Overview of the Cerebral Great Vein
The great cerebral vein is a venous structure located in the midline, formed by the confluence of the great cerebral vein and Rosenthal’s basilic vein, which converges posteriorly with the inferior sagittal sinus to form a straight sinus that drains the thalamus, medial aspect of the temporal lobe, occipital lobe, and supraopercipital cerebellar peduncle. Large cerebral venous tumors are primarily verrucous dilatations of the large cerebral veins, rather than true venous tumors. Traditionally, the disease has been considered difficult to diagnose and treat, with a poor prognosis. However, recently, due to the development and advancement of neuroimaging, microsurgery and endovascular interventional techniques, both diagnosis and treatment have been significantly improved, and the prognosis has also been improved. However, the disability and mortality rates of this disease are still high, and it is still a difficult problem for neurosurgery.
Etiology
The large cerebral vein originates from the venous return system that drains the intermediate structures of the choroid plexus. Initially, the vein does not communicate with the deep internal cerebral vein, and at about 11 weeks of embryonic development, the posterior part of the vein communicates with the internal cerebral vein to form the large cerebral vein, and the anterior part of the vein deteriorates and eventually disappears. During the 6th to 11th week of embryonic development, if the anterior part of the cerebral vein fails to degenerate and occlude normally due to abnormal embryonic development for some reason, an arteriovenous fistula can be formed. The two basic mechanisms for the development of this disease are the impact of high pressure blood flow caused by the short circuit of the arteriovenous system and the occlusion of the dural venous sinuses.
Symptoms
In large cerebral venous aneurysms, the clinical manifestations of the lesions can be categorized into four age groups according to the age of onset:
1. Neonatal group
Typical presentation is high-output, preloaded heart failure shortly after birth, which occurs in almost all children. A persistent intracranial murmur is audible on cranial auscultation. Jugular venous oxygen saturation is markedly elevated. Cranial CR and MRI reveal aneurysmal lesions, and numerous tiny supplying arteries are seen at the anterior and inferior margins of the lesions on angiography. Ultrasonography also reveals persistent blood flow within the internal jugular vein, unlike the fluctuating flow that is normal. Anechoic shadows can be detected at the lesion and the blood flow is also persistent. Surgical treatment of intracranial lesions does not improve intractable heart failure and can induce myocardial infarction due to intraoperative lowering of blood pressure. Most children die of heart failure. The mechanisms of brain injury occur mainly by arterial blood theft, cerebral ischemia secondary to heart failure, hemorrhagic infarction, lesion compression and surgical trauma.
2. Infant group
Clinically, they are divided into two groups according to the presence or absence of a history of cardiac decompensation.
(1) Cardiac decompensation was present in the neonatal period, but it was relieved by treatment or relieved on its own. Increased head circumference and intracranial murmur, which is obvious on auscultation of the posterior lateral side of the head, appear from 1 to 12 months after birth.
(2) No history of cardiac decompensation. The infant is seen for increased head circumference and hydrocephalus is found. Chest radiographs may reveal cardiac hypertrophy.
The ventricles may be markedly enlarged, involving the lateral and third ventricles.There is no paraventricular edema on CT or MRI. Increased pressure in the sagittal sinuses and venous system, which affects the cerebrospinal fluid absorption barrier, is generally recognized as the main cause of ventricular enlargement. Usually cerebral angiography reveals a filling cystic lesion, and turbulence can be observed dynamically as the contrast agent washes into the cyst. Occasionally, thrombosis within the lesion completely occludes the cystic cavity and fails to visualize it. If thrombus forms on the wall of the capsule and the capsule lumen is present, a “target sign” can be visualized on CT.
Epilepsy is also the main clinical manifestation in this group of children. Prolonged intracerebral blood theft can cause cerebral ischemia. Cerebral infarction and degenerative changes are the pathologic basis of epilepsy.
3. Children
Most of the children above 2 years of age develop with increased head circumference. Some children may have subarachnoid hemorrhage, and the heart may be mildly enlarged. Intracranial murmurs may be heard on cranial auscultation. However, it needs to be differentiated from physiologic intracranial murmurs in children. Generally in normal infants or children, the murmur can also be heard in the skull or ophthalmoplegia, with the ophthalmoplegia or the temporal side obvious, the murmur increases in systole, and the murmur disappears when the carotid artery is compressed. However, the murmur of large cerebral venous tumor is obvious near the parietal nodes and the posterior part of the midline, and it is stronger in newborns and infants, and can be heard in both systole and diastole, or can be continuous.
4. Adult group
Includes older children, adolescents or young adults. Clinical manifestations are various: subarachnoid hemorrhage, pineal region occupation, high intracranial pressure and hydrocephalus. Cranial CT or MRI can be used for differential diagnosis. Pathophysiologically, patients have small arteriovenous fistulae with low flow rates or are secondary to large cerebral venous tumors.
Examination
1. Cranial X-ray film
Calcification of the lesion vessels is occasionally seen in the infant group, and intracranial calcified spots are common in the child and adult groups, in addition to signs of increased intracranial pressure. It shows complete or incomplete annular calcification in the pineal region with a diameter of more than 2.5 cm.
2. Cerebral angiography
Cerebral angiography is the main tool to confirm the diagnosis of large cerebral venous tumor. At least 3 selective cerebral angiograms should be done, including bilateral internal carotid arteries and one side vertebral artery; it is better to perform digital subtraction whole brain selective angiography, so that the large cerebral venous tumor can be shown more clearly, and the “blood-stealing” arteries and refluxing veins can be more clearly defined.
3.CT scan
It shows an ovoid high-density image with neat margins in the pineal region, often accompanied by symmetrical ventricular enlargement above the third ventricle; secondary cases may have irregularly shaped high and low density shadows with uneven density in front of it. Enhanced scanning can be seen with rounded high-density phase, continuous up to the skull enhancement shadow, suggesting the dilatation of the straight sinus.
4.MRI examination
MRI of large cerebral venous tumor is very typical, which is a round signal-less area caused by blood flow effect, with clear boundary, especially in sagittal position, not only the tumor capsule can be seen, but also the draining straight sinus and cerebral sickle sinus can be seen.
5.Others
MR angiography and Doppler ultrasonography are effective auxiliary means for the diagnosis of large cerebral venous tumor. Especially for children with unclosed fontanel, Doppler ultrasound can determine the intracranial hemodynamic changes and blood flow pattern in the lesion, which provides a noninvasive means of lesion screening. Evaluation of concomitant systemic conditions such as cardiopulmonary and cerebral function can be performed using arterial blood gas analysis, chest radiographs, electroencephalograms, electrocardiograms, renal function, and blood electrolyte tests.
Diagnosis
It mainly depends on the age of onset and clinical manifestations, but radiologic examination is needed to confirm the diagnosis. Neonates with persistent heart failure with intracranial vascular murmur; infants with hydrocephalus should be considered as a possible cause of the disease, and the diagnosis can be basically confirmed for those who can hear intracranial vascular murmur or those who have subarachnoid hemorrhage. Cerebral angiography, CT scan or MRI can be used to further confirm the diagnosis.
Treatment
The appropriate timing and optimal treatment plan are selected according to the patient’s age and clinical presentation. In neonates, cardiovascular symptoms are often life-threatening, so the preferred treatment should be to stabilize the general condition and control cardiac dysfunction. If the symptomatic treatment is effective, regular follow-up can be performed. Cranial CT, MRI, intracranial ultrasonography, and head circumference measurement can provide information about the changes of intracranial lesions, and can be used as a means of follow-up judgment. If the condition is stabilized, further treatment of the primary disease will be carried out after the child is 6 months old. In children older than 6 months, care should be taken in the management to try to avoid long-term damage caused by intracranial ischemia. Large cerebral venous aneurysms can cause high pressure and poor reflux in neighboring veins. Chronic ischemia of the brainstem can lead to irreversible calcified foci in the brain, causing mental retardation.
Lesions found at older ages, if asymptomatic, can be carefully examined to exclude other diseases and closely followed up in conjunction with imaging. Individual large cerebral venous tumors, especially low-flow lesions, have the potential for self-occlusion and thrombosis. For those with corresponding clinical symptoms, in principle, the removal of venous hypertension and cerebral ischemia is the main therapeutic objective.