doi: 10.2169/internalmedicine.0764-22
Intern Med Advance Publication
http://internmed.jp

【 CASE REPORT 】

‘Dense Inverted Triangle Sign’ in Cerebral Venous
Thrombosis
Akiyuki Hiraga 1, Yutaka Watabe 1 and Satoshi Kuwabara 2

Abstract:
The early diagnosis of cerebral venous thrombosis in the emergency department is challenging. A 70-yearold man presented to the emergency department after falling with new-onset convulsions. Brain unenhanced
computed tomography (CT) revealed right frontal hemorrhage indicative of traumatic subarachnoid hemorrhage (SAH). Brain unenhanced CT on day 2 revealed increased density in the anterior superior sagittal sinus
(SSS), namely ‘dense inverted triangle sign.’ Brain magnetic resonance venography showed a filling defect in
the anterior SSS. When interpreting unenhanced brain CT findings in the setting of acute convulsions or cortical stroke, including SAH, cerebral sinus abnormalities near stroke foci should be evaluated carefully.
Key words: computed tomography, superior sagittal sinus, cerebral venous thrombosis, dense sign,
subarachnoid hemorrhage
(Intern Med Advance Publication)
(DOI: 10.2169/internalmedicine.0764-22)

Introduction

Case Report

Cerebral venous thrombosis (CVT), a rare type of cerebrovascular disease, is often overlooked because it can
mimic other disorders; this ultimately results in a delayed
diagnosis (1). In fact, a recent study in a large cohort
showed that the mean time from the onset of symptoms to
the diagnosis of CVT was 11.8 days (2). Although magnetic
resonance venography (MRV) is the gold standard for diagnosing CVT (1), it is not routinely performed unless CVT is
clinically suspected (3). Therefore, suspicion of CVT by unenhanced computed tomography (CT) is important.
However, the utility of serial unenhanced CT for diagnosing CVT is not well known. Furthermore, abnormalities of
the anterior superior sagittal sinus (SSS) on unenhanced CT
are not a well-known finding in CVT.
We herein report a case of CVT that was initially misdiagnosed in the emergency department (ED) as traumatic
subarachnoid hemorrhage (SAH) in which a change in the
anterior SSS density on brain serial CT was helpful for
making a correct diagnosis.

A 70-year-old man with a history of diabetes mellitus
presented to the ED with new-onset convulsions. His wife
had found him lying unconscious and convulsing at home.
He had a history of gastric cancer and had undergone total
gastrectomy 11 years prior.
On an examination, his blood pressure was 161/80
mmHg. His Glasgow Coma Scale (GCS) score was 7/15 (E1
V1M5); we observed right-sided conjugate eye deviation
and generalized tonic-clonic seizures. Laboratory tests revealed the following: white blood cell count, 14,700/μL; hemoglobin, 11.4 g/dL; creatinine, 1.08 mg/dL; sodium, 139
mEq/L; potassium, 4.4 mEq/L; glucose, 472 mg/dL; glycohemoglobin, 9.7%; and D-dimer, 4.0 μg/mL. Arterial blood
gas levels were consistent with metabolic acidosis (pH
6.857; bicarbonate, 7.1 mmol/L). Unenhanced brain CT revealed right frontal hemorrhage mainly in cortical areas, indicative of SAH (Figure A). He was diagnosed with diabetic
ketoacidosis, status epilepticus, and possible traumatic SAH.
Intravenous (IV) diazepam was repeatedly administered
for convulsions, followed by IV fosphenytoin. He was intubated and admitted to the intensive-care unit (ICU) for fur-

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Department of Neurology, Chiba Rosai Hospital, Japan and ２ Department of Neurology, Graduate School of Medicine, Chiba University, Japan
Received: July 31, 2022; Accepted: September 21, 2022; Advance Publication by J-STAGE: November 30, 2022
Correspondence to Akiyuki Hiraga, hiragaa@yahoo.co.jp

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Intern Med Advance Publication

DOI: 10.2169/internalmedicine.0764-22

Figure. Unenhanced brain computed tomography (CT) at first examination (A, C) and on day 2
after hospitalization (B, D). (C) and (D) are enlarged views of the superior sagittal sinus (SSS). CT on
day 1 shows right mild cortical subarachnoid hemorrhage (arrows) (A). There is no increased density
in the SSS on day 1 (A, C). CT on day 2 shows increased density in the anterior SSS (’dense inverted
triangle sign’), but not in the posterior SSS (B, D). Arrows in (B, C, D) indicates SSS. (E, F) Magnetic
resonance venography (MRV). MRV on day 2 shows a filling defect in the anterior SSS (arrows) (E).
MRV on day 79 shows improvements in this abnormality (arrows) (F).

ther management with IV insulin. Brain unenhanced CT on
day 2 revealed an increased density in the anterior SSS that
had not been seen on the initial scan (Figure B, C, D). The
posterior SSS did not show any increase in density. Brain
MRV showed a filling defect in the anterior SSS, indicative
of CVT (Figure E). Further laboratory testing showed normal levels of protein C, protein S, antithrombin, and anticardiolipin antibodies; however, serum vitamin B12 was low
(198 pg/mL; reference range: 233-914 pg/mL), and the serum homocysteine level was high (26.6 nmol/L; reference
range: 3.7-13.5 nmol/mL).
CVT was believed to have been the result of diabetic ketoacidosis and hyperhomocysteinemia after gastrectomy. Intravenous heparin was initiated, followed by warfarin and
intramuscular mecobalamin. His seizures were effectively
controlled by levetiracetam. His GCS score improved to 14/
15 (E4V4M6) on day 3 of hospitalization. He was discharged on day 20 without any neurological deficits. MRV
on day 79 showed improvement of prior abnormalities (Figure F). The patients had no relapse one year after the onset.

Discussion
Our patient showed an acute convulsive state, and initial
CT showed isolated SAH without a high dense sign in the
cerebral sinus. The present case highlights two clinically important issues concerning the early diagnosis of CVT. First,
CVT can manifest as isolated SAH in unenhanced CT, mimicking other causes, such as traumatic SAH. Second, the
dense sign in anterior SSS without a posterior SSS abnormality was only confirmed by follow-up CT in this case.
SAH is thought to be a rare manifestation of CVT (4, 5).
Early studies from the 2010s showed that 3%-4% of CVT
cases had SAH (6, 7). However, a recent study showed that
SAH is not uncommon in CVT; although isolated SAH is
rare (4%), 24% of hemorrhagic CVT patients presented with
SAH (8). This study also suggests that a combination of
hemorrhage subtypes (especially parenchymal bleed with
SAH) or the presence of sulcal SAH should raise suspicion
about CVT as the cause of intracranial hemorrhage (8). Our
case was challenging to diagnose at the initial examination.
There were no eyewitnesses for the fall, so his SAH was initially diagnosed as of traumatic origin; however, his falling
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Intern Med Advance Publication

DOI: 10.2169/internalmedicine.0764-22

Written informed consent was obtained from the patient for
the publication of this case report and accompanying images.

could have been caused by convulsion due to CVT. Our
case indicates that CVT is an important differential diagnosis of isolated cortical SAH.
As seen in our case, increased density may only be located at the anterior SSS on follow-up unenhanced CT,
highlighting a pitfall in evaluating brain imaging in the ED
and ICU setting. Although unenhanced brain CT is necessary for the assessment of seizures and unconsciousness,
cerebral sinus abnormalities can be easily missed because
clinicians may focus on other more apparent abnormalities,
such as the evidence of a stroke. Previously, unenhanced CT
findings in CVT mainly focused on the posterior SSS. Abnormal findings of posterior SSS have classically been
known as a ‘dense triangle sign’ (increased density in the
posterior SSS) on unenhanced CT and as an ‘empty delta/
triangle sign’ (defect of contrast) on enhanced CT (3, 9, 10).
A study among Asians showed that the dense triangle sign
was positive in more than half of patients with CVT involving the SSS (3). In contrast, our patient did not show the
dense triangle sign; however, he showed similar findings
only in the anterior SSS. We propose that an abnormal imaging finding in the anterior SSS in patients with CVT be
called the ‘dense inverted triangle sign.’
In conclusion, partial CVT can manifest a dense sign of
restricted cerebral sinus that can be easily overlooked. When
interpreting unenhanced brain CT in the setting of acute
convulsions or cortical stroke, including SAH, cerebral sinus
abnormalities near stroke foci should be evaluated carefully.
Physicians should consider follow-up if the etiology is not
confirmed at the first examination.

Funding
This research received no specific grant from any funding
agency in the public, commercial, or not-for-profit sectors.

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The authors state that they have no Conflict of Interest (COI).
Declarations
The authors declare no competing interests relevant to the
content of this manuscript.

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