MRI of cerebral veins

Formation and Visualization of the Venous System

Venous drainage from brain structures is established early in embryogenesis. The choroid plexus (choroid plexus), arising in the region of the vascular fissure in the roof of the future third ventricle, is initially drained by the median prosencephalic vein. During development, this structure becomes the precursor to the vein of Galen.

Modern neuroimaging techniques allow for highly accurate assessment of the venous vasculature. The standard for detailed brain evaluation is 1.5 T and 3 T MRI systems. Utilizing specific pulse sequences enables not only visualization of the vessels themselves, but also differentiation of thrombus formation stages and evaluation of adjacent parenchyma (including cortical thickness, which normally ranges from 2 to 5 mm).

Venous Sinus and Deep Vein Thrombosis

Occlusion of deep venous sinuses and cortical veins is a life-threatening condition most frequently observed in children with significant dehydration. The clinical presentation (severe headache, prolonged seizures, altered consciousness) is often indistinguishable from underlying infectious processes such as meningitis. In such cases, neuroimaging is mandatory to confirm the diagnosis.

Cavernous sinus thrombosis is less common and is typically associated with the spread of infection from the paranasal sinuses, orbit, or odontogenic sources. Involvement of cranial nerves (III and IV pairs) in this location leads to ophthalmoplegia.

MRI Semiotics of Venous Thrombosis:

• T1-weighted images demonstrate shortening of relaxation time within the affected vessels (e.g., internal cerebral veins and the vein of Galen), corresponding to the presence of methemoglobin.
• On ADC maps (ADC map), focal restricted diffusion (an area of low signal) may be detected in the deep white matter, indicating the development of a cerebral infarction secondary to venous congestion.

Venous Occlusion in Traumatic Brain Injury

In non-accidental head trauma (abuse), the primary injury is frequently rupture followed by thrombosis of the cerebral bridging veins (cerebral bridging veins). This leads to the formation of subdural hematomas, which are not a consequence of secondary brain edema or hypoxia.

MRI has significantly higher sensitivity than CT for detecting small extra-axial collections and vascular injuries. Rupture or thrombosis of bridging veins is most clearly visualized on specific sequences (T2* or SWI) sensitive to the paramagnetic properties of blood.

Key MRI Signs: Loss of the magnetic resonance signal within the lumen of occluded veins is described in radiology as the «tadpole» sign (tadpole sign) or the «lollipop» sign (lollipop sign). Thrombosis of deep intramedullary veins may also be clearly identified on these sequences.

Aneurysmal Malformations of the Vein of Galen

Aneurysmal malformations of the vein of Galen (VGAM) are a unique congenital anomaly of intracranial circulation, representing an enlarged median venous structure with multiple arteriovenous (AV) shunts. High arteriovenous blood flow leads to aneurysmal dilation of the vessel.

Clinical manifestations of VGAM directly depend on the patient's age:

1. Neonates: dominated by symptoms of severe heart failure.
2. Infants and Young Children: the degree of blood shunting is lower; hydrocephalus and cerebral parenchymal atrophy come to the forefront.
3. Older Children: headaches, seizure disorders, and a high risk of spontaneous intracerebral or subarachnoid hemorrhage are typical.

Role of MRI in VGAM: Imaging allows visualization of the dilated venous pouch itself, determination of the location of fistulas and feeding arteries, assessment of venous drainage pathways, and detection of thrombotic masses within the pouch. Additionally, MRI is essential for evaluating the extent of brain tissue damage (detecting focal infarctions or generalized atrophy). Cerebral angiography remains the gold standard for diagnosis and is frequently combined with endovascular treatment.

Class and exam questions

What else to study on this topic

• Complications of neuroinfections: hydrocephalus, subdural empyemas, and ventriculitis.
• Differential diagnosis of subdural hemorrhages: accidental versus abusive trauma.
• Benign macrocrania and criteria for assessing subarachnoid space enlargement.
• Use of ADC maps for verifying focal cerebral infarctions.
• Patterns of hypoxic-ischemic brain injury in premature infants (PVL).

Other Topics in "Pediatric Diagnostic Radiology"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.