Post-radiation neurotoxicity and necrosis
Complications following radiation therapy are particularly prominent in children during brain tissue maturation phases (maturation phases). One of the typical sequelae is post-radiation leukoencephalopathy.
On T2-FLAIR MRI, the pathology appears as bilateral white matter hyperintensities (white matter hyperintensities). A key diagnostic sign is that the pathological process always spares the subcortical U-fibers and the corpus callosum (corpus callosum). According to the National Cancer Institute grading, the severity is divided into three degrees:
- Focal periventricular hyperintensity.
- Extension of pathological foci to the centrum semiovale (centrum semiovale).
- Total confluent white matter hyperintensity.
Radiation necrosis is most commonly localized in the white matter within the irradiation zone of tumors or arteriovenous malformations. Its pathogenesis is based on secondary injury: small cerebral vessels undergo changes, their walls thicken, leading to necrosis.
Diagnostic imaging of severe traumatic brain injuries
Skull base fractures are often associated with a high risk of mortality due to vascular and nerve damage.
- Clival fractures (clival fractures) result from high-energy axial loading. They threaten fatal injury to the basilar artery and brainstem. Transverse clival fractures frequently involve Dorello's canal (Dorello’s canal), causing abducens nerve (CN VI) palsy, and may also injure the internal carotid artery.
- Injuries of the petrous part of the temporal bone are visualized on CT as a disruption of the incudomalleolar joint. Meanwhile, the otic capsule may remain uninvolved. Trauma to the tegmen tympani is sometimes accompanied by herniation of the meninges and the formation of a meningoencephalocele.
Digital subtraction angiography (an invasive method for stent placement preparation), as well as CT and MR angiography, are used to detect vascular injuries. Indications for these in blunt trauma are strictly regulated by the Denver criteria (Le Fort II–III fractures, axonal injury with coma < 6 points, C1–C3 vertebral fractures, and other factors).
Angiography and perfusion: CT or MRI?
Although MRI is safe and does not use ionizing radiation, computed tomography angiography (CTA) has several clinical advantages. It is faster, suitable for patients with pacemakers or claustrophobia, and allows for the assessment of dynamic contrast extravasation (active hematoma expansion). CTA is the method of choice for detecting intracranial aneurysms in subarachnoid hemorrhage (SAH) with a sensitivity exceeding 90%.
- CT venography requires a scan delay. When using dual-source systems, the skull bones are effectively subtracted. The method allows for the assessment of venous sinus invasion by tumors or their thrombosis.
- CT perfusion is indispensable in stroke centers for mapping the penumbra (the reversible ischemic zone), which is critical for deciding on thrombectomy or thrombolysis. It is also used to detect delayed vasospasm (usually one week after SAH).
Neuroimaging in pediatric trauma
The historical term "shaken baby syndrome" has now been replaced by the more accurate abusive head trauma (abusive head trauma). Modern biomechanics proves that shaking alone without mechanical impact is insufficient to produce the classic triad: subdural hematoma, encephalopathy, and retinal hemorrhage. Infants under 6 months are at the highest risk.
According to ACR and RCR guidelines, the imaging algorithm is stratified by age:
- Full skeletal survey is mandatory for all children under 2 years of age to search for occult fractures.
- Brain CT is indicated for any child under 1 year with suspected physical abuse or encephalopathy.
- Urgent MRI is performed if CT reveals a hematoma. MRI outperforms CT in detecting cortical shearing and hypoxic-ischemic injuries at 3–5 days.
In complex cases, bone scintigraphy is prescribed, which must be performed strictly by personnel with pediatric experience.
To classify the grade of post-radiation leukoencephalopathy, remember the expansion rule: I — periventricular only (foci), II — extends to the centrum semiovale, III — completely confluent into a single zone.
Class and exam questions
Why does radiation necrosis occur predominantly in the white matter of the brain?
This is a secondary pathological process. It develops due to radiation-induced thickening of the walls of small brain vessels, which primarily supply blood specifically to the white matter.
In what cases of blunt neck trauma is angiography strictly mandatory?
Indications are strictly determined by the Denver criteria. These include skull base fractures involving the carotid canal, cervical subluxations, new neurological deficits, and arterial bleeding.
What is CT perfusion used for in strokes?
The main objective of this study is to determine the penumbra zone. If viable tissue with reversible ischemia is identified, the patient may undergo endovascular thrombectomy.
What diagnoses subdural hemorrhages in infants more effectively: CT or MRI?
At 3–5 days post-injury, MRI is significantly more sensitive to subdural and subarachnoid hemorrhages and also better visualizes cortical injuries.
What else to study on this topic
- Denver criteria: full list of indications for vascular screening in trauma.
- Clinical examples of endovascular aneurysm treatment: coil embolization and WEB device placement.
- The role and risks of digital subtraction angiography (DSA) in interventional radiology.
- Evaluation of cerebral blood flow using CT perfusion before and after acetazolamide administration.
- Differential diagnosis of incudomalleolar disruptions of the temporal bone on CT.
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