluated. Hounsfield Units
(HUs) of thrombus when present as well as that of normal superior sagittal and sigmoid sinuses were measured. HU of thrombus
was compared to that of normal vessels with and without standardisation to the average HU of the internal carotid arteries. Results.
299 CTVs were retrieved, 26 with a thrombus. Both raw and standardised HU measurements were significantly higher in CVST
(𝑝 < 0.0001) compared to normal vessels. Both raw and standardised HUs are good predictors of CVST. A HU of ≥67 and a
standardised measurement of≥1.5 are associated with high probability of CVST on NCT. Conclusion. Cerebral venous sinus HU
measurements may help improve sensitivity and specificity of NCT for venous sinus thrombosis and avoid potentially unnecessary
follow-up examinations.

1. Introduction

Cerebral venous sinus thrombosis (CVST) is an uncommon
cerebrovascular event, accounting for 0.5–1% of cases of
stroke and affecting 1 in 500,000 people [1]. CVST is a
disease of young adults (<50 years old) predominantly [2] and
is diagnosed based on clinical suspicion with confirmatory
neuroimaging [3]. Patients with CVST exhibit a wide range
of nonspecific signs and symptoms creating a diagnostic
challenge for the clinician and radiologist alike [3]. Headache
is the commonest reported symptom in patients with CVST.
It is present in ninety percent of cases and reflects raised
intracranial pressure [2].

MRI is the noninvasive imaging technique of choice for
diagnosing CVST, it is however not universally available
in the acute setting [3–6]. CT venography (CTV) has now
emerged as an alternative diagnostic test, which is at least
as good as MRI and in some cases better, with the added
advantage of being more readily available [7]. Previously, the

gold standard for imaging and diagnosing CVST was digital
subtraction cerebral angiography. This is not routinely used
and has been superseded by CTV and MRV [3, 8–10].

As most patients with CVST present with nonspecific
symptoms and often CVST is not immediately suspected,
patients are likely to have nonenhanced head CT (NCT) at
presentation. NCT is the examination of choice for screening
patients with nonspecific neurological presentations in the
context of low suspicion of CVST [4]. NCT may be reported
as normal in up to two-thirds of patients with venous
sinus thrombosis. When abnormal, the findings on NCT are
often subtle and nonspecific in the early stages and include
“hyper-dense” venous sinuses and cerebral swelling. Small
recent studies have shown that venous sinus hyperdensity
is a sensitive sign for CVST [11, 12]. Venous infarcts and
fragmented haemorrhage are late signs [4].

Making a timely diagnosis of CVST is of utmost impor-
tance as prompt anticoagulation is thought to prevent
thrombus propagation. This in turn prevents ensuing venous

Hindawi Publishing Corporation
Radiology Research and Practice
Volume 2015, Article ID 581437, 5 pages
http://dx.doi.org/10.1155/2015/581437

http://dx.doi.org/10.1155/2015/581437


2 Radiology Research and Practice

Table 1: Patients’ characteristics.

CVST (𝑛 = 26) No CVST (𝑛 = 224)
Median age 38.7 [21.1–63.6] 43.3 [17.3–88.7]
Sex M = 13, F = 13 M = 87, F = 137
Haemorrhage 5 33
Same day NCT and CTV 21 127

Table 2: Distribution of CVST.

Vessel Number of vessels with thrombus
Internal jugular vein 4
Transverse sinus 15
Sigmoid sinus 14
Superior sagittal sinus 11
Torcula herophili 2
Total vessels with CVST 46
CT: computed tomogaphy, NCT: non-enhanced CT, CTV: CT venogram,
CVST: cerebral venous sinus thrombosis.

infarcts and haemorrhage thereby reducing mortality and
long-term neurological sequelae [13]. There remains, how-
ever, much debate surrounding optimal management of
patients with CVST.

2. Aim

In this study we sought to retrospectively evaluate the
density (Hounsfield Units) of cerebral venous sinuses in
nonenhanced head CT examinations in patients with and
without a cerebral venous sinus thrombus as confirmed
on CT venography. We also sought to evaluate whether
standardising venous sinus HU measurements to those of
the corresponding internal carotid arteries would improve
diagnostic accuracy.

3. Materials and Methods

Institutional review board approval was obtained and
informed consent waived prior to commencing this retro-
spective study.

All CTVs performed on adult patients in three teaching
hospitals between September 2011 and November 2013 were
retrospectively retrieved. These were reviewed and divided
into positive CTVs and negative ones. The preceding or
subsequent NCTs, within seven days of the CTV, were
evaluated.

Only unique CTVs were included. Patients who under-
went a neurosurgical procedure in the preceding 10 days
were excluded as extra-axial blood products may affect our
measurements. Follow-up CTVs, where the patient is known
to have an old thrombus, were also excluded. We also
excluded hypoplastic venous sinuses and heavily calcified
ICAs from the analysis.

The site of thrombus was identified from the CTV, where
applicable, and the Hounsfield Units (HUs) of the corre-
sponding cerebral venous sinus in the NCT were measured.

In negative studies, HU of the superior sagittal sinus (SSS)
and both sigmoid sinuses were recorded (Figure 1).

In both groups, HUs of both intracranial portions of the
internal carotid arteries (ICAs) as they exit the carotid canal
were measured (Figure 1).

The HUs of the cerebral venous sinuses with and without
thrombus were compared before and after normalisation to
the average HU of the corresponding ICAs (see the following
equation):

Standardised measurment

=
HU of venous sinus

((HU of right ICA+HU of left ICA)/2)
.

(1)

In our institution patients with CVST are anticoagulated with
unfractionated heparin acutely in the absence of contraindi-
cations then changed to warfarin once stable and ready for
discharge.

GraphPad Prism 5.0 for Mac OS X (GraphPad Software
Inc., San Diego, CA, USA) was used for statistical analysis.
Student’s t-test was used to compare HUs. Fischer’s exact test
was used to compare categorical data.

Receiver operating characteristic (ROC) curves were
derived and the area under the ROC curves (AUC) was
calculated. 95% confidence intervals were used to test the
hypothesis that the AUC is 0.5.

Microsoft Excel for Mac 2011 v 14.0.0 (Microsoft Cor-
poration, One Microsoft Way, Redmond, WA) was used to
compare the AUCs of unpaired ROC curves (raw HU versus
per patient HU and standardized HU versus per patient HU)
using the method described by Hanley and McNeil [14].

MedCalc version 12.7.0 (MedCalc Software, Acacialaan
22, 8400 Ostend, Belgium), was used to compare the AUC of
paired ROC curves, that is, raw versus standardized HU [15].
p values<0.05 were considered significant.

3.1. NCT and CTV Protocols

3.1.1. CTV Protocol. Axial NCTs were performed on
Somatom Definition AS CT scanners (Siemens Medical
Solutions, Forchheim, Germany) with the following
parameters: 320–360 mAs, 120 kV, and slice collimation of
12× 0.75 mm for the posterior fossa and 12× 1.5 mm for the
rest of the brain.

CTVs were performed 45 s after administration of intra-
venous iodinated contrast at 3/4 mL/s. The detector configu-
ration was 16×0.75 mm.

All scans were performed from the top of the C1 lamina
to the top of the calvarium, parallel to the floor of the anterior
fossa avoiding the eyes.

4. Results

299 CTVs were retrieved. 22 postoperative (postneurosur-
gical procedure) studies were excluded. 24 studies were
excluded, as there was no preceding or follow-up NCT within
seven days of the index CTV. Five hypoplastic venous sinuses
and six heavily calcified ICAs were excluded from analysis.



Radiology Research and Practice 3

(a) (b)

(c)

Figure 1: Images from NCT demonstrating sites of HU measurements from (a) superior sagittal sinus at the vertex, (b) sigmoid sinus, and
(c) intracranial ICA just distal to the carotid canals.

100

80

60

40

20

H
U

 o
f v

en
ou

s s
in

us

Thrombus Normal sinous Thrombus Normal sinous

3

2

1

0

R
at

io
 o

f H
U

s o
f v

en
ou

s s
in

us
/I

C
A

Raw cerebral venous sinus HU
Cerebral venous sinus HU normalised to ICA

∗∗∗∗

∗∗∗∗

Figure 2: Comparison of cerebral venous sinus HU before and after
standardisation to the ICAs in patients with and without CVST.∗∗
∗∗=𝑝< 0.0001 two-tailed Student’s t-test.

The remaining 250 unique patients with a median age of
42 had a CTV and NCT within seven days of each other with
a median of 0 days and a range of [−1, 6.6]. 148 patients had
a CTV immediately following their NCT. Two patients had
an NCT 24 hours following CTV. No patients underwent an
NCT less than 24 hours following their CTV.

26 patients had a CTV proven CVST with a median age
of 38.7 while 224 patients had normal CTVs; they had a
median age of 43.3. 19% (5/26) of those with a CVST an
acute intracranial haemorrhage evidence on NCT, compared

100

100

50

50

0

0

Se
ns

iti
vi

ty
 (%

)

100 − specificity (%)

ROC curve of raw HU. AUC = 0.879
ROC curve of standardised HU. AUC = 0.899

Figure 3: ROC curves comparing the difference between raw HU
and standardized measurements.

with 15% (33/224) from the normal CTV group. Only 10.4%
of patients with a suspected CVST had a proven thrombus
on CT venography. There was no significant difference in
age, sex, or incidence of intracranial haemorrhage between
the two groups with𝑝 values of 0.3800 (two-tailed Student’s
t-test), 0.2953, and 0.5641 (Fisher’s exact test), respectively.
Demographic data are shown in Table 1 and distribution of
CVST is shown in Table 2.



4 Radiology Research and Practice

100

50

0

(%
)

20 40 60 80

HU of cerebral venous sinus

Specificity (%)
Sensitivity (%)

Figure 4: Graph demonstrating changes in sensitivity and speci-
ficity at different HU cutoffs for standardised HU measurement. The
dotted lines represent our proposed HU cutoffs with high negative
and positive predictive values for venous sinus thrombosis.

4.1. Vessel HU Analysis. 768 venous sinuses were analysed,
46 with a CVST and 720 without. The average HU of vessels
containing a thrombus was 68 ± 1.56 (𝑛 = 46) which was
significantly higher than that of normal vessels 52 ± 0.28
(𝑛 = 720) (𝑝< 0.0001, two-tailed t-test) (Figure 2).

In an attempt to eliminate HU fluctuations caused by low
haemoglobin, haemodilution, dehydration, and so forth, we
standardised the venous sinus HUs to the average HU of the
corresponding ICAs.

The ratio of sinuses containing thrombus was1.44±0.04
(𝑛 = 46). The ratio in sinuses without thrombus was 1.07 ±
0.01 (𝑛 = 720). This was significantly different (𝑝< 0.0001by
the two-tailed t-test).

4.2. Diagnostic Performance of Raw versus Standardized
Measurements. ROC curves were derived from the raw and
standardized HUs (Figure 3). The diagnostic performance of
raw venous sinus HUs and standardized HUs expressed as
the area under the curve (AUC) were 0.899 (95% CI [0.875–
0.919]) and 0.879 (95% CI [0.853–0.901]), respectively. The
AUCs show that both measurements were good predictors
of CVST (𝑝 < 0.0001). Standardized HU measurements
perform slightly better compared with raw HU albeit not
reaching statistical significance (𝑝= 0.6078).

5. Discussion

Although nonenhanced head CT is thought to have a low
sensitivity and specificity for CVST, Roland et al. estimate
the sensitivity at 73% [16]. This may be even lower in normal
clinical practice, when CVST is not suspected nor mentioned
in the clinical detail.

In a recent small study, cerebral venous sinus measure-
ments in NCT were shown to be of value in detecting CVST
[12]. The study included a small number of controls without

venous sinus thrombus and their suggested cutoff HU of 62
is likely to yield a significant number of false positive studies
resulting in unnecessary follow-up examinations [12]. Our
study has a larger control population showing wide variation
in normal venous sinus HU and is likely to be more reflective
of general clinical practice.

Black et al. have previously demonstrated a significant
difference in venous sinus densities between patients with
and without CVST, although they assumed that patients with
a normal NCT have no CVST without a confirmatory CTV or
MRV [11]. Our results more robustly confirm these findings as
all our patients have had a CTV. Our results show that when
assessing cerebral venous sinuses on NCT, HU measurements
are a useful objective adjunct to subjective assessment in
detecting CVST.

Black et al. have also demonstrated a correlation between
the patient’s hematocrit and venous sinus density [11]. With
that in mind, we standardised venous sinus HU measure-
ments to those of the average ICAs. We postulated that
standardization may eliminate some of the physiological
variations encountered such as haemodilution, dehydration,
and anemia.

The area under the ROC curves for the standardized HUs
was 0.899 (95% CI [0.875–0.919]) compared with 0.879 (95%
CI [0.853–0.901]) for raw HU measurements although the
difference did not reach statistical significance (𝑝 = 0.6078)
using DeLong’s paired measurements ROC analysis [15]. Both
methods have a strong correlation with the presence or
absence of CVST with𝑝< 0.0001.

Black et al. also noted that patients with a CVST often had
a HU> 70, whereas most patients without a CVST had HU
<70 and also showed that a HU/hematocrit ratio of>2 has a
good correlation with CVST. Our results, on the other hand,
demonstrate that using 70 as a cutoff is likely to result in a
significant number of false-negative studies.

A recent study demonstrated that the sensitivity of venous
sinus hyperdensity on NCT may be as high as 100% with
a specificity reaching 95%. This is also likely to be an
overestimate as the reading radiologists had only one task of
visually scoring the venous sinuses on NCTs [17].

Cerebral venous sinuses with a HU of<58 are associated
with a low probability of CVST (likelihood ration (LR) of
0.187). A venous sinus with HU of ≥67 on the other hand
is associated with a high probability of CVST (LR 27.621). A
cerebral venous sinus with a CVS/ICA ratio of<1 is associated
with a low probability of CVST (LR 0.0619), while a CVS/ICA
ratio of ≥1.5 yields a LR of 25.043 and a high probability of
CVST (Figure 4).

Old thrombus however may also have a low HU and
may be missed despite HU measurements. If the patient’s
symptoms are long standing, a CTV or MRV may still be
warranted. CVST in anaemic patients and those with low
haematocrit may also be of low density. Low HU measure-
ments cannot exclude a thrombus in such cases.

The aim of this study is not to provide an alternative
to CT or MR venography but to provide the reader with
more confidence in their observations on NCT. It remains
imperative for the reader to analyse the NCT images as usual,
but with the added benefit of being able to objectively assess



Radiology Research and Practice 5

the density of a suspicious venous sinus. Although venous
sinus HU measurements may be helpful when interpreting a
CT, they rely on the reader’s judgment initially as one will not
routinely sample every cerebral venous sinus to assess HU.
Instead, only when there is concern regarding a venous sinus
will the reader proceed to HU measurements.

The number of positive cases in this study is relatively
small potentially affecting the generalizability of our data.
This is a function of CVST being a rare diagnosis. A larger
study with multicentre collaboration may be more useful to
assess the generalizability of our data.

The fact that we did not use the raw CT data may intro-
duce some errors into our HU measurements. We decided
to use this for practical reasons, as the raw data was not
readily available, which is the case in usual clinical practice.
Despite this HU we showed a good correlation between HU
measurement with and without standardisation and CTV
results making it a clinically useful, practical tool. Although,
HU measurements correlate well with CTV findings; one
cannot extrapolate from our results that this can translate
into better pick-up rates of CVST from NCT. To assess this, a
further study is needed to assess if using HU measurements
improves the radiologist’s pick-up rate of CVST.

Objective HU measurements of suspicious cerebral
venous sinus appearances on NCT may provide an additional
tool in the radiologist’s arsenal to increase reporting confi-
dence of the relatively rare clinical entity of cerebral venous
sins thrombosis guiding further imaging and management.

Abbreviations

CT: Computed tomography
NCT: Nonenhanced CT
HU: Hounsfield units
ICA: Internal carotid artery
CVST: Cerebral venous sinus thrombus
AUC: Area under the curve
ROC: Receiver operating characteristic.

Disclosure

Partial results were presented at the Royal Society of
Medicine’s Radiology Section: Emergency Radiology Event
(November 2013).

Conflict of Interests

The authors declare no conflict of interests.

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