Radiological diagnosis of cerebral venous thrombosis in paediatric age group by Magnetic resonance venography: Pictorial essay

Cerebral venous thrombosis (CVT) in paediatric age group is often associated with nonspecific clinical complaints. Underdiagnosis or misdiagnosis of cerebral venous thrombosis can lead to severe consequences. Associated findings and complications include haemorrhagic infarction, cortical laminar necrosis, hypoxic ischemic encephalopathy, parenchymal atrophy and extra-axial haemorrhage. Morbidity and mortality can be significant and long-term neurological sequelae include developmental delay, seizures, sensorimotor and visual deficits. This review highlights the need for early detection of CVT, its associations and complications by Magnetic resonance imaging with Magnetic resonance venography. The various etiologies have also been Discussed.


Introduction
Cerebral venous thrombosis (CVT) in children is a multifactorial disease that, in the majority of cases, results from a combination of prothrombotic risk factors and / or the underlying clinical condition [1]. It is a serious disease that is being increasingly diagnosed, mainly because of more sensitive diagnostic procedures and increasing clinical awareness of the disease. The clinical presentation shows a wide spectrum of symptoms, eg, seizures, papilloedema, headache, lack of consciousness or lethargy, and focal neurological deficits [2]. We present a total of 13 paediatric patients of age group 1-14 years with cerebral venous thrombosis. The study was conducted in St John's Medical College, Bangalore from June 2012 to November 2015. Out of 13 patients , the most common presentation was headache-6, followed by seizure-4, diarrhea, vomiting -3 and altered sensorium -2 ( Figure 2).
The various manifestations seen were venous infarcts in 2 patients out of 13, cortical laminar necrosis in 1, hypoxic ischemic encephalopathy in 1, subarachnoid hemorrhage in 1, parenchymal haemorrhage in 1, and cerebral atrophy in 1 ( Figure 4).

Discussion
CVT in children is a result of complex multifactorial elements which result in a prothrombotic state, usually arising from the interaction of acute and chronic pathologies [13]. The majority of children (65%) have at least two risk factors with 40% having more than three risk factors. [3,18] (Table 1).
An Indian study conducted in Nizam's institute Hyderabad showed pediatric population constituted 9.4% of the study population [15]. Another Indian study conducted between 2001 and 2010 reported that 39 of its 624 CVT patients were children [14].
Cerebral venous system can be divided into two basic components. [4][5][6] A) Superficial System;The superficial system comprises of sagittal sinuses and cortical veins and these drain superficial surfaces of both cerebral hemispheres. B) Deep System; The deep system comprises of lateral sinus, straight sinus and sigmoid sinus along with draining deeper cortical veins. Both these systems mostly drain themselves into internal jugular veins. Superficial cerebral venous system The superficial cerebral veins can be divided into three collecting systems [6]. First, a mediodorsal group draining into superior sagittal sinus (SSS) and the straight sinus (SS); Second, a lateroventral group draining into the lateral sinus; Third, an anterior group draining into the cavernous sinus.These veins are linked by the great anastomotic vein of Trolard, which connects the SSS to the middle cerebral veins. These are themselves connected to the lateral sinus (LS) by the vein of Labbe.
The veins of the posterior fossa may again be divided into three groups: a) Superior group draining into the Galenicsystemb) Anterior group draining into Petrosalsinus c) Posterior group draining into the torcularHerophili and neighbouring transverse sinuses. The veins of the posterior fossa are variable in course and angiographic diagnosis of their occlusion is extremely difficult.
The Superior Sagittal Sinus (SSS) starts at the foramen caecum and runs backwards towards the internal occipital protuberance, where it joins with the straight sinus and lateral sinus to form the torcular Herophili. Its anterior part is narrow or sometimes absent, replaced by two superior cerebral veins that join behind the coronal suture. This fact should be borne in mind while evaluating for cerebral venous thrombosis (CVT). The SSS drain major part of the cerebral hemispheres.
The cavernous sinuses drain blood from the orbits, the inferior parts of the frontal and parietal lobe and from the superior and inferior petrosal sinuses. Blood from them flow into the internal jugular veins.
The straight sinus is formed by the union of inferior sagittal sinus and the great vein of Galen. The inferior sagittal sinus runs in the free edge of falxcerebri and unites with the vein of Galen to form the straight sinus. It runs backwards in the center of the tentorium cerebelli at the attachment of the falxcerebri, emptying into the torcularherophili at the internal occipital protuberance.
The lateral sinuses extend from torcularherophili to jugular bulbs and consist of a transverse and sigmoid portion. They receive blood from the cerebellum, the brain stem and posterior parts of the hemisphere. They are also joined by some diploic veins and small veins from the middle ear. There are numerous LS anatomic variations that may be misinterpreted as sinus occlusion [9]. B) Deep cerebral venous system The deep cerebral veins are more important than superficial veins fromthe angiographic point of view [8]. Three veins unite just behind the interventricular foramen of Monro to form the internal cerebral vein. These include choroid vein, septal vein and thalamostriate vein.
The Choroid vein runs from the choroid plexus of the lateral ventricle. The septal vein runs from the region of the septum pellucidum in the anterior horn of the lateral ventricle and the thalamostriate vein runs anteriorly in the floor of the lateral ventricle in the thalamostriate groove between the thalamus and lentiform nucleus. The point of union of these veins is called the venous angle. The internal cerebral veins of each side run posteriorly in the roof of the third ventricle and unite beneath the splenium of the corpus callosum to form the great cerebral vein. The internal cerebral veins, which lie within 2 mm of the midline, are the most important deep veins since they can be used to diagnose midline shifts. [10] The great cerebral vein of Galen is a short (1-2 cm long), thick vein that passes posterosuperiorly behind the splenium of corpus callosum in the quadrigeminal cistern. It receives the basal veinsand the posterior fossa veins and drains to the anterior end of the straight sinus where this unites with the inferior sagittal sinus.
The basal vein of Rosenthal begins at the anterior perforated substance by the union of anterior cerebral vein, middle cerebral vein and the striate vein [11]. The basal vein on each side passes around the midbrain to join the great cerebral vein.
In summary, blood from the deep white matter of the cerebral hemisphere and from the basal ganglia, is drained by internal cerebral veins. [10] and basal veins of Rosenthal, which join to form the great vein of Galen that drains into the straight sinus. With the exception of wide variations of basal vein, the deep system is rather constant compared to the superficial venous system [12]. Hence their thrombosis is easy to recognize. Two major pathophysiological mechanisms contribute to the clinical presentation of cerebral venous thrombosis ( Figure 6). First, thrombosis of cerebral veins or sinuses can result in increased venular and capillary pressure. As local venous pressure continues to rise, decreased cerebral perfusion results in ischemic injury and cytotoxic edema, disruption of the bloodbrain barrier leads to vasogenicedema, and venous and capillary rupture culminates in parenchymal hemorrhage. (Figure 7) Thrombosis of cerebral sinuses increases venous pressure, impairs cerebrospinal fluid absorption, and ultimately leads to increased intracranial pressure [16].
Clinical manifestations of CSVT are non-specific and may be subtle. Most of the clinical scenarios occur at all ages and the clinician should consider this diagnosis in a wide range of acute neurological presentations in childhood, including seizures, coma, stroke, headache and raised intracranial pressure. (Figure 8). CSVT may also be an important determinant of outcome in nontraumatic coma [17,18].

Case review with imaging findings
Case 1-Reported here is a 7 months old female who presented with history of status epilepticus and altered sensorium.  Axial T2*GRE (Fig 1a), DWI (1b) and MRV (1c) showing partial thrombosis of the vein of Galen with straight sinus extension, thrombosis of the superior sagittal sinus and the draining cortical veins with features of cortical laminar necrosis involving bilateral frontal lobes and post central gyri.
MRI with MRV showed partial thrombosis of the vein of Galen with straight sinus extension,thrombosis of the superior sagittal sinus and the draining cortical veins with features of cortical laminar necrosis involving bilateral frontal lobes and post central gyri. (Figure 1).

Case 2-
Reported here is a 8 yr old female withknown history of ALL who presented with severe headache.   Axial DWI (Fig 3a), T1 (3b) and MRV (3c) showing restricted diffusion in corpus callosum and right frontal and bitemporal periventricular white matter with bilateral transverse sinus thrombosis.

Figure 2a
MRI with MRV showed restricted diffusion in corpus callosum, right frontal and bitemporal periventricular white matter with bilateral transverse sinus thrombosis (Figure 3).

Case 4-
Reported here is a 10 day old male child with history of diarrhoea, failure to thrive, severe dehydration and subtle seizures.     Axial T2 FLAIR (Fig 6a ),GRE (6b) and MRV (6c) showing significant fronto temporal atrophy with filling defect in the superior sagital sinus, bilateral transverse, right sigmoid sinus and partly the straight sinus with blooming on GRE.
MRI with MRV showed significant fronto temporal atrophy with filling defect in the superior sagittal sinus, bilateral transverse, right sigmoid sinus and partly the straight sinus with blooming on GRE suggestive of thrombosis ( Figure 6).

Case 7-
Reported here is a 14 yr old male with history of headache and vomiting.    Left posterior temporal cortical vein involvement was also noted.Sulcal T2 FLAIR hyperintensity in left temporoparietal region -suggestive of SAH.

Figure 7a
MRI with MRV showed thrombosis of superior sagittal sinus just proximal to the confluence,torcularherophili, left transverse sinuses & the left sigmoid sinus. Left posterior temporal cortical vein involvement was also noted. Sulcal T2 FLAIR hyperintensity in the left temporoparietalregion suggestive of SAH. (Figure 8).

Learning Points
 Cerebral venous thrombosis (CVT) in paediatric age group is often associated with varied clinical presentations and etiologies.  Findings,associations and complications of cerebral venous thrombosis can be accurately diagnosed by Magnetic resonance imaging with Magnetic resonance venography.
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